All_AS_F331_questions[1]

1.

In April 1986, the nuclear reactor at Chernobyl in the Soviet Union exploded, releasing a mixture of radioactive isotopes into the atmosphere. One of the main isotopes released was 53 I which can cause cancer, though in controlled amounts it is used as a tracer. (i) In the following table, write the numbers of protons, electrons and 131 neutrons in an atom of 53 I . number of particles protons neutrons electrons[1]131

(ii)

What is meant by the term isotopes? ..................................................................................................................................... .....................................................................................................................................[2]

(iii) Radioactive isotopes are unstable and many decay by emitting either - or -particles. The table below summarises some of the properties of - and -particles. Complete the table by choosing words or numbers from the following list: small; large; nil; paper; aluminium foil; -particle lead; 0; 1; +2; +1

property relative charge relative mass stopped by deflection by electric field

-particle

4 paper

negligible

large[2]

Weald of Kent Grammar School for Girls

1

(iv)

The relative atomic mass of iodine is given in the Periodic Table as 126.9. Explain why this value is not a whole number. ..................................................................................................................................... .....................................................................................................................................[1] [Total 6 marks]

2.

In April 1986, the nuclear reactor at Chernobyl in the Soviet Union exploded, releasing a mixture of radioactive isotopes into the atmosphere. One of the main isotopes released was (i) Radioactive isotopes such as131 131 53 I 131 53 I

.

can cause cancers.

However, 53 I can be used as a radioactive tracer for investigating patients suffering from a possible deficiency of iodine. Suggest how it can be explained to a patient that it is relatively safe to use a dangerous radioactive substance as a tracer in their bodies. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................[2]

(ii)

131 The half-life of 53 I is 8 days. A sample manufactured for use in hospitals has an original count rate of 16 000 counts per minute. It can be used as a tracer as long as its count rate is at or above 500 counts per minute. 131 53 I

For how long after manufacture can

be used as a tracer?

................................... days[2] [Total 4 marks]

3.

In 1911, Geiger and Marsden fired -particles at gold foil and found that most passed through unchanged, while just a few were deflected by large amounts. This was evidence for the nuclear model of the atom. Explain the results of the Geiger and Marsden experiments using a nuclear model of the atom. ............................................................................................................................................... ............................................................................................................................................... ............................................................................................................................................... ............................................................................................................................................... ............................................................................................................................................... ............................................................................................................................................... ............................................................................................................................................... ............................................................................................................................................... ...............................................................................................................................................[Total 3 marks]


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4.

Cans of self-heating coffee were available until recently. Inside the can, in separate compartments, were calcium oxide and water. When a button was pressed these reacted together to give enough heat to warm up the coffee. (a) What term is used to describe a reaction that gives out heat? .....................................................................................................................................[1]

(b)

The reaction between calcium oxide, CaO, and excess water forms calcium hydroxide solution. Write a balanced equation for the reaction below. Include state symbols.

[2]

(c)

A group of students set out to determine the enthalpy change of this reaction by 3 placing a known mass of calcium oxide into 250 cm of water in an insulated flask and measuring the temperature rise. The group of students recorded the measurements shown in the table below. mass of calcium oxide used volume of water used temperature rise 10 g 250 cm 50 C3

Calculate the heat transferred to the water (in kJ) by the reaction of 1.0 mol of CaO(s). Give your answer to two significant figures. specific heat capacity of water = 4.2 kJ K1

kg ; density of water = 1.0 g cm

1

3

heat transferred = .................... kJ[4]

(d)

The reaction will produce solid calcium hydroxide if the exact molar ratio of water to calcium oxide is used, as represented by the balanced equation in (b) above. (i) Suggest one reason why it is very difficult to measure this enthalpy change directly. ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................[1]


5

(ii)

This enthalpy change can, however, be measured indirectly using an enthalpy cycle as shown below. c a + l c i u m h y d r o o x i d e + H a t e w c h l o r i c a c i d r c a l c iu m + h y d r o h y d r o x i d c h l o r i c a c

H

1

H c a l c iu m c h w a t e r l o

2

+

r i d

e

Explain how the cycle can be used to calculate the enthalpy change H. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................[2]

(e)

Magnesium oxide is a possible alternative substance to use in the self-heating cans. Use your knowledge of the Periodic Table to suggest why magnesium oxide might be considered a possible alternative to calcium oxide. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................[2] [Total 12 marks]

5.

Environmental issues are a vital consideration in chemistry, with the idea of green chemistry becoming more and more important. (a) In the left hand column below are some of the pollutants emitted from car exhausts. For each pollutant, briefly explain in the right hand column how the pollutants are formed. The first one has been done for you. pollutant oxides of nitrogen carbon monoxide oxides of sulfur hydrocarbons[Total 3 marks]

how the pollutants in the exhaust gases are formed From the reaction of nitrogen and oxygen gas in the air, at the high temperatures of the combustion chamber.


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6.

Reforming is a process which converts straight-chain alkanes into new compounds that burn more effectively in engines, reducing pollution. These new compounds include branched alkanes, cycloalkanes and arenes. Classify the molecules in the table by ticking the appropriate boxes. hydrocarbon straight-chain branched chain cycloalkane arene

CH3(CH2)5CH3

C6H6

[Total 2 marks]

7.

Heterogeneous catalysts are often used in the reforming process. The process is called platforming when the catalyst is platinum metal. Coke (from side reactions in the process) reduces the efficiency of the catalyst. Describe the stages involved in heterogeneous catalysis and explain why the formation of coke can cause the platinum to become ineffective. In your answer, you should use appropriate technical terms, spelled correctly. ............................................................................................................................................... ............................................................................................................................................... ............................................................................................................................................... ............................................................................................................................................... ............................................................................................................................................... ............................................................................................................................................... ...............................................................................................................................................[Total 5 marks]

8.

An approach towards greener cars is to change the fuel. One possible alternative fuel is biodiesel. This can be manufactured from soya beans. (i) Suggest one possible advantage of a fuel manufactured from soya beans. ..................................................................................................................................... .....................................................................................................................................[1]


9

(ii)

Biodiesel can be used on its own or blended with ordinary diesel. Describe and explain what happens to the entropy of the system when this blending (or mixing) occurs, compared with the unblended compounds. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................[3]

(iii)

Biodiesel molecules contain oxygen atoms. What general name is given to such molecules that can be added to fuels to improve performance? .....................................................................................................................................[1]

(iv)

Emissions of most pollutants are reduced when biodiesel is used instead of petroleum diesel, with one exception. The exception is that levels of nitrogen oxides (NOx) increase in the exhaust. A reason for this might be that the temperature at which biodiesel burns in the engine is higher than for petroleum diesel. Draw a dot-and-cross diagram for a nitrogen molecule. Use it to explain why a large amount of energy would be needed to break up the molecule.

dot-and-cross diagram for a nitrogen molecule ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................[4] [Total 9 marks]


11

9.

Most of the chemical elements found on Earth were produced in stars. Absorption and emission atomic spectra show the presence of elements in the stars. The wavelengths involved are in the UV or visible portion of the electromagnetic spectrum. (i) The labelled diagrams below represent part of an atomic absorption spectrum and an atomic emission spectrum, drawn to the same scale. A B C D E

f r e

q

u

e

n

c y s p e c t r u m

a b s o r p t i o n

F

G

H

I

J

f r e

q

u

e

n

c y s p e c t r u m

e m

i s s i o n

Using the letters (AJ), choose a line from the spectra which would correspond to: 1. the line of lowest frequency in the emission spectrum; ..................................................................................................................................... 2. the line representing the absorption of the largest amount of energy. .....................................................................................................................................[2]

(ii)

The emission and absorption spectra shown are for the same element. What evidence is there from the two spectra that this is the case? .....................................................................................................................................[1] [Total 3 marks]

10.

Elements react together to form molecules in the dense clouds in interstellar space. These molecules can be detected by the characteristic radiowaves they emit. Molecules of H2S, NH3 and OCS (similar to CO2) have been discovered. (i) Complete the dot-and-cross diagram for each molecule in the boxes below.

H

x

x x

H

S

HH

N

H O

C

S

[3]

(ii)

Use the theory of electron pair repulsion to decide which of the possible shapes below represents the shape of each molecule. Write the formula of each of the molecules H2S, NH3 and OCS underneath its shape.

[3]

(iii)

What is the significance of the wedge ( ) and the dotted line ( on the left?

) in the shape

..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................[1] [Total 7 marks]


13

11.

Radio-astronomy revealed the possible presence of long chains of carbon atoms in outer space. In the 1980s, Professor Harry Kroto and other workers were investigating these chains. Professor Kroto was trying to recreate, in the laboratory, conditions that might account for the presence of carbon chains. He tried vaporising carbon rods in an electric arc and he analysed the soot from the vaporised carbon in a mass spectrometer. (i) In a time-of-flight mass spectrometer, how are the ions accelerated and why do they take different times to reach the detector? ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................[2]

(ii)

A simplified version of the mass spectrum is shown below. On the basis of this spectrum, Professor Kroto suggested the presence of a C60 molecule.

i n

t e ty n

s i

5

0

0

6

0 0

7 0 m /z

0

8

0

0

Explain how the mass spectrum indicates the presence of a C60 molecule. ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................[2]

(iii)

This C60 form of carbon (later named buckminsterfullerene) is unusual in that it is a simple molecule. Up until this discovery the only two forms of carbon thought to exist were the giant molecular structures of diamond and graphite. Below is a table showing some physical and chemical properties of the three forms of carbon. Tick two boxes in the last column which correspond to a property that supports only the simple molecular model for C60. property supports simple molecular model

property

diamond

graphite

C60

density/g cm3

3.52

1.92.3

1.69

hardness scale (hardest 10 softest 1) melting point/C

10

12

12

3550

36523697

sublimes around 800

solubility

insoluble

insoluble

soluble in organic solvents[2] [Total 6 marks]


15

12.

Information for Candidates Advance notice 1 2 3 The article below is needed in preparation for the question in the externally assessed examination F332. You will need to read the article carefully and also have covered the learning outcomes for unit F332 (Chemistry of Natural Resources). You will be expected to apply your knowledge and understanding of the work covered in the unit to answer this question. There are 20 marks available on the paper for this question. You can seek advice from your teacher about the content of the article and you can discuss it with others in your class. You may also investigate the topic yourself using any resources available to you. You will not be able to bring your copy of the article, or other materials, into the examination. The examination paper will contain a fresh copy of the article as an insert. You will not have time to read this article for the first time in the examination if you are to complete the examination paper within the specified time. However, you should refer to the article when answering the questions.

4

5

6

Getting tyred with chemistry! Adapted from Chris Ferguson, Chemistry Review, 2002, Volume 11, Issue 4, ' Getting Tyred with Chemistry. Next time you are out on a mountain bike, in a car or even an aeroplane, stop and think about the chemistry involved in the tyres you are travelling on. Those tyres are pneumatic tyres containing compressed air and, on your vehicle, they perform a variety of functions. Since the Scotsman, Robert William Thompson, filed the first patent for a pneumatic tyre in 1845, tyre technology has developed a huge amount and many of these improvements are due to chemistry. Typically, a rubber tyre is composed of rubbers (both natural and synthetic), carbon black, oils and resins, curing agents and anti-ageing chemicals. No tyre is complete without all of these components and each one has a varied and interesting chemistry. Natural rubber Natural rubber can be obtained from bushes from many parts of the world (e.g. Brazil, Sri Lanka and Malaysia). However, by far the best and most widely used source is the Hevea braziliensis tree originating from South America. The rubber is obtained as latex, a colloidal dispersion of nanoscale rubber particles in water. At the beginning of the twentieth century, C. D. Harries showed that natural rubber consists of repeating units. It was initially believed that the structural units were joined to form rings, but it was soon established that they are joined in long chains. These chains have the structure shown in Fig. 1 and can be produced synthetically by joining isoprene (2-methylbuta-1, 3-diene) units to give a polymer structure. In natural rubber, the configuration across the double bond is 98% cis. This cis arrangement gives rise to rubbers property of increasing in strength when stretched, by allowing the chains to form crystalline regions. Notice that the addition polymerisation of natural rubber is not a simple reaction, such as happens when ethene polymerises. Two double bonds in isoprene open to form a polymer that contains only one double bond in its repeating unit.

isoprene (2-methylbuta-1,3,diene)

poly(isoprene) natural rubber

Fig. 1 The structure of the isoprene monomer and natural rubber Natural rubber has many limitations. It cannot be used on its own to make tyres due to its thermoplastic nature. It would become very hard in the winter and during the summer it would melt into a sticky, smelly mess. Imagine riding a bicycle that would stick to the road in summer! Fortunately the problem of its thermoplastic nature is overcome by curing natural rubber by heating with sulfur, as described in a later paragraph.


17

Synthetic rubber Synthetic rubber was first produced by carrying out the polymerisation of dienes (alkenes containing two double bonds) in the laboratory. Since it is impossible to recreate the exact conditions for natural rubber synthesis, the laboratory-based syntheses initially gave poor quality products. For example, early attempts at polymerising isoprene in the laboratory gave synthetic rubber as a mixture of cis and trans isomers. The best synthetic rubber is a co-polymer, obtained by combining a diene and an alkene. Thus polymerisation of butadiene with phenylethene (styrene) gives the copolymer, styrene-butadiene rubber (SBR), Fig. 2.

To produce this natural-like synthetic rubber, a process called emulsion polymerisation is used. In this process, butadiene and styrene are polymerised in water with a surfactant to give a colloidal dispersion of the polymer in water. This process is often done at 5 C (rather than above 50 C, as is more normal for an emulsion polymerisation) to give the desired rubber properties. Another variety of synthetic rubber is known as butyl rubber and is produced by polymerising 2-methylpropene. The polymer in this case is a saturated hydrocarbon. Nowadays, many types of synthetic rubber are available for use in tyres. H H 2C C H C H CH 2 b u t a d i e n e C C H ( s t y r e n e ) H

p h e n y l e t h e n e Fig. 2 Structures of monomeric building blocks

Curing agents In 1839, Charles Goodyear discovered, accidentally, that heating rubber and sulfur together produced a new version of rubber that did not flow or become sticky at higher temperatures. This process of sulfur curing is called vulcanisation after Vulcan, the Roman God of fire. The chemical process of vulcanisation is called cross-linking and it changes the property of rubber to the hard, durable material we associate with car and bike tyres. Fig. 3 shows a schematic diagram of cross-linking.

Fig. 3 Sulfur

This produces a more rigid structure, which limits the movement of polymer chains. Unfortunately, vulcanisation with sulfur is a slow process, taking about 8 hours for the rubber to cure. A typical car tyre is cured for 15 minutes at 150 C. However, the time can be reduced by the addition of accelerators such as those shown in Fig. 4.

Fig. 4 Accelerator molecules

Accelerators increase the rate of cure by catalysing the addition of sulfur chains to the rubber molecules.

Anti-ageing chemicals A tyre is subjected to quite harsh operating conditions. Factors such as heat, fatigue, weathering and exposure to ultraviolet light all reduce the life of a tyre. You will probably be aware of the effect sunlight has on a rubber band. Therefore, various chemicals are added to prevent tyre degradation.

Tyred out! Tyres are very important in all our lives and it is likely that they will continue to be so for the foreseeable future. An important question is where do all the used tyres go? Tyres are inherently strong and this makes them almost impossible to destroy after use. In the USA, 250 million used tyres are produced each year and at the moment most (about 75%) are simply buried in landfill. But this and other methods of disposal can have a serious impact on the environment. Some tyres are recycled to make products such as cushioned surfaces for childrens playgrounds. An exciting project for chemists of the future would be to develop an environmentally friendly tyre.


19

13.

Heterogeneous catalysts play an extremely important role in many chemical reactions, including the control of polluting emissions and in the manufacture of various chemicals. (a) Many cars now have three-way catalytic converters fitted. The following diagram illustrates how they work. a N C H (i)xO

ir r t er e a r c o r C O t 2o H C H 2t o n v et o r t e r N 2 C O C 2O O + 2 C H O2 O

O C

f r o e n g

m f r o i n Ne

nxO

t

c o t o

n2N

v e

Write the formula for one specific molecule that could be represented by NOx. ...........................................................................................................................[1]

(ii)

Suggest the meaning of the letters HC in the diagram. ...........................................................................................................................[1]

(iii)

Explain the presence of CO in the gases from the engine. ...........................................................................................................................[1]

(iv)

The three-way catalytic converter involves both a reduction and an oxidation phase. Why is the conversion of NOx to N2 described as reduction? ...........................................................................................................................[1]

(b)

(i) Diesel exhaust contains a higher proportion of particulates than petrol exhaust. Particulates are very small solid soot particles. Suggest and explain why diesel fuel produces more particulates than petrol. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................[3]

(ii)

Diesel engines without catalytic converters produce less NOx than an equivalent petrol engine. Explain the formation of NOx in petrol engines. Suggest why less NOx is formed in a diesel engine. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................[3] [Total 10 marks]


21

14.

The diagram illustrates a model for heterogeneous catalysis.

g S t e p

a 1

s

m

o

l e

c u

le

s

S S t e p 2 S S t e p 3 t e p 4 S t e p 5

t e p

6

The following phrases describe some of the steps labelled on the above diagram. Write the numbers of the step or steps corresponding to each phrase. Bonds in reactants weaken and break New bonds in products form Diffusion from catalyst surface Step(s) ................................................. Step(s) ................................................. Step(s) .................................................[Total 3 marks]

15.

Catalysts also play a role in the oil industry in the production of more useful hydrocarbons from longer chain fractions. Zeolite catalysts replaced the traditional silica/alumina catalysts in the 1960s. The following box illustrates some of the reactions catalysed by zeolites.

A

B

C

D

(i)

Use words from the following list to describe reactions A to D. isomerisation reforming cracking

reaction A .................................................... reaction B .................................................... reaction C .................................................... reaction D ....................................................[4]

(ii)

By what type of formula are the molecules represented? ....................................................................................................................................[1]

(iii)

Give the molecular formula and name of the molecule formed in reaction B. molecular formula ................................................................................................... name ........................................................................................................................[4]


23

(iv)

Suggest one reason why the hydrocarbon formed in reaction B is more useful than the hydrocarbon it is made from. .................................................................................................................................... ....................................................................................................................................[1] [Total 10 marks]

16.

Major art galleries employ chemists to ensure that the condition of irreplaceable paintings is maintained. This often involves identifying the pigments the artists used. One pigment used by Renoir in many of his paintings was the Group 2 compound strontium chromate, known as lemon yellow. Strontium chromate is an ionic compound with the formula SrCrO4. (i) What is the charge on the chromate ion? ...................................................................[1]

(ii)

In the chromate ion there are four bonding sets of electrons, and no lone pairs, around the covalently bonded central chromium atom. Draw a diagram below to show the three dimensional shape of the chromate ion.

c h

r o

m

a

t e

io

n[2] [Total 3 marks]

17.

Analysis of pigments such as lemon yellow can be done by vaporising a tiny sample of the pigment and analysing the emission spectrum produced. A simplified section of the emission spectrum produced by strontium in the visible region is shown below.

z (i) What is the quantity labelled as z on the above spectrum? ....................................................................................................................................[1]


25

(ii)

Explain: why excited atoms emit light why the emission spectrum consists of discrete lines why there are sets of lines.

You are advised to draft out your answer in rough first and then present your explanation in a logical order. You may use diagrams in your answer.

explanation .............................................................................................................. .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... ....................................................................................................................................[5]

(iii)

Strontium also produces an absorption spectrum. Describe two similarities and one difference between the appearance of the emission and absorption spectra of strontium. similarities ................................................................................................................ .................................................................................................................................... .................................................................................................................................... difference ................................................................................................................. ....................................................................................................................................[3] [Total 9 marks]

18.

One Group 2 compound found in paintings is gypsum, a form of calcium sulphate. The solubility of Group 2 sulphates decreases down the group. Give two properties of other Group 2 compounds that decrease down the group. ............................................................................................................................................... ...............................................................................................................................................[Total 2 marks]

19.

The work of many chemists was influential in the development of the Periodic Table. Modern Periodic Tables list the elements in order of increasing atomic number. (a) The atomic number gives information about the structure of the atom. What two pieces of information does it give? .................................................................................................................................... ....................................................................................................................................[2]


27

(b)

Early Periodic Tables, such as that devised by Mendeleev (shown below), listed the then known elements in order of their relative atomic mass. Mendeleev reversed the positions of tellurium and iodine (as shown in bold in the table).T V C M F N H = 1 B B C N O F L i = 7 C ? ? E ? Y ? I n e = = = = = = 9 1 1 1 2 1 4 1 6 1 9 C l N a = r t = = a = 4 = = 7 3 5 .B5 r = 2 3 4 0 5 5 6 6 0 5 . 6 T . 4 Al = 2 7 . ?4 M = g 6 = 8 2 2 8 A = = S C r e L a D i h = 1 2 8 ? 1 2 7 K = = = = = 8 9 7 2 3 9 . 6 B S e 4 U 3 1 3 T 2e 8 0 I r Z = ? s = n 6 5 1 1 6 = = 7 7 7 9 0 5 = . i e = r n = C i = = = = 5 o 5 5 5 5 6 = 5 9 0 1 2 5 R R N M h u P d Z r b o = = = = = = 9 9 9 0 4 6

1 0 4 . 4 1 0 4 . 4 1 0 6 .

C

S i = P = S = =

. 4

9 4 9 5 1 1 8 ?

(i)

Suggest why Mendeleev thought it necessary to reverse the positions of tellurium and iodine. ........................................................................................................................... ...........................................................................................................................[1]

(ii)

A modern definition of relative atomic mass is the weighted mean of the isotopic masses of all the naturally occurring isotopes of an element. There are eight isotopes of tellurium. Complete the following table and use it to calculate the relative atomic mass of tellurium. Give your answer to three significant figures. isotope tellurium-120 tellurium-122 tellurium-123 tellurium-124 tellurium-125 tellurium-126 tellurium-128 tellurium-130 percentage abundance 0.09 2.46 0.87 4.61 6.99 18.71 31.79 isotopic mass percentage abundance 11 300 107 572 874 2357

relative atomic mass = ................................[3]

(iii)

Mendeleev would not have been able to do the above calculation because the existence of isotopes was not known. Which sub-atomic particle is responsible for the existence of isotopes? ...........................................................................................................................[1]


29

(c)

Another chemist looking for patterns in the properties of the elements around the time of Mendeleev was Julius Lothar Meyer. Lothar Meyer looked at how the atomic volume of an element varies with its relative atomic mass. A simplified version of the graph he plotted is shown below. Atomic volume against relative atomic mass 6 5 4 a t o / c 3m m 0 0 0

ic v o lu m e 3r 0m p e o le 2 1 0 0 1 0 r e 2 l a 0 t iv e a 3 0 t o m ic 4 0 m a s s 5 0 6 0 0

(i)

Which group of elements form the peaks in Meyers graph? ...........................................................................................................................[1]

(ii)

How does the atomic volume change as you go from left to right across a period? ...........................................................................................................................[1] [Total 9 marks]

20.

Since the time of Mendeleev and Lothar Meyer many more elements have been discovered. Sir William Ramsey discovered argon in 1894. He removed oxygen and nitrogen from air and found he was left with about one percent which was the gas argon. (i) The oxygen can be removed by passing air over hot copper. Copper oxide, CuO, is formed. Write a balanced equation for this reaction. Include state symbols.[2]

(ii)

The nitrogen was removed by passing it over hot magnesium. This produced a white solid called magnesium nitride, Mg3N2. The balanced equation for this reaction is given below. 3Mg(s) + N2(g) Mg3N2(s) Calculate the number of moles of nitrogen gas in 1 dm of air at room temperature and pressure. Assume air to be 80% nitrogen gas by volume and that one mole of gas occupies 3 24dm at room temperature and pressure.3

moles = ................................[2]

(iii)

Use the equation above and your answer to (i) to calculate the mass of 3 magnesium that would react with the nitrogen in 1 dm of air, at room temperature and pressure. Ar: Mg, 24

mass = ................................ g[2] [Total 6 marks]


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21.

The American chemist Glenn T. Seaborg made the element neptunium, Np, by firing neutrons at uranium atoms. Some of these neutrons stuck to the uranium nucleus and then the nucleus emitted an electron. (i) Complete the following nuclear equation representing the formation of neptunium atoms from an isotope of uranium.

[3]

(ii)

It is not possible to make neptunium atoms by firing protons at uranium atoms. Suggest a reason why this is unlikely to work. .................................................................................................................................... .................................................................................................................................... ....................................................................................................................................[2] [Total 5 marks]

22.

The booster engines on the Space Shuttle use solid propellants. The main ingredients of the most widely used solid propellant are powdered aluminium and the oxidiser ammonium perchlorate, NH4ClO4. (a) The reaction of the ammonium perchlorate with aluminium can be represented by the equation below. 10Al(s) + 6NH4ClO4(s) 5Al2O3(s) + 6HCl(g) + 9H2O(l) + 3N2(g) The standard enthalpy change for this reaction can be calculated indirectly using an enthalpy cycle. The enthalpy cycle below uses standard enthalpy change of formation values.

1

0l A

( s )4 = 1 7

+ 7 1 0

6

4

N

H

1

Hl m

C o l

O

( s )

2

l3

5

A

k J

=

1

1 k 5 Jm0 o l 6 1 +l

1

0l A

( s 2)

+

3

N

( g

)

2

+

1

2

H

( g

)2

3

C

(i)

Explain the term standard enthalpy change of formation. .......................................................................................................................... .......................................................................................................................... ..........................................................................................................................[3]

(ii)

Use the cycle and values provided to calculate the standard enthalpy change, H1 , for this reaction.

H1 = ................................ kJ mol

1

[2]

(iii)

The values for H2 and H3 do not include standard enthalpy change of formation values for two of the substances in the equation. Name the two substances and explain why they do not contribute to H2 and H3 . substances ................................................... and ........................................ explanation .................................................................................................... ..........................................................................................................................[2]

(b)

A hydrocarbon polymer is also added to the propellant to bind the aluminium and perchlorate together. The hydrocarbon binder burns to produce the same products as the hydrocarbons in petrol. Name three possible products from this combustion. ......................................... ; ......................................... ; ............................................[3]


33

(c)

At the high operating temperature of the solid rocket boosters, a small proportion of nitrogen molecules dissociate into nitrogen atoms. (i) Draw a dot-cross diagram for the nitrogen molecule. Show all outer shell electrons.

[2]

(ii)

Suggest why it is very difficult to break the nitrogen molecule into its atoms. .......................................................................................................................... ..........................................................................................................................[2]

(d)

The reaction shown in the equation is accompanied by a large increase in entropy. Explain why you would predict this increase in entropy from the equation for the reaction. .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... ....................................................................................................................................[4] [Total 18 marks]

23.

One widely available type of smoke detector contains a radioisotope of americium (Am), americium-241. This isotope, contained in a separate container within the detector, decays by alpha emission. The alpha particles emitted by the americium-241 collide with air molecules in the chamber and produce ions. (a) Use your Periodic Table to complete the following equation for the decay of americium-241.

2 9

4

A 5

1

m

a

+

[3]

(b)

Although alpha particles are normally hazardous to health, the alpha particles generated in smoke detectors do not pose a risk provided the detector is not damaged in any way.

(i)

Suggest why there is no significant health risk in normal usage of smoke detectors. .......................................................................................................................... ..........................................................................................................................[2]

(ii)

Suggest how alpha particles cause ionisation of air molecules in the smoke detector. .......................................................................................................................... ..........................................................................................................................[1] [Total 6 marks]


35

24.

The americium in smoke detectors is in the form of an oxide. A sample of the oxide contains 88.3% by mass of americium. (i) Calculate the empirical formula of the oxide. Ar: Am, 241; O, 16

empirical formula = ................................[2]

(ii)

0.008 moles of americium oxide is enough for 5000 smoke detectors. Calculate the mass, in grams, of americium oxide per smoke detector. Give your answer to one significant figure.

mass = ................................g[3] [Total 5 marks]

25.

Another isotope of americium is americium-243. (i) Complete the following table for the two isotopes, americium-243 and americium-241. isotope americium-243 americium-241[3]

protons

neutrons

electrons

(ii)

Americium-243 is produced by the beta decay of an isotope of plutonium. Fill in the mass number and atomic number of this plutonium isotope in the appropriate places below.

P

u

[2] [Total 5 marks]

26.

Low sulphur fuel is now a familiar label on the pumps at petrol stations. The removal of sulphur from diesel and petrol significantly reduces the emission of toxic oxides of sulphur from vehicle exhausts. (i) One oxide of sulphur is the gas sulphur dioxide, SO2. One way to represent the bonding in sulphur dioxide is given below.

O = S OUse the structure above to draw a dot-cross diagram in the box below. Show all outer electrons.

O(ii)

S

O[3]

The actual shape of the sulphur dioxide molecule is V-shaped. Explain why you would predict this shape for the SO2 molecule. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................[3] [Total 6 marks]


37

27.

Sulphur dioxide reacts with water and oxygen in the atmosphere to produce acid rain, a dilute solution of sulphuric acid. Write a balanced equation to show the formation of sulphuric acid from the reaction between sulphur dioxide, water and oxygen. Include state symbols.

[Total 3 marks]

28.

(a) One process used to remove sulphur compounds from petroleum and diesel is called hydroprocessing. This process uses catalysts consisting of metals deposited as thin layers on porous aluminium supports. (i) Name the type of catalysis used in hydroprocessing. ...........................................................................................................................[1]

(ii)

Suggest two reasons for the metals being used as thin layers. ........................................................................................................................... ...........................................................................................................................[2]

(b)

Hydroprocessing converts the sulphur compounds in the fuel to the gas hydrogen sulphide, H2S. Some of the hydrogen sulphide produced is oxidised to sulphur dioxide and water as shown in equation 1. 2H2S(g) + 3O2(g) 2SO2(g) + 2H2O(g) equation 1 The sulphur dioxide produced is then reacted with the remaining hydrogen sulphide to produce solid sulphur as follows. 2H2S(g) + SO2(g) 3S(s) + 2H2O(l) equation 2 (i) What volume of oxygen is needed to react with 1 dm of hydrogen sulphide gas in equation 1? Assume the gases are under the same conditions of temperature and pressure. volume = ................................dm3 3

[1]

(ii)

Suggest why oil companies convert the sulphur compounds into sulphur. ........................................................................................................................... ...........................................................................................................................[1]

(c)

The reaction represented by equation 2 is accompanied by an entropy change. 2H2S(g) + SO2(g) 3S(s) + 2H2O(l) equation 2 The table below contains some statements relating to this reaction or to the idea of entropy in general. Four of these statements are correct. Put a tick in the box next to each correct statement. statement Entropy can be thought of in terms of the number of ways of arrangement of a chemical system. The entropy change in equation 2 above has a positive sign. Entropy is a measure of the disorder of a system. A substance in the solid state has higher entropy than when molten. The symbol for entropy is S. The reaction in equation 2 is accompanied by a decrease in entropy.[3] [Total 8 marks]

( )


39

29.

(a) Use the bond enthalpy data provided below to work out an enthalpy change for the reaction in the equation below. 2H2S(g) + 3O2(g) 2SO2(g) + 2H2O(g) bond HS S=O S O HO O=O bond enthalpy/kJ mol 364 525 265 464 4981

Clearly lay out all your working using the grid below. bonds broken enthalpy change bonds formed enthalpy change

total for breaking bonds

total for forming new bonds

overall enthalpy change/kJ mol

1

[4]

(b)

The calculated value using the bond enthalpies above is not the same as the enthalpy change for this reaction done under standard conditions. Suggest one reason for the difference in values. ....................................................................................................................................[1] [Total 5 marks]

30.

A scientific approach to cooking is seen by some chefs as increasingly important. Knowledge of the nature of some reactions and the molecules involved in preparing exciting dishes is now much better understood. The table below shows molecules contributing to some characteristic flavours. letter A molecule flavour orange

B O O C H O

cucumber

strawberries O

(i)

Which letter(s) show a molecule or molecules with an alcohol group ...................... that is a hydrocarbon ....................... with an ether group ......................... with an alkene group .......................[4]


41

(ii)

The above formulae are skeletal. Give the molecular formula for molecule A. ....................................................................................................................................[1]

(iii)

What extra piece of information does a skeletal formula provide that is not given by a molecular formula? ....................................................................................................................................[1] [Total 6 marks]

31.

Baking powder is used in the manufacture of foodstuffs that require a honeycomb structure, such as bread. Baking powder contains sodium hydrogencarbonate, NaHCO3. This decomposes on heating as shown below. 2NaHCO3(s) Na2CO3(s) + CO2(g) + H2O(l) 10g of sodium hydrogencarbonate were needed in the manufacture of a sponge cake. Calculate the maximum volume (in dm ) of carbon dioxide that could be produced, at room temperature and pressure, by decomposing this mass of sodium hydrogencarbonate. One mole of any gas has a volume of 24 dm at room temperature and pressure. Ar: Na, 23; H, 1.0; C,12; O,163 3

volume = ................................dm

3

[Total 3 marks]

32.

The calcium ion content of water can affect both the colour and texture of cooked vegetables. Hard water areas contain relatively high concentrations of calcium ions. This is caused by groundwater running over naturally occurring calcium compounds such as limestone, an impure form of calcium carbonate. (i) Describe the trend in the solubility of the Group 2 carbonates. .................................................................................................................................... ....................................................................................................................................[1]

(ii)

The Group 2 elements form 2+ ions more easily as the group is descended and this is directly related to their reactivity. Describe and compare the reactivity of calcium and magnesium metals with water. Include a balanced equation in your answer. .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... ....................................................................................................................................[5] [Total 6 marks]


43

33.

Chemists play an important role in developing fuels for the future. One area of interest has been in the hydrogen economy where chemists have been looking at the possibilities of using hydrogen as a fuel, either directly or indirectly. (i) Hydrogen can be burnt as a fuel in an internal combustion engine. Give one advantage of hydrogen over petrol. ....................................................................................................................................[1]

(ii)

Describe one way in which hydrogen can be produced. .................................................................................................................................... ....................................................................................................................................[1]

(iii)

Why might your method of production in (i) not save fossil fuels? .................................................................................................................................... ....................................................................................................................................[1] [Total 3 marks]

34.

One novel way of producing hydrogen is to use Powerballs. These contain the ionic compound sodium hydride, NaH, encapsulated inside poly(ethene) spheres. The Powerballs are stored in water and are cut open automatically to allow the sodium hydride to react with the water and produce hydrogen when required. (i) The hydride ion is H . Draw a dot-cross diagram to represent both of the ions in sodium hydride. You should show outer electrons only.

[2]

(ii)

The reaction of the sodium hydride with water produces sodium hydroxide solution as well as hydrogen. Write a balanced equation for this reaction.

[2]

(iii)

One hazard involved in this process is the flammability of hydrogen. Suggest another chemical hazard. ....................................................................................................................................[1] [Total 5 marks]

35.

Methanol can be used in internal combustion engines. (i) One advantage of methanol is that it has a high octane number. Explain the term octane number. .................................................................................................................................... .................................................................................................................................... ....................................................................................................................................[2]

(ii)

Draw the full structural formulae for both the branched chain alcohols containing four carbon atoms. Give the names of the alcohols you have drawn.

name: ...............................................

name: ...............................................[4] [Total 6 marks]


45

36.

Nuclear fusion reactions readily occur in the Sun. However, in 1989 two scientists 2 claimed to have fused atoms of the hydrogen isotope 1H using only simple laboratory apparatus. This experiment was described as cold fusion. (a)2 (i) Give one similarity and one difference between 1H and the usual isotope of hydrogen.

similarity .......................................................................................................... difference .........................................................................................................[2]

(ii)

Complete the following equation to show the fusion of two atoms of the 2 hydrogen isotope 1H . 2 1H [2]2

(iii)

What happens in a nuclear fusion reaction? ........................................................................................................................... ...........................................................................................................................[2]

(b)

Many other scientists were doubtful about the cold fusion experiment. (i) Explain, in terms of charges, why it is difficult to get two nuclei to fuse together. ........................................................................................................................... ...........................................................................................................................[2]

(ii)

What conditions in the Sun make fusion possible? ........................................................................................................................... ...........................................................................................................................[2] [Total 10 marks]

37.

A mass spectrum of hydrogen gas showed a peak at mass 2. (i) Identify the two possible particles that would give rise to this peak. ..................................................................................................................................... .....................................................................................................................................[3]

(ii)

Other peaks occur at mass 3 and mass 4. Suggest possible explanations for these peaks. mass 3 ........................................................................................................................ mass 4 ........................................................................................................................[2]

(iii)

What information does the height of a peak in a mass spectrum give you? .....................................................................................................................................[1] [Total 6 marks]

38.

The Group 2 metal magnesium and its compounds are used in a variety of situations. One of the main sources of magnesium metal is from magnesium ions (Mg ) in sea water. The first stage in the production of magnesium is to mix the sea water with a slurry of calcium hydroxide. This precipitates magnesium hydroxide. (a) This reaction can be represented as follows. Mg (aq) + Ca(OH)2(aq) Mg(OH)2(..) + Ca (.....) Complete the state symbols on the product side of the equation.[1]2+ 2+ 2+

(b)

The above reaction relies on the fact that the solubility of the Group 2 hydroxides increases down the group. Give one other chemical property of the Group 2 elements or their compounds that shows an increase down the group. .....................................................................................................................................[1]

(c)

The magnesium hydroxide produced in the equation above can be heated to47


produce magnesium oxide or reacted with hydrochloric acid to make magnesium chloride. Draw an electron dot-cross diagram, in the space below, to show the ions present in magnesium chloride. Show outer electron shells only.

[4]

(d)

The magnesium chloride is electrolysed to form magnesium metal. Magnesium metal is an excellent conductor of electricity. Use your knowledge of bonding in metals to suggest why metals are good conductors of electricity. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................[2] [Total 8 marks]

39.

Sea water contains about 0.13% by mass of magnesium (as the magnesium ion). Calculate the number of moles of magnesium in 1.0 dm of sea water. Give your answer to two significant figures. Assume the density of sea water is 1.0 g cm . 1.0 dm = 1000 cm ; Ar: Mg, 243 3 3 3

number of moles .......................................... mol[Total 4 marks]


49

40.

Magnesium oxide is used as a furnace lining because of its very high melting point. Below is a bar chart showing the melting point of some Group 2 metal oxides. Suggest the temperature at which magnesium oxide melts. m 3 5 0 0 e l t i n g p o in t o f G r o u p 2 o x id e s

m

e

l t i n

g

3 0 0 0 p o in t 2 5 0 0 2 1 1 5 0 5 0 0 0 0 0 0 0 M 0 0 0

/

K m e lt in g p o i n t / K

g

O G r o u

C p

a

O 2

S o x i d e

r O

melting point of magnesium oxide = .............................................. K[Total 1 mark]

41.

Athletes suffering from stiff or injured muscles often make use of cold or hot packs, depending on the nature of the problem. Cold packs can reduce inflammation. Some packs contain water and solid ammonium nitrate in separate compartments. Breaking the divide between the two compartments and shaking leads to a considerable drop in temperature as the ammonium nitrate dissolves. (i) Complete and label the enthalpy level diagram below to represent a reaction that causes a temperature decrease in the surroundings. Use the following labels: reactants; products; enthalpy change of reaction

e

n t h

a

lp

y

/

H

p r o

g

r e

s s

o

f

r e

a

c t i o n[3]

(ii)

What name is given to a reaction or process causing a temperature decrease in the surroundings? .....................................................................................................................................[1] [Total 4 marks]


51

42.

A chemical reaction involving the ammonium compound ammonium bicarbonate, (NH4)HCO3, and causing a large decrease in temperature is given below. (NH4)HCO3(s) + HCl(aq) CO2(g) + H2O(l) + NH4Cl(aq) (i) The enthalpy change for this reaction can be determined indirectly using an energy cycle. A suitable energy cycle for this reaction is given below. Use this and the enthalpy changes of formation given in the table to calculate the enthalpy change for the reaction, Hr. Give an appropriate sign with your answer. ( N4

)H H

C3 ( s O )

+ l ( a Hq

)C

C

2O(

g

)

2

+ O

( lH )

4 +C

l ( a N q H)

e

l e

m

e

n

t s

in

t h

e

ir

s t a

n

d

a

r d

s t a

t e

u

n

d

e

r

t h

e

enthalpy change of formation compound (NH4)HCO3(s) HCl(aq) CO2(g) H2O(l) NH4Cl(aq) Hf/ kJ mol 849 165 394 286 3001

Hr = ................................... kJ mol

1

[4]

(ii)

The enthalpy change for this reaction could be measured directly from experiment by adding solid ammonium bicarbonate to dilute hydrochloric acid in an appropriate container. Describe the essential measurements that would need to be taken in order to determine this enthalpy change. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................[4]

(iii)

This reaction is accompanied by an increase in entropy. There are differences in the magnitude of the entropy of solids, liquids and gases. describe and explain these differences account for the increase in entropy in the reaction in the equation.

..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................[4] [Total 12 marks]


53

43.

One type of hot pack that is on the market contains a moist mixture of finely divided iron, common salt and charcoal sealed in a plastic cover inside an outer cloth bag. On breaking the plastic inner seal, the iron oxidises rapidly in air causing the temperature to rise markedly. The iron oxide Fe2O3 is formed. (i) Write a balanced equation for this oxidation reaction. Include the state symbols.

[2]

(ii)

Suggest a purpose for the charcoal/salt mixture. .....................................................................................................................................[1] [Total 3 marks]

44.

Liquefied petroleum gas is a general term used for liquefied C3 or C4 alkanes. It can be used as an automobile fuel, when it is usually called autogas. Well over 100 000 cars in the UK run on autogas and the number is increasing. (a) In the UK, autogas consists almost entirely of the C3 alkane, propane. (i) The alkanes are a homologous series of hydrocarbons and can be represented by a general formula. Give the general formula for alkanes. ...........................................................................................................................[1]

(ii)

Suggest one reason why propane is liquefied. ...........................................................................................................................[1]

(b)

In Europe, most autogas is a mixture of C3 and C4 alkanes. (i) There are two C4 alkanes. Draw skeletal formulae and give the name of each of these alkanes in the boxes below.

name ...................................................

name ...................................................[3]

(ii)

What name is given to molecules with different structures but the same molecular formula? ...........................................................................................................................[1] [Total 6 marks]


55

45.

Liquefied petroleum gas is a general term used for liquefied C3 or C4 alkanes. It can be used as an automobile fuel, when it is usually called autogas. Well over 100 000 cars in the UK run on autogas and the number is increasing. (a) Autogas produces considerably less carbon monoxide and unburnt hydrocarbons than ordinary petrol. One reason suggested for this is that autogas mixes much more thoroughly with air in the combustion chamber and therefore combustion is more complete. (i) The equation for the complete combustion of the C3 alkane, propane, is written below. C3H8(g) + 5O2(g) 3CO2(g) + 4H2O(g) Calculate the volume of air that would be needed to exactly react with 1.0 3 dm of propane gas. Assume that air contains 20% by volume of oxygen and that all measurements are made under the same conditions of temperature and pressure.

volume of air = .......................................... dm

3

[2]

(ii)

Why must the measurements all be conducted under the same conditions of temperature and pressure? ........................................................................................................................... ...........................................................................................................................[1]

(iii)

Give one reason why it is desirable to reduce carbon monoxide emissions. ...........................................................................................................................[1]

(iv)

Give a different reason why hydrocarbon emissions should also be reduced. ........................................................................................................................... ...........................................................................................................................[1]

(v)

Explain, in terms of bond breaking and bond making, why the combustion of a fuel gives out heat. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................[3]

(b)

Autogas has a higher octane number than ordinary petrol. Explain in terms of the molecules involved why the octane number is higher for autogas. Why is a fuel with a high octane number an advantage?

..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................[4] [Total 12 marks]


57

46.

Liquefied petroleum gas is a general term used for liquefied C3 or C4 alkanes. It can be used as an automobile fuel, when it is usually called autogas. Well over 100 000 cars in the UK run on autogas and the number is increasing. Energy density is the energy transferred on burning 1.0 kg of fuel. The energy density for petrol is about 48 000 kJ kg . It is higher for autogas. (i) Calculate the energy density for autogas assuming it to be 100% propane. Show your working Hc propane = 2 220 kJ mol ; Mr: C3H8 = 441 1

energy density of autogas = ..................................... kJ kg

1

[3]

(ii)

Why is the energy density of autogas higher than that of petrol? ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................[2] [Total 5 marks]

47.

Consumers are demanding food which is fresher and has a longer shelf-life. Packaging technology makes use of some simple chemical reactions to control the composition of the head space (the space between the food and package). Some of these reactions control the levels of oxygen, carbon dioxide, moisture and ethene in the head space. Oxygen in the head space often accelerates food spoilage. Iron metal in sachets removes oxygen and is said to act as an oxygen scavenger. The iron reacts with the oxygen, in the presence of moisture, as shown in the following equation. Balance the equation. 4Fe(s) + ..O2(g) + ..H2O(l) 4Fe(OH)3(s)[Total 2 marks]

48.

Carbon dioxide regulation is particularly important in coffee packaging. The CO2 is scavenged by reacting it with moist calcium oxide contained in sachets. The product is calcium carbonate, and the equation is written below. CaO(s) + CO2(g) CaCO3(s) (i) What property of calcium oxide means it reacts readily with carbon dioxide? ....................................................................................................................................[1]

(ii)

The solubility of the carbonates of the elements in Group 2 decreases as you go down the group. Name a Group 2 property which increases as you go down the group. ....................................................................................................................................[1]


59

(iii)

The sachets contain 0.80 g of calcium oxide. Calculate the maximum volume of 3 carbon dioxide (in cm ) that could be removed by the reaction in the equation above. Give your answer to two significant figures. 1.0 dm = 1000 cm ; Ar: Ca, 40; O, 16 One mole of gas occupies 24dm at room temperature and pressure.3 3 3

volume = .......................................... cm

3

[4] [Total 6 marks]

49.

Ethene, CH2CH2, is a hydrocarbon gas which can accelerate softening and ageing in fruit. (i) Classify each of the hydrocarbons below as an alkane, alkene, cycloalkane or arene. The first one has been done for you. hydrocarbon CH2CH2 classification alkene

CH2CHCH2CH3

C6H14[4]

(ii)

The ethene molecule can be represented by the following structure.

H H C

H C H

The bond angles shown in this representation are not the actual bond angles in the molecule. Suggest a value for the HCH bond angle and explain this in terms of electron pair repulsion theory. Give the overall shape of the ethene molecule. bond angle = .................................. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................[5]

(iii)

Ethene is produced in cracking reactions. Explain the term cracking as used in the petrochemical industry. .................................................................................................................................... ....................................................................................................................................[2]


61

(iv)

In catalytic cracking, some of the hydrocarbons decompose to produce carbon. This can render the catalyst inactive. Describe how a heterogeneous catalyst works and suggest why the presence of carbon can cause the catalyst to become inactive. .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... ....................................................................................................................................[5]

(v)

Naturally occurring compounds called zeolites are used as heterogeneous catalysts but can also be used in food packaging to lower the moisture content in the head space. What feature of the structure of zeolites makes them good at absorbing small molecules? .................................................................................................................................... .................................................................................................................................... ....................................................................................................................................[2] [Total 18 marks]

50.

Dying stars often give off carbon, indeed some particularly carbon-rich stars are surrounded by a haze of carbon molecules of different structures and molecular masses. A simplified mass spectrum which shows the presence of a carbon molecule is shown below. What is the formula of the carbon molecule that gives rise to peak A?

7 6 i n t e n

0

0

0

0 0 0 s it y 5 0 0 0 4 3 2 1 0 0 0 0 0 0 0 0 0 0 0 0 0 4 4 5 2 6 0 o f 6 8 t o A

n

u

m

b

e

r

c a

r b

o

n

a

answer .................................................[Total 1 mark]

51.

The age of carbon-containing materials can be measured using radiocarbon dating. The radioactive carbon-14 isotope is found in small amounts in all living organisms, and the proportion of this isotope remains constant until the organism dies. (i) How does the atomic structure of carbon-14 differ from that of the more common carbon-12 atom? .................................................................................................................................... .................................................................................................................................... ....................................................................................................................................[2]


63

(ii)

When a carbon-containing organism dies, the radioactivity due to the carbon-14 atoms present halves approximately every 6000 years as these atoms undergo radioactive decay. Cheap ethanol, C2H5OH, manufactured from crude oil, can be used in fake wines instead of ethanol derived from the fermentation of grapes. This fake wine, however, shows very little radioactivity compared to genuine wine. Using the information above, suggest why fake wine shows very little radioactivity. .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... ....................................................................................................................................[3] [Total 5 marks]

52.

The presence of atoms or ions of individual elements in the gas surrounding stars is shown by atomic emission spectroscopy. Describe the appearance of an atomic emission spectrum. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................[Total 3 marks]

53.

Caesium is stored under oil because it reacts rapidly with oxygen to form a highly dangerous superoxide. Analysis of a sample of the superoxide showed the compound to contain 80.6% caesium by mass, the rest being oxygen. Calculate the empirical formula for the superoxide. Show your working. Ar:Cs, 133; O, 16

empirical formula .................................................[Total 3 marks]

54.

Ion propulsion systems using xenon propel the space probe, Deep Space 1. (i) Xenon is found in Group 0 of the Periodic Table. Explain, in simple terms, how the electronic structure of an element is related to its group. .................................................................................................................................... .................................................................................................................................... ....................................................................................................................................[2]

(ii)

There are nine naturally occurring isotopes of xenon. Explain the term isotopes. .................................................................................................................................... .................................................................................................................................... ....................................................................................................................................[2] [Total 4 marks]


65

55.

Higher than expected levels of the xenon isotope, xenon-129, are found in some stony meteorites. This is thought to be because of the radioactive decay of iodine-129. Write a nuclear equation in the space below to represent the radioactive decay of iodine-129 to xenon-129.

[Total 3 marks]

56.

Nitrous oxide, N2O, can be injected into an internal combustion engine in order to significantly increase power output. Nitrous injection has been used in high performa

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