1

Farr High School

NATIONAL 5 CHEMISTRY

Unit 3

Chemistry in Society

Question Booklet

2

Metals 1. a) Describe in detail what metallic bonding is. You should use the words positive ions and delocalised electrons in your answer.

3D lattice of positive ions held together by the electrostatic attraction with the ‘sea’ of delocalised electrons which attract the positive ions and balances the repulsion between positive ions.

b) Use the idea of metallic bonding to explain why metals are good electrical conductors.

As the electrons are free to move through the lattice structure this also allows electrical charge to easily move through metal lattices.

2. Explain what is meant by the following words: a) lattice b) malleable a) regular repeating 3D pattern (lattice) b) can be easily re-shaped 3. Give the names of a) two metals which are more reactive than magnesium sodium, calcium, potassium, lithium b) two metals which are less reactive than copper silver, gold, mercury 4. Complete the word equations for the following reactions. Write a balanced symbol equation for each reaction. a) sodium + water sodium hydroxide + hydrogen 2Na + 2H2O 2NaOH + H2

b) magnesium + hydrochloric acid magnesium chloride + hydrogen Mg + 2HCl MgCl2 + H2

c) calcium + oxygen calcium oxide 2Ca + O2 2CaO

5. In each of the reactions in question 4, write an ion electron equation to show the oxidation of the metal atoms. Na Na+ + e-

Mg Mg2+ + e-

Ca Ca2+ + e- 6. How could the following metals be extracted from their ores? a) mercury b) copper c) iron d) aluminium heat oxide heat oxide with C heat oxide with C electrolysis 7. Use your half-equation data sheet to help you decide whether each of these reactions is

oxidation, reduction, redox or neither.

a) Cu going to Cu2+ oxidation b) Mg2+ going to Mg. reduction

c) Reacting aluminium with oxygen to form aluminium oxide. redox

3

d) Adding magnesium to hydrochloric acid and producing hydrogen gas. redox

e) displacing tin from tin (II) chloride solution by adding zinc to it. redox f) Iron (III) oxide changing to iron. redox

8. Calculate the % mass of a) sodium in sodium oxide Na2O. 74% b) aluminium in aluminium oxide Al2O3. 53% c) copper in copper (II) oxide CuO. 79.9% 9. How much a) aluminium can be obtained from 1kg of aluminium sulphate Al2(SO4)3? 158kg b) potassium could be extracted from 200kg of potassium oxide K2O? 166kg 10. 1000kg of rock containing lead ore was mined. The rock was found to contain 5% lead oxide PbO2. What mass of lead can be extracted from the 1000kg of rock? 43.5kg 11. 100000kg of rock containing tin ore was mined. The rock was found to contain 12% tin oxide SnO2. What mass of tin can be extracted from the 100000kg of rock? 9444kg 12. A miner extracted 50kg of rock containing haematite. The rock contained 20% iron oxide (Fe2O3). What mass of iron could be extracted from the 50kg of rock? 7kg

13. Solders are alloys of lead (melting point 327oC) and tin (melting point 232oC). The table shows the melting points of solders containing different percentages of tin.

Percentage tin in solder (by mass)

Melting point/oC

10 20 30 40 50 60 70 80 90

305 280 260 240 215 190 190 200 215

(a) Draw a line graph of melting point against the percentage tin in solders.

4

(b) State the percentage of lead present in the solder with the lowest melting point. 30% or 40% (c) Why are alloys of metals made? In order to improve the properties of the metal. (d) Solders which do not contain lead are made. They are used to solder pipes for drinking water. Suggest why this has been done.

Lead is poisonous and if water pipes contain lead some ions could dissolve in the drinking water and be consumed by humans.

14. A group of pupils set up the following cell. (a) What is the purpose of the soaked filter paper? Ion bridge to allow charge to flow and complete the circuit. (b) Name a metal which could replace nickel and give a lower reading on the voltmeter. You may wish to use page 7 of the data booklet. Tin or lead (c) A cell (battery) has several advantages over mains electricity. Give one advantage. Portable devices or some are rechargeable.

0

50

100

150

200

250

300

350

0 10 20 30 40 50 60 70 80 90 100

Me

ltin

g p

oin

t (°

C)

% Sn in solder

Comparison of solders

5

15. The cells which power heart pacemakers contain lithium metal. Explain why lithium metal is a good choice for the negative electrode.

Near the top of the electrochemical series so will produce a high voltage as you can pick a much lower metal to generate a high voltage.

16. The results obtained when the metals A,B and C were tested in a cell using metal D as a standard are shown below.

a) Suggest the name of a suitable electrolyte solution. Sodium chloride b)

Metals Voltmeter reading/ V

A and D 0.75

B and D 1.65

C and D 1.18

Place the four metals in an electrochemical series starting with the metal highest in the series.

B > C > A > D

17. A pupil placed a strip of nickel on top of a piece of silver and connected both to a voltmeter, but the meter gave no reading. a) Explain why there was no reading on the voltmeter. There is no electrolyte to allow charge to flow. b) What would the pupil have to do to get a reading on the voltmeter? Connect the metals with an electrolyte. c) The pupil looked up nickel in the electrochemical series and found that it was between zinc and iron. Which pair of the following metals would give the highest meter reading? i) Nickel and silver or zinc and silver? Zinc and silver ii) Nickel and silver or iron and silver? Iron and silver d) What is meant by the term ‘electrolyte’?

A compound that conducts owing to the movement of ions either when dissolved in water or metal.

6

18.

a) What is the direction of the electron flow in the external circuit? Zinc to copper b) What difference there would be in the voltage reading if the zinc and zinc sulphate solution were replaced by magnesium and magnesium sulphate solution. Increase in voltage c) Write an ion electron equation for the reaction at i) the zinc electrode

Zn(s) → Zn2+(aq) + 2e-

ii) the copper electrode. Cu2+(aq) + 2e- → Cu(s) d) Which electrode i) increases in mass? copper ii) decreases in mass? zinc 19. In Australia flow cells are used to store the energy from solar cells. a) The reaction taking place at electrode A when the cell is providing electricity is: Zn Zn2+ + 2e- Name the type of chemical reaction taking place at electrode A. oxidation

7

b) State the direction of electron flow. A to B c) Name the non-metal, that conducts electricity, which could be used as an electrode. graphite 20. A student set up the cell shown: The reaction taking place at electrode Y is: 2I-(aq) I2 + 2e- a) Name the type of chemical reaction taking place at electrode Y. reduction b) State the direction of the electron flow. X to Y c) Describe a test, including the result, which would show that iodine had formed at electrode Y.

Add a few drops of starch solution and the iodine will change from orange to blue/black.

d) Write the ion-electron equations for the chemical reaction taking place at electrode X and Y.

2I-(aq) → I2(aq) + 2e-

Br2(aq) → 2Br-(aq) + 2e-

8

Fertilisers

1. Why has the need for fertilisers risen sharply in the last 60 years? World population has vastly increased therefore requiring higher food outputs globally therefore incentivising the need for more fertilisers.

2. What is the purpose of fertilisers? Provide the elements required for plant growth. 3. Copy and complete the table to show the essential elements provided by fertilisers.

Compound Element Why plants need it Signs of deficiency

Nitrates Nitrogen Essential for photosynt- hesis. Required for proteins.

Yellowing of leaves

Potassium salts Potassium Plant growth and Reproduction.

Brown scorching and curling of leaves.

Phosphates Phosphorus Helps roots to grow and buds to form.

Poor growth and leaves turn blue/green.

4. Name two natural fertilisers. Guano (bird droppings) and leguminous plants (green compost). 5. What information can you get from the NPK number on a bag of fertiliser? % mass of each element in the fertiliser. 6. Briefly explain two environmental impacts of fertilisers. Eutrophication and pollute water supplies. 7. What is the laboratory test for ammonia gas? Damp red litmus paper turns blue. Damp pH paper turns blue/purple. 8. Nitrogen and hydrogen are converted to ammonia in the Haber process. a) Write a symbol equation for the reaction.

N2(g) + 3H2(g) ⇌ 2NH3(g) b) What is the source of the reactants for the process?

Methane + steam → hydrogen hydrogen + air → water + nitrogen c) Why is the formation of ammonia from nitrogen and hydrogen described as a reversible reaction? Both the forwards and backwards reactions are occurring at the same time. d) In order to get the optimum yield, what temperature and pressure are used during the manufacture of ammonia?

T = 450°C P = 200atm e) Why is an iron catalyst used during the Haber process? To get a fast reaction at a relatively low temperature.

9

9. Nitrogen is essential for healthy plant growth. Nitrogen from the atmosphere can be fixed in a number of ways. a) X is a natural process which takes place in the atmosphere, producing nitrogen dioxide gas. What provides the energy for this process? lightning b) What is present in the root nodules of some plants which convert nitrogen from the atmosphere into nitrogen compounds? bacteria c) The Haber Process is the industrial method of converting nitrogen into a nitrogen compound. Name the nitrogen compound produced. ammonia d) The nitrogen compound produced in the Haber Process dissolves in water. The graph shows the solubility of the nitrogen compound at different temperatures. Write a general statement describing the effect of temperature on the solubility of the nitrogen compound. As the temperature increases the solubility of ammonia decreases. 10. a) What makes ammonium nitrate such a useful fertiliser? soluble b) Which three materials are used to manufacture nitric acid? Ammonia, air, and platinum gauze catalyst (and oxygen) c) Why is the manufacture of ammonium nitrate described as a neutralisation process? It is the salt produced from the reaction between ammonia and nitric acid.

(Acid + alkali)

10

11. The flow diagram shows how ammonia is converted to nitric acid.

a) Name the industrial process used to manufacture nitric acid Ostwald process b) The reactor contains a platinum catalyst. Why is it not necessary to continue heating the catalyst once the reaction has started? The oxidation of ammonia is exothermic so temperature stays high. c) Name substance X. water d) The reaction is carried out at temperatures between 380 °C and 450 °C. Why are higher temperatures not used? As then the product would decompose too quickly in the backward reaction. e) Ammonia and nitric acid react together to form ammonium nitrate, NH4NO3 Calculate the percentage by mass of nitrogen in ammonium nitrate (show your working clearly). GFM (NH4NO3) = 80g 2 x N = 28g (28/80)x100 = 35% 12. Calculate the percentage by mass of nitrogen in each of the following compounds

which are used as fertilisers. a) Sodium nitrate 16.5% b) Calcium nitrate 17% c) Ammonium nitrate 35% d) Ammonium sulphate 21.2% 13. Calculate the % of phosphorus in sodium phosphate. 19% 14. Calculate the % potassium in potassium nitrate. 38.6%

11

Nuclear Chemistry 1. Explain what is meant by nuclear radiation. Radiation emitted from the nucleus of a radioactive isotope (particles or waves). 2. What is meant by the term ionisation? The energy required to free electrons from atoms. 3. A radioactive source has an activity of 68 becquerels. a) What does the word “activity” mean in this context?

The rate at which a source of unstable nuclei decays measured in decays per second.

b) How many nuclear decays would occur in this source in 1 minute? 4080 decays 4. It is thought that most of the Helium gas in our atmosphere comes from alpha particles taking electrons from other atoms in the air. a) What word can be used, here, to describe the action of the alpha particles on atoms in the air. reduction b) Alpha can be “absorbed” by 10cm of air. What do you think happens to the alpha particles once they are absorbed by air. They decay to form stable particles. 5. a) What absorbs beta radiation? Thin sheet of metal. b) What absorbs gamma radiation? Thick concrete or lead. 6. What 3 precautions could a radiation worker take in order to reduce the risk of over exposure while working with nuclear radiation? Lead vest, radiation badge, thick concrete walls, minimum exposure during workday 7. State 4 sources of background radiation on Earth? Cosmic rays, rocks, soil, living things. 8. There are 2 types of nuclear reaction; fission and fusion. a) Explain what is meant by each type of reaction. Fusion – light nuclei fuse to make heavier nuclei and energy is released

Fission – breaking up of a nucleus by bombardment of heavy atoms with neutrons which releases more neutrons so a chain reaction occurs and energy is released

b) Which type of reaction takes place in a nuclear reactor? fission c) Which type of reaction causes the formation of a variety of elements in the stars? fusion d) Which type of reaction requires very high temperatures? fusion e) Both reactions give out lots of energy, but which one does not generate radioactive waste? fusion

12

9. Explain, with the aid of a diagram, how a “chain reaction” can occur?

10. Look at the following nuclear reactions and decide whether each one is a fission or a fusion reaction. a) fusion b) fission 11. The initial activity of a radioactive isotope is 400 Bq. The sample has a half-life of 2

minutes and is allowed to decay for 8 minutes. Calculate the final activity of the isotope.

25Bq 12. Radioactive rocks emit radiation which can be harmful. A rock sample has an activity of

160 Bq and emits radiation over a 3 day period. What is the final activity of these rocks given that their half-life is 12 hours.

2.5Bq 13. An isotope of indium is left decaying for 4 hours. The half-life of the source is 60

minutes and the initial activity is 200 counts per minute. Calculate the final activity of the isotope.

12.5 counts per minute 14. A sample of radioactive uranium has an initial activity of 600 kBq. After 10 days its

activity has dropped to 150 kBq. Use this information to calculate the half-life of the source.

5 days 15. A sample of caesium has an initial activity of 1400 kBq. After 9 minutes its activity has

dropped to 175 kBq. Use this information to calculate the half-life of the source. 3 minutes 16. Calculate the half-life of a radioactive sample which has an initial activity of 2 000 Bq

that drops to 125 Bq in a period of 16 hours. 4 hours 17. A radioactive source has a half life of 2 days. What fraction of its activity remains after:

a) 2 days b) 6 days c) 20 days?

½ 1/8 1/1016

13

18. Radioactive Caesium has a half life of 32 minutes. What fraction of its activity remains after:

a) 32 minutes b) 64 minutes c) 160 minutes? ½ ¼ 1/24

19. A radioactive sample has a half life of 20 seconds. How long has the sample been decaying if the fraction of its initial activity that remains is:

a) 1/4 b) 1/16 c) 1/64? 20 seconds 80 seconds 120 seconds

20. Use the graphs to find the half-life of source A and source B.

4 minutes 8 minutes

21. A student sets up the following apparatus to measure the half-life of a radioactive

sample of cobalt 60. Since the experiment is carried out in a sealed container we can assume background radiation is negligible.

She obtained the following results.

Time (mins) 0 10 20 30 40 50 60 70

Activity (Counts per minute) 800 600 410 310 200 150 100 75

Use these results to plot a graph of activity against time and use it to find the half-life of the radioactive source.

20 minutes

0

200

400

600

800

1000

0 20 40 60 80

Act

ivit

y (C

ou

nts

pe

r m

inu

te)

Time (mins)

Half-life

14

22. Use the graph below to answer the following questions.

a) What is the half life of the source?

8 days b) What should be the activity of the source after 32 days? 5 Bq

23. During an experiment with a radioactive source, Eddie and Ann measured a background count of 14 counts per minute. With the source in place, they recorded readings of 94 counts per minute and, 3 hours later, 24 counts per minute. Use their results to calculate the half life of the source. 1 hour 24. An experiment to measure the half life of a radioactive source was set up and the background activity was measured as 15 Bq. A measurement of activity beside the source dropped from 375 Bq to 60 Bq over a 9 day period. Calculate the half life of the source. 3 days 25. On a day when the background count was measured as 30 counts per minute, the folowing readings were obtained from a radioactive source. The readings have not been corrected for background.

a) Plot a corrected graph of activity against time for the source only.

b) Calculate the half life of the source.

3 hours

0

50

100

150

200

250

0 2 4 6 8Act

ivit

y (c

ou

nts

pe

r m

inu

te)

Time (hours)

Activity (corrected) against time

Time (hours)

0 1 2 3 4 5 6 7

Activity (counts per minute)

230 190 160 130 110 95 80 70

15

26. An isotope of carbon, carbon-14, forms when neutrons entering the upper atmosphere react with atoms of nitrogen-14. a) What is meant by an isotope? Atoms of an element with the same atomic number but different mass number. b) How is an atom of carbon-14 different to an atom of carbon-12? 2 more neutrons in carbon 14. Carbon-14 is radioactive and decays to nitrogen-14, with the emission of a beta particle.

c) Write a balanced nuclear equation for this process.

𝐶 → 𝑁 + 𝑒−10

714

614

All living things contain carbon, a small amount of which is carbon-14. The half-life of carbon-14 is 5600 years. By comparing the amount of carbon-14 in a living organism and a dead one, scientists can work out how long ago the organism died.

d) Suggest why the method is not useful for dating objects that are only a few years old.

The half-life is 5600 years old so not enough C-14 would have decayed to make quantifiable measurements.

e) Suggest why the method is not useful for dating very old objects - for example diamonds, which are millions of years old. No C-14 is present any longer (minimal amounts). 27. When welders join thick steel plates it is important that the joint is completely filled with metal. This ensures there are no air pockets in the metal weld, as this would weaken the joint. One method of checking for air pockets is to use a radioactive source on one side of the joint. A detector placed as shown measures the count rate on the other side. a) The radioactive source and detector are moved along the weld. How would the count rate change when the detector moves over an air pocket? Explain your answer.

It would increase as there is a lower level of resistance to the penetration of the radiation in the air pocket.

b) Which of the radiations alpha, beta or gamma must be used? Explain your answer. Gamma as alpha cannot travel far enough and beta would be stopped by the steel. c) X-rays are sometimes used to detect air pockets. How does the wavelength of X- rays compare with gamma rays? X-rays have a longer wavelength.

16

28. Thickness of paper can be tested using a radioactive source. This source emits beta particles. The source is on one side of the paper and the detector (Geiger Muller Tube) is on the other side. The paper rolls through the rollers as shown.

a) What are beta particles? High speed(velocity) electrons

b) Why are beta particles the more suitable than alpha or gamma rays for this job? Alpha doesn’t penetrate paper. Gamma can only be stopped by lead.

Below are results for the Geiger counter for 70 secs of paper passing through the rollers.

TIME (SECS) 10 20 30 40 50 60 70

TOTAL COUNT (since start) 50 100 150 195 235 275 315

COUNT EVERY 10 SECS 50 50 50 45 40 40 40

c) Complete the table to show the count for each 10 sec period.

d) What happened to the thickness of paper? Explain your answer.

Thickness increased as the count decreased. e) At what time did the paper begin to change thickness?

30-40 seconds

17

Materials 1. What is meant by the following words: a) monomer small molecules that can join together to produce a large molecule b) polymer large molecule formed by the joining of smaller molecules c) polymerisation the chemical reaction in which monomers join to make polymers 2. Copy and complete the table giving the correct monomer or polymer name.

Monomer Polymer

ethene poly(ethene)

vinyl chloride Polyvinylchloride(PVC)

propene poly(propene)

styrene polystyrene

urethane poly(urethane)

saccharide poly(saccharide)

tetrafluoroethylene Polytetrafluoroethylene(PTFE)

3. Polythene is an addition polymer. What is meant by the term addition polymer? The polymer is formed by the addition reaction of unsaturated monomers. 4. A list of hydrocarbons is given below: chloroethene polyethene propene PVC phenylethene polystyrene What is the name of: a) the monomer used to make polypropene. propene b) the polymer made from ethene polyethene c) the polymer made from chloroethene polychloroethene d) the polymer made from phenylethene polyphenylethene

18

5. Copy and complete the table for each polymer.

6. “Teflon” has the structure : CHF CHF CHF CF2 CF2 CF2

a) Identify the repeating unit.

b) Draw the structural formula of the monomer. c) Write the molecular formula of the monomer. C2HF3

Name of monomer

Structure of monomer

Name of polymer Structure of polymer

(showing 3 monomer units joined)

Repeating unit

ethene

polyethene

chloroethene

polychloroethene

propene

polypropene

phenylethene

(styrene)

polyphenylethene (polystyrene)

tetrafluoro ethene

polytetrafluoroethene

19

7. “Orlon” is a synthetic fibre made from monomers with the following structure:

a) Draw the structural formula for the repeating unit of Orlon.

b) Draw the full structure when 3 units join together.

c) What poisonous gas will come off when Orlon is burned ? hydrogen cyanide (HCN)

8. When superglue sets a polymer is formed. The monomer has the following structure. Draw a section of a superglue molecule, showing 3 monomer units joined together and

bracket the repeating unit.

n

20

9. A co-polymer is formed when two different monomers are joined together so that the required properties are obtained. The following structure shows part of a co-polymer molecule.

a) Copy the structure and bracket the repeating unit.

b) Draw the structure of the two monomers used to make the above co-polymer.

10. Polyvinyldichloride (PVDC) is a plastic used in food packaging. The structure of part of a PVDC molecule is shown. a) Draw the full structural formula for the monomer used to make PVDC.

b) Name a toxic gas produced when PVDC burns. Hydrogen chloride (HCl)

n

21

11. Why are the following important in our diet? a) carbohydrates b) proteins c) fats and oils energy growth and repair energy and insulation 12. What elements are present in all carbohydrates? Carbon, hydrogen and oxygen 13. Describe the test and positive result for a) glucose b) starch a) warm benedict’s solution – blue → orange b) iodine solution – orange → blue/black 14. Starch can be broken down into glucose by the enzyme amylase. a) What is an enzyme? A biological catalyst b) The optimum temperature for amylase is 37oC. What is meant by the term optimum temperature? Enzyme’s catalytic activity is optimised. c) What happens to enzymes if they are heated to 50 oC? They are denatured d) Give another way that starch can be broken down into glucose. Hydrolysis

22

Chemical Analysis 1. When sulphur dioxide dissolves in water in the atmosphere “acid rain” is produced. a) Compared with pure water, does acid rain contain a higher, the same or a lower concentration of hydrogen ions higher b) The table shows information about the solubility of sulphur dioxide. Draw a line graph of solubility against temperature

2. The table shows the mass of various pollutants produced by recycling aluminium. a) Present the information as a bar graph

0

5

10

15

20

25

0 10 20 30 40 50 60 70

Solu

bili

ty (

g/1

00

cm3 )

Temperature (°C)

Solubility of sulfur dioxide

23

b) When sulphur dioxide reacts with water in the atmosphere, acid rain is produced. Give one example of a damaging effect of acid rain. Statues eroded, buildings eroded, polluted lakes c) Write the balanced chemical equation for the formation of acid rain. SO3 + H2O → H2SO4 3. Calculate the concentration of sodium hydroxide if 50cm3 of the alkali exactly neutralised 100cm3 of 1 mol l-1 of hydrochloric acid solution. 2 mol l-1

4. Calculate the volume of 0.25 mol l-1 sodium hydroxide if the alkali exactly neutralised 25 cm3 of 0.5 mol l-1 hydrochloric acid solution. 0.05 l 5. Calculate the concentration of hydrochloric acid if 100cm3 if the acid exactly neutralised 25cm3 of 0.5 mol l-1 sodium hydroxide solution. 0.13 mol l-1

6. Calculate the concentration of sodium hydroxide if 50cm3 if the alkali exactly neutralised 100cm3 of 1 mol l-1 sulphuric acid solution. 2 mol l-1

7. Calculate the volume of 0.25 mol l-1 sodium hydroxide if the alkali exactly neutralised 50 cm3 of 0.5 mol l-1 sulphuric acid solution. 0.1 l 8. Calculate the concentration of sulphuric acid if 25cm3 if the acid exactly neutralised 25cm3 of 0.5 mol l-1 sodium hydroxide solution. 0.5 mol l-1

0

1

2

3

4

5

6

7

8

sulfur dioxide dust carbonmonoxide

nitrogen oxides hydrocarbons

Mas

s o

f p

ollu

tan

t p

rod

uce

d p

er

ton

ne

of

alu

min

ium

(k

g)

Pollutant

Mass of pollutants produced from recycling aluminium

24

9. Biologists from the Institute of Terrestrial Ecology have been monitoring the spawning success of salmon and par survival rates in the head water of an important local salmon river. Data collected for the past 5 years suggest poor fertilisation of the salmon ova and high mortality of salmon par. The lead scientist commissioned an environmental chemist from the Macaulay Land Research Institute to establish whether acid rain could be the cause of the poor survival and fertilisation rates. The environmental chemist collected samples over a 12 month period. Her titration results for the month of June and experimental set-up are shown below. The equation for the reaction is: H2SO4 + 2NaOH Na2SO4 + 2H2O a) Using the results in the table, calculate the concentration of acid in the river sample required to neutralise the sodium hydroxide solution. 1 x 10-3 mol l-1

b) How could she improve the reliability of her advice to her ecology colleague. Repeat with fresh samples, take samples from different parts of the river, collect samples multiple times a month