QUESTION and ANSWER BOOKLET (1)

Time allowed: Three hours

(An extra 10 minutes is allowed for reading this paper.)

South Pacific Form Seven Certificate

CHEMISTRY 2020

INSTRUCTIONS

Write your Student Personal Identification Number (SPIN) in the space provided on the top right-hand corner of this page.

Answer ALL QUESTIONS. Write your answers in the spaces provided in this booklet.

If you need more space for answers, ask the Supervisor for extra paper. Write your SPIN on all extra sheets used and clearly number the questions. Attach the extra sheets at the appropriate places in this booklet.

Major Learning Outcomes (Achievement Standards)

Skill Level & Number of Questions Weight/

Time Level 1

Uni-structural

Level 2 Multi-

structural

Level 3 Relational

Level 4 Extended Abstract

Strand 1: Atomic Structure, Bonding and Related Properties

Interpret information about selected properties of elements and compounds in relation to atomic structure.

8 3 2 - 20%

51 min

Strand 2: Energy Changes in Chemical and Physical Processes

Use thermochemical data to determine energy changes in chemical and physical processes.

2 1 - 1 8%

21 min

Strand 3: Aqueous Equilibrium Systems Relate the properties of aqueous solutions to the nature and concentration of dissolved species.

5 3 1 - 14%

36 min

Strand 4: Oxidation–Reduction Reactions Apply oxidation–reduction principles to electrochemical cells and compare the relative strength of oxidants and reductants, and deduce the direction of spontaneous reactions.

- 1 1 - 5%

13 min

Strand 5: Organic Chemistry Use information about the structure and reactions of organic molecules to solve problems in organic chemistry.

3 5 2 1 23%

59 min

TOTAL 18 13 6 2 70%

180 min

Check that this booklet contains pages 2–17 in the correct order and that none of these pages are blank.

HAND THIS BOOKLET TO THE SUPERVISOR AT THE END OF THE EXAMINATION.

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STRAND 1: ATOMIC STRUCTURE, BONDING AND RELATED PROPERTIES

1.1 Define the term electron configuration.

1.2 Write the ground state electron configuration of an iron (Fe) atom.

1.3 One of the ways of expressing the size of atoms is with the atomic radius.

Describe the general trend in atomic radii of the elements across the Period

and down the Group in the Periodic Table.

Use the information below to answer questions 1.4a and 1.4b.

Phosphorus pentachloride (PCl5) is prepared by reacting phosphorus

trichloride (PCl3) with chlorine (Cl2):

PCl3 + Cl2 → PCl5

1.4a Name the shape of phosphorus trichloride (PCl3) molecule.

1.4b Draw the Lewis structure of phosphorus pentachloride (PCl5) molecule.

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Use the information below to answer questions 1.5a and 1.5b. The structure of three organic compounds and their boiling points are given below:

Compound Structure Boiling Point

A C C CH

H

H H

H H

H

H

−42 °C

B C C CH

H

H Cl

H H

H

H

35.7 °C

C C C CH

H

H OH

H H

H

H

82.3 °C

1.5a Identify the intermolecular forces present in Compound A, which is the reason for its low boiling point.

1.5b Explain the difference between the boiling points of Compound B and Compound C by comparing the molecular forces present in each compound.

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Use the information given below to answer questions 1.6a–1.6c.

A substance that contains unstable atomic nuclei is considered to be

radioactive. For example, all naturally occurring isotopes of the element

thorium (Th) exhibit radioactivity.

1.6a Define the term radioactivity.

1.6b The Th232 isotope produces the Ra228 isotope and emits ionising radiation in

the form of a particle.

Write the balanced nuclear equation for this reaction and name the particle.

1.6c The Ra228 isotope is also radioactive. It produces Ac228 and emits ionising

radiation in the form of a particle. State a feature of this reaction.

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Use the information below to answer questions 1.7a–1.7c.

During a laboratory investigation, a student mixed separate solutions of Ag+, Zn2+ and Cu2+ ions with dilute ammonia (NH3) solution and recorded the following observations:

Ion Observation after mixing with ammonia

Ag+ A brown precipitate formed before it dissolved in excess ammonia to give a colourless solution

Zn2+ A white precipitate formed before it dissolved in excess ammonia to give a colourless solution

Cu2+ A light blue precipitate formed before it dissolved in excess ammonia to give a deep blue solution

1.7a Name the group of metals which Ag, Cu and Zn belong to.

1.7b When excess dilute ammonia reacts with Zn2+, the formula of the species formed is [Zn(NH3)]42+.

Name this species.

1.7c Write balanced chemical equations to account for the observations when ammonia reacted with Cu2+ ions.

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STRAND 2: ENERGY CHANGES IN CHEMICAL AND PHYSICAL PROCESSES

2.1 Bond enthalpies can be used to determine the enthalpy change of reactions. Define the term bond enthalpy.

2.2 Name the enthalpy change involved in the reaction given below, where both

the reactants and products are at standard state conditions.

1

2 H2 (g) +

1

2 Cl2 (g) → HCl (g)

2.3 Combustion reactions are an extremely important class of chemical reactions

used in everyday life.

List two characteristics of a combustion reaction.

2.4 Glucose (C6H12O6) is a simple sugar and is necessary for cellular respiration.

It releases energy by reacting with oxygen to form carbon dioxide and water:

C6H12O6 (s) + 6O2 (g) → 6CO2 (g) + 6H2O (l)

Using the data provided in the table below, calculate the amount of energy

released when one gram of glucose reacts as above (Molar mass of glucose

is 180 g mol-1):

Substance ΔHof (kJ mol-1)

C6H12O6 (s) −1273.3

O2 (g) 0.0

CO2 (g) −393.5

H2O (l) −285.8

In your response:

state the method used;

show all calculations clearly; and

inlcude symbols, signs and units.

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STRAND 3: AQUEOUS EQUILIBRIUM SYSTEMS

Use the information below to answer questions 3.1a and 3.1b.

The air pollutant, nitric oxide (NO), can be removed from vehicle exhaust systems by reacting it with carbon monoxide (CO) in the presence of a catalyst. At 300°C, the value of the equilibrium constant for the reaction is 2.2 × 1059.

2NO (g) + 2CO (g) ⇌ N2 (g) + 2CO2 (g)

3.1a What does the equilibrium constant value indicate about the position of the

above equilibrium system?

3.1b Write the equilibrium constant expression for the above reaction, using appropriate terms and symbols.

3.2 An aqueous solution of potassium nitrate (KNO3) is an example of a strong

electrolyte. What does the term strong electrolyte mean?

Use the information below to answer questions 3.3a–3.3d.

Ethanoic acid (CH3COOH) establishes equilibrium in water with ethanoate ions (CH3COO-) and hydrogen ions (H+):

CH3COOH (aq) ⇌ CH3COO- (aq) + H+ (aq)

A buffer solution is made by adding solid sodium ethanoate (CH3COONa) to

an aqueous solution of ethanoic acid.

3.3a Define buffer solution.

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3.3b Identify one feature of the sodium ethanoate-ethanoic acid buffer solution.

3.3c Explain how a mixture of sodium ethanoate and ethanoic acid can act as a

buffer. Your response should include relevant balanced equations.

3.3d Calculate the pH of a buffer solution in which the concentration of sodium

ethanoate is 0.090 mol L-1 and the concentration of ethanoic acid is 0.050 mol

L-1. Ka (CH3COOH) = 1.8 × 10-5 at 25°C.

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Use the information below to answer questions 3.4a and 3.4b.

The salt, lead chloride (PbCl2), is sparingly soluble in water. The following

equilibrium is set up between the solid and its ions in a saturated solution:

PbCl2 (s) ⇌ Pb2+ (aq) + 2Cl- (aq)

3.4a At 25°C, the solubility product (Ks) of PbCl2 is 1.7 × 10-5.

Calculate the solubility (in mol L-1) of lead chloride in water at 25°C.

3.4b An attempt is made to dissolve lead chloride in 0.1 M sodium chloride (NaCl)

solution instead of water. The solubility of lead chloride is found to be lower in

sodium chloride solution when compared to in water.

What is this phenomenon known as?

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STRAND 4: OXIDATION–REDUCTION REACTIONS

4.1 An electrochemical cell is constructed as shown below.

Given the following standard reduction potentials (E°) at 25°C, show that the electrochemical cell will undergo a spontaneous reaction. Include relevant calculations and the overall cell reaction in your response.

Zn2+ (aq) + 2e- → Zn (s) E° = -0.76 V

Ag+ (aq) + e- → Ag (s) E° = +0.80 V

4.2 Describe the difference between an electrolytic cell and a galvanic cell in terms of their energy conversion.

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STRAND 5: ORGANIC CHEMISTRY

Use the information below to answer questions 5.1a and 5.1b.

Some organic compounds can exist as enantiomers. An example is the compound 2-bromopentane (C5H11Br).

CH2 CH2

CH CH3

Br

CH3

2-bromopentane

5.1a What are enantiomers?

5.1b Clearly identify the structural feature in 2-bromopentane that enables it to exhibit enantiomerism and draw its enantiomers.

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5.1c The main reason enantiomers are highly emphasised comes down to the interesting properties they have. Using a suitable example, discuss the concept of enantiomerism as it is applied to everyday life situations.

Include the following in your response:

- the properties of enantiomers; - a specific area of application; and - important implications or considerations.

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Use the information below to answer questions 5.2a and 5.2b.

The different physical and chemical properties of isomers can be used to distinguish them. For example, the isomers propanal and propanone can be distinguished using suitable laboratory tests. The structures of propanal and propanone are given below.

C

O

H

C

H

H

C

H

H

H C HC

O

C

H

H

H

H

H

Propanal Propanone

5.2a Propanal and propanone belong to the constitutional (structural) isomer group, which can be split again into three main subgroups.

List any two subgroups of constitutional isomers.

5.2b Explain how acidified potassium dichromate (K2Cr2O7) solution can be used to distinguish between propanal and propanone.

Your response should include:

i. any observation made; ii. the type of reaction occurring; and iii. the relevant chemical equation to account for the observation (a

balanced equation is not necessary but structure of any organic product must be shown).

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Use the information below to answer questions 5.3a–5.3d.

Alcohols occupy a central position in organic chemistry. They can be prepared from many other kinds of compounds and they can be transformed into a wide assortment of compounds. Some common reactions of propan-1-ol are shown in the reaction map below.

5.3a Identify Reaction X.

5.3b Identify the class of organic compounds that Product A belongs to and give the IUPAC name of Product A.

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Propan-1-ol

Product A

Product B

Reaction Y

PBr3

C

O

Cl

C

H

H

C

H

H

C

H

H

H

Reaction Z

Reaction X

LiAlH4/H+

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5.3c Describe Reaction Y in terms of reaction type, reagent and reaction condition.

5.3d Give the name of Reaction Z and structure of Product B.

Name of Reaction Z

Structure of Product B

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5.4 Polyethylene terephthalate (PET or PETE) is a general-purpose polymer. The following two compounds can link together to form PET.

CC

OH

OO

OHCH2 CH2 OHOH

benzene-1,4-dicarboxylic acid ethane-1,2-diol

Identify one feature of the polymerisation reaction that would occur between the above two compounds.

5.5 There are many important uses of polymers in everyday life due to its useful properties.

Describe one general property of polymers with its relevant application in real life.

THE END

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