[uks] Chemistry 2004(mock) Paper1(e)

Section A (Answer ALL questions.) 1.

The table below lists the atoms of silicon and their relative abundance. Isotopes Relative abundance (%)

28

Si x

29

Si y

30

Si 3.1

(a)

Suggest a term to indicate the relationship among 28Si, 29Si and 30Si.

(b)

(i)

What is the meaning of relative atomic mass?

(ii)

If the relative atomic mass of silicon is 28.09, calculate the values of x and y.

(c)

Explain briefly why 29Si and 30Si react with oxygen in the same way as Si to form quartz. (6 marks)

28

2.

The experimental results of three metal oxides are summarized in the following table : Metal oxides XO Y2O Experiments Action of heat on metal No observable No observable oxide change change Heating metal oxide with Grey solid No observable carbon formed change

Z2O Metal Z formed Grey solid formed

(a)

Write an equation for the heating of metal oxide (Z2O).

(b)

Write an equation for the reaction between XO and heated carbon.

(c)

(i)

Suggest what Y might be.

(ii)

Give TWO reasons to explain your suggestion.

(d) y

Arrange the three metals in descending order of reactivity. your answer.

Explain (8 marks)

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3.

Lemon juice contains citric acid which causes the sour taste. a tribasic acid with the formula as H3 A. (a)

Citric acid is a weak acid.

Citric acid is

Explain the term ‘weak acid’.

(b) 25 cm3 of a sample of lemon juice is transferred to a conical flask. T The solution required 10 cm3 of 0.3 M ammonia solution to reach the e end-point, at which the citric acid has been completely neutralized. A As a result, the concentration of citric acid in lemon juice can be deterdetermined by the above process. (i)

Name the above process.

(ii)

Suggest an equipment to transfer 25 cm3 of lemon juice to conical flask.

(iii) Given that the relative molecular mass of citric acid is 192, c calculate the concentration of citric acid in terms of g dm-3 in the sample of lemon juice. (7 marks)

For questions 4 and 5, candidates are required to give paragraph- length answers. For each of these two questions, 3 of the marks will be awarded for effective communication of knowledge in chemistry. 4.

Describe briefly how you would obtain pure copper from brass (an alloy containing copper and zinc). (8 marks)

5.

Describe, with the help of equations, three different chemical properties of concentrated sulphuric acid. (9 marks)

End of Section A 2004-MOCK EXAM.-CHEM 1-3

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Section B (Answer any THREE questions.) 6.

(a)

Ethanol can be manufactured by fermentation of glucose. Glucose

A

Reaction chamber

process X

Ethanol

(i)

Name A and write a balanced equation for the reaction between glucose and A.

(ii)

Explain why only a dilute solution of ethanol is obtained from the fermentation of glucose in the reaction chamber.

g

(iii) Name the process X which gives high concentration of ethanol.

c e e

(iv) Some perfumes contain the compound ‘ethyl ethanoate’ which can be prepared from ethanol in the school laboratory. Write equations with suitable reagents and conditions, show how the ethyl ethanoate can be obtained from ethanol. (10 marks) (This question is continued on the next page.)

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6. (b) (i) Why do iron fences in cities of high nitrogen dioxide concenconcentrconcentration corrode faster than the fences in countryside ? (ii)

The overall equation for rusting is

→ 2Fe2O3·nH2O(s) 4Fe(s) + 3O2(g) + 2nH2O(l) 

w

Originally, an iron fence had a mass of 10.02 kg. After six months, it weighs 11.09 kg. After all the rust is carefully removed, its weight drops to 8.85 kg. (1)

Find the mass of iron turned into rust.

(2)

Find the mass of rust formed.

(3)

Calculate the value of n in the formula Fe2O3·nH2O.

(Relative atomic masses : H = 1.0, O = 16.0, Fe = 56.0 ) (8 marks)

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7.

(a) t

Catalytic converter can reduce the content of pollutants emitted from the car exhaust.

(i) substan catalyt (ii)

Write the chemical equation for the conversion of harmful substances in the car exhaust into harmless substances in the catalytic converter. Explain briefly why (1)

cars using catalytic converter must also use unleaded petrol.

(2)

though petroleum contains only a very small amount of nitrogen, large amount of nitrogen oxides are formed in car engines. (4 marks)

nit

(b)

A solution is formed when chlorine gas is bubbled into water. (i)

Write an equation for the reaction between chlorine and water. What is the colour of the solution formed?

(ii)

Suggest a reason why it would be dangerous to use chlorine water and other acid together.

(iii) Describe and explain the observable changes when a blue litmus paper is put into chlorine water. (iv) (1) (2) b

Why is chlorine water usually stored in brown bottle? Give one other chemical which is also stored in brown bottle. (9 marks)

(This question is continued on the next page.)

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7.

(c)

s

Cracking of alkanes is an important chemical process. (i)

What is meant by cracking?

(ii)

State TWO importance of cracking.

(iii) Draw a simple laboratory set-up that is commonly used in the school laboratory for cracking. (5 marks)

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8.

(a)

The following table shows the properties of three types of dry cells. Zinc-carbon cell Charge capacity (mA hour) Price ($) Voltage over discharge Shape

600

10000

120

2.5

8 Falls very slowly Cylindrical

10

Falls rapidly Cylindrical

Constant Button

(i)

The above three types of cells are primary cells. meaning of ‘primary cells’?

(ii)

By calculating their price per charge capacity, find out which cell is the most ‘cost-effective’.

m

What is the

(iii) (1)

Write the half equations of the reaction occurred at the anode and cathode of zinc-carbon cell.

(2)

Manganese(IV) oxide is present in the zinc-carbon cell, explain, with the help of equation, its function.

anode

exp

u

Alkalinesilver oxide cell manganese cell

(iv) Suggest one type of the above cells that is most suitable to be used in video camera. (v)

State one use of silver oxide cell. (9 marks)

(This question is continued on the next page.)

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8.

(b) b

Kevlar is a polymer used in the manufacture of bullet-proof jackets and shock-resistant materials. The repeating unit of Kevlar is shown below. O O H H C

C–N

N

(i)

Draw the structures of the monomers of Kevlar.

(ii) m

Write an equation to show the formation of Kevlar from its monomers.

(iii) Name the type of reaction that produces Kevlar from its monomonomers. (iv) o r u

(c) c

Kevlar has very high tensile strength. Hence, on many offshore oil drilling platforms, steel ropes have been replaced by Kevlar ropes. Apart from tensile strength, state two advantages of using Kevlar ropes on oil drilling platforms. (6 marks)

Write equation and state observable changes of the reaction between copper and concentrated nitric acid. (3 marks)

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9.

(a). A student prepared ammonia gas by heating ammonium sulphate with sodium hydroxide solution. The set-up is shown below.

gas jar

moist red litmus paper drying agent

heat

(i) (1) ammon (2) (ii) o

ammonium sulphate and sodium hydroxide solution

Write a balanced equation for the reaction between ammonium sulphate and sodium hydroxide solution. Explain whether or not it is a redox reaction.

State the function of the moist red litmus paper and state its observable changes during the experiment.

(This question is continued on the next page.)

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9.

(a) v p

(iii) It is known that 10 g of ammonium sulphate is used to react with excess sodium hydroxide solution. Calculate the theoretical volume of ammonia gas collected at room temperature and pressure. (Relative atomic masses of H= 1, N =14, O = 16 and S = 32; molar volume of any gas at room temperature and pressure = 24 dm3)

i e p

(iv) Ammonia reacts with oxygen in 2 different ways. One reaction involves the use of platinum catalyst and one is not. Give an equation for the reaction between ammonia with oxygen in the presence of platinum and explain its importance in the production of nitric acid. (10 marks)

(This question is continued on the next page.)

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9.

(b) The following set-up is used for the electrolysis of concentrated sodiusodium chloride solution.

positive electrode

negative electrode

t

(i)

Suggest a suitable material for making the two electrodes.

(ii)

It is known that 20 cm3 of gas X is collected in the negative electrode when the electrolysis stops. (1) t

Write the equations for the reactions taken place in both electrodes.

(2) Find the theoretical volume of gas Y collected in the positipositive electrode at the end of the electrolysis. (3) (iii) (1)

(2)

State an assumption for the above calculation. What changes can be observed when a few drops of methyl orange is added to the final solution? Suggest what the final solution is. (8 marks)

END OF PAPER 2004-MOCK EXAM.-CHEM 1-12

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