Candidate’s Signature...1. (a) Write the electron configuration of calcium (atomic number 20) and magnesium (atomic number 12). ... Complete the table below to show the observations

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Name _______________________________________________ Index No._______________________

Candidate’s Signature ______________

Date ____________________________

233/1

CHEMISTRY

PAPER 1

THEORY

JULY / AUGUST 2013

2 HOURS

MAKUENI DISTRICT JOINT FORM 4 EXAMINATION 2013

Kenya Certificate of Secondary Education

CHEMISTRY

PAPER 1

THEORY

JULY / AUGUST 2013

2 HOURS

INSTRUCTIONS TO CANDIDATES

1. Write your name and index number in the spaces provided above.

2. Sign and write the date of examination.

3. Answer ALL the questions in the spaces provided in the question paper.

4. Mathematical tables and silent electronic calculators may be used.

5. All working MUST be clearly shown where necessary.

6. This paper consists of 14 printed pages.

7. Candidates should check the question paper to ascertain that all the pages are printed as indicated

and that no questions are missing.

FOR EXAMINER’S USE ONLY

QUESTIONS MAXIMUM SCORE CANDIDATE’S SCORE

1 – 31 80


This paper consists of 14 printed pages

Turn Over

1. (a) Write the electron configuration of calcium (atomic number 20) and magnesium

(atomic number 12).

Calcium ____________________________ ( ½ mark )

Magnesium _________________________ ( ½ mark)

(b) Explain why calcium is more reactive than magnesium. ( 2 marks )

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2. (a) Complete the table below to show the observations made when concentrated

sulphuric (VI) acid is added to the substances shown.

Substance Observation

Crystals of white sugar (i)

Copper (II) sulphate crystals (ii)

(b) Name one fertilizer made from sulphuric (VI) acid. (1 mark)

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3. A solution of chlorine in tetrachloromethane turns colourless when ethene gas is bubbled through it

(a) What type of reaction takes place? (1 mark )

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(b) Write an equation for the above reaction. (1 mark )

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4. The diagram below is a set up of apparatus used to react ammonia gas with iron (II) chloride solution


Ammonia gas

Funnel

Beaker Iron (II) chloride solution

MAKUENI DISTRICT JOINT FORM IV EXAM 2013 CHEMISTRY P.1 2

(a) State the observation made in the beaker in the first few minutes. (1 mark)

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(b) Explain why a funnel is used to deliver the ammonia into the solution. (1 mark )

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5. Study the flow chart below and answer the questions that follow.

Gas Gas

ZnS(s) O2 (g) Zn O (s) Coke Zn (s)

Heat Step 2

Step 1

Step 3 Conc. H2SO4

Zn SO4 (aq) Gas R

(a) What condition is necessary for step 2 to occur? (1 mark )

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(b) Name (i) Gas R ______________________________ (1 mark)

(ii)One use of zinc other than galvanizing iron. (1 mark)

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6. When Xcm3 of 0.5M zinc nitrate solution were reacted with excess ammonium carbonate

solution, the mass of zinc carbonate formed was 12.5g.

(a) Write the ionic equation for the reaction that took place. (1 mark)

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(b) Calculate the value of X.

(C = 12.0, Zn = 65.0, O = 16.0 ) (2 marks )

7. Bronze is an alloy of copper and another metal.

(a) Name the other metal __________________________________________________ ( 1 mark)

(b) Give one use of bronze. ( 1 mark )

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8. Dilute sulphuric (VI) acid was electrolyzed using the set up represented by the diagram below.

Gas A Bulb Gas B Dilute sulphuric (VI) acid Platinum electrodes


(a) Write an equation for the reaction that produces gas B. (1 marks )

(b) Describe how gas A can be identified. (1 mark)

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(c ) Explain the difference in brightness of the bulb if ethanoic acid is used in place

of sulphuric (VI) acid. ( 1 mark )

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9. (a) State Graham’s law of diffusion. ( 1 mark )

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(b) Gas E takes 110 seconds to diffuses through a porous plug. Gas E has a relative

molecular mass of 34. How long will it take for the same amount of ammonia gas to

diffuse under the same conditions? (N = 14, H = 1 ) ( 2 marks )

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10. The scheme below represents the manufacture of a cleansing agent Y.


Conc. OSO3H

H2SO4

NaOH

Cleansing agent Y

(i) Draw the structure of Y and state the type of cleansing agent to which Y belongs. (2marks )

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(ii) State one advantage of using Y on the environment. (1 mark )

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11. The graph below shows volume of hydrogen gas collected against time when a 2cm

magnesium ribbon was reacted with 2M hydrochloric acid.

Volume of H2(g)

produced

Time (sec)

(a) On the same axes sketch the curve Y obtained when a 2cm magnesium ribbon was

reacted with 2M ethanoic acid. (1 mark)

(b) Write an equation for the reaction between ethanoic acid and magnesium. ( 1 mark)

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12. The diagram shows an incomplete set-up for the laboratory preparation and collection


of chlorine gas. Study it and answer the questions that follow.

Conc. HCl Water Black solid Q

(a) Complete the set up to show how dry chlorine gas can be collected. (2 marks )

(b) Name substance Q ______________________________________________ (1 mark )


13. (a) Write the systematic names of the following compounds.

(i) CH3 CH2 C CCH3 _________________________________ ( 1 mark )

(ii) CH3 CH CH2 OH

CH3 ________________________________ (1 mark )

(b) Draw the structure of 2, 3-dibromobutane. (1 mark )

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14. The diagram below shows how a magnesium is reacted with steam.

Magnesium

Wet cotton Gas C


(a) Identify the condition required in the set up for gas C to be produced. (1 mark)

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(b) Write an equation for the reaction that produces gas C in the set up after the

condition in (a) above is applied. (1 mark)

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(c ) Why is it not advisable to use sodium in place of magnesium? (1 mark)

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15 Study the bond energies given below to answer the question that follows.

Bond Bond energy (kJmol-1

)

H – H 432

C = C 610

C – C 346

C – H 413


Butene can be converted into butane in the equation:

CH3 CH2 CH = CH2 + H2 CH3 CH2 CH2 CH3

Determine the enthalpy change in the reaction. (2 marks )


16. Water and kerosene are immiscible liquids.

(a) Draw the apparatus that can suitably be used to separate the liquids and label

the layers. (2 marks )

(b) Name the most suitable method used to separate kerosene and petrol. (1 mark )

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17. The diagram below shows some steps used in the manufacture of sodium carbonate by

the solvary process.

Ammonium

Chloride

Ammonium

chloride +

Concentrated sodium CO2 (g) sodium hydrogen Step

chloride Step I carbonate II

Sodium

Substance D Hydrogencarbonate

Step III

Sodium carbonate


(a) Name substance D ___________________________________________ ( 1 mark )

(b) What process takes place in step II? ( 1 marks )

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(c ) Write an equation for the reaction taking place in step III. (1 mark )

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18. Describe how a solid sample of copper (II) carbonate can be prepared starting with

copper metal. (3 marks )

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19. Sulphur (IV) oxide and nitrogen (IV) oxide gases are released from car exhaust fumes.

Explain two ways these gases affect the environment. ( 2 marks )

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20. The table below shows some tests carried out on solid F and the observations made.

Test Observations

I) Heat solid F then cool Solid changed from white to yellow.

II) Add dilute hydrochloric acid to solid F A colourless solution was formed with

effervescence.

III) Add excess sodium hydroxide to the

colourless solution in test III

A white precipitate was formed which dissolved

to form a colourless solution.


(a) Write the formula of the:

Cation in solid N (1 mark )

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Anion in solid N (1 mark )

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(b) Write the ionic equation for the formation of the colourless solution in step III. (1 mark )

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21. The grid below shows part of the periodic table. The letters used are not the actual

symbols of the elements.

L P

M N

K

(a) Select the:

(i) element with the largest atomic size _________________________________ ( ½ mark )

(ii) most reactive non-metal _________________________________________ ( ½ mark )

(b) On the grid, show the position of element T which forms T3-

ions with electron

configuration 2.8.8 ( 1 mark)

22. (a) A few drops of freshly prepared iron (II) sulphate solution were added to sodium

nitrate solution in a test tube. Concentrated sulphuric acid was added carefully to

the mixture. State the observations that were made. ( 1 mark )

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(b) (i) Write an equation for the reaction that occurs when solid sodium nitrate is

strongly heated. (1 mark)

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(ii) State the test for the gas produced in b(i) above. (1 mark )

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23. When carbon (IV) oxide gas was passed through calcium hydroxide solution, a white

precipitate was formed.

(a) Write an equation for the reaction that took place. (1 mark)

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(b) State and explain the observation made when excess carbon (IV) oxide gas was

bubbled through the white precipitate. ( 2 marks )

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24. The table below gives standard electrode potentials for metals represented by the letters

R, S, T and U. Study it and answer the questions that follow.

Metal Standard electrode potential (V)

R -0.13

S -0.76

T + 0.34

U + 0.85

(a) Which metal can be displaced from a solution of its salt by all the other metals in

the table? Give a reason. ( 2 marks )

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(b) Determine the emf of the cell R / R2+

// U2+

/ U (1 mark )



25. Study the set-up below and answer the questions that follow.

Gas W

Water

Calcium metal

(a) What physical property of calcium is demonstrated in the set-up? (1 mark)

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(b) Write the equation leading to the formation of gas W. (1 mark )

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(c ) State the observation made if the water was replaced with dilute sulphuric (VI) acid. (1 mark)

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26. (a) The table below shows the pH values of solutions A, B, C, D, E, F, G, and H. Study it and

answer the questions that follow.

Solution A B C D E F G H

pH 1.0 4.0 5.0 6.5 7.0 7.5 8.0 11.0

Select the solution which is likely to be:

(i) Sodium chloride ________________________________________ ( ½ mark )

(ii) Lime water ____________________________________________ ( ½ mark )



(b) Equal amounts of zinc powder were added to 15cm3 of 1M ethanoic acid and 15cm

3

of 1M hydrochloric acid in separate boiling tubes. The amount of hydrogen gas liberated

after 2 minutes in the boiling tubes was different. Explain this difference. ( 2 marks)

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27. Study the energy level diagram below and answer the questions that follow.

Reactants

Energy

kJmol-1

Products

Reaction path

(a) Identify the kind of reaction represented by the diagram. Explain. (2 marks )

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(b) Label on the diagram the:

(i) Activation energy, Ea ( ½ mark )

(ii) Enthalpy of reaction, H ( ½ mark )

28. Determine the oxidation number of manganese in:

(i) MnO2 (1 mark )


(ii) MnO4 - (1 mark )


29. Copper (II) chloride solution and graphite are both capable of conducting electricity. What is the

major difference between the two substances in their electrical conductivity? ( 1 mark)

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30. What is the name given to the smallest repeating unit of a polymer? (1 mark)

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31. The figure below shows a radioactive source. Complete the diagram by showing the

deflection of the different types of emissions. (2 marks )

Radioactive

Source +

Electric field



233/1

CHEMISTRY

PAPER 1

THEORY

JULY / AUGUST 2013



CHEMISTRY

PAPER 1

THEORY

JULY / AUGUST 2013

MARKING SCHEME

1. (a) C a – 2.8.8.2 1

Mg – 2.8.2 1

(b) The two valence electrons in calcium are further away from the nucleus compared to those

in magnesium and thus they are readily released .

2. (a) (i) The crystals are charred to a black mass // black spongy solid formed.

(ii) Solid changes from blue to white powder .

(b) Ammonium sulphate / (NH4)2SO4

3. (a) Addition reaction

(b) C2H4 + Cl2 C2H4Cl2

Or CH2 = CH2 + Cl2 CH2Cl CH2Cl

4. (a) A green precipitate is formed


(b) To prevent sucking back / to increase the surface area of absorption since ammonia is

highly soluble.

5. (a) Heat /high temperature

(b) (i) Sulphur (IV) oxide / SO2

(ii) – Batteries / dry cells as the negative terminal

- Electroplating

6. (a) Zn2+

(aq) + CO32-

(aq) ZnCO3 (s)

(b) Moles of ZnCO3 = 12.5

125

= 0.1 moles 1

Mole ratio Zn2+

: ZnCO3 = 1 : 1

Moles of Zn2+

= 0.1 1

0.5M Zn2+

1000cm3

0.1M ?


Turn Over

= 0.1 x 1000 1

0.5

= 200cm3

1

7. (a) Tin

(b) Making coins / utensils / statues / belts / jewellery / cabinet handles

8. (a) 4OH- (aq) 2H2O (l) + O2 (g) + 4e

-

(b) Insert a burning splint 1 in a gas jar of gas A. The gas burns with a pop sound 1

to show it is hydrogen gas.

(c ) The bulb is brighter with sulphuric acid 1. Sulphuric acid is a strong acid which is fully

ionized 1 / Ethanoic acid is a weak acid which ionizes partially hence the bulb will dim.

9. (a) Under the same condition of temperature and pressure, the rate of diffusion of a gas is

inversely proportional to the square root of its density.

(b) TE = ME NH3 = 14 + 3 = 17 1

TNH3 MNH3

110 = 34

TNH3 17 1

TNH3 = 110

2 1


= 77.78 sec

10. (i)

OSO3Na

Soapless detergent 1

(ii) Pollutes the environment since it is non-biodegradable

11. (a)

Volume of H2(g)

produced 1

Curved Y 1

Time (sec)

(b) Mg(s) + 2CH3 COOH (aq) (CH3COO)2Mg (s) + H2 (g)

2

12 (a) Concentrated sulphuric acid Dry chlorine

- Workability of set-up

- Suitable drying agent 1

- Collection method 1

(b) Manganese (IV) oxide / Mn O2 (s) / Lead (IV) oxide / PbO2 (s)

13. (a) (i) Pent-2-yne

(ii) 2-methylpropan-1-ol


(b) H Br H H

H C C C C H

H H Br H

14. (a) Heat

(b) Mg (s) + H2O (g) MgO (s) + H2 (g)

(c ) Sodium reacts explosively with steam

15. H – E bonds broken + E bonds formed

= 3 (C –H ) + C = C + H – H + 5 (C – H) + C – C

= 3(413) + 610 + 432 + - (5(413) + 346)

= 2281 – 2411

= -130kJmol-1

16. (a) Kerosene Water

- Diagram

- Labelling – Kerosene floating 1

- Water bottom 1

(b) Fractional distillation

3

17. (a) Ammonia

(b) Filtration / crystallization

(c ) 2Na HCO3 (s) Na2 CO3 (s) + CO2 (g) + H2O (l)

18. Add excess copper metal to concentrated nitric acid 1 in a beaker / Add excess copper metal

to concentrated sulphuric (VI) acid.

- Filter out the excess / unreacted copper 1

- Add aqueous sodium carbonate or potassium carbonate to the filtrate 1

- Filter the resulting mixture 1 and wash the residue 1

- Dry the residue 1 between filter papers.

NB: Reject dilute HNO3 / H2SO4 / HCl

19. - The two gases dissolve in rain water in the atmosphere causing acid rain which is harmful to

plants and corrodes concrete and iron structures.

- The two gases are poisonous so inhalation can cause respiratory disorders

20. (a) (i) Zn2+


(ii) CO32-

(b) Zn(OH)2 (s) + 2OH- (aq) [ Zn (OH)4]

2- (aq)

21 (a) (i) K

(ii) P

(b) Group 5, period 3 on the grid

22. (a) A brown ring was seen at the junction between the two layers of liquids.

(b) (i) 2NaNO3 (s) Heat 2NaNO2 (s) + O2 (g)

(ii) Relights a glowing splint

23. (a) Ca(OH)2 (aq) + CO2 (g) CaCO3 (s) + H2O (l)

(b) The white precipitate dissolves forming a colourless solution . The white calcium carbonate

and water reacts with carbon (IV) oxide producing soluble calcium hydrogen carbonate 1

24. (a) U. It is the weakest reducing agent / has weakest reducing power / most easily

reduced / has highest +ve potential / is the strongest oxidizing agent.

(b) Emfcell = E reduced – Eoxidized

= 0.85 – (-0.13(1

= + 0.98V 1

25. (a) It sinks in water /denser than water

(b) Ca(s) + 2H2O (l) Ca(OH)2 (aq) + H2(g)

(c ) The reaction proceeds for a short time then stops

26. (a) (i) E 1

(ii) H 1

4

(b) More hydrogen gas was produced in the reaction involving hydrochloric acid .

Hydrochloric acid is a strong acid which produces more hydrogen ions in the reaction

hence more hydrogen gas.

27. (a) Exothermic reaction . The products have lower energy than the reactants

(b)

Reactants Ea

Energy

kJmol-1

H

Products


Reaction path

28. (i) + 4

(ii) + 7

29. Copper (II) chloride solution conducts by mobile ions while graphite conducts by delocalized

electrons

30. Monomer

31.

NB: has more deflection than

Radioactive

Source

+

Electric field

5

Name _______________________________________________ Index No._______________________

Candidate’s Signature ______________

Date ____________________________

233/2

CHEMISTRY

PAPER 2

THEORY

JULY / AUGUST 2013


2 HOURS



CHEMISTRY

PAPER 2

THEORY

JULY / AUGUST 2013

2 HOURS

INSTRUCTIONS TO CANDIDATES

1. Write your name and index number in the spaces provided above.

2. Answer ALL the questions in the spaces provided.

3. Mathematical tables and silent electronic calculators may be used.

4. All working MUST be clearly shown where necessary.

FOR EXAMINER’S USE ONLY

QUESTIONS MAXIMUM SCORE CANDIDATE’S SCORE

1 13

2 12

3 10

4 11

5 9

6 11

7 14

TOTAL 80


Turn Over

1. The table below contains some information of elements belonging to the same group on the periodic

table. (The letters are not actual symbols of the elements). Use it to answer the questions that

follow.

Element Ionisation energy Standard electrode

potential ‘E’

Atomic radius

(nm)

Ionic radius

(nm) First Second


W 549 1064 -2.89 1.91 1.13

X 738 1451 -2.37 1.36 0.65

Y 502 965 -2.90 1.98 1.35

Z 589 1145 -2.87 1.74 0.97

(a) (i) What is ionization energy? (1 mark)

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(ii) Explain why the second ionization energy is higher than the first ionization energy. (1 mark)

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(b) Which of the elements is the most reactive? (1 mark)

___________________________________________________________________

Give a reason for your answer. (1 mark)

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(c ) Arrange the elements according to the way they appear in the periodic table down the group. ( 1 mark)

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(d) A cell was made by connecting two half-cells of elements X and Y. Work out the e.m.f

of the cell. ( 1 mark )


(e) Element W was to be extracted from its ore. What would be the most suitable method to use?


____________________________________________________________________

Give a reason for your answer. (2 marks )

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(f) Limestone is a common compound in many areas and it affects the quality of water originating

from such areas.

(i) What is the chemical name for limestone? (1 mark )

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(ii) What type of water hardness is caused by the presence of limestone? (1 mark)

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(iii) The set up below was used to remove hardness of water. Identify this method. (1 mark)

Na+ Na

+

Na+ Na

+

Na+ Na

+

Na+ Na

+

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(iv) The above system eventually lacks the ability to soften hard water. Explain how it can be

reactivated. ( 1 mark)

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(v) State one advantage of hard water. (1 mark)

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2. (A) The table below gives some information about some oxides. Study the information and answer the

questions that follow.

Formulae

of oxide

Melting

point

Effect of adding

water to oxide

Effect of electric current on

molten oxide

Effect of adding

aqueous sodium

hydroxide to oxide

Na2O 920 Dissolves readily Conducts electricity Na(s)

and O2 are produced

(a)

P2O5 563 Dissolves readily (b) (c )

SO3 17 Dissolves readily Does not conduct Reacts readily

Al2O3 2045 Does not dissolve

readily

(d) Reacts readily

(a) Complete the table by filling the blank spaces a to d . (2 marks )

(b) Write equations for the reactions that take place between.

(i) SO3 (g) and water. (1 mark)

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(ii) SO3 (g) and sodium hydroxide. (1 mark)

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(c ) Why is it not advisable to carry out reaction b(i) above in the laboratory? (1 mark)

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(d) Explain the difference between the melting point of P2O5 and SO3. (1 mark)

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(e) Phosphorus (V) oxide dissolves in water to form phosphoric acid. Explain how the ability

of concentrated phosphoric acid to conduct an electric current compare to that of dilute

phosphoric acid. (2 marks )

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2. (B) The reaction scheme below is for the industrial manufacture of hydrochloric acid.

Hydrogen gas

Water

Chlorine gas Burning Gaseous

Chamber substance

Glass beads

Tap

Tap

Hydrochloric acid

(i) Write an equation for the reaction that occurs in the burning chamber. (1 mark)

_____________________________________________________________________________

_____________________________________________________________________________

_____________________________________________________________________________

_____________________________________________________________________________

(ii) What is the purpose of the glass beads in the absorption chamber. (1 mark)

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(iii) Given the percentage purity of the hydrochloric acid manufactured is 35% and its

density is 1.18g/cm3. Determine the concentration of the acid ( H = 1, Cl = 35.5 ) ( 2 marks )



3. The apparatus shown below were used to determine the molar heat of displacement of copper.

Thermometer Polystyrene cup Copper (II) sulphate + zinc metal solution Plastic beaker

1.0g of zinc powder was added to 50cm3 of 0.2M copper (II) sulphate solution and the mixture stirred

gently. The temperature rose from 210C to 28

0C.

(a) Explain the reason why?

(i) A glass rod was used to stir the mixture instead of iron. (1 mark)

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(ii) Polystyrene cup was used instead of a glass beaker. (1 mark)

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(b) Write a chemical equation for the above reaction. (1 mark)

_____________________________________________________________________________


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(c ) Calculate:-

(i) The number of moles of copper (II) sulphate solution. (1 mark)


(ii) The molar heat of displacement of copper (specific heat capacity of

solution = 4.2 J/g/k, density of solution = 1g/cm3 (2 marks )

(d) Why is the molar heat of displacement obtained in c(ii) above lower than the actual value? (1 mark)

_____________________________________________________________________________

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_____________________________________________________________________________

(e) Draw an energy level diagram for the reaction above. (2 marks )

(f) If magnesium ribbon was used in place of zinc, compare the H value with that of zinc.

Give a reason. ( 1 mark )


_____________________________________________________________________________

_____________________________________________________________________________

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4.(a) The flow chart below shows a series of reactions starting with propanol. Study it and

answer the questions that follow.

Polymer F Process 3 A Hydrogen chloride E

Gas

Process 1

Conc. H2SO4 1700C

B KMnO4 / H+ Propanol Propanoic acid C

H2SO4 (l) Process 2


(i)Name products: (1½marks)

A _____________________________________

B _____________________________________

C _____________________________________

(ii) Name processes (1½marks)

Process 1 ______________________________________

Process 2 ______________________________________

Process 3 ______________________________________

(iii) Draw the structural formulae of the products E and B

E (1 mark) B ( 1 mark )

(iv) In what class of compounds does product C belong? ( 1 mark)

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(v) Draw the structural formulae of polymer F with two repeating units. (1 mark)

(vi) State two advantages of using synthetic polymers. ( 1 mark)

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(b) Study the diagram below and answer the questions that follow.

Flame Gas R to sunction pump Ice salt mixture Substance P Butane

(i) Write an equation for the combustion reaction. (1 mark)


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(ii) The pH value of a solution of substance R is found to be less than 7. Explain this

observation. ( 1 mark)

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(iii) Explain why butanol is soluble in water unlike butane gas. (1 mark)

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5. The flow diagram below shows some reactions of dry air. Study it and answer the

questions that follow.

Solid F

Dry air Copper

Heat

Magnesium + Mixture of NaOH (aq) Gas Y

Heat gases Step I

350 atm Step II

4500C and

finely Gas D

Solid A Solid B divided iron

Water Gas Z

Substance C Gas X


(a) Identify the following (2 marks )

(i) Solid A _____________________________________

(ii) Solid B _____________________________________

(iii) Gas D _____________________________________

(iv) Gas Z ______________________________________

(b) Why is the amount of solid B obtained much less than solid A? (1 mark)

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(c ) Write a balanced chemical equation for the reaction between solid B and water. (1 mark)

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(d) How can gas Y be obtained from gas X in the laboratory? Explain using a chemical equation. (2 marks)

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(e) Which gas is absorbed by sodium hydroxide in step I. ( ½ mark)

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(f) Gas Y obtained in step I is impure, name one impurity it contains. ( ½ mark )

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(g) (i) What is the name given to the process that occur in step II. ( 1 mark)

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(ii) Explain the effect of using much lower temperature than that in step II. (1 mark )

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6. The flow chart below outlines some processes involved in the extraction of copper from copper

pyrites. Study it and answer the questions that follow.

Ore P Powdered Concentrate

Ore

Air Hot air

Gas L

2nd

roasting Cu2S Smelting 1st roasting

furnace furnace furnace

Cu2S Slag M

Cu2O Compound

G

Gas L

Impure copper J Pure copper

(a) Name the following: (2 marks )

(i) Ore P ______________________________________

(ii) Gas L ______________________________________

(iii) Slag M ____________________________________

(iv) The impure copper J __________________________


(b) (i) Explain how the ore is concentrated. (1 mark)

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(ii) Why is it necessary to grind the ore into powder. ( ½ mark)

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(c ) Give the purpose of adding silicon (IV) oxide compound G into the smelting furnace. (1 mark)

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(d) Pure copper is obtained from impure copper by electrolysis. Name the material used as anode,

cathode and electrolyte. (1½ marks)

Anode __________________________________________

Cathode _________________________________________

Electrolyte _______________________________________

(e) What effects does this process of copper extraction have to the environment. (1 mark)

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(f) State two uses of copper metal. (2 marks )

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(g) A current of 100 Amperes was passed for 20 days. Hat mass of copper in kg was

deposited at the cathode. (Cu = 64, If = 96500 C ) (2 marks )

MAKUENI DISTRICT JOINT FORM IV EXAM 2013 CHEMISTRY P.2 12.

7. (i) The table below shows the results obtained when sodium carbonate was reacted with excess 0.5m

sulphuric (VI) acid at room temperature.

Time sec 0 10 20 30 40 50 60 70 80

Volume of CO2 (cm3 ) 0 35 61 82 95 100 103 105 105

(a) On the grid provided, plot a graph of the volume of CO2 against time. (3 marks )



(b) Use the graph to determine volume of CO2 evolved at 25th

second. (1 mark)


(c ) At what time did the reaction stop? (1 mark)

(d) Write a balanced chemical equation to show the reaction that took place between sodium

carbonate and sulphuric (VI) acid. ( 1 mark)

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(e) Calculate the mass of sodium carbonate used in this reaction. (Na = 23, C = 12, O = 16,

volume of gas at r.t.p = 24dm3 ) ( 2 marks )

(f) If the same experiment was repeated using excess 1.0M sulphuric acid instead of 0.5M

sulphuric acid. What would be the effect on the time taken. ( 1 mark)

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7. (ii) 12g of a mixture of sodium carbonate and sodium sulphate were mixed with distilled water in

a flask and topped up to 1,000cm3. 25cm

3 of this solution required 12.5cm

3 of 0.2M

sulphuric (VI) acid for complete reaction.

(a) Which substance in the mixture reacted with dilute sulphuric (VI) acid solution? (1 mark)

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(b) Calculate the number of moles of the sulphuric (VI) acid which recated with the substance. (1 mark)

(c ) Determine the number of moles of the substance in (a) above which took part in the reaction. (1 mark)

(d) Determine the molarity of the substance which reacted with sulphuric (VI) acid. (1 mark)

(e) What is the mass of the substance which reacted in the mixture?

Na = 23, C = 12, O = 16, S = 32 ) (1 mark )



233/2

CHEMISTRY

PAPER 2

THEORY

JULY / AUGUST 2013



CHEMISTRY

PAPER 2

THEORY

JULY / AUGUST 2013

MARKING SCHEME

1. (a) (i) The amount of energy required to remove an electron from an atom in gaseous state.

(ii) The second ionization electron is removed from an already positive or charged ion.

(b) Y

Reason: Y has the largest atomic radius which means electrons are loosely attracted to the

nucleus hence easily removed.

(c ) X, Z, W, Y

(d) Ered – Eoxd

= -2.37 – (-2.90)

= -2.37 + 2.90 = 0.53V

(e) Electrolysis

Reason: It is a very reactive element and the common reducing agents would not reduce

its ore.

(f) (i) Calcium carbonate

(ii) Temporary hardness

(iii) Ion exchange method or permutit or zeolite process.

(iv) Wash with brine / concentrated / saturated sodium chloride.

(v) - Formation of strong teeth or bones

- Formation of animal shells Any correct one

- Lead pipes do not dissolve NB: One must be one, if more are given

They must be correct if not

correct, no score


2. (A) (a) a – No reaction

b – Does not conduct

c – Readily reacts

d – Conducts electricity AL(s) and O2 are produced.


Turn Over

(b) SO3 (g) + H2 O (l) H2 SO4 (aq) NB; If letters are joined, No score

- If state symbols are missing even if it is

one or it is wrong penalize ½ mk

(ii) S O3 (g) + 2 Na OH (aq) Na2 SO4 (aq) + H2 O (l)

(c ) Recation is highly exothermic producing mist of acid droplets in air.

(d) Both P2 O5 and SO3 molecules are linked up by van der waals forces, they are stronger

in P2 O5 which is a larger molecule compared to SO3.

(e) Concentrated phosphoric acid is a poor conductor because it is only partially dissociated and

has few ions, where as dilute phosphoric acid is a better conductor because it is fully

dissociated with many or more ions.

2. (B) (i) Cl2 (g) + H2 (g) 2HCl (g) ( 1 mark)

(ii) To increase the surface area of absorption. (1 mark)

(iii) Mass of HCl in 1cm3 = 1.18g

= 1.18 x 35

/100 = 0.413g ½

Mass of HCl in 1,000cm3 0.413 x 1000 = 413g ½

Molarity = mass / litre

RMM

= 413 ½

36.5 = 11.32M ½

3. (a) (i) Iron being higher than copper in the reactivity series will go in solution displacing Cu2+

ions. Glass has no effect (1mk) / Iron will absorb some of the heat produced.

(ii) Polystyrene is a poor conductor of heat than glass therefore no heat loss. 1mk

(b) CuSO4 (aq) + Zn (s) Zn SO4 (aq) + Cu (s)

NB: Penalise


- Missing state symbols ½ mk or incorrect

- Joined letters fully penalize

(c ) Calculate:

(i) No.of moles = molarity x volume

1000

= 0.2 x 50

1000

= 0.01 moles

(ii) Heat = mass x specific heat capacity x temperature change

MCT

= 50 x 4.2 x ( 28 – 21 )

= 1470J NB: Penalise for small letter J i.e j

2

0.01 moles give 1470J

1 mole ?

1 x 1470 = 147,000J

0.01

= 147KJ / Mole

(d) - Assumption that solution has some density and specific capacity as water.

- Neglecting mass of zinc used.

- Neglecting heat capacities of beaker, metal and thermometer.

(e)

NB; Labelling Axis – ½ mk

Showing reactants above products – 1mk

Zn (s) + Cu SO4 (aq) Enthalpy change – ½ mk

-147KJ

ZnSO4 (aq) + Cu (s)

Reaction path / process ½

(f) H value with magnesium will be higher than with zinc. Magnesium is higher in the

reactivity series. Mg is more reactive than zinc.

4. (a) (i) A – Propene

B – Propanoic acid

C – Propylpropanoate

(ii) Processes 1 – Dehydration

Processes 2 – Esterification

Processes 3 – Polymerisation

Ener

gy K

JMol-1

½


(iii) A) H H H B) H H

O

H C C C Cl H C C C

OH

H H H H H

(iv) Esters

(v) H CH3 H CH3

C C C C

H H H H n

(v) - Are cheap.

- Can be mould into many complex shapes.

- Resistant to corrosion by acids, alkalis, air and water.

- Colourful and attractive. (Any 2 each ½ )

3

(b) (i) 2C4 H10 (g) + 13O2 (g) 8CO2 (g) + 10H2 O (g)

(ii) Carbon (IV) oxide is acidic gas, it dissolves in water to form a weak carbonic acid

hence the Ph is below 7.

(iii) Butanol has a polar end ( O – H) which establishes hydrogen bonds with the water

molecules unlike butene which is molecular.

5. (a) (i) Solid A – Magnesium oxide

(ii) Solid B – Magnesium nitride

(iii) Gas D – Hydrogen gas

(iv) Gas Z – Ammonia gas

(b) Oxygen is more reactive than nitrogen, hence reacts faster and completely with magnesium,

nitrogen is less reactive and a little of it (N2) reacts with magnesium.

(c ) Mg3 N2 + 6H2 O (l) 3Mg(OH) 2 (s) + 2NH3 (g)

(d) Pass gas X, NH3 through heated copper (II) oxide. The ammonia will be oxidized to

nitrogen gas.

2NH3 (g) + 3Cu O(s) N2 (g) + 3Cu (s) + 3H2O (l)

(e) Carbon (IV) oxide

(f) Helium, Neon, Argon or any other Noble gas


(g) (i) Haber process

(ii) More ammonia gas will be produced

Low temperature favours forward reaction since it is exothermic

6. (a) (i) Copper pyrites or (Cu FeS2)

Gas l – Sulphur (IV) oxide

Slag M- Iron (II) silicate / Fe SiO3

J – Blister copper

(b) (i) Through froth floatation, it is mixed with water, oil and air and then stirred.

(ii) To increase surface area.

(c ) To facilitate removal of iron (II) oxide impurity

FeO (s) + Si O2 (s) FeSiO3 (s)

(d) Anode – Impure copper

Cathode – Strips of pure copper

Electrolyte – Copper (II) sulphate

(e) Pollutes the environment as the sulphur (IV) oxide produced is an air pollutant.

(f) Making electrical wires.

Making soldering instruments.

Making alloys e.g brass (Cu, Zn) brinze (Cu + Tin)

4

(g) Q = 1t

= 100 x 20 x 24 x 60 x 60

= 172, 800, 00oC ½

2 x 96500C deposit = 64g of Cu

172,800,000C ?

172,800,000 x 64 ½ = 57301.5544g ½

193,000

Mass in kg = 57301.5544 = 57.3kg of copper ½

1,000

7. (i) (a) Scale = 1

Plotting = 1

Smooth curve = 1


5

7. (ii) (a) Sodium carbonate (Na2 CO3 )

(b) Molarity of H2 SO4 = 0.2M

0.2 moles = 1,000cm3

? 12.5cm3

0.2 x 12.5

1,000 = 0.0025 moles

(c ) Na2 CO3 (aq) + H2 SO4 (aq) Na2 SO4 (aq) + CO2 (g) + H2 O (l)

From the mole ratio moles of Na2 CO3 = moles of H2 SO4

= 0.0025 moles

(d) 25cm3 of Na2 CO3 contains 0.0025 moles

1000cm3 ?

1,000 x 0.0025


25

= 0.1 moles in 1000cm3

Molarity of Na2 CO3 = 0.1M

(e) R.M.M of Na2 CO3 = 46 + 12 + 48 = 106

1 mole = 106g

0.1 mole ?

0.1 x 106 = 10.6g

1

7. (b) 71cm3 1cm

3

(c ) 70th

second

(d) Na2 CO3 (s) + H2 SO4 (aq) Na2 SO4 (aq) + H2 O (l) + CO2 (g)

(e) Mole ratio Na2 CO3 : CO2

1 : 1

1 mole 24,000cm3

? 105cm3

105 x 1 = 0.004375 moles

24,000

Mole ratio = 1 : 1

Moles of Na2 CO3 = moles of CO2 = 0.004375

Moles = mass

RMM

0.004375 = x

106

X = 106 x 0.004375

= 0.46375g

(f) Time will shorten or will be less.


ANSWERS:

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Documents

Candidate’s Signature...1. (a) Write the electron configuration of calcium (atomic number 20) and magnesium (atomic number 12). ... Complete the table below to show the observations