PAPER 1

THEORY

OCT./NOV. 2007

2 hours

1. The diagram below shows a “Jiko” when in use. Study it and answer the

questions that follow.

a) Identify the gas formed at region A. (1mk)

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b) State and explain the observation made at region B. (2mks)

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2. 15.0cm³ of ethanoic acid (CH₃COOH) was dissolved in water to make 500cm3 of solution. Calculate the concentration of the solution in moles per litre.

(C=12.0;H=1.0;O=16.0; density of ethanoic acid is 1.05 g/cm³) (3mks)

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3. Both chlorine and iodine are halogens.

a) What are halogens? (1mk)

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b) In terms of structure and bonding, explain why the boiling point of chlorine is lower than that of iodine. (2mks)

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4. The diagram above shows a Bunsen burner when in use.

Name the regions labeled C and D. (2mks)

C …………………………………………………………………………..

D ………………………………………………………………………….

5. When a student was stung by a nettle plant, a teacher applied an aqueous solution

of ammonia to the affected area of the skin and the student was relieved of pain .Explain. (2mks)

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6. In an experiment, a few drops of concentrated nitric acid were added to aqueous iron(II) sulphate in a test – tube. Excess sodium hydroxide solution was then added to the mixture.

a) State the observations that were made when:

i) Concentrated nitric acid was added to aqueous iron (II) sulphate(1mk)

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ii) Excess sodium hydroxide was added to the mixture. (1mk)

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b) Write and ionic equation for the reaction which occurred in (a) (ii) above.(1mk)

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7. a) Use the information given below to draw a labeled diagram of an

electrochemical cell that can be constructed to measure the electromotive force between G and J.

G2+(aq) + 2e                  G(s) ; E = – 0.74 V

J2+(aq)+ 2e                    J(s); E = -0.14 V

b) Calculate the E value for the cell constructed in (a) above. (1mk)

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8. Explain why there is general increase in the first ionization energies of the

elements in period 3 of the periodic table from left to right. (2mks)

9. Study the flow chart below and answer the question that follows.

1. Warm

2. Filter

3. Cool Filtrate

 

Identify: (3mks)

a) Solution K

b) Solid L

c) Gas M

1. The thermo chemical equations for the formation of hydrogen peroxide under standard conditions are:

H2(g) +O2(g) H2O2(g); ∆Hθf = -133kJmol^-1

H2(g) +O2(g) H20(l);∆Hθ=-188 kJmol -1

Write the thermo chemical equation for the molar heat of vaporization of hydrogen peroxide. (2mks

1. The set-up above was used to collect a dry sample of a gas.

Give two reasons why the set-up cannot be used to collect carbon (IV) oxide gas. (2mks)

12. a) State the Charles law (1mk)

b) The volume of a sample of nitrogen gas at a temperature of 291 K and 1.0×10⁵

Pascal’s was 3.5 x 10^-2m3. Calculate the temperature at which the volume of the gas would be 2.8 x 10-2m3 at 1.0 x 10⁵ Pascal. (2mks)

13. a) name the process that takes place when:

(i) Crystals of zinc nitrate change into solution when exposed to air (1mk)

(ii) An alcohol reacts with an organic acid in the presence of a catalyst to form a sweet smelling compound. (1mk)

b) Propane can be changed into methane and ethane as shown in the equation below;

CH₃CH₂CH_3(g) High temperature CH_4(g) + C2H_4(g) (1mk)

Name the process undergone by propane. (1mk)

14. a) Distinguish between nuclear fission and nuclear fusion. (2mks)

• 1. Describe how solid wastes containing radioactive substances should be disposed of. (1mk)

15. a) Explain why permanent hardness in water cannot be removed by boiling.(2mks)

b) Name two methods that can be used to remove permanent hardness from water.

(1mk)

16 The table below shows the tests that were carried out on solid N and the observations made.

I	Test	Observations
II	Dilute hydrochloric acid was added to solid N.	A colourless solution was formed.
III	To the colourless solution obtained in test II, excess sodium hydroxide solution was added.	A white precipitate was formed which dissolved to form a colourless solution.

Write the formula of the anion in;

a) Solid N (1mk)

b) The colourless solution formed in test III (1mk)

17. The relative formula mass of a hydrocarbon is 58. Draw and name two possible structures of the hydrocarbon (C=12.0; H=1.0) (3mks)

18. starting with sodium metal, describe how a sample of crystals of sodium hydrogen carbonate may be prepared. (3mks)

19 The flow chart below shows steps used in the extraction of zinc from one of its ores.

 

 

a) Name the process that is used in step 2 to concentrate the ore. (1mk)

b) Write an equation for the reaction which takes place in step 3. (1 mark)

c) Name one use of zinc other than galvanizing. (1mk)

• 1. An alcohol has the following composition by mass: hydrogen 13.5%, oxygen 21.6% and carbon 64.9%
     1. Determine the empirical formula of the alcohol(C=12.0; H=1.0’)=16.0). (2mks)

21. a) When brine is electrolyzed using inert electrodes, chlorine gas is liberated at the anode instead of oxygen. Explain this observation. (2mks)

b) Name the product formed at the cathode. (1 mk)

22. 6.84g of aluminium sulphate were dissolve in 150cm3 of water. Calculate the molar concentration of the sulphate ions in the solution. (Relative formula mass of aluminium sulphate is 342)

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23. The table below shows the relative molecular masses and the boiling points of pentane and propan-1-01

	Relative molecular mass	Boiling point(oC)
Pentane	72	36
Propan-10-1	60	97

 

Explain why the boiling point of propane 1-1-01 is higher than that of pentane. (2mks)

24. State and explain the observations made when excess ammonia gas reacts with chlorine

gas (3mks)

25. The diagram above shows a student’s set-up for the preparation and collection of hydrogen gas.

(a) How would the final volume of hydrogen gas produced be affected if 80cm3 of 0,75

M hydrochloric acid was used? (1mk)

(b) Give a reason why helium is increasingly being preferred to hydrogen in weather

balloons.

• • 1. The table below shows the number of valence electrons of the element P, Q and R.

Element	P	Q	R
Number of valence electrons	3	5	2

1. Explain why p and R would not be expected to form a compound. (1mk)
2. Write an equation to show the effect of heat on the carbonate of R (1mk)
3. Write the formula for the most stable ion or q. (1mk)

27. The diagram below formula for the most stable ion of Q. (1mk)

On the same axis, sketch the graph for the decomposition of hydrogen peroxide when manganese (IV) oxide is added. (2mks)

28. During the electrolysis of aqueous silver nitrate, a current of 5.0a was passed through the electrolysis for 3 hours.

a) Write the equation for reaction which took place at the anode. (1mk)

b) Calculate the mass of silver deposited (Ag = 108; IF=96500C) (2mks)

29 The diagram below is a section of a model of the structure of element T.

a) State the type of bonding that exists in T. (1mk)

b) In which group of the period table does element T belong? Give a reason. (2mks)

30. Below is a sketch of a graph showing the change in viscosity? (Ease of flow) with temperature when solid sulphur is heated.

Describe what happens to the sulphur molecules when sulphur is heated from 150⁰C to about 200⁰C.

 

CHEMISTRY

Paper 2

THEORY Oct/Nov. 2007

1. (a) State two factors that should be considered when choosing fuel for cooking (2mks)

(b) The diagram below represents a set – up that was used to determine the molar heat of

combustion of ethanol

During the experiment, the data given below was recorded

Volume of water 450cm³

Initial temperature of water 25⁰ C

Final temperature of water 46.5⁰C

Mass of ethanol + Lamp before burning 125.5g

Mass of ethanol + lamp after burning 124.0g

Calculate the:

(i) Heat evolved during the experiment (density of water = 1g/cm³

Specific heat capacity of water = 4.2 Jg^-1K^-1 ( 3 mks)

(ii) Molar heat of combustion of ethanol (C = 12.0, O = 16.0, H=1.0) ( 2 mks)

(c) Write the equation for the complete combustion of ethanol ( 1mk)

(d) The value of the molar heat of combustion of ethanol obtained in (b) (ii) above is lower than the theoretical value. State two sources of error in the experiment. ( 2 mks)

2. (a) Give the systematic names of the following compounds

(b) State the observations made when Propan – I- ol reacts with:

(i) Acidified potassium dichromate (VI) Solution ( 1mk)

(ii) Sodium metal ( 1mk)

(c) Ethanol obtained from glucose can be converted to ethane as shown below

 

Step 1

Step II

C₆H₁₂O₆ C₂H₅OH CH₂ ≡ CH₂

Name and describe the process that take place in steps I and II

Step I (1 ½ mks)

Step II ( 1 ½ mks)

(d) Compounds A and B have the same molecular formula C₃H₆O₂. Compound A liberates carbon (IV) oxide on addition of aqueous sodium carbonate while compound B does not. Compound B has a sweet smell. Draw the possible structures of:

(i) Compound A ( 1 mark)

 

(ii) Compound B ( 1 mk)

(e) Give two reasons why the disposal of polymers such as polychloroethane by burning pollutes the environment. ( 2 mks)

3. The flow chart above shows a sequence of chemical reactions starting with copper study it and answer the questions that follow.

(a) In step 1, excess 3M nitric acid was added to 0.5g of copper powder

(i) State two observations which were made when the reactions was in progress (2mks)

(ii) Explain why dilute hydrochloric acid cannot be used in step 1 ( 1mk)

(iii) I Write the equation for the reaction that took place in step 1 (1mk)

II Calculate the volume of 3M nitric that was needed to react completely with 0.5g of copper powder. (Cu = 63.5) ( 3 mk)

(b) Give the names of the types of reactions that took place in steps 4 and 5 ( 1 mk)

Step 4

Step 5

(c) Apart from the good conductivity of electricity, state two other properties that make it possible for copper to be extensively used in the electrical industry. 2mks)

4. (a) Methanol is manufactured from carbon (IV) oxide and hydrogen gas according to

the equation:

CO₂(g) + 3H₂(g) CH₃OH(g) + H₂O(g)

The reaction is carried out in the presence of a chromium catalyst at 700K and 30kPa. Under these conditions, equilibrium is reacted when 2% of the carbon (IV) oxide is converted to methanol

(i) How does the rate of the forward reaction compare with that of the reverse reaction when 2% of the carbon (IV) oxide is converted to methanol? ( 1 mk)

(ii) Explain how each of the following would affect the yield of methanol:

I Reduction (2mks)

II Using a more efficient catalyst (2mks)

(iii) If the reaction is carried out at 500K and 30kPa, the percentage of carbon (IV) oxide converted to methanol is higher than 2%

I what is the sign of ∆H for the reaction? Give a reason (2mks)

II Explain why in practice the reaction is carried out at 700K but NOT at 500K

(1mk)

(b) Hydrogen peroxide decomposes according to the following equation:

2H₂O₂(aq) →2H₂O(l) + O₂ (g)

In an experiment, the rate of decomposition of hydrogen peroxide was found to be 6.0 x 10^-8 mol dm^-3 S^-1.

(i) Calculate the number of moles per dm³ of hydrogen peroxide that had decomposed within the first 2 minutes (2mks)

(ii) In another experiment, the rate of decomposition was found to be 1.8 x 10^-7 mol dm^-3S^-1. The difference in two rates could have been caused by addition of a catalyst. State, giving reasons, one other factor that may have caused the difference in two rates of decomposition (2mks)

5. (a) The diagram below represents part of the structure of a sodium chloride crystal.

The position of one of the sodium ions in the crystal is shown as

(i) On the diagram, mark the position of the other three sodium ions ( 2 mks)

(ii) The melting and boiling points of sodium chloride are 801⁰C and 1413⁰C

respectively.

Explain why sodium chloride does not conduct electricity at 25⁰C, but does so at

temperatures between 801⁰ C and 1413⁰C ( 2 mks)

(b) Give a reason why ammonia gas is highly soluble in water ( 2mks)

(c) The structure of an ammonia ion is shown below:

Name the type of bond represented in the diagram by N → H ( 1 mark)

(d) Carbon exists in different crystalline forms. Some of these forms were recently discovered in soot and are called fullerenes

(i) What name is given to different crystalline forms of the same element?

(1mk)

(ii) Fullerenes dissolve in methylbenzene while the other forms of carbon do

not.

Given that soot is a mixture of fullerenes and other solid forms of carbon, describe how crystals of fullerenes can be obtained from soot. ( 3mks)

(iii) The relative molecular mass of one of the fullerenes is 720. What is the molecular formula of this fullerene? (C=12.00 ( 1 mk)

6. (a) The elements nitrogen, phosphorous and potassium are essential for plant

growth.

(i) Potassium in fertilizers may be in the form of potassium nitrate

Describe how a sample of a fertilizer may be tested to find out if it contained nitrate ions. (2mks)

(ii) Calculate the mass of nitrogen present if a 25kg bag contained pure ammonium phosphate, (NH₄)₂ HPO₄. (N = 14.0, H=1.0, P = 31.0, O = 16.0

(2mks)

(b) The table below shows the solubility of ammonium phosphate in water at different temperatures.

Temperature (C0)	Solubility of ammonium phosphate in g/100g water
10	63.0
20	69.0
30	75.0
40	82.0
50	89.0
60	97.0

(i) On the grid provided, draw the solubility curve of ammonium phosphate

(Temperature on x – axis) (3 mks)

(ii) Using the graph, determine the solubility of ammonium phosphate at 25⁰C ( 1 mk)

(iii) 100g of a saturated solution of ammonium phosphate was prepared at 25⁰C

I what is meant by a saturated solution? ( 1mk)

II Calculate the mass of ammonium phosphate which was used to prepare the saturated solution ( 2 mks)

(c) The graph below shows how the PH value of soil in a farm changed over a period of

time

(i) Describe how the pH of the soil can be determined (2mks)

(ii) State one factor that may have been responsible for the change in the soil pH in

the time interval AB ( 1 mk)

7. The diagram above shows the set up used in an experiment to prepare chlorine gas and react it with aluminium foil. Study it and answer the question that follow

 

(a) In the experiment, concentrated hydrochloric acid and potassium manganate (VII) were used to prepare chlorine gas. State two precautions that should be taken in carrying out this experiment. (2mks)

(b) Write the formula of another compound that could be used instead of potassium manganate (VII) ( 1 mk)

(c) Explain why it is necessary to allow the acid to drip slowly onto potassium manganate (VII) before the aluminium foil is heated. ( 2 mks)

(d) State the property of the product formed in the combustion tube that makes it possible for it to be collected in the receiver ( 1mk)

(e) When 1.08g of aluminum foil were heated in a stream of chlorine gas, the mass of the product formed was 3.47 g

Calculate the:

(i) Maximum mass of the product formed if chlorine was in excess;

(Al= 27; Cl = 35.5)

(ii) Percentage yield of the product formed ( 1 mk)

(f) Phosphorous trichloride is a liquid at room temperature. What modification should be made to set up if it is to be used to prepare phosphorous trichloride? ( 1 mk)