THE PRESIDENT'S OFFICE

MINISTRY OF REGIONAL GOVERNMENT AND LOCAL GOVERNMENT

PRE-NATIONAL  EXAMINATION SERIES-1

CHEMISTRY  FORM-4

2020

TIME: 3:00 HRS

Instructions

1. This paper consists of sections A, B and C with a total of fourteen (14) questions.
2. Answer all questions in sections A and B and one (1) question from section C.
3. Cellular phones and any unauthorised materials are not allowed in the examination room.
4. Write your Examination Number on every page of your answer booklet(s).
5. The following constants may be used.

Atomic masses: H 1, O- 16, N- 14, S = 32, Zn - 65, Cl -35.5, cu - 64.

Avogadros number= 6.02 x 10²³

GMV at s.t.p =22.4 dm³ .

1 Faraday= 96,500 coulombs.

Standard pressure = 760 mm Hg. Standard temperature 273 K.

1 litre =1 dm³ =1000 cm 3.

SECTION A (15 Marks)

Answer all questions in this section.

1. For each of the items (i) — (x), choose the correct answer from among the given alternatives and write its letter beside the item number in the answer booklet provided.

(i) "Water is referred to as the universal solvent". What does this mean? 

1. Water is neither acidic nor basic as compared to other liquids.
2. Water exists in three states of matter than any other liquids.
3. Water dissolves both organic and inorganic solutes. 
4. Water is used more domestically than any other liquids.
5. Water dissolves more substances than any other known liquids.

 (ii) A current of 0.2 A was passed through an electrolyte for 16 minutes and 40 seconds. What is the quantity of electricity produced in coulombs?

1.  2000 C  
2. 1000 C 
3.  200 C 
4.  0.20 C 
5.  7686 C.

(iii) Substance X liberates chlorine gas from acidified potassium chloride. The behaviour of X is described as:

1.  an oxidising agent    
2.  an oxidising and reducing agent
3.  catalyst   
4.  a reducing agent
5.  bleaching agent.

(iv) Which carbonate is the most stable to heat?

1.  Calcium carbonate   
2.  Copper (II) carbonate
3.  Lead (II) carbonate 
4.  Zinc carbonate 
5. .Iron (II) carbonate.

(v)  Aluminium does not react with water and does not corrode much in air because

1.  it is below hydrogen in the reactivity series
2.  it forms a stable carbonate which prevents reactions
3.  the metal is covered with a protective coating of an oxide 
4.  aluminium ions have positive charges
5.  it is very stable.

(vi) Which of the following compounds does NOT belong to the alkenes homologous series?

1.  C₂H₄ 
2.  C₃H₆  
3.  C₄H ₈ 
4.  C₅H₁₀ 
5.  C₆H ₁₄.

(vii) Which of the following is NOT among the composition of air?

1. Noble gases 
2. Carbon dioxide 
3. Nitrogen 
4. Hydrogen 
5. Water vapour. 

(viii)   Chlorine ion, Cl^- differs from chlorine atom because it has       

1.   more protons. 
2.  less protons. 
3.  more electrons. 
4.  less electrons. 
5.  more neutrons.

(ix) Which of the following pairs of compounds can be used in the preparation of calcium sulphate?

1. Calcium carbonate and sodium sulphate
2. Calcium chloride and ammonium sulphate
3. Calcium hydroxide and barium sulphate 
4. Calcium nitrate and lead (II) sulphate 
5. Calcium chloride and barium sulphate. 

(x)  Which of the following solutions is the most concentrated?

1. 50 g of calcium carbonate in 100 cm³ of water
2. 60 g of sodium chloride in 200 cm³ of water
3. 65 g of potassium nitrate in 100 cm³ of water
4. 120 g of potassium sulphate in 200 cm³ of water
5. 50 g of sodium hydroxide in 200 cm³ of water.

2.  Match the items in List A which the responses in List B by writing the letter of the correct response beside the item number in the answer booklet provided.

SECTION B (70 Marks)

Answer all questions in this section.

3. (a) (i) State Avogadro’s law of gaseous volume.

(ii) Find the volume of oxygen gas required to burn completely 1 dm³ of methane. CH4 + 2O  2(_g) ? CO  2 + 2H  2O. 

(iii) What is the volume of carbon dioxide formed in the reaction at (ii) (4 marks)

(b) Define the following terms:

(i) Mole

(ii) Molecular weight (2 marks)

4. (a) Ammonia gas can be prepared by heating an ammonium salt with an alkali

(i) Name the most common pair of reagents suitable for this reaction.

(ii) Write the equation for the reaction. (4 marks)

(b) Ammonia is very soluble in water and less dense than air. How does each of the properties determine the way in which ammonia is collected in a gas jar? 

5. (a) Differentiate empirical formula from molecular formula

(b) Calculate the empirical formula for a compound with the following composition: lead 8.32 g, sulphur 1.28 g, oxygen 2.56 g (relative atomic wt of lead = 207, sulphur = 32, oxygen = 16)

6. (a) Classify the following reactions into oxidation and reduction reactions.

(i)  S( s) + O 2( g) ? SO 2( g)

(ii) N2( g) + 3H 2( g) ? 2NH 3( g)

(iii) Fe2+ (aq) ­ e ­  ? Fe3+ (aq)

(iv) Fe³⁺ _(aq) ­ e  ^­  ? Fe²⁺ _(aq)  (4 marks)

(b) What is the oxidation number of iron in iron (III) chloride? (3 marks)

7.(a) Explain the meaning of the following:

(i) Malleable

(ii) Ductile

(iii) Brittle 

(b) Give an account of the following

(i) Anhydrous copper (II) sulphate becomes coloured when exposed to the air for a long time.

(ii) Carbon dioxide can be collected by the downward delivery method.

(iii) Concentrated sulphuric acid is not used for drying hydrogen sulphide gas.

(iv) Sodium metal is kept in paraffin oil. 

8. (a) (i) What is the first step to take when you want to identify the contents of a given salt containing one anion and one cation?

(ii) In a solution of water, identify a solute and a solvent. Justify your answer. 

(b) Sodium is a solid while chlorine is a gas at room temperature although they are in the same period in the periodic table. What is the cause of this difference?

9. (a) (i) Name three gases which should not be produced in order to prevent the destruction of ozone layer. 

 (ii) List and explain three effects of ozone layer depletion.

(b) Lack of safe water for domestic and industrial uses is a serious problem in most of Tanzanian towns. The major cause of this problem is pollution in the water sources. Slate three methods that could make water from a pond or a well be safe for drinking.

10. (a) (i) Name the products formed when nitrates of potassium and zinc decompose by heat. 

 (ii) Suggest why the nitrates of zinc and potassium behave differently on heating.

(b) Mention two uses of sodium nitrate.

11. (a) Which ways are the fossil fuels detrimental to the environment? Give four points. 

(b)  Briefly explain how biogas is produced by using domestic waste.

12. (a) (i)  Define isomerism.

(ii) Draw and name two structural formulae of the isomers of C4H8.

(b) Carbon dioxide can be prepared by adding an acid to calcium carbonate.

(i) Using a named acid, write a balanced chemical equation for the reaction. (ii) Name all the products formed in (b) (i)

SECTION C (15 Marks)

Answer one (1) question from this section.

13. Describe the cause, two effects and measures to be undertaken in order to prevent/reduce the amounts of acid rain.

14. 0.48g of a metal, M was placed in a test tube and hot copper (II) sulphate solution was added to it and stirred until the reaction stopped. The metal (M) displaced copper from copper (II) sulphate solution. Copper was filtered, washed with water, dried at 100⁰ C  and the mass found to be 1.27g. Given that, the balanced chemical reaction that occurred is M _(s)  + CuSO  _4(aq)  MSO  _4(aq)  + Cu  _(s) 

(a) Calculate;

1. The number of moles of copper that were formed and the number of moles of M that were used in the reaction.
2. The relative atomic mass of M and hence identify metal M.

(b) State the appearance of the metal formed (Cu).

(c) With ionic equations, explain why the reaction can be considered to involve both oxidation and reduction.