CHEMISTRY 1 FORM FOUR MOCK EXAMINATION, KILIMANJARO MARKING SCHEME

THE PRESIDENT’S OFFICE

REGIONAL ADMINISTRATION AND LOCAL GOVERNMENT

KILIMANJARO REGIONAL COMMISSIONER’S OFFICE

FORM FOUR MOCK EXAMINATION

CHEMISTRY 1 MARKING SCHEME

01.

1mark@ = 10 marks

02.

1mark @ = 05 marks

03.a)i) Close the air hole and Connect the burner to the gas using a rubber tubing

ii) Light the match and hold it at the top of the chimney

iii) Open the gas slowly to half way then to fully open position

iv) Open the air holes slowly after the gas is lit

(1 Marks@=4 Marks)

(b) i) It is transparent and do not corrode by chemicals

ii) They prevent soaking of water.

(1marks@ = 2marks)

(c) Because small change in volume can show large difference in volume. (1 mark)

4.(a) When we breath in carbon (ii) oxide, combines with haemoglobin form carbonyl haemoglobin that do not release oxygen to the body cell hence living cells lacks oxygen as a result a person may die. (03 marks).

(b) i) Water

ii) Sand

iii) Foam

(@1 mark = 3 marks)

(c) Fire class A (01 mark)

5.(a) i) Due to presence of delocalized electrons that are free to move.

ii) When high voltage of electric current is passed through it gives characteristic colour

iii) Water is plenty and accessible than any other component in first aid kit.

iv) Filtration is slow process but centrifuge separate quickly solid from liquid.

v) Heat and moisture from the exhaust increase the rate of reaction where by accelerate rusting

(1mark@ = 5 marks)

(b) Solution

1 mole of ammonia occupies 22.4dm³ at STP.

X moles occupies 22.4dm³at STP.

i.e.

1mole = 22.4dm³

X =22.4dm³

X = 2.24mol/dm³

22.4dm³

= 0.1mol.

(01mark)

Consider equation

N₂(g) + 3H₂g 2NH₃(g)

Mole ration is 1:2.

The number of moles of N2 required is given by

o.1 mol x 1 = 0.05mol.

2

Therefore 0.05 moles of Nitrogen gas required to produce 2.24dm³ of ammonia at STP.

1. ark)
   

6.(a) i) Finely divided iron (01 mark)

ii) Hydrogen – obtained from electrolysis of water or natural gas (01 mark)

nitrogen; obtained from air by fractional distillation of liquid air (01 mark)

(b) i) Reaction moves forward because it is exothermic

ii) Reaction moves forward (01 mark)

(C) Le Chatelier’s principle. (01 mark)

“When a system in equilibrium subjected to a change the position of equilibrium will change so as to eliminate effect of change” (01 mark)

7.(i) 20 ( 01 mark )

ii) x

(2marks)

iii) Atomic mass = 40 (01 mark)

7.(b) (i) Sulphur dioxide. (01 mark)

(ii) Na2SO3 + 2 HCl NaCl + SO2 + S + H2O (1 Mark)

(iii) dissolve rain water forming sulphurous acid that pollute the environment.

(01 mark)

8(a)

(1mark@ = 4 marks)

(b) concentration

Roasting

Smelting

1. mark @ = 3 marks)
   

9. (a) Uses of matter

• Matter used for transportation example water
  
• Matter used for construction e.g. Bricks
  
• Matter used for photosynthesis example carbon dioxides
  

  (3pts = 3 marks)
  

   

(b) Simplify communication

– Enable learners to understand elements quickly (02 marks)

(c)Using unhydrous copper (II) Sulphate

Using cobalt chloride

1. arks@ = 2marks)
   

10.(i) Cathode – Hydrogen (01 mark)

Anode – Oxygen

(ii)

(02 Marks)

(iii) At anode

4 OH^– 2H2O + O₂ + 4 e^–

At cathode

2 H⁺(aq) + 2e^– H2(g)

Number of moles of oxygen

4 mole of e = 1Mol of O₂

0.02 Mol =?

= 0.02 x 1= 0.005mol. (1.5 marks)

4

Number of mole of H2

2 Mols of e = 1 Mol of H2

0.02 Mol = x

= 0.01 Mol (1.5 Marks)

1. (a) Diamond
   

Graphite

Amorphous

(1mark @)

b) Carbon dioxide turns lime water milky

c) Na₂S₂O_3(aq) + 2HCl_(aq)      2NaCl_(aq) + SO_2(g) + S_(s) + H₂O_(l) (01 mark)

2Na_(aq)⁺ + S₂O_3(aq)^2-+ 2H⁺ + 2Cl^– 2Na⁺ _(aq) + 2Cl^–_(aq) + SO_2(g) +S_(s) + H₂O_(l)

S₂O₃^2-_(aq)
+ 2H⁺_(aq) SO_2(s) + S_(s) + H₂O_(l) (02 marks)

12.(a) Alkyl group; is hydrocarbon with one hydrogen atom removed.( 01 Mark)

(b) i) CnH_2n+2

ii) C_nH_2n

iii) C_nH_2n+1OH (01 mark@)

c) i) 8- chlorohept 3-yne.

ii) 3, 3-dimethylbutan-2-ol

iii) Butane (01 mark @)

13. Meaning of environmental degradation (1.5 marks)

Measures to minimize environmental degradation( any 6 pts @ 2marks)

• Lower impact mining technique
  
• Use of eco- friendly equipment
  
• Reusing mining waste
  
• Shutting illegal mining
  
• Rehabilitating mining sites.
  
• Improving mining sustainability
  

  Conclusion 1.5 marks
  

14.meaning of soil fertility (1.5 marks)

Importance of soil fertility (6 points @ 2marks)

• Provide nutrient to the plants
  
• Provides support
  
• Prevents plants from diseases
  
• Provides support to the plant
  
• Ensure high yield
  
• Improve soil aeration
  

Conclusion (1.5 marks)