ZANZIBAR ADVANCED SECONDARY SCHOOLS

FORM FIVE JOINT EXAMINATIONS

ADVANCED CERTIFICATE OF SECONDARY EDUCATION
EXAMINATION

132/1 CHEMISTRY 1
(For Both School and Private Candidates)
Time: 3Hours Thursday, 23rd April 2021 p.m.
Instructions

1. This paper consists of TEN (10) questions in section A and B.

2. Answer ALL questions from section A and TWO (2) questions from section B.

3. Each question of section A carries TEN (10) marks and of section B carries FIFTEEN (15) marks.

4. Mathematical tables and non-programmable calculators may be used.

5. Cellular phones are not allowed in the examination room.

6. Write your Examination number in each answer paper.

7. For calculations you may use the following constants:

Rydberg constant RH =1.09678 x107 m-1

Gas constant, R = 8.314Jmol-1K-1 or 0.082 atm mol-1 K-1 dm3

GMV = 22.4dm3.

1litre = 1dm3 = 1000cm3.

Standard temperature = 273 K.

Standard pressure = 760mmHg.

Planck constant, h =6.63 x10-34 Js

Velocity of light, C =3.0 x 108 m/s

Atomic mass: N = 14, C = 12, H =1, Cl = 35.5, O = 16, Hg = 200.59, Cr = 51.9

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Form five joint examination 2021 chemistry
 SECTION A (70 Marks)

Answer ALL questions in this section.

1. (a) Give the meaning of diagonal relationship. (01 mark)

(b)(i) Explain two shortcomings of Mendeleev’s periodic table. (02 marks)

(ii) Magnesium react with hydrogen to form compound A, which is a white solid at room
temperature. It also reacts with hydrochloric acid to form gas B and an aqueous solution of
compound C. Identify the products of these reactions and write balanced equations for each
reaction. (04 marks)

(c) Consider atoms with the following electronic configuration.

A 1s22s22p63s2, B 1s22s22p63s1, C 1s22s22p6.

Which atom has the largest first ionization energy, and which one has the smallest second
ionization energy? Explain your choice. (03 marks)

2. (a) Which of the following pairs is expected to have the larger bond angle? Explain your choice.
i. H2O and NH3
ii. PH3 and NH3 (04 marks)

(b) Two different bond lengths are observed in the PF5 molecules but only one bond length is
observed in SF6. Explain the difference. (03 marks)

(c) The two molecules indicated below are capable of intramolecular hydrogen bonding. Which is
likely to form more stable hydrogen bond? Suggest a reason for your choice.

(03 marks)

3. (a) The lowering of vapour pressures of solvent by a non volatile solute is reflected in an elevation of
the boiling point and a depression of the freezing point of the solvent. State two laws governing these
phenomena. (03 marks)
(b)A 0.0140g sample of an ionic compound with the formula Cr(NH3)5Cl3 was dissolved in water to
give 27.0ml of solution at 25oC. The osmotic pressure was determined to be 119 mmHg. How many
ions are obtained from each formula unit when the compound is dissolving in water. (05 marks)
(c) State two applications of freezing point depression. (02 marks)

4. (a) Define the following.

i. Mean bond enthalpy.
ii. The second electron affinity.
iii. The standard enthalpy of atomisation. (03 marks)
(b) Explain why;
i. Loss of an electron from a sodium atom is an endothermic process.
ii. Gain of an electron by a chlorine atom is exothermic process. (03 marks)

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Form five joint examination 2021 chemistry
 (c) The standard enthalpy of formation of methane is 74.8KJ/mol. The enthalpies of atomization of
graphite and hydrogen are +715 and +218 KJ/mol of atoms in the gas phase. Calculate the mean
C-H bond energy. (04 marks)

5. (a) Mention four parameters of the gas. (02 marks)

(b) A mixture of gases at 760 torr contain 55.0% nitrogen, 25.0% oxygen, and 20% carbondioxide by
volume. What is the partial pressure of each gas in Nm-2. (04 marks)
(c) Mercury diffusion pumps may be used in the laboratory to produce a high vacuum. Cold traps are
generally placed between the pump and the system to be evacuated. These cause the
condensation of mercury vapour and prevent mercury from diffusing back into the system. The
minimum pressure of mercury that can exist in the system is the vapour pressure of mercury at
the temperature of a cold trap. Calculate the number of mercury atoms per unit volume in a cold
trap maintained at -120oC. The vapour pressure of mercury at this temperature is 10-16 torr.
(04 marks)
6. (a) Explain the following.
i. Aufbau building up principle.
ii. Dual nature of matter. (03 marks)
(b) Describe two differences between mass number and atomic mass. (04 marks)
(c) (i) What aspect of the Bohr model of the atom does the Heisenberg Uncertainty principle
discredit? (01marks)
(ii) A hydrogen atom has a radius of 0.05nm with a position accuracy of 1.0%. What is the
uncertainty in determining the velocity? (02marks)

7. (a) Explain the following term as applied in metal compound.

i. Effloroscence substances.
ii. Hygroscopic substances. (02 marks)
(b) Complete and balance the following chemical equations.

i. FeSO4(aq) + Na2CO3(aq)
ii. MgCl2.6H2O(s) →

iii. PbO2(s) + HCl(aq)

iv. CaSO4.2H2O(s) → (08 marks)

SECTION B (30 Marks)

Answer any TWO questions in this section.

8. (a) (i) After an ozonolysis experiment, the only product was ethanal. The chemist who did the
experiment correctly claimed that there were two different structures for the starting material. What
were they? (03 marks)
(ii) Land that has been used as a site for rubbish dumps has sometimes been used later as building
land. There have been cases of explosions occuring in houses buit on such land. What causes the
explosions? Explain briefly. (03 marks)

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Form five joint examination 2021 chemistry
 (b) A student wanted to make propane by the Wurtz reaction. He decided that a mixture of
iodomethane and iodoethane would be needed. Was he correct? What would be made in the reaction?
(04 marks)
(c)(i) A student said that the reason why alkenes are unsaturated is that they can be made by
removing water from alcohol. Was she correct? (02 marks)
(ii) What will be made if but-2-ene

is reacted with Baeyer’s reagent? (03 marks)

9. (a) A student suggested that, ignoring complecating factors, when a group substituted at the ortho and
para positions, we should expect to get about twice as much of the ortho pruduct as para product.
i. Why is this a reasonable suggestion?
ii. Suggest a reason why, in practice, this, idea ration seldom occurs. (05 marks)

(b) Consider the following;

Boiling point of hydrochloric acid -85oC.
Boiling point of water 100oC.
Boiling point of azeotropic mixture 108.5oC at 79.8% composition of water.
i. Draw the boiling point-composition diagram for mixture of hydrogen chloride and water.
ii. What type of deviation from Raoult’s law does the solution show?
iii. What would be produced if a solution of hydrochoric acid were distilled?
(10 marks)
10. (a) Explain why
i. Alkynes with terminal hydrogens have acidic properties, while alkenes and alkane with
terminal hydrogens have no acidic properties?
ii. The lone pair of compounds with sp3 hybrid orbital is more reactive compounds than
compounds with sp2 and sp hybrid orbitals.
iii. Cyanides and carbonyl compounds less reactive than alcohols and amines?
iv. Among unsaturated hydrocarbons, it is only alkenes which show cis-trans isomerism.
(09 marks)

(b) Explain the similarities between the following:

i. E2 elimination mechanism and SN2 substitution mechanism.

ii. E1 elimination mechanism and SN1 substitution mechanism. (06 marks)

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Form five joint examination 2021 chemistry