Paper III & II: Objective & Essay – Chemistry – 10:00am – 1:00pm

CHEMISTRY OBJ
01-10: EBAAAAAACC
11-20: BCBCACADCA
21-30: AACBDDAACD
31-40: CCACCACCDE
41-50: EDCCDDBDAC
51-60: CBACCDCBCD

Completed!

CHEMISTRY ESSAY
(1ai)
(i) KAl(SO₄)₂. 12H₂O
(ii) Na₂SO₄

(1aii)
Number of moles of sodium reascted = reacting mass/molar mass
= 3.6/23
= 0.1565moles
Number of moles of oxygen reacted = (1/4) x Number of sodium
= 1/4 x (3.6/23)
= 0.03913
Reacting mass of oxygen = Number of moles x molar mass
= 0.03913 x (16×2)
= 1.252grams

(1bi)
Air in gaseous form is first passed through caustic soda to remove CO₂. It is compressed and cooled until ut becomes a liquid at -200°C. It is then led to a fractionating column. On distillation, Nitrogen which has a lowet boiling point of -196°C is evolced first leaving behind Oxygen in liquid form. Further heating converts the liquid to a gas at -183°C.

(1bii)
(i) It is used for combustion
(ii) It is used for artificial respiration

(1biii)
This is because room temperature is warmer

(1biv)
(i) Methyl orange
(ii) Phenophthalein

(1ci)
An ion is an atom or molecule which has a net electric charge due to the loss or gain of one or more electrons.

(1cii)
HCl gas doesn’t contain ions

(1cii)
(i) Noble gases: Neon, Helium
(ii) Halogens: Iodine, Fluorine
(iii) Alkaline earth metals: Calcium, Magnesium

(1civ)
Halogens attain stable octet configuration by accepting an electron from donors Group I elements.

(1di)
A sol is a colloid where solid particles are dispersed in liquid medium.

(1dii)
Jelly

(1diii)
(i) Acid-base titrations are used to determine the percentage purity of a substance
(ii) Acid-base titrations are important to determine the number of water molecules in a hydrate.
°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°
(2ai)
A molar solution of a compound contains one mole or the molar mass of the compound in one dm³ of the solution.

(2aii)
(i) Identification of gases
(ii) Identification of acidic and metallic radicals

(2aiii)
(i) Purification of bauxite
(ii) Electrolysis of alumina

(2bi)

(2bii)
This is because of the presence of copper which is a transition metal

(2bii)
(i) Methanamide is a liquid while the rest amides are crystalline solids
(ii) Melting points and boiling points of aides are much higher than expected.

(2ci)
(i) Heavy chemicals are produced in very large quantities in industries While fine chemicals are produced in small quantities for specific purposes
(ii) Heavy chemicals are in a crude state While fine chemicals are purified.

(2cii)
(i) Million’s reagent
(ii) Feeling’s solution

(2ciii)
Graham’s law of diffusion states that at a constant temperature and pressure the rate of diffusion of a gas is inversely proportional to the square root of its density.

(2civ)
RO₂/RCH₄ = √(MCH₄/MO₂)
5/(200/t) = √[(12+4)/(16×2)]
5t/200 = √16/32
t/40 = 1/√2
t = 40/√2
t = (40/√2) × (√2/√2)
t = 20√2 seconds
Time taken = 28.28 seconds.

°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°
(5)

°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°
(6a)

(6b)