JAMB Chemistry Past Questions & Answers - Page 63

311.

The presence of ammonia gas in a desiccator can exclusively be removed by

A.

phosphorus (V) oxide

B.

fused calcium chloride

C.

calcium oxide

D.

concentrated tetraoxosulphate (VI) acid

Correct answer is D

Ammonia gas can be removed from a dessicator by adding a conc. H2SO4 so as to neutralize it since ammonia gas is basic.

312.

The collision theory explains reaction rates in terms of

A.

size of the product

B.

frequency of collision of the reactants

C.

size of reactant

D.

frequency of collision of the products

Correct answer is B

Collision theory is the theory used to predict the rates of chemical reactions, particularly for gases. The collision theory is based on the assumption that for a reaction to occur it is necessary for the reacting species (atoms or molecules) to come together or collide with one another.

313.

The end products of burning a candle in the atmosphere are water and 

A.

carbon (II) oxide

B.

sulphur (IV) oxide

C.

carbon (IV) oxide

D.

sulphur (VI) oxide

Correct answer is C

When we ignite a candle, the hydrocarbon reacts with oxygen (in excess) to produce carbon dioxide and water. The burning sets an air current which gives dome shape to candle flame and it helps to get complete combustion at the bottom and the outer surface of the flame.

CO\(_2\) is produced

314.

2SO\(_2\) \(_{(g) }\)+ O\(_2\) \(_{(g) }\) ↔ 2SO\(_3\)\(_{(g) }\) ΔH = -395.7kJmol\(^{-1}\)
In the equation, an increase in temperature will shift the equilibrium position to the

A.

left and equilibrium constant decreases

B.

left and equilibrium constant increases

C.

right and equilibrium constant increases

D.

right and equilibrium constant decreases

Correct answer is A

This is typical of what happens with any equilibrium where the forward reaction is exothermic. Increasing the temperature decreases the value of the equilibrium constant. Where the forward reaction is endothermic, increasing the temperature increases the value of the equilibrium constant. Endothermic reaction has a Positive Enthalpy change. Exothermic reaction has a negative enthalpy change.

315.

The hydrogen ion concentration of a sample of orange juice is 2.0 X 10\(^{-11}\)moldm\(^{-3}\). What is its p\(^{OH}\)? [log102 = 0.3010]

A.

3.30

B.

13.00

C.

10.70

D.

11.30

Correct answer is A

PH+POH=14
p\(^{H}\) = Log [H\(^+\)]

p[H\(^+\) ] = 2.0 X 10\(^{-11}\)moldm\(^{-3}\)

  p\(^{H}\) = Log [2.0 X 10\(^{-11}\)]

  p\(^{H}\) = 10.70

10.70+ p\(^{OH}\) =14
p\(^{OH}\) = 14 -10.70

= 3.30