WAEC Chemistry Past Questions & Answers - Page 51

251.

Consider the following reaction equation: \(2NO_{(g)} + O_{{2}{(g)}} \to 2NO_{{2}{(g)}}\). What is the change in the oxidation number of nitrogen?

A.

+2 to 0

B.

+2 to -2

C.

+2 to +4

D.

+4 to +2

Correct answer is C

In NO, the oxidation number for nitrogen is N - 2 = 0

⇒ N = +2

In \(NO_{2}\), we have N - (2x2) =0

N - 4 =0

N =+4

252.

The common feature of reactions at the anode is that

A.

electrons are consumed

B.

ions are reduced

C.

oxidation is involved

D.

the electrode dissolves

Correct answer is C

In both the electrochemical cell and the electrolytic cell, at the anode, oxidation is involved.

253.

Chemical reactions occurs when the colliding reactants have energy that is

A.

less than the activation energy

B.

greater than the activation energy

C.

greater than the energy of the product

D.

less than the energy of effective collision

Correct answer is B

The energy of the reactants must be more than the activation energy in order for product to be formed.

254.

Soluble salts can be prepared by the following methods except

A.

neutralization

B.

reaction of an acid with trioxocarbonate(IV) salt

C.

double decomposition

D.

reaction of an acid with electropositive metals

Correct answer is C

Soluble salts cannot be produced by double decomposition( precipitation of an insoluble salt)

255.

The property of a chemical reaction that is affected by the presence of a catalyst is

A.

activation energy

B.

free energy

C.

equilibrium position

D.

enthalpy change

Correct answer is A

The activation energy is the amount of energy that is required to form products in a reaction. The presence of a catalyst helps to speed up the reaction such that the energy needed for the reaction is reduced.