WAEC Chemistry Past Questions & Answers - Page 17

81.

Which of the following acids would form normal salt only?

A.

Tetraoxosulphate(VI) acid

B.

Trioxonitrate(V) acid

C.

Tetraoxophosphate(V) acid

D.

Trioxosulphate(IV) acid

Correct answer is A

Normal salts are formed when all the replaceable hydrogen ions in the acid have been completely replaced by metallic ions

82.

Consider the following reaction equation:
CaO + SiO\(_{2}\) ------> CaSiO\(_{3}\)
Silicon(IV) oxide is acting as

A.

a basic oxide

B.

a reducing agent

C.

an acidic oxide

D.

an oxidizing agent

Correct answer is C

Silicon dioxide is an acidic oxide. It will react with strong bases to form silicate salts, SiO\(_{2}\) is acidic oxide because Si is non-metal. Oxides of non-metals are acidic in nature.

83.

Before a reaction could take place, there should be

A.

ionization of reactant particles

B.

breakage of bonds of products

C.

breakage of bonds of reactants

D.

ionization of product particles

Correct answer is C

Activation energy must be achieved before reaction begin. This is because in any chemical reaction, chemical bonds in the reactants are broken, and new bonds in the products are formed

84.

A white precipitate was formed when BaCl\(_{2(aq)}\) was added to an aqueous solution
of a salt X. The precipitate dissolved in dilute HCl with rapid effervescence. Salt X is likely to contain

A.

SO\(_{4}\) \(^{2-}\) ions

B.

SO\(_{3}\) \(^{2-}\) ions

C.

NO\(_{3}\)- ions

D.

SO\(_{3}\) \(^{2-}\)- ions

Correct answer is D

Effervescence is the formation of gas bubbles in a liquid by a chemical reaction. An example of effervescence is the release of carbon dioxide which bubbles as a gas from the liquid when limestone chips, which are composed of calcium carbonate, are added to dilute hydrochloric acid.

85.

Increasing the temperature generally

A.

decreases the solubility of a solid in a liquid but increases the solubility of a gas in a liquid.

B.

increases the solubility of a solid in a liquid but decreases the solubility of a gas in a liquid.

C.

increases the solubility of both a solid and a gas in a liquid

D.

decreases the solubility of both a solid and a gas in a liquid

Correct answer is B

-The solubility of gases in liquids decreases with increasing temperature. Conversely, adding heat to the solution provides thermal energy that overcomes the attractive forces between the gas and the solvent molecules, thereby decreasing the solubility of the gas
-The solubility of most solid or liquid solutes increases with increasing temperature