JAMB Chemistry Past Questions & Answers - Page 81

401.

\(^{226}_{88}Ra\) → \(^x_{86}Rn\) + alpha particle

A.

226

B.

220

C.

227

D.

222

Correct answer is D

\(^{226}_{88}Ra\) → \(^x_{86}Rn\) + \(^4_{2}He\)

\(^4_{2}He\) = alpha particle

considering the summation of the mass number

226 = x + 4

x = 226 - 4

x = 222

402.

When ΔH is negative, a reaction is said to be

A.

endothermic

B.

exothermic

C.

reversible

D.

ionic

Correct answer is B

When ΔH is negative, heat is liberated to the surrounding and it connotes an exothermic reaction.
ΔH = −ve

403.

The ideal gas laws and equations are true for all gases at

A.

low pressures and lower temperatures

B.

low temperatures and high pressures

C.

high pressures and high temperatures

D.

low pressure and high temperatures

Correct answer is D

At high temperature and low pressure, the vanderwaal equation is reduced to ideal gas equation.

i.e, [P + \(\frac{a}{v^2}\)] [v - b] = RT is reduced to PV = nRT

Generally, a gas behaves more like an ideal gas at higher temperature and lower pressure as the potential energy due to intermolecular forces, it becomes less significant compared with the particles kinetic energy and the size of the molecules, then it becomes less significant compared to the empty space between them.

404.

The salt formed from a weak acid and a strong base hydrolyzes in water to form

A.

A saturated solution

B.

an acidic solution

C.

a buffer solution

D.

an alkaline solution

Correct answer is D

This is a solution formed from the hydrolyses of an alkali in water.

405.

Incomplete oxidation of ethanol yields

A.

CH3COOH

B.

CH3COCH3

C.

CH3CH2OCH2CH3

D.

CH3CHO

Correct answer is D

C2H5OH → CH3CHO → CH3COOH
Ethanol.....oxidation Ethanal........Ethanoic Acid
Primary alcohol oxidises to aldehyde and later to carboxylic acid.
Secondary alcohol oxidises to ketones.
Ethanol is an example of primary alcohol and primary alcohol can be oxidised to aldehyde and carboxylic acid. Wherein, incomplete oxidation of primary alcohol yields aldehyde also known as alkanal while complete oxidation of primary alcohol yields carboxylic acid.