WAEC Chemistry Past Questions & Answers - Page 66

326.

What is the mass of solute in 500\(cm^{3}\) of 0.005\(moldm^{-3}\) \(H_{2}SO_{4}\)? ( H = 1, S = 32.0, O=16.0)

A.

0.490g

B.

0.049g

C.

0.245g

D.

0.0245g

Correct answer is C

Using 

n = cv where n = no of mole, c = molar concentration(mol/dm3) and v = volume( dm3)

volume =  500\(cm^{3}\) = 0.5dm3, c = 0.005\(moldm^{-3}\)

number of mole(n) = c x v = 0.5 X 0.005 = 0.0025mol.

but n = \(\frac{mass}{ molar mass}\) =  0.0025 = \(\frac{mass}{ 98}\) (where 98g/mol is the molar mass of H2SO4)

mass of H2SO4 = 0.0025 x 98 = 0.245g.

327.

Consider the following equilibrium reaction: \(2AB_{{2}{(g)}} + B_{{2}{(g)}} \to 2AB_{{3}{(g)}}\). \(\Delta H= -X kJmol^{-1}\). The backward reaction will be favored by

A.

a decrease in pressure

B.

an increase in pressure

C.

a decrease in temperature

D.

an introduction of a positive catalyst

Correct answer is A

The equilibrium position is shifted to the left with a decrease in pressure in this system because the number of gaseous molecules on the right is less. (Le-Chatelier's principle).

328.

Ethene is produced from ethanol by

A.

decomposition

B.

hydrolysis

C.

ozonolysis

D.

dehydration

Correct answer is D

Ethene can be gotten from the dehydration of ethanol in the presence of excess  \(H_{2}SO_{4}\) or \(H_{3}PO_{4}\).

329.

Consider the following reaction equation: \(Br_{2} + 2KI \to 2KBr + I_{2}\). Bromine is acting as

A.

an oxidizing agent

B.

a reducing agent

C.

an acid

D.

a base

Correct answer is A

No explanation has been provided for this answer.

330.

An organic compound has the empirical formula \(CH_{2}\). If its molar mass is 42\(gmol^{-1}\), what is its molecular formula?  (C = 12.0, H = 1.0)

A.

\(C_{2}H_{4}\)

B.

\(C_{3}H_{4}\)

C.

\(C_{3}H_{6}\)

D.

\(C_{4}H_{8}\)

Correct answer is C

Given the molecular formula, \(CH_{2}\).

The empirical formula will be \((CH_{2})n\)= 42

\((12+(2\times1))n =42\)

⇒ \(14n =42\)

n = 3, hence the empirical formula is \(C_{3}H_{6}\)