JAMB Chemistry Past Questions & Answers - Page 44

216.

If the cost of electricity required to discharge 10g of an ion X\(^{3+}\) is N20.00, how much would it cost to discharge 6g of ion Y\(^{2+}\)?

[1 faraday = 96,500C, atomic masses are X = 27, Y = 24]

A.

N10.00

B.

N6.00

C.

N20.00

D.

N9.00

Correct answer is D

X\(^{3+}\) + 3e\(^-\) \(\to\) X

3F = 27g

xF = 10g

\(\frac{x}{3} = \frac{10}{27} \implies x = \frac{10}{9} F\)

\(\frac{10}{9}\)F \(\equiv\) N20.00

1F is equivalent to x

\(\frac{1}{\frac{10}{9}} = \frac{x}{20}\)

\(\frac{9}{10} = \frac{x}{20} \implies x = N18.00\)

1F is equivalent to N18.00.

Y\(^{2+}\) + 2e\(^-\) \(\to\) Y

2F = 24g

xF = 6g

x = \(\frac{6 \times 2}{24} = \frac{1}{2} F\)

1F = N18.00

\(\frac{1}{2}\)F = \(\frac{1}{2} \times N18.00\)

= N9.00

217.

Hydrogen diffused through a porous plug

A.

thrice as fast as oxygen

B.

at the same speed as oxygen

C.

four times as fast as oxygen

D.

twice as fast as oxygen

Correct answer is C

Using Graham's Law of Diffusion,

\(\frac{R_1}{R_2} = \sqrt{\frac{m_2}{m_1}}\)

\(\frac{R_H}{R_O} = \sqrt{\frac{m_O}{m_H}}\)

\(\frac{R_H}{R_O} = \sqrt{\frac{32}{2}}\)

\(\frac{R_H}{R_O} = \sqrt{16} = 4\)

\(\therefore R_H = 4 \times R_O\)

Therefore, hydrogen diffuses 4 times faster than oxygen.

218.

The emission of two successive beta particles from the nucleus \(^{32} _{15} P\) will produce

A.

\(^{30} _{14}\)Si

B.

\(^{32} _{13}\)Al

C.

\(^{32} _{17}\)Cl

D.

\(^{32} _{16}\)S

Correct answer is C

\(^{32} _{15}\)P \(\to\) 2\(^{0} _{-1}\)e + \(^{a} _{b}\)X

32 = 2(0) + a

a = 32

15 = 2(-1) + b

b = 15 + 2

b = 17

\(\therefore\) \(^{a} _{b}\)X = \(^{32} _{17}\)Cl

219.

The velocity, V of a gas is related to its mass, M by (k = proportionality constant)

A.

V = \(\frac{k}{M}\)

B.

V = \(\frac{k}{M^{\frac{1}{2}}}\)

C.

V = \(kM^2\)

D.

V = \((\frac{k}{M})^{\frac{1}{2}}\)

Correct answer is B

Recall:

V = \(\sqrt{\frac{3RT}{M}}\)

\(\therefore V \propto \frac{1}{\sqrt{M}}\)

\(V = \frac{k}{\sqrt{M}}\)

V = \(\frac{k}{M^{\frac{1}{2}}}\)

220.

X is a substance which liberates CO\(_2\) on treatment with concentrated H\(_2\)SO\(_4\). A warm solution of X can decolorize acidified KMnO\(_4\). X is

A.

HCOOH

B.

NaHCO\(_3\)

C.

FeCO\(_3\)

D.

H\(_2\)C\(_2\)O\(_4\)

Correct answer is D

It should be noted that for X to liberate CO\(_2\), X must be a carbonate or an oxalate. Since X decolorizes KMnO\(_4\), X must be an oxalate. 

Therefore, X is H\(_2\)C\(_2\)O\(_4\).