JAMB Chemistry Past Questions & Answers - Page 48

236.

In the reaction:
M + N → P
ΔH = +Q kJ

Which of the following would increase the concentration of the product?

A.

Adding a suitable catalyst

B.

Increasing the concentration of P

C.

Increasing the temperature

D.

Decreasing the temperature

Correct answer is C

No explanation has been provided for this answer.

237.

Sulphur exists in six forms in the solid state. This property is known as

A.

Isomerism

B.

Allotropy

C.

Isotopy

D.

Isomorphism

Correct answer is B

No explanation has been provided for this answer.

238.

In the reaction between sodium hydroxide and tetraoxosulphate (VI) solutions, what volume of 0.5 molar sodium hydroxide would exactly neutralize 10cm\(^3\) of 1.25 molar tetraoxosulphate (vi) acid?

A.

25cm\(^3\)

B.

10cm\(^3\)

C.

20cm\(^3\)

D.

50cm\(^3\)

Correct answer is D

Equation of reaction : 2NaOH + H\(_2\)SO\(_4\) → Na\(_2\)SO\(_4\) + 2H\(_2\)O
Concentration of a base, CB = 0.5M
Volume of acid, V\(_A\) = 10cm\(^3\)
Concentration of an acid, C\(_A\) = 1.25M
Volume of base, V\(_B\) = ?
Recall:

\(\frac{C_A V_A}{C_B V_B} = \frac{n_A}{n_B}\) ... (1)

N.B: From the equation,

\(\frac{n_A}{n_B} = \frac{1}{2}\)

From (1)

\(\frac{1.25 \times 10}{0.5 \times V_B} = \frac{1}{2}\)

\(\frac{12.5}{0.5V_B} = \frac{1}{2}\)

25 = 0.5V\(_B\)
VB = 50.0 cm\(^3\)

239.

Consider the equation below:

Cr\(_2\)O\(_7 ^{2-}\) + 6Fe\(^{2+}\) + 14H\(^{+}\) \(\to\) 2Cr\(^{3+}\) + 6Fe\(^{3+}\) + 7H\(_2\)O.

The oxidation number of chromium changes from

A.

+5 to +3

B.

+6 to +3

C.

-2 to +3

D.

+7 to +3

Correct answer is B

Cr\(_2\)O\(_7 ^{2-}\) + 6Fe\(^{2+}\) + 14H\(^{+}\) \(\to\) 2Cr\(^{3+}\) + 6Fe\(^{3+}\) + 7H\(_2\)O

The oxidation of Cr in Cr\(_2\)O\(_7 ^{2-}\) :

Let the oxidation of Cr = x; 

2x + (-2 x 7) = -2 \(\implies\) 2x - 14 = -2

2x = 12 ; x = +6

Hence, the change in oxidation of Cr = +6 to +3

240.

Which of the following pairs cannot be represented with a chemical formula?

A.

air and bronze

B.

bronze and sodium chloride

C.

copper and sodium chloride

D.

caustic soda and washing soda

Correct answer is A

No explanation has been provided for this answer.