JAMB Chemistry Past Questions & Answers - Page 420

2,096.

(1/2)Zn2+(aq) + e- → (1/2) Zn(s)
In the reaction above, calculate the quantity of electricity required to discharge zinc.
[F = 96 500 C mol-1]

A.

0.965 * 104C

B.

4.820 * 104C

C.

9.650 * 104C

D.

48.200 * 104C

Correct answer is C

1 mol → 96500 * 2
0.5 mol → X
X = 0.5 * 96500 * 2
= 9.650 * 104C

2,097.

MnO\(_{4(aq)}^{-1}\) + 8H\(^+ _{(aq)}\) + Y → Mn\(^{2+} _{(aq)}\) + 4H\(_2\)O\(_{(l)}\)
Y in the equation above represents

A.

2e-

B.

3e-

C.

5e-

D.

7e-

Correct answer is C

We want the number of charges on both sides of the equation to be the same. 

i.e. number of charges on the reactant side = the number of charges on the product side. 

                                                                    -1 + 8  =  2

                                                                            7 = 2

difference in number of charges = 5, hence Y = 5.

2,098.

The pOH of a solution of 0.25 mol dm-3 of hydrochloric acid is

A.

12.40

B.

13.40

C.

14.40

D.

14.60

Correct answer is B

pOH = -log [2.5 * 10-1]
= -log[-0.3979 + 1]
= 13.40

2,099.

In which order are the following salts sensitive to light?

A.

Agl > AgCl > AgBr

B.

AgCl > Agl > AgBr

C.

AgBr > AgCl > Agl

D.

AgCl > AgBr > Agl

Correct answer is C

light sensitivities of the silver halides: AgBr > AgCl > AgI. Notably; AgBr is used in production of photographic chemicals.

2,100.

HCL(aq) + H2O(l) H3O+(aq) + Cl-(aq)
In the reaction above, Cl-(aq) is the

A.

conjugate acid

B.

acid

C.

conjugate base

D.

base

Correct answer is C

No explanation has been provided for this answer.