JAMB Chemistry Past Questions & Answers - Page 360

1,796.

If the heat of combustion of hydrogen is -285.8kJ,
What is the heat of formation of water?

A.

+571.6 kJ

B.

-571.6 kJ

C.

-285.8 kJ

D.

+285.8 kJ

Correct answer is C

No explanation has been provided for this answer.

1,797.

Na2CO3(g) + 2HCl(aq) → 2NaCl(aq) + H2O(l) + CO2(g)
How many moles of sodium trioxocarbonate (IV) are there in a 25 cm3 solution which required 10cm3 of 0.05 mol dm-3 hydrochloric acid solution to neutralize it?

A.

1.000 mole

B.

0.100 mole

C.

0.010 mole

D.

0.111 mole

Correct answer is C

\(\frac{C_A V_A}{C_BV_B} = \frac{a}{b}\)

\(\frac{0.05 \times 10}{C_B \times 25} = \frac{2}{1}\)

50CB = 0.5

CB = \(\frac{0.5}{50} = \frac{1}{100}\)

= 0.01

1,798.

In the electrolysis of CuSO4(g) using platinum electrodes, the reaction at the anode is

A.

4H+ + 4e- → 2H2

B.

4OH- + 4e- → 2H2O + O2

C.

2OH - 2e- → 2OH

D.

2OH- + 2OH- → 2H2O + O2

Correct answer is B

4OH<sup>-</sup> + 4e<sup>-</sup> → 2H<sub>2</sub>O + O<sub>2</sub> is the reaction of sun at the anode in the electrolysis of CuSO4 (g) 

1,799.

In which of the following is the oxidation number of sulphur equal to -2?

A.

SO3

B.

S8

C.

H2S

D.

SO2

Correct answer is C

No explanation has been provided for this answer.

1,800.

The solution that will conduct the highest amount of electricity is?

A.

0.5 mol dm-3 of hydrochloric acid

B.

2.0 mol dm-3 of hydrochloric acid

C.

0.5 mol dm-3 ethanoic acid

D.

2.0 mol dm-3 ethanoic acid

Correct answer is B

Hence, for most aqueous solutions, the more ions, the higher the conductivity.

Strong electrolytes ionize completely e.g strong acid, strong bases and some salts

While weak electrolytes ionize only partially e.g CH3COOH is regarded as acetic acid. 
It is a weak electrolyte. Acetic acid is regarded as weak electrolyte because its dissociation constant is low.