JAMB Chemistry Past Questions & Answers

1,441.

The standard enthalpies of formation of CO_2(g), H₂O(g) and CO_(g) in kJ mol^- are -394, -242 and -110 respectively. What is the standard enthalpy change for the reaction CO_(g) + H_2(g)O → CO_2(g) + H_2(g)?

-42 KJ mol^-

+42 KJ mol^-

-262 KJ mol^-

+262 KJ mol^-

View answer & explanation

Correct answer is A

Standard enthalpy change of a process = ∆H° process = ∆H° _F reactant - D_F° products

1,442.

A reaction takes places spontaneously if?

∆G = O

∆S < O and ∆H > O

∆H < T ∆S

∆G > O

View answer & explanation

Correct answer is C

No explanation has been provided for this answer.

1,443.

The oxidation states of chlorine in HOCL, HCLO₃ and HCLO₄ are respectively?

-1, +5, and +7

-1, -5 and 7

+1, +3 and +4

+1, +5 and +7

View answer & explanation

Correct answer is D

No explanation has been provided for this answer.

1,444.

Which of the reactions occurs at the anode during the electrolysis of a very dilute aqueous solution of sodium chloride?

OH^- - e → OH

CIsup>- - e → CI

OHsup>- + CIsup>-HCI + O₂

Na₊ - esup>- Hg (Na)/(Hg) amalgam

View answer & explanation

Correct answer is A

No explanation has been provided for this answer.

1,445.

During the electrolysis of a salt of a metal M, a current of 0.5 A flows from for 32 minutes 10 seconds and deposits 0.325 g of M, What is the charge of the metal ion?

(M = 65, If = 96,500 C per mole of electron)

View answer & explanation

Correct answer is B

Ampere = (Coulomb) x (Sec) x 1930 secs = 965 coulombs (unit of current)
But quantity of electricity = current x time = (Coulomb)/(Sec) x time
If 0.5 A for 32 mins 10 secs; Quantity of electricity = (0.5 coulomb)/(Sec x 1930) secs
= 965 coulombs
Since 965 coulombs give 0.325 g M
i.e1 coulombs = (0.325)/(965) g
∴96500 coulombs = (0.30)/(965) x 96500 =32.5 g
∴(65 g)/(32.5) = 2

inference: it takes 2 Faraday of electricity to deposit 1 mole of M. Therefore, the change on M ion = 2.