Consider the reactions : 2 S 2 O 3 2 - a q + I 2 s → S 4 O 6 2 - a q + 2 I - a q S 2 O 3 2 - a q + 2 B r 2 l + 5 H 2 O l → 2 S O 4 2 - a q + 4 B r - a q + 10 H + a q Why does the same reductant, thiosulphate react differently with iodine and bromine?

2 S 2 O 3 2 - a q + I 2 s → S 4 O 6 2 - a q + 2 I - a q Oxidation : 2 S 2 O 3 2 - a q → S 4 O 6 2 - a q + 2 e - O.N. of S is changing from + 2 to + 2 . 5 . S 2 O 3 2 - (thiosulphate) is getting oxidized so it will act as a reducing agent. Reduction : 2 e - + I 2 s → 2 I - a q O.N. of I is changing from 0 to - 1 . i.e. I 2 is getting reduced so it will act as an oxidising agent. S 2 O 3 2 - a q + 2 B r 2 l + 5 H 2 O l → 2 S O 4 2 - a q + 4 B r - a q + 10 H + a q Oxidation : S 2 O 3 2 - a q → 2 S O 4 2 - a q The O.N. of sulphur is changing from + 2 to + 6 . Reduction : B r 2 l + 2 e - → 2 B r - a q Bromine is a stronger oxidising agent than iodine as sulphur is getting oxidised to its maximum oxidation state of + 6 in case of bromine. That's why thiosulphate reacts with Br 2 and I 2 differently.

Consider the reactions: (a) H 3 P O 2 a q + 4 A g N O 3 a q + 2 H 2 O l → H 3 P O 4 a q + 4 A g s + 4 H N O 3 a q (b) H 3 P O 2 a q + 2 C u S O 4 a q + 2 H 2 O l → H 3 P O 4 a q + 2 C u s + H 2 S O 4 a q (c) C 6 H 5 C H O l + 2 A g N H 3 2 + a q + 3 O H - a q → C 6 H 5 C O O - a q + 2 A g s + 4 N H 3 a q + 2 H 2 O l (d) C 6 H 5 C H O l + 2 C u 2 + a q + 5 O H - a q → No change observed. What inference do you draw about the behavior of A g + and C u 2 + from these reactions?

In reaction (a) A g + ( a q ) + e - → A g s The oxidation state of Ag changes from + 1 to 0 . In reaction (b) C u + 2 ( a q ) + 2 e - → C u s The oxidation state of Cu changes from + 2 to 0 . Hence, both Ag + and C u 2 + act as oxidising agents in reactions (a) and (b) respectively. In reaction (c) Ag ( NH 3 ) 2 + ( aq ) → Ag ( s ) The oxidation state of Ag changes from + 1 to 0 . Ag + oxidises C 6 H 5 C H O to C 6 H 5 C O O - (O.N. of C changes from 0 to + 2 ) but in reaction (d), C u 2 + cannot oxidise C 6 H 5 C H O . Hence, we can conclude that Ag + is a stronger oxidising agent than C u 2 + .

E M B I B E

Chemistry Part II Textbook for Class XI>Chapter 1 - Redox Reactions>EXERCISES>Q 8.13

MEDIUM

11th CBSE

IMPORTANT

Earn 100

Identify the substance oxidised, reduced, oxidising agent and reducing agent of the following reaction:
$2 A g B r (s) + C_{6} H_{6} O_{2} (a q) \to 2 A g (s) + 2 H B r (a q) + C_{6} H_{4} O_{2} (a q)$

Important Questions on Redox Reactions

HARD

11th CBSE

IMPORTANT

Chemistry Part II Textbook for Class XI>Chapter 1 - Redox Reactions>EXERCISES>Q 8.13

Identify the substance oxidized, reduced, oxidising agent, and reducing agent for the following reaction:

HCHO (l) + 2 {[Ag ({NH}_{3})_{2}]}^{+} (aq) + 3 {OH}^{-} (aq) \to 2 Ag (s) + {HCOO}^{-} (aq) + 4 {NH}_{3} (aq) + 2 H_{2} O (l)

HARD

11th CBSE

IMPORTANT

Chemistry Part II Textbook for Class XI>Chapter 1 - Redox Reactions>EXERCISES>Q 8.13

Identify the substance oxidized, reduced, oxidizing agent, and reducing agent in the following reaction: $HCHO (l) + 2 {Cu}^{2 +} (aq) + 5 {OH}^{-} (aq) \to {Cu}_{2} O (s) + {HCOO}^{-} (aq) + 3 H_{2} O (l)$