List of top Chemistry Questions on Classical Idea Of Redox Reactions – Oxidation And Reduction Reactions asked in CBSE Class XI

Consider the reactions:
\(2S_2O_3^{2-}(aq) + I_2(s) \rightarrow S_4O_6^{2-}(aq) + 2I ^- (aq)\)
\(S_2O_3^{2-}(aq) + 2Br_2(l) + 5 H_2O(l) \rightarrow 2SO_4^{2-}(aq) + 4Br ^- (aq) + 10H ^+ (aq)\) 
Why does the same reductant, thiosulphate react differently with iodine and bromine?

How do you count for the following observations?

1. Though alkaline potassium permanganate and acidic potassium permanganate both are used as oxidants, yet in the manufacture of benzoic acid from toluene we use alcoholic potassium permanganate as an oxidant. Why? Write a balanced redox equation for the reaction.
2. When concentrated sulphuric acid is added to an inorganic mixture containing chloride, we get colourless pungent smelling gas HCl, but if the mixture contains bromide then we get red vapour of bromine. Why?

Chlorine is used to purify drinking water. Excess of chlorine is harmful. The excess of chlorine is removed by treating with sulphur dioxide. Present a balanced equation for this redox change taking place in water.

Consider the reactions: 
(a) \(6 \,CO_2(g) + 6H_2O(l) \rightarrow C_6H_{12}O_6(aq) + 6O_2(g)\) 
(b) \(O_3(g) + H_2O_2(l) \rightarrow  H_2O(l) + 2O_2(g)\) 
Why it is more appropriate to write these reactions as: (a) \(6\,CO_2(g) + 12H_2O(l) \rightarrow  C_6H_{12}O_6(aq) + 6H_2O(l) + 6O_2(g)\) 
(b) \(O_3(g) + H_2O_2(l) \rightarrow H_2O(l) + O_2(g) + O_2(g)\) 
Also suggest a technique to investigate the path of the above (a) and (b) redox reactions.

Justify that the following reactions are redox reactions:

1. \(CuO(s) + H_2(g) \rightarrow Cu(s) + H_2O(g) \)
2. \(Fe_2O_3(s) + 3CO(g) \rightarrow 2Fe(s) + 3CO_2(g) \)
3. \(4BCl_3(g) + 3LiAlH_4(s) \rightarrow 2B_2H_6(g) + 3LiCl(s) + 3 AlCl_3 (s) \)
4. \(2K(s) + F_2(g) \rightarrow 2K+F^- (s) \)
5. \(4 NH_3(g) + 5 O_2(g) \rightarrow 4NO(g) + 6H_2O(g)\)

Fluorine reacts with ice and results in the change:
\(H_2O(s) + F_2{(g)} \rightarrow HF{(g)} + HOF{(g)}\) Justify that this reaction is a redox reaction.

Write the formulae for the following compounds: 
(a) Mercury (II) chloride (b) Nickel (II) sulphate 
(c) Tin (IV) oxide (d) Thallium (I) sulphate 
(e) Iron (III) sulphate (f) Chromium (III) oxide

While sulphur dioxide and hydrogen peroxide can act as oxidising as well as reducing agents in their reactions, ozone and nitric acid act only as oxidants. Why?

Justify giving reactions that among halogens, fluorine is the best oxidant and among hydrohalic compounds, hydroiodic acid is the best reductant.