Chemistry NCERT Exemplar Solutions Class 11th Chapter Eight

In which of the following compounds, an element exhibits two different oxidation states.

(i) NH₂OH

(ii) NH₄NO₃

(iii) N₂H₄

(iv) N₃H

The oxidation number of an element in a compound is evaluated on the basis of certain rules. Which of the following rules is not correct in this respect?

(i) The oxidation number of hydrogen is always +1.

(ii) The algebraic sum of all the oxidation numbers in a compound is zero.

(iii) An element in the free or the uncombined state bears oxidation number zero.

(iv) In all its compounds, the oxidation number of fluorine is – 1

Thiosulphate reacts differently with iodine and bromine in the reactions given below: 

2S₂O₃^2– + I₂ → S₄O₆^2– + 2I^– S₂O₃^2–+ 2Br₂ + 5H₂O → 2SO₄^2– + 2Br^– + 10H

Which of the following statements justifies the above dual behaviour of thiosulphate?

(i) Bromine is a stronger oxidant than iodine.

(ii) Bromine is a weaker oxidant than iodine.

(iii) Thiosulphate undergoes oxidation by bromine and reduction by iodine in these reactions.

(iv) Bromine undergoes oxidation and iodine undergoes reduction in these reactions.

Using the standard electrode potential, find out the pair between which redox reaction is not feasible.

EᶱV values : Fe³⁺/Fe²⁺ = + 0.77; I2 /I^– = + 0.54

Cu²⁺/Cu = + 0.34; Ag⁺ /Ag = + 0.80 V

(i) Fe³⁺ and I^–

(ii) Ag⁺ and Cu

(iii) Fe³⁺ and Cu

(iv) Ag and Fe³⁺

EᶱV  values of some redox couples are given below. On the basis of these values choose the correct option.

EᶱV values : Br₂ /Br^– = + 1.90; Ag⁺ /Ag(s) = +0.80

Cu₂₊/Cu(s) = + 0.34; I₂ (s)/I^– = + 0.54

(i) Cu will reduce Br^–

(ii) Cu will reduce Ag

(iii) Cu will reduce I^–

(iv) Cu will reduce Br₂

The more positive the value of EV , the greater is the tendency of the species to get reduced. Using the standard electrode potential of redox couples given below find out which of the following is the strongest oxidising agent.

EV values: Fe³+/Fe²⁺ = + 0.77; I₂ (s)/I^– = + 0.54;

Cu₂⁺/Cu = + 0.34; Ag⁺/Ag = + 0.80V

(i) Fe³⁺

(ii) I₂ (s)

(iii) Cu²⁺

(iv) Ag⁺

Which of the following is not an example of redox reaction?

(i) CuO + H₂ → Cu + H₂O

(ii) Fe₂O₃ + 3CO → 2Fe + 3CO₂

(iii) 2K + F₂ → 2KF

(iv) BaCl₂ + H₂ SO₄ → BaSO₄ + 2HCl

Balance the following ionic equations

(i) Cr₂ O₇^2– + H⁺ + I^– → Cr³⁺ + I₂ + H₂O

(ii) Cr₂ O₇^2– + Fe₂⁺ + H⁺ → Cr₃⁺ + Fe₃⁺ + H₂O

(iii) MnO₄^–  + SO₃^2– + H⁺ → Mn₂⁺ + SO₄^2–  + H₂O

(iv) MnO₄^–  + H⁺ + Br^– → Mn₂⁺ + Br² + H₂O

Identify the redox reactions out of the following reactions and identify the oxidising and reducing agents in them. 

(i) 3HCl(aq) + HNO₃ (aq) → Cl₂ (g) + NOCl (g) + 2H₂O (l )

(ii) HgCl₂ (aq) + 2KI (aq) → HgI₂ (s) + 2KCl (aq)

(iii) Fe₂O₃ (s) + 3CO (g) →   2Fe (s) + 3CO₂ (g)

(iv) PCl₃ (l) + 3H₂O (l) → 3HCl (aq) + H₃ PO₃ (aq)

(v) 4NH₃ + 3O₂ (g) → 2N₂ (g) + 6H₂O (g)

Balance the following equations by the oxidation number method

(i) Fe²⁺ + H⁺ + Cr₂^2–O₇ → Cr₃⁺ + Fe₃⁺ + H₂O

(ii) I₂ + NO₃^–  → NO₂ + IO₃ ^–

(iii) I ₂ + S₂O₃^2–  → I^– + S₄O₆^2–

^{(iv) MnO₂ + C₂ O₄2– → Mn₂+ + CO₂}