Types of Redox Reactions - UNSOLVED PRACTICE SET

Q7. Define and give one example each of:

(a) Combination redox reaction

(b) Decomposition redox reaction

Q8. What is a displacement redox reaction? Distinguish between metal displacement and non-metal displacement reactions with one example each.

Q9. Identify the type of redox reaction in each case:

(a) 2HgO → 2Hg + O₂

(b) Fe + CuSO₄ → FeSO₄ + Cu

(c) 2Na + Cl₂ → 2NaCl

(d) 2H₂O₂ → 2H₂O + O₂

Q10. Explain what is meant by a disproportionation reaction. Why is it called 'disproportionation'?

Q11. In the reaction 3Cl₂ + 6NaOH → 5NaCl + NaClO₃ + 3H₂O, identify the element that undergoes disproportionation and calculate the change in its oxidation number.

Q12. A student claims that all decomposition reactions are redox reactions. Is the student correct? Give an example to support your answer.

Q13. (a) Classify redox reactions into four main types with one example for each.

(b) Identify the type of redox reaction in each of the following and justify your answer:

(i) 2Na + Cl₂ → 2NaCl

(ii) 2AgBr → 2Ag + Br₂ (on exposure to light)

(iii) Zn + 2HCl → ZnCl₂ + H₂

(iv) 2H₂O₂ → 2H₂O + O₂

(c) Explain why the reaction between AgNO₃ and NaCl is not a redox reaction, even though it involves ionic compounds.

Q14. (a) Define disproportionation reaction with a suitable example. What are the necessary conditions for an element to undergo disproportionation?

(b) Identify which of the following species can undergo disproportionation and write the balanced equation:

(i) Cl₂ in hot NaOH

(ii) H₂O₂

(iii) Cu⁺

(iv) MnO₄²⁻ in acidic medium

(c) Explain why F₂ does not undergo disproportionation, unlike other halogens.

Q15. (a) Explain the difference between intramolecular and intermolecular redox reactions with examples.

(b) Classify the following as intramolecular or intermolecular redox reactions:

(i) 2KClO₃ → 2KCl + 3O₂

(ii) 2H₂ + O₂ → 2H₂O

(iii) NH₄NO₃ → N₂O + 2H₂O

(iv) Zn + CuSO₄ → ZnSO₄ + Cu

(c) In the Indian context, explain the following as redox reactions and identify their types:

(i) The thermite reaction used for welding railway tracks: 2Al + Fe₂O₃ → 2Fe + Al₂O₃

(ii) The decomposition of ammonium nitrate used in cold packs

Q16. Analyse each of the following reactions and answer the questions:

(a) 2Na(s) + Cl₂(g) → 2NaCl(s)

Identify the type of redox reaction

Calculate the change in oxidation number for each element

Identify the oxidising and reducing agents

(b) 2Ag₂O(s) → 4Ag(s) + O₂(g)

Identify the type of redox reaction

Calculate the change in oxidation number for each element

Explain why this reaction is used in the silvering of mirrors

(c) Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)

Identify the type of redox reaction

Calculate the change in oxidation number for each element

Explain the reactivity series principle demonstrated by this reaction

(d) 3Cl₂(g) + 6NaOH(aq) → 5NaCl(aq) + NaClO₃(aq) + 3H₂O(l)

Identify the type of redox reaction

Calculate the change in oxidation number of chlorine

Identify which product is formed by oxidation and which by reduction

Q17. Consider the following set of reactions and classify each:

(a) 2KNO₃(s) → 2KNO₂(s) + O₂(g)

(b) C(s) + O₂(g) → CO₂(g)

(c) Br₂(aq) + 2KI(aq) → 2KBr(aq) + I₂(aq)

(d) 2H₂O₂(aq) → 2H₂O(l) + O₂(g)

(e) Cu(s) + 2AgNO₃(aq) → Cu(NO₃)₂(aq) + 2Ag(s)

(f) 4NH₃(g) + 5O₂(g) → 4NO(g) + 6H₂O(g)

For each reaction:

(i) Classify as combination, decomposition, displacement, or disproportionation

(ii) Identify the element oxidised and the element reduced

(iii) Calculate the total number of electrons transferred in the balanced equation

Q18. In India, different types of redox reactions have practical applications:

(a) In photography, silver bromide in film decomposes on exposure to light: 2AgBr → 2Ag + Br₂. Identify the type of redox reaction. Calculate the mass of silver deposited when 0.5 g of AgBr decomposes completely. (M of AgBr = 188 g/mol, M of Ag = 108 g/mol)

(b) The extraction of iron from haematite in a blast furnace involves: Fe₂O₃ + 3CO → 2Fe + 3CO₂. Identify the type of redox reaction. Calculate how many kg of CO are required to produce 1 tonne (1000 kg) of iron. (M of Fe = 56 g/mol, M of CO = 28 g/mol)

(c) In water treatment, chlorine gas is used for disinfection: Cl₂ + H₂O → HCl + HOCl. Identify the type of redox reaction. Explain why this is considered a disproportionation reaction. Calculate the oxidation number of chlorine in each product.

(d) A student observes that old copper vessels develop a green coating while iron vessels develop reddish-brown rust. Write the reactions for both processes, identify the types of redox reactions, and compare the oxidation numbers of the metals involved.