JEE Advanced Previous Year Questions (2020 - 2021): Redox Reaction PDF Download

2021

Q1: A sample (5.6 g) containing iron is completely dissolved in cold dilute HCl to prepare a 250 mL of solution. Titration of 25.0 mL of this solution requires 12.5 mL of 0.03 M KMnO₄ solution to reach the end point. Number of moles of Fe²⁺ present in 250 mL solution is x  10^-2 (consider complete dissolution of FeCl₂). The amount of iron present in the sample is y% by weight.
(Assume: KMnO₄ reacts only with Fe²⁺ in the solution
Use : Molar mass of iron as 56 g mol^-1)    [JEE Advanced 2021 Paper 2]
The value of x is ______.
Ans: 1.875

Using relation,

n₂M₁V₁ = n₁M₂V₂ [n₁ and n₂ are number of moles of Fe²⁺ and MnO^-₄ reacting]

The volume of x is 1.88.

Q2: A sample (5.6 g) containing iron is completely dissolved in cold dilute HCl to prepare a 250 mL of solution. Titration of 25.0 mL of this solution requires 12.5 mL of 0.03 M KMnO₄ solution to reach the end point. Number of moles of Fe²⁺ present in 250 mL solution is x  10^-2 (consider complete dissolution of FeCl₂). The amount of iron present in the sample is y% by weight.
(Assume : KMnO₄ reacts only with Fe²⁺ in the solution
Use : Molar mass of iron as 56 g mol^-1)
The value of y is ______.     [JEE Advanced 2021 Paper 2]
Ans: 18.75
Mass of sample = 5.6 g
Number of moles of Fe = 1.88  x 10^-2 mol
Molar mass of Fe = 56 g/mol
Mass of F_e = Moles of Fe  x Molar mass


⇒ y = 18.75%
The value of y is 18.75.

Q3: Ozonolysis of ClO₂ produces an oxide of chlorine. The average oxidation state of chlorine in this oxide is __________.   [JEE Advanced 2021 Paper 2]
Ans: 6

Oxidation state of Cl in Cl2O6 = 2x + 6(2) = 0
2x  - 12 = 0
2x = 12 ⇒  x = + 6
Average oxidation state of Cl in Cl₂O₆ is 6.

2020

Q1: Choose the correct statement(s) among the following:   [JEE Advanced 2020 Paper 2]
(a) SnCl₂ . 2H₂O is a reducing agent.
(b) SnO₂ reacts with KOH to form K₂[Sn(OH)₆].
(c) A solution of PbCl₂ in HCl contains Pb²⁺ and Cl⁻ ions.
(d) The reaction of Pb₃O₄ with hot dilute nitric acid to give PbO₂ is a redox reaction.
Ans: (a, b)
Sn²⁺ of stannous chloride dihydrate (SnCl₂ . 2H₂O) tends to convert into Sn⁴⁺.
Hence, statement (a) is correct.
(b) SnO₂ reacts with KOH and gives K₂SnO₃ . 3H₂O or K₂[Sn(OH)₆] because it is amphoteric in nature.


Hence, statement (b) is correct.

(c) In conc. HCl, PbCl₂ exists as chloroplumbous acid, H₂[PbCl₄]

Hence, statement (c) is incorrect.
(d) Pb₃O₄ is a mixture of

It is not a redox reaction. Thus, the statement (d) is incorrect.