Class 11 Chemistry Redox Reactions Exam Questions

Redox Reactions MCQ Questions with Answers Class 11 Chemistry

Question. Which element undergoes disproportionation in water?

(1) Cl₂

(2) F₂

(3) K

(4) Cs

 Answer (1)

Question. Which of the following processes does not involve oxidation of iron? 

(1) Liberation of H₂ from steam by iron at high temperature

(2) Rusting of iron sheets

(3) Decolourization of blue CuSO₄ solution by iron

(4) Formation of Fe(CO)₅ from Fe

Answer (4)

Question. In which of the following compounds, nitrogen exhibits highest oxidation state? 

(1) N₃H

(2) NH₂OH

(3) N2H₄

(4) NH₃

Answer (1)

Question. Standard electrode potential for Sn⁴⁺ / Sn²⁺ couple is +0.15 V and that for the Cr³⁺ / Cr couple is–0.74 V. These two couples in their standard state are connected to make a cell. The cell potential will be

(1) +1.83 V

(2) +1.19 V

(3) +0.89 V

(4) +0.18 V

Answer (3)

Question. Standard reduction electrode potential of three metals X, Y and Z are –1.2 V, +0.5 V and –3.0 V respectively.The reducing power of these metals will be

(1) X > Y > Z

(2) Y > Z > X

(3) Y > X > Z

(4) Z > X > Y

Answer (4)

Question. A : Oxidation number of carbon in HCN is +4.
                 R : Oxidation state and valency is same for carbon.

Answer (4)

Question. The oxide, which cannot act as a reducing agent, is

(1) CO₂

(2) ClO₂

(3) NO₂

(4) SO2

Answer (1)

Question. A : Fluorine acts as a stronger oxidising agent than chlorine.
                 R : Standard reduction potential of fluorine is higher than Cl₂.

Answer (1)

Question. Oxidation states of P in H4P2O5, H4P2O6, H4P2O7 are respectively 

(1) +3, +5, +4

(2) +5, +3, +4

(3) +5, +4, +3

(4) +3, +4, +5

Answer (4)

LEVEL – 1

1. Define oxidation and reduction in terms of oxidation number.

Ans: Increase in Oxidation Number is Oxidation and decrease in Oxidation Number is called reduction.

2. What is meant by disproportionation? Give one example.

Ans: In a disproportionation reaction an element simultaneously oxidized and reduced.

3. What is O.N. of sulphur in H₂SO₄?

Ans: +6

4. Identify the central atom in the following and predict their O.S. HNO₃

Ans: central atom:- N; O.S. +5

5. Out of Zn and Cu which is more reactive?

Ans: Zn.

6. What is galvanization?

Ans: Coating of a less reactive metal with a more reactive metal e.g.- coatingof iron surface with Zn to prevent rusting of iron.

7. How is standard cell potential calculated using standard electrode potential?

9. The formation of sodium chloride from gaseous sodium and gaseous chlorideis a redox process justify.

Ans: Na atom get oxidize and Cl is reduced.

LEVEL – 2

1. Write the balanced redox reaction .

2. Identify the strongest & weakest reducing agent from the following metals:

Zn, Cu, Na, Ag, Sn

Ans: Strongest reducing agent: Na, weakest reducing agent: Ag.

3. Determine the oxidation no. of all the atoms in the following oxidants:KMnO4, K₂Cr₂O₇ and KClO₄

Ans :

In KMnO₄ K = +1, Mn = +7, O = -2

In K₂Cr₂O₇K = +1, Cr = +6, O = -2

In KClO₄K = +1, Cl = =+7, O = -2

4. Determine the oxidation no. of all the atoms in the following species:Na₂O₂and OF₂.

Ans:

In Na₂O₂Na = +1, O = -1

InOF₂, F = -1, O = +2

5. Is it possible to store:

(i) H₂SO₄ in Al container?

(ii) CuSO₄ solution in Zn vessel?

Ans : (i) yes. (ii) No.

8. Predict all the possible oxidation states of Cl in its compounds.

Ans: 0, -1, +1, +3, +5, +7

9. Formulate possible compounds of ‘Cl ‘in its O.S.is: 0, -1, +1, +3, +5, +7

Ans: Cl₂, HCl, HOCl, HOClO, HOClO₂, HOClO₃ respectively.

10. List three measures used to prevent rusting of iron.

Ans:

(i) galvanization(coating iron by a more reactive metal)

(ii) greasing/oiling

(iii) painting.

LEVEL – 3

1. Write short notes on :

(a) Electrochemical series

(b) redox reactions

(c) oxidizing agents

Ans : (a) Electrochemical series :- arrangement of metals(non-metals also)in increasing order of their reducing power or vice versa. (b) Reactions in which both Oxidation and reduction take place simultaneously are REDOX reactions. (c) Oxidizing agents : chemical specie which can oxidize the other one or can reduce itself.

2. Calculate O. S. of sulphur in the following oxoacids of S : H₂SO₄, H₂SO₃ , H₂S₂O₈ and H₂S₂O₇

Ans : +6, +4, +6 and +6 respectively.

3. Explain role of salt bridge in Daniel cell.

Ans :

(a) it completes the electric circuit in the cell.

(b) It maintains the electric neutrality in the cell.

4. Account for the followings :

(i) sulphur exhibits variable oxidation states.

(ii) Fluorine exhibits only -1 O.S.

(iii) Oxygen can’t extend its valency from 2.

Ans.

(i) Due to the presence of vacant d orbitals in sulphur.

(ii) It is most electronegative element

(iii) Small size/unavailability of vacant d orbitals in O 5. Complete and balance the following equations:

6. Identify the oxidizing and reducing agents in the following equations:

7 . Arrange the following in increasing order of their reducing power: Cu, Ag, Au, Zn, Fe, Al, Na, Mg, Pt(SHE), Hg, Ca, K

Ans : Au, Hg, Ag, Cu, Pt(SHE), Fe, Zn, Al, Mg, Na, Ca, K

LEVEL – 4

1.What is SHE? What is its use?Draw its diagram.

Ans : Standard Hydrogen Electrode (SHE) has been selected to have zero standard potential at all temperatures. It consists of a platinum foilcoated with platinum black (finely divided platinum) dipping partially into an aqueous solution in which the activity (approximate concentration 1M) of hydrogen ion is unity and hydrogen gas is bubbled through the solution at 1 bar pressure. The potential of the other half cell is measured by constructing a cell in which reference electrode is standard hydrogen electrode. The potential of the other half cell is equal to the potential of the cell.

2. We spend crore of Rupees and even thousands of lives every year due tocorrosion. How can it be prevented? Explain.

Ans : (i) By Galvanization: Coating of a less reactive metal with a more reactive metal e.g.- coating of iron surface with Zn to prevent rusting of iron.

(ii) By greasing /oiling (to keep away the object from the contact of air&moisture.)

(iii)By painting (to keep away the object from the contact of air &moisture.)