Organic Chemistry Questions and Answers – Redox Reactions

This set of Organic Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Redox Reactions”.

1. KMnO4 reacts with oxalic acid according to the equation given below. Here 20 mL of 0.1 M KMnO4 is equivalent to how many mL and molarity of H2C2O4?
2MnO4 + 5C2O4 + 16H+ → 2Mn+1 + 10CO2 + 8H2O
a) 20 mL of 0.5 M H2C2O4
b) 50 mL of 0.5 M H2C2O4
c) 50 mL of 0.1 M H2C2O4
d) 20 mL of 0.1 M H2C2O4
View Answer

Answer: c
Explanation: In any reaction number of equivalent reacted are equal
∴ neq (KMnO4) = neq (C2 O42-)
Also, neq = n × nf
In given problem:
∴ neq(KMnO4) = neq (C2 O42-)
n × nf = (n × nf) C2 O4
Also, (M × V × nf) KMnO4 = 0.1 × 20 × 5 = 10
And, (n × nf) C2 O4 = 50 × 0.1 × 2 = 10

2. Excess of KI reacts with CuSO4 solution and then Na2S2O3 solution is added to it. Which of the statement is incorrect for this reaction?
a) Na2S2O3 is oxidized
b) CuI2 is formed
c) Cu2I2 is formed
d) Evolved I2 is reduced
View Answer

Answer: b
Explanation: (1) KI + CuSO4 → I2
(2) I2 + Na2S2O3 → NaI + Na2S2O6
(a) Na2S2O3 is oxidized to Na2S2O6
(b) Cu2I2 is formed as CuI2 disproportionate.

3. How many number of moles of KMnO4 will react with 180 gm H2C2O4 according to given reaction?
KMnO4 + H2C2O4 → 2C02 + Mn2+
a) 4/5
b) 2/5
c) 1/5
d) 4/3
View Answer

Answer: a
Explanation: neqKMnO4 = neqH2C2O4
n × nf = n × nf
n × 5 = wM × 2
n = 18090 × 25 = 45.
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4. What is the mass of K2Cr2O7 required to produce 254 gm I2 from KI solution? Given: K2Cr2O7 + 2KI → 2Cr3+ + I2
a) 49 g
b) 98 g
c) 9.8 g
d) 4.9 g
View Answer

Answer: b
Explanation:
Number of moles of KMnO4 will react with 180 gm H2C2O4 according to given reaction is 4/5
neqK2Cr2O7 = neqI2
n × nf = n × nf
wM × 6 = wM × 2
w/294 × 6= 254/254 × 2
w = 98g.

5. What is the volume of 0.05 M KMnO4 which will react with 50 ml of 0.1 M H2S in acidic medium (H2S → S02)?
a) 60 ml
b) 6 ml
c) 12 ml
d) 120 ml
View Answer

Answer: d
Explanation:
The mass of K2Cr2O7 required to produce 254 gm I2 from KI solution is 98 g
neqKMnO4 = neq H2S
M × V × nf = M × V × nf
0.05 × V × 5 = 0.1 × 50 × 6
V = 120 mL.
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6. What is the mass of Fe304 if it reacts completely with 25 ml of 0.3m K2Cr2O7?
a) 1 .44 g
b) 10.44 g
c) 104.4 g
d) 14.4 g
View Answer

Answer: b
Explanation:
The volume of 0.05 M KMnO4 which react with 50 ml of 0.1 M H2S in acidic medium is 120 ml
neqFe3O4 = neq K2Cr2O7
wM × nf = 0.3 * 25 * 6
w = (0.3×25×6×232)/1
w = 10.44 g.

7. What is the concentration of H2O2 solution of 20 ml of H2O2 solution which will react completely with 10 ml of 2 M KMnO4 in acidic medium?
a) 1.25 M
b) 5 M
c) 2.5 M
d) 25 M
View Answer

Answer: c
Explanation:
The mass of Fe304 if it reacts completely with 25 ml of 0.3m K2Cr2O7 is 10.44 g

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neq (H2O2) = neq (KMnO4)
M × 20 × 2 = 2 × 10 × 5
Ans = 2.5 M.

8. How many moles of KCI are required to produce 10 mol Cl2 by the reaction with KCIO3?
a) 1.66 mole
b) 13.33 mole
c) 0.66 mole
d) 16.66 mole
View Answer

Answer: d
Explanation:
The concentration of H2O2 solution of 20 ml of 2 M KMnO4 in acidic medium is 2.5 M
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9. How many moles of KMnO4 are required for complete oxidation of 1.25 mol Cu2S?
Cu2S → Cu+2 + SO2
a) 1 mole
b) 3 moles
c) 2 moles
d) 5 moles
View Answer

Answer: c
Explanation:
The moles of KCI are required to produce 10 mol Cl2 by reaction with KCIO3 is 16.66 mole
neq (KMnO4) = neq (Cu2S)
n × 5 = 1.25 × 8
n = 2.

10. What is the volume strength of H2O2 of its 11.2 ml requires 30 ml of 0.5 M 2Cr2O7?
a) 35
b) 55
c) 25
d) 45
View Answer

Answer: d
Explanation: Volume strength of H2O2 = 11.2 × M H2O2 = 5.6 × N H2O2
The volume strength of H2O2 of its 11.2 ml requires 30 ml of 0.5 M 2Cr2O7 is 45
neq (H2O2) = neq (KMnO4)
M × 11.2 × 2 = 0.5 × 30 × 6
M = 4.017. Therfore, Volume strength = 11.2 × 4 = 45.

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