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Topic 4 : Balancing of Redox Reactions

1. ⇒  (JEE Main 2023 (Online) 8th April Morning Shift)

2 IO 3 + x I + 12 H + 6 I 2 + 6 H 2 O

What is the value of x ?

A. 10

B. 2

C. 12

D. 6

Correct option is (A)

The reaction given is a disproportionation reaction where iodine ( I 2 ) undergoes both oxidation and reduction. Disproportionation reactions are a type of redox reaction where an element is simultaneously oxidized and reduced.

In the process, iodine gets oxidized from 0 oxidation state (in I 2 ) to +5 oxidation state (in IO 3 ), and reduced from 0 oxidation state (in I 2 ) to -1 oxidation state (in I ).

The n-factor is the total change in oxidation state per molecule that undergoes the redox reaction. In this case, the n-factor for IO 3 is 5 (as iodine goes from 0 to +5) and for I , it's 1 (as iodine goes from 0 to -1).

Now, to balance the redox reaction, the total increase in oxidation state (total oxidation) must equal the total decrease in oxidation state (total reduction). Hence, the molar ratio of IO 3 to I must be 1:5.

So, the balanced reaction would be:

IO 3 + 6 H + + 5 I 3 I 2 + 3 H 2 O

This equation yields 3 moles of I 2 , but the original equation needs to produce 6 moles of I 2 , so the entire equation is multiplied by 2:

2 IO 3 + 12 H + + 10 I 6 I 2 + 6 H 2 O

This tells us that to get 6 moles of I 2 , you need 10 moles of I . So, x = 10

   

2. ⇒  (JEE Main 2022 (Online) 25th June Evening Shift)

The neutralization occurs when 10 mL of 0.1M acid 'A' is allowed to react with 30 mL of 0.05 M base M(OH)2. The basicity of the acid 'A' is __________.

[M is a metal]

Correct option is 3

Milieq of acid A = Milieq of base M ( O H ) 2

( M × V × n  Factor  A = ( M × V × n  Factor  ) M ( OH ) 2 [ n  Factor of  M ( OH ) 2 = 2 ] 0.1 × 10 × n -Factor  = 0.05 × 30 × 2 ( n  Factor  ) A = 3

Hence basicity of acid A is 3.

3. ⇒  (JEE Main 2020 (Online) 4th September Evening Slot)

A 100 mL solution was made by adding 1.43 g of Na2CO3.xH2O. The normality of the solution is 0.1 N. The value of x is _____.

(The atomic mass of Na is 23 g/mol)

Correct option is 10

Molar mass of Na2CO3.xH2O

= 23 × 2 + 12 + 48 + 18x

= 46 + 12 + 48 + 18x

= (106 + 18x)

As nfactor in dissolution will be determined from net cationic or anionic charge; which is 2

Eq wt = M 2 = (53 + 9x)

volume = 100 ml = 0.1 Litre

Normality =

No. of equivalents of solute
Volume of solution (in L)


0.1= 1.43 53 + 9 x 0.1

53 + 9x = 143

9x = 90

x = 10

4. ⇒  ( JEE Main 2019 (Online) 8th April Morning Slot)

In order to oxidise a mixture of one mole of each of FeC2O4, Fe2(C2O4)3, FeSO4 and Fe2(SO4)3 in acidic medium, the number of moles of KMnO4 required is

A. 1.5

B. 3

C. 2

D. 1

Correct option is (C)

JEE Main 2019 (Online) 8th April Morning Slot Chemistry - Redox Reactions Question 36 English Explanation

Equivalent of KMnO4 = Eq of FeC2O4 + Eq of Fe2(C2O4)3 + FeSO4

moles of KMnO4 × 5 = 3 × 1 + 6 × 1 + 1 × 1

moles of KMnO4 = 10 5 = 2

   

5. ⇒  (JEE Main 2014 (Offline))

In which of the following reactions H2O2 acts as a reducing agent?
1. H2O2 + 2H+ + 2e- 2H2O
2. H2O2 - 2e- O2 + 2H+
3. H2O2 + 2e- 2OH-
4. H2O2 + 2OH- - 2e- O2 + 2H2O

A. 1,2

B. 3,4

C. 1,3

D. 2,4

Correct option is (D)

The reducing agent loses electron during redox reaction i.e. oxidises itself.

( 1 ) H 2 O 2 1 + 2 H + + 2 e 2 H 2 O 2 ( Re d . )

( 2 ) H 2 O 2 1 O 2 0 + 2 H + + 2 e ( O x . )

( 3 ) H 2 O 2 1 + 2 e 2 O 2 H ( R e d . )

( 4 ) H 2 O 2 1 + 2 O H O 2 0 + H 2 O + 2 e ( O x . )

   

6. ⇒  (JEE Main 2013 (Offline))

Consider the following reaction:

x M n O 4 + y C 2 O 4 2 + zH+ xMn2+ + 2yCO2 + z 2 H 2 O

The value's of x, y and z in the reaction are, respectively

A. 5, 2 and 16

B. 2, 5 and 8

C. 2, 5 and 16

D. 5, 2 and 8

Correct option is (C)

After balancing the reaction we get

2 M n O 4 + 5 C 2 O 4 2 + 16H+ 2Mn2+ + 10CO2 + 8 H 2 O

x = 2, y = 5 and z = 16