Question

What is the equivalent mass of IO₄^- when it is converted into acidic I₂ in Acidic medium?
1. M/6
2. M/7
3. M/5
4. M/4

Answer 1

Correct Answer - Option 2 : M/7

Concept:

Equivalent mass:

• It is the amount of substance that combines with 1g of hydrogen or 8 g of oxygen or 35.5g of chlorine.
• The formula for calculating the equivalent mass of a substance undergoing redox reaction is given by:

\(Equivalent\;weight = \frac{{formula\;mass}}{{no\;of\;electrons\;exchanged}}\)

Equivalent weight = Molecular weight / Valency factor

 

Equivalent weight =  Molecular weight / n-factor

Eq Wt = M / x

• Where n-factor varies for different species as follows:
  • For elements: x = valency of element
  • For acid: x = no. of replaceable H+ ions per acid molecule
  • For the base: x = no. of replaceable OH- ions per basic molecule
  • For reducing or oxidizing agent, x = total change in oxidation state per molecule.

Calculation:

Given:

The reaction is IO4- → I2.

• Balancing the Iodine and oxygen atoms on both sides we get,

2IO4- → I2 + 8H₂O

• Balancing the Hydrogen atoms we get,

2IO4-  + 16H⁺ → I2 + 8H2O

• Balancing the charge, we get:

2IO4-  + 16H+ + 14e^- → I2 + 8H2O

• The oxidation state of Iodine in  IO4- is +7.
• The oxidation state of I in I₂ is 0.
• The change in oxidation state = + 7.
• Hence, seven electrons are exchanged in total per IO4- ion in the reaction.
• Let the mass of  IO4- be 'M' . As it undergoes redox reaction, the equivalent mass will be given by:

\(Equivalent\;weight = \frac{{formula\;mass}}{{no\;of\;electrons\;exchanged}}\)

Equivalent mass = M / 7.

Hence,  the equivalent mass of IO4- when it is converted into acidic I2 in an acidic medium is M/7.