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.