Question

In the standardisation of Na₂S₂O₃ using K₂Cr₂O₇ by iodometry, the equivalent weight of K₂Cr₂O₇ is ______.

Options

• (molecular weight)/2

• (molecular weight)/6

• (molecular weight)/3

• same as molecular weight

Answer 1

In the standardisation of Na₂S₂O₃ using K₂Cr₂O₇ by iodometry, the equivalent weight of K₂Cr₂O₇ is (molecular weight)/6.

Explanation:

In an acidic medium, potassium dichromate (K₂Cr₂O₇) acts as a strong oxidising agent. In redox reactions, 1 mole of K₂Cr₂O₇ accepts 6 electrons as shown in the half-reaction:

\[\ce{Cr2O^{2-}_7 + 14H+ + 6e- -> 2Cr^{3+} + 7H2O}\]

So its n-factor is 6. Therefore, the equivalent weight is equal to (molecular weight)/6.