In the standardization of `Na_2S_2O_3` using `K_2Cr_2O_7` by iodometry, the equivalent mass of `K_2Cr_2O_7` is

Options

A. (molar mass)/2
B. (molar mass)/6
C. (molar mass)/3
D. same as molar mass

Answer

B

Explanation

As this is a redox titration involving gain of electrons , equivalent mass = (molar mass)/number of electrons involved = (molar mass)/6. The reaction is `, Cr_2 O_7^(2-) + 14 H^(+) + 6e^(-) to 2Cr^(3+) + 7H_2O`