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 massy/number of electrons involved=(molar mass)/6. The reaction is, ` Cr_2 O_(7)^(2-) + 14 H^(+) + 6e^(-) to 2Cr^(3+) + 7 H_2 O`