In the standardization of Na2S2O3 using K2Cr2O7 by iodometry, the equivalent weight of K2Cr2O7 is a. (molecular weight)/2 b. (molecular weight)/6 c. (molecular weight)/3 d. same as molecular weight

Sol. the following reaction occur between S_2 O_3^(2-) and 〖Cr〗_2 O_7^(2-) : 26H+ + 〖3S〗_2 O_3^(2-) + 〖4Cr〗_2 O_7^(2-) → 6SO_3^(2-) + 8Cr3+ + 13H2O Change in oxidation number of 〖Cr〗_2 O_4^(2-) per formula unit is 6 (it is always fixed for 〖Cr〗_2 O_7^(2-)). Hence, equivalent weight of K2Cr2O7 = (Molecular weight)/6 the following reaction occur between S_2 O_3^(2-) and 〖Cr〗_2 O_7^(2-) : 26H+ + 〖3S〗_2 O_3^(2-) + 〖4Cr〗_2 O_7^(2-) → 6SO_3^(2-) + 8Cr3+ + 13H2O Change in oxidation number of 〖Cr〗_2 O_4^(2-) per formula unit is 6 (it is always fixed for 〖Cr〗_2 O_7^(2-)). Hence, equivalent weight of K2Cr2O7 = (Molecular weight)/6