In the standardisation of N2S2O3 using K2Cr2O7 by iodometry, the equivalent weight of K2Cr2O7 is

Question

In the standardisation of N2S2O3 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

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Salim Ahmed Kawsar · Answer 1 · Feb 05, 2023 15:29:48

Answer: The following reaction occur between S2O3^(2-) and Cr2O7^(2-) :
26H+ + 3S2 O3^(2-) + 4Cr2O7^(2-) → 6SO3^(2-) + 8Cr3+ + 13H2O
Change in oxidation number of Cr2O4^(2-) per formula unit is 6 (it is always fixed for Cr2O7^(2-)).
Hence, equivalent weight of K2Cr2O7 = (Molecular weight)/6

Salim Ahmed Kawsar · Answer 2 · Feb 05, 2023 15:29:48

Answer is (molecular weight)/6

Potassium Dichromate is used to standardize Sodium Thiosulfate solutions. In acidic solution, Potassium Dichromate oxidizes Potassium Iodide to Iodine; the Iodine thus generated can then be titrated with the Thiosulfate solution using Starch Indicator:

Cr2O72- + 6 I- + 14 H+ → 2 Cr3+ + 3 I2 + 7 H2O

Since each molecule of it is releasing 6 electrons its equivalent wt is m.wt/6

K2Cr2O7 Cr is in 6+ it is converted in to Cr3+ that is accepting 3 e- for two Cr3+ 6 e-s.

In the standardisation of N2S2O3 using K2Cr2O7 by iodometry, the equivalent weight of K2Cr2O7 is

2 Answers