Potassium dichromate (K2Cr2O7) is a strong oxidizing agent. Select the correct statements from the following:
(A) It is used for preparation of many azo compounds.
(B) With the decreasing pH of the solution, dichromates changes into chromates.
(C) In acidified solution equivalent weight of dichromate is M/5
(D) The bond angle between Cr-O-Cr is 126°.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A) and (D) only
Potassium dichromate is an orange compound of chromium in the +6 oxidation state. In acid it is a strong oxidising agent, and each chromium goes from +6 to +3:
\( \displaystyle \ce{Cr2O7^2- + 14H^+ + 6e^- -> 2Cr^3+ + 7H2O} \)
(A) It is used for preparation of many azo compounds. — Correct. Potassium dichromate is used in the leather industry and as an oxidant for preparing many azo compounds.
(B) With the decreasing pH of the solution, dichromates changes into chromates. — Incorrect. Decreasing pH means the solution becomes more acidic. In acid, chromate changes into dichromate; dichromate changes into chromate only when the pH is increased.
(C) In acidified solution equivalent weight of dichromate is M/5 — Incorrect. Each Cr goes from +6 to +3, so one \( \ce{Cr2O7^{2-}} \) takes up 2 × 3 = 6 electrons:
\( \displaystyle \text{Equivalent weight}=\frac{M}{6}=\frac{294}{6}=49 \)
(D) The bond angle between Cr-O-Cr is 126°. — Correct. The bridging oxygen joins the two tetrahedra at an angle of 126°.
NCERT (2026-27 edition):
Potassium Dichromate K2Cr2O7
