CBSE Class 12 Chemistry 2023: question 21

Hints

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Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

1. (a) In acidic medium, permanganate oxidises nitrite to nitrate and is itself reduced to $\mathrm{M}{\mathrm{n}}^{2+}$:
   $2Mn{\mathrm{O}}_4^{-}(\mathrm{aq})+5N{\mathrm{O}}_2^{-}(\mathrm{aq})+6{\mathrm{H}}^{+}(\mathrm{aq})\to 2M{\mathrm{n}}^{2+}(\mathrm{aq})+5N{\mathrm{O}}_3^{-}(\mathrm{aq})+3{\mathrm{H}}_2\mathrm{O}(\mathrm{l})$

   1 mark

2. (b) Dichromate is reduced to chromium(III) in acidic medium:
   $\mathrm{C}{\mathrm{r}}_2{\mathrm{O}}_7^{2-}(\mathrm{aq})+14{\mathrm{H}}^{+}(\mathrm{aq})+6{\mathrm{e}}^{-}\to 2C{\mathrm{r}}^{3+}(\mathrm{aq})+7{\mathrm{H}}_2\mathrm{O}(\mathrm{l})$

   1 mark

Answer: (a) 2Mn²⁺ + 5NO₃⁻ + 3H₂O; (b) 2Cr³⁺ + 7H₂O

Revise the chapter

• Chapter: The d- and f-Block Elements (notes, formulas, where marks are lost and every past question)
• Topic: Potassium Dichromate and Potassium Permanganate