Chemistry Class 12 NCERT Solutions: Chapter 8 The d and f Block Elements Part 3

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Q: 13. How is the variability in oxidation states of transition metals different from that of the non-transition metals? Illustrate with examples.

Answer:

In transition elements, the oxidation state can vary from to the highest oxidation state by removing all its valence electrons. Also, in transition elements, the oxidation states differ by 1 . In non7transition elements, the oxidation states differ by , for example, and and , etc.

Q: 14. Describe the preparation of potassium dichromate from iron chromite ore. What is the effect of increasing on a solution of potassium dichromate?

Answer

Potassium dichromate is prepared from chromite ore in the following steps.

Step(1): Preparation of sodium chromate

Step (2): Conversion of sodium chromate into sodium dichromate

Step(3): Conversion of sodium dichromate to potassium dichromate

Potassium chloride being less soluble than sodium chloride is obtained in the form of orange coloured crystals and can be removed by filtration.

The dichromate ion exists in equilibrium with chromate at .

However, by changing the they can be interconverted.

Q: 15. Describe the oxidising action of potassium dichromate and write the ionic equations for its reaction with

(i) Iodide

(ii) Iron(II) solution and

(iii)

Answer:

acts as a very strong oxidising agent in the acidic medium.

takes up electrons to get reduced and acts as an oxidising agent. The reaction of with other iodide, iron(II) solution, and are given below.

(i) oxidizes iodide to iodine

(ii) oxidizes (II) solution to iron (III) solution i.e. ferrous ions to ferric ions

(iii) oxidizes to sulphur