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ISC Class 12 Chemistry Solved Question Paper 2016

Short Answer Type

41.

How will you obtain pure potassium permanganate (KMnO₄) crystals from its ore, pyrolusite? Give the step involved and the reactions.

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42.

For the reaction:
$2 NO left parenthesis straight g right parenthesis space rightwards harpoon over leftwards harpoon space straight N subscript 2 left parenthesis straight g right parenthesis space plus straight O subscript 2 left parenthesis straight g right parenthesis space semicolon increment straight H space equals space minus space heat straight K subscript straight c space equals space 2.5 space straight x space 10 squared space at space 298 straight K$

what will happen to concentration of N₂ if:
i) Temperature is decreased to 273K
ii) Pressure is reduced.

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43.
What will be the value of van't Hoff factor (i) Of benzoic acid if it dimerised in aqueous solution? How will the experimental weight vary as compared to the normal molecular weight?

In the aqueous solution, benzoic acid gets self-association because of hydrogen bonding.
The value of Van't Hoff factor is 0.5.
Molar mass of benzoic acid is 122g mol^-1. But the observed molar mass 242 g mol^-1 which is nearly double the expected molar mass, 122 g mol-1. This indicated an association of benzoic acid molecules in benzene solution into dimers.

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