Chemistry Class 11 NCERT Solutions: Chapter 7 Equilibrium Part 28 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Q: 71. What is the maximum concentration of equimolar solutions of ferrous sulphate and sodium sulphide so that when mixed in equal volumes, there is no precipitation of iron sulphide? (For iron sulphide, .


Let the maximum concentration of each solution be x mol/L. After mixing, the volume of the concentrations of each solution will be reduced to half i.e.. , .




If the concentrations of both solutions are equal to or less than M, then there will be no precipitation of iron sulphide.

Q: 72. What is the minimum volume of water required to dissolve 1g of calcium sulphate at 298 K? (For calcium sulphate, ) .

Water Dissolving Another Compound


Let the solubility of be S.


Molecular mass of

Solubility of in gram/L

This means that we need 1L of water to dissolve

Therefore, to dissolve 1g of we require of water

Q: 73. The concentration of sulphide ion in 0.1M HCl solution saturated with hydrogen sulphide is M. If 10 mL of this is added to 5 mL of 0.04 M solution of the following: . in which of these solutions precipitation will take place? Give

Structure of Hydrogen Sulphide

Answer: For precipitation to take place, it is required that the calculated ionic product exceeds the value.

Before mixing:

Ionic Product

This ionic product exceeds the of and CdS. Therefore, precipitation will occur in

CdCl2 and ZnCl2 solutions.

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