Equilibrium

AIPMT 2005MCQMedium📈 Topic in 38% papers+4−1

Ques. 1AIPMT 2005

H2S gas when passed through a solution of cations containing HCl precipitates the cations of second group of qualitative analysis but not those belonging to the fourth group. It is because

presence of HCl decreases the sulphide ion concentration
solubility product of group II sulphides is more than that of group IV sulphides
presence of HCl increases the sulphide ion concentration
sulphides of group IV cations are unstable in HCl.

Answer

(1) presence of HCl decreases the sulphide ion concentration

Solution

H2S 2H+ + S2-

As per NCERT, HCl supplies the common ion H+, which suppresses the ionisation of H2S (common ion effect).

⇒ The concentration of S2- ions becomes very low.

∵ Group II sulphides (CuS, PbS, CdS …) have very low Ksp, their ionic product still exceeds Ksp and they precipitate.

∵ Group IV sulphides (ZnS, MnS, NiS, CoS) have higher Ksp, their ionic product stays below Ksp and they do not precipitate.

∴ The presence of HCl decreases the sulphide ion concentration.

Answer: (1)

Keep practising — Equilibrium

Ques. 2AIPMT 2005

Equilibrium constants K1 and K2 for the following equilibria: NO(g) + 12O2(g) K1 NO2(g) and 2NO2(g) K2 2NO(g) + O2(g) are related as

K2 = 1/K12
K2 = K12
K2 = 1/K1
K2 = K1/2

Ques. 3AIPMT 2004

The solubility product of a sparingly soluble salt AX2 is 3.2 10-11. Its solubility (in moles/L) is

5.6 10-6
3.1 10-4
2 10-4
4 10-4

Ques. 4AIPMT 2004

The rapid change of pH near the stoichiometric point of an acid-base titration is the basis of indicator detection. pH of the solution is related to ratio of the concentrations of the conjugate acid (HIn) and base (In-) forms of the indicator by the expression

[In-][HIn] = pKIn - pH
[HIn][In-] = pKIn - pH
[HIn][In-] = pH - pKIn
[In-][HIn] = pH - pKIn

Ques. 5AIPMT 2003

The equilibrium constants of the following are N2 + 3H2 2NH3; K1 N2 + O2 2NO; K2 H2 + 12O2 H2O; K3 The equilibrium constant (K) of the reaction : 2NH3 + 52O2 2NO + 3H2O will be