Question

Introduction to Qualitative Analysis Post-Lab Questions: (show logic for full credit) 1. Write the equilibrium-constant expression for each of the following reactions. Remember how to handle the concentrations of solids or water. a. N_(g) + 3H2(g) + 2NH,(g) b. HCN(aq) H(aq) + CN (aq) c. PbCl(s) Pb2"(aq) + 2Cl(aq) d. NH3(aq) + H2O(l) = NH,'(aq) + OH (aq) e. HF(aq) = H'(aq) + F(aq) 2. 2. What is the pH of a solution if [H'] = 2.0 x 10 M? b. What is the concentration of H' if the pH of a solution is 10.35?

Answer 1

1. Ans :-

Equilibrium constant (K_c) is equal to the " ratio of product of the molar concentration of products to the product of the molar concentration of reactants raised to the power of stoichiometric coefficient at equilibrium stage of the reaction" .

While writing the expression of K_c, concentration of pure solids and liquids are considered as constant because at equilibrium their is almost negligible change in their concentration.

(a). Given Equilibrium reaction is :

N₂ (g) + 3 H₂ (g) <----------------> 2 NH₃ (g)

Expression of K_c is :

Kc = [NH3]2 / [N2].[H2]3

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(b). Given Equilibrium reaction is :

HCN (aq) <----------------> H⁺ (aq) + CN^- (aq)

Expression of K_c is :

Kc = [H+].[CN-]/ [HCN]

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(c). Given Equilibrium reaction is :

PbCl₂ (s) <----------------> Pb²⁺ (aq) + 2 Cl^- (aq)

Expression of K_c is :

Kc = [Pb2+].[Cl- ]2

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(d). Given Equilibrium reaction is :

NH₃ (aq) + H₂O (l) <----------------> NH₄⁺ (aq) + OH^- (aq)

Expression of K_c is :

Kc = [NH4+].[OH- ] / [NH3]

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(e). Given Equilibrium reaction is :

HF (aq) <----------------> H⁺ (aq) + F^- (aq)

Expression of K_c is :

Kc = [H+].[F- ] / [HF]

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2.(a) Ans :-

As, pH = - log [H⁺]

pH = - log (2.0 x 10^-5)

pH = 4.70

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(b). [H⁺] = 10^-pH

[H⁺] = 10^-10.35

[H+] = 4.47 x 10-11 M