Introduction

H2S is a toxic gas commonly used in qualitative analysis. It is important to understand its solubility in water at standard temperature and pressure (STP) and the corresponding value of K(H), which represents the equilibrium constant for the dissolution of H2S in water.

Solubility of H2S in Water at STP

The solubility of H2S in water at STP refers to the maximum amount of H2S that can dissolve in a given amount of water at a specific temperature and pressure. In this case, the solubility of H2S is given as 0.195.

Equilibrium Constant (K(H))

The equilibrium constant, K(H), represents the ratio of the concentrations of the products to the concentrations of the reactants at equilibrium. For the dissolution of H2S in water, the equilibrium constant can be expressed as follows:

H2S (g) ⇌ 2H+ (aq) + S2- (aq)

The equilibrium constant expression for this reaction is:

K(H) = [H+]^2 [S2-] / [H2S]

Since H2S is a weak acid, it will partially dissociate in water, leading to the formation of H+ and S2- ions. The concentration of H2S can be determined using the solubility value of 0.195, which corresponds to the concentration of H2S in the solution at equilibrium.

Determining the Value of K(H)

To find the value of K(H), we need to know the concentrations of H+ and S2- ions at equilibrium. Since the solubility of H2S is given as 0.195, we can assume that the concentration of H2S at equilibrium is also 0.195 M.

Since H2S dissociates into 2H+ and S2-, the concentrations of H+ and S2- ions will be twice the concentration of H2S. Therefore, [H+] = [S2-] = 2 * 0.195 = 0.39 M.

Substituting these values into the equilibrium constant expression, we have:

K(H) = (0.39)^2 / 0.195

K(H) = 1.5216 / 0.195

K(H) = 7.804

Therefore, the value of K(H) for the dissolution of H2S in water at STP is 7.804.

Conclusion

In conclusion, the solubility of H2S in water at STP is 0.195, and the corresponding value of K(H) for the dissolution of H2S in water can be calculated as 7.804. This value represents the equilibrium constant for the dissociation of H2S into H+ and S2- ions in water. Understanding the solubility and equilibrium constant of H2S is important in qualitative analysis and other applications where the behavior of H2S in aqueous solutions needs to be considered.

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