Assuming that no equilibria other than dissolution are involved, calculate the concentration of all solute species in each of the following solution of salt in contact with a solution containing a common ion. Show that changes in the initial concentrations:

PbCl2(s) in 0.631 M MgCl2 (MgCl2 is strong electrolyte)
Ksp PbCl2 = 1.6 × 10−5

Respuesta :

The concentration of all solute species in the solution are:

[tex][Mg^{2+} ] = 0.631 M \\ [Pb] = 1.0 \times 10^{-5} M \\[Cl^{-} ] = 1.26 M[/tex]

MgCl₂ (0.631 M) is a strong electrolyte that dissociates according to the following equation.

MgCl₂(aq) ⇒ Mg²⁺(aq) + 2 Cl⁻(aq)

Considering the molar ratios, the initial concentrations of Mg²⁺ and Cl⁻ are:

[tex]\frac{0.631 mol MgCl_2}{L} \times \frac{1molMg^{2+} }{1molMgCl_2} = \frac{0.631molMg^{2+}}{L} \\\frac{0.631 mol MgCl_2}{L} \times \frac{2molCl^{-} }{1molMgCl_2} = \frac{1.26molCl^{-}}{L}[/tex]

Cl⁻ is a common ion between MgCl₂ and PbCl₂. To consider the solution equilibrium for PbCl₂ (a sparingly soluble salt), we will make an ICE chart.

        PbCl₂(s) ⇄ Pb²⁺(aq) + 2 Cl⁻(aq)

I                            0               1.26

C                          +x              +2x

E                            x             1.26+x

The solubility product constant, Ksp, is:

[tex]Ksp = 1.6 \times 10^{-5} = [Pb^{2+} ][Cl^{-} ]^{2} = (x) (1.26+x)^{2}[/tex]

Since 1.26 >>> x, 1.26 + x ≈ 1.26.

[tex]Ksp = 1.6 \times 10^{-5} = (x) (1.26)^{2}\\x = 1.0 \times 10^{-5}[/tex]

The concentration of all solute species in the solution are:

[tex][Mg^{2+} ] = 0.631 M\\ [Pb] = x = 1.0 \times 10^{-5} M\\[Cl^{-} ] = 1.26+x = 1.26 M[/tex]

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