Question

Scenes A to C represent aqueous solutions of the slightly soluble salt MZ (only the ions of this salt are shown):

$\mathbf{MZ}\mathbf{\left(}\mathbf{s}\mathbf{\right)}\mathbf{\rightleftharpoons }{\mathbf{M}}^{\mathbf{2}\mathbf{+}}\mathbf{\left(}\mathbf{aq}\mathbf{\right)}\mathbf{+}{\mathbf{Z}}^{\mathbf{2}\mathbf{-}}\mathbf{\left(}\mathbf{aq}\mathbf{\right)}$

(a) Which scene represents the solution just after solid MZ is stirred thoroughly in distilled water?

(b) If each sphere represents$\mathbf{2}\mathbf{.}\mathbf{5}\mathbf{\times }{\mathbf{10}}^{\mathbf{-}\mathbf{6}}\mathbf{M}$ of ions, what is the${\mathbf{K}}_{\mathbf{sp}}$ of MZ?

(c) Which scene represents the solution after${\mathbf{Na}}_{\mathbf{2}}\mathbf{Z}\mathbf{\left(}\mathbf{aq}\mathbf{\right)}$is added?

(d) If ${\mathbf{Z}}^{\mathbf{2}\mathbf{-}}$is$\mathbf{C}{{\mathbf{O}}_{\mathbf{3}}}^{\mathbf{2}\mathbf{-}}$, which scene represents the solution after thehas been lowered?

Short answer

1. The scene represents the solution just after solid MZ is stirred thoroughly in distilled water is picture B.
2. The value of MZ is $1.0\times {10}^{-10}\mathrm{M}$.
3. The picture C is the correct situation.
4. The correct option is picture A.

Step-by-step solution

Definition of Concept.

Solubility: The maximum amount of solute that can be dissolved in the solvent at equilibrium is defined as solubility.

Constant of soluble product: For equilibrium between solids and their respective ions in a solution, the solubility product constant is defined. In general, the term "solubility product" refers to water-equilibrium insoluble or slightly soluble ionic substances.

 Find the scene represents the solution just after solid MZ is stirred thoroughly in distilled water.

(a)

First we can write the dissolution equation for MZ:

$\begin{array}{l}\mathrm{MZ}\left(\mathrm{s}\right)\mathrm{C}{\mathrm{M}}^{2+}\left(\mathrm{aq}\right)+{\mathrm{Z}}^{2-}\left(\mathrm{aq}\right)\\ \mathrm{Ksp}=\left[{\mathrm{M}}^{2+}\right]\left[{\mathrm{Z}}^{2-}\right]\end{array}$

Simply look for the picture in which the concentrations of ${\mathrm{M}}^{2+}$and${\mathrm{Z}}^{2-}$ are equal, which is picture B.

Therefore, the required answer is picture B.

Find the Ksp of MZ.

(b)

Considering the given information:

$\mathrm{c}\left(\mathrm{eachion}\right)=2.5\times {10}^{-6}\mathrm{M}$

We can see that each species has four ions, so ${\text{K}}_{\text{sp}}$expression will look like this.

as an example:

$\begin{array}{c}\mathrm{Ksp}=\left[{\mathrm{M}}^{2+}\right]\left[{\mathrm{Z}}^{2-}\right]\\ =4\times 2.5\times {10}^{-6}\times 4\times 2.5\times {10}^{-6}\\ =1\times {10}^{-10}\end{array}$

Therefore, the required value is $1\times {10}^{-10}$.

Find the scene represents the solution after Na2Z(aq) is added

(c)

If we add ${\mathrm{Na}}_2\mathrm{Z}$, the concentration of ${\mathrm{Z}}^{2+}$increases and the concentration of ${\mathrm{M}}^{2+}$decreases, so that would be picture $C$.

 Find the scene represents the solution after the pH has been lowered.

(d)

A lower pH indicates that there is less base in the solution. It is said that ${\mathrm{Z}}^{2-}$represents carbonate ion, which is basic, so picture A would have lowered pH .