At [tex]\(25^{\circ} C\)[/tex], only 0.0260 mol of the generic salt [tex]\(AB_3\)[/tex] is soluble in 1.00 L of water. What is the [tex]\(K_{\text{sp}}\)[/tex] of the salt at [tex]\(25^{\circ} C\)[/tex]?

[tex]\[
\begin{array}{l}
AB_3(s) \rightleftharpoons A^{3+}(aq) + 3B^{-}(aq) \\
K_{\text{sp}} = 1.22 \times 10^{-3}
\end{array}
\][/tex]



Answer :

Let’s solve the problem step-by-step.

1. Determine the concentrations of the ions:
- We are given that 0.0260 moles of the salt [tex]\( AB_3 \)[/tex] are soluble in 1.00 L of water.
- When [tex]\( AB_3 \)[/tex] dissolves in water, it dissociates according to the equation:
[tex]\[ AB_3(s) \rightleftharpoons A^{3+}(aq) + 3B^-(aq) \][/tex]
- For each mole of [tex]\( AB_3 \)[/tex] that dissolves, it releases 1 mole of [tex]\( A^{3+} \)[/tex] ions and 3 moles of [tex]\( B^- \)[/tex] ions.

2. Calculate the concentration of [tex]\( A^{3+} \)[/tex]:
- The concentration of [tex]\( A^{3+} \)[/tex] ions will be equal to the number of moles of [tex]\( AB_3 \)[/tex] dissolved, since 1 mole of [tex]\( AB_3 \)[/tex] produces 1 mole of [tex]\( A^{3+} \)[/tex].
[tex]\[ [A^{3+}] = 0.0260 \, \text{M} \][/tex]

3. Calculate the concentration of [tex]\( B^- \)[/tex]:
- The concentration of [tex]\( B^- \)[/tex] ions will be three times the number of moles of [tex]\( AB_3 \)[/tex] dissolved, since 1 mole of [tex]\( AB_3 \)[/tex] produces 3 moles of [tex]\( B^- \)[/tex].
[tex]\[ [B^-] = 3 \times 0.0260 \, \text{M} = 0.0780 \, \text{M} \][/tex]

4. Write the expression for the solubility product constant ([tex]\( K_{sp} \)[/tex]):
- The [tex]\( K_{sp} \)[/tex] expression for the salt [tex]\( AB_3 \)[/tex] is given by:
[tex]\[ K_{sp} = [A^{3+}] \times [B^-]^3 \][/tex]

5. Substitute the concentrations into the [tex]\( K_{sp} \)[/tex] expression:
- We have [tex]\( [A^{3+}] = 0.0260 \, \text{M} \)[/tex] and [tex]\( [B^-] = 0.0780 \, \text{M} \)[/tex].

[tex]\[ K_{sp} = (0.0260) \times (0.0780)^3 \][/tex]

6. Calculate [tex]\( K_{sp} \)[/tex]:
- Perform the calculations:
[tex]\[ K_{sp} = 0.0260 \times (0.0780)^3 = 0.0260 \times 0.000474552 = 1.2338352 \times 10^{-5} \][/tex]

So, the solubility product constant [tex]\( K_{sp} \)[/tex] of the salt [tex]\( AB_3 \)[/tex] at [tex]\( 25^{\circ}C \)[/tex] is [tex]\( 1.2338352 \times 10^{-5} \)[/tex].