Check Your Understanding Which of the following compounds would be soluble in water at room temperature?

(a) $\mathrm{NH}_4 \mathrm{Cl}$ ,

(b) $\mathrm{KOH}$ ,

(c) $\mathrm{Ca}\left(\mathrm{CH}_3 \mathrm{COO}\right)_2$ ,

(d) $\mathrm{Ba}_3\left(\mathrm{PO}_4\right)_2$

Solution

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Strategy : Solubility guidelines for common ions are given in Table 3.1 (page 74) . So we will identify the ions in each compound and consult the table as needed to determine the solubilities.

a) $NH_{4}Cl$ : From the solubility guidelines in Table 3.1, we see that compounds containing $NH_{4}^{+}$ and $Cl^{-}$ tend to be soluble and that no com- mon exceptions are mentioned. So we predict that $NH_{4}Cl$ should be $\textbf{soluble}$ .

b) $KOH$ : From the solubility guidelines in Table 3.1, we see that compounds containing $OH^{-}$ tend to be insoluble but $KOH$ is listed among the $\textbf{exceptions}$ . Thus $KOH$ should be $\textbf{soluble}$ .

c) $Ca(CH_{3}OO)_{2}$ : From the solubility guidelines in Table 3.1, we see that compounds containing $CH_{3}OO^{-}$ tend to be soluble and $Ca(CH_{3}OO)_{2}$ is $\textbf{not listed among the exceptions}$ . Thus $Ca(CH_{3}OO)_{2}$ should be $\textbf{soluble}$ .

d) $Ba_{3}(PO_{4})_{2}$ : From the solubility guidelines in Table 3.1, we see that compounds containing $PO_{4}^{3-}$ tend to be insoluble and $Ba_{3}(PO_{4})_{2}$ is $\textbf{not listed among the exceptions}$ . Thus $Ba_{3}(PO_{4})_{2}$ should be $\textbf{insoluble}$ . .