Using solubility guidelines, predict whether each of the following compounds is soluble or insoluble in water: (a) \(\mathrm{Hg}_{2} \mathrm{SO}_{4}\) (b) \(\mathrm{NH}_{4} \mathrm{OH}\), (c) \(\mathrm{Ni}\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{2}\) (d) \(\mathrm{AgNO}_{3}\), (e) FeCO \(_{3}\)

Some of the solubility guideline rules are as follows: 1. All salts containing alkali metals, ammonium (\(\mathrm{NH}_{4}^{+}\)), and nitrates (\(\mathrm{NO}_{3}^{-}\)) are soluble. 2. All salts containing acetates (\(\mathrm{CH}_{3}\mathrm{COO}^{-}\)) and sulfates (\(\mathrm{SO}_{4}^{2-}\)) are soluble, with a few exceptions (e.g., silver, lead, and mercury(I)). 3. All salts containing the halides (e.g., \(\mathrm{Cl}^{-}\), \(\mathrm{Br}^{-}\), \(\mathrm{I}^{-}\)) are soluble, with a few exceptions (e.g., silver, lead, and mercury(I)). 4. All salts containing carbonates (\(\mathrm{CO}_{3}^{2-}\)), phosphates (\(\mathrm{PO}_{4}^{3-}\)), and sulfides (\(\mathrm{S}^{2-}\)) are insoluble, with a few exceptions for the alkali metals and ammonium. Now we will apply the guidelines to each compound in the exercise: (a) \(\mathrm{Hg}_{2} \mathrm{SO}_{4}\)

Although most sulfates are soluble, there are a few exceptions, including mercury(I) sulfate. In this case, we have \(\mathrm{Hg}_{2} \mathrm{SO}_{4}\) which is mercury(I) sulfate. Therefore, this compound is insoluble in water. (b) \(\mathrm{NH}_{4} \mathrm{OH}\)

The compound contains the ammonium ion \(\mathrm{NH}_{4}^{+}\). According to the solubility guideline rules, all salts containing ammonium ions are soluble. Therefore, \(\mathrm{NH}_{4} \mathrm{OH}\) is soluble in water. (c) \(\mathrm{Ni}\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{2}\)

This compound contains the acetate ion \(\mathrm{CH}_{3}\mathrm{COO}^{-}\). All salts containing acetates are soluble in water, as stated in the solubility guidelines. Therefore, \(\mathrm{Ni}\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{2}\) is soluble in water. (d) \(\mathrm{AgNO}_{3}\)

This compound contains the nitrate ion \(\mathrm{NO}_{3}^{-}\). According to the solubility guidelines, all salts containing nitrates are soluble in water. Therefore, \(\mathrm{AgNO}_{3}\) is soluble in water. (e) FeCO \(_{3}\)

This compound contains a carbonate ion \(\mathrm{CO}_{3}^{2-}\). The solubility guidelines state that all salts containing carbonates are insoluble in water, with a few exceptions for alkali metals and ammonium. Since iron (Fe) does not belong to either of these exceptions, FeCO \(_{3}\) is insoluble in water.