Question

Predict whether each of the following compounds is soluble in water: \((\mathbf{a})\mathrm{AgI},(\mathbf{b}) \mathrm{Na}_{2} \mathrm{CO}_{3},(\mathbf{c}) \mathrm{BaCl}_{2},(\mathbf{d}) \mathrm{Al}(\mathrm{OH})_{3}$$(\mathbf{e})\mathrm{Zn}\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{2}\).

Short answer

Based on the solubility rules, the compounds can be predicted as follows: - \(\mathrm{AgI}\) is insoluble in water. - \(\mathrm{Na}_{2}\mathrm{CO}_{3}\) is soluble in water. - \(\mathrm{BaCl}_{2}\) is soluble in water. - \(\mathrm{Al(OH)}_{3}\) is insoluble in water. - \(\mathrm{Zn(CH}_{3}\mathrm{COO})_{2}\) is soluble in water.

Step-by-step solution

List the solubility rules

Solubility rules: 1. All nitrates, acetates, and perchlorates are soluble. 2. All alkali metal compounds and ammonium compounds are soluble. 3. Most chlorides, bromides, and iodides are soluble, except those of silver (Ag), lead (Pb), and mercury (Hg). 4. Most sulfates are soluble, except those of calcium (Ca), strontium (Sr), barium (Ba), lead (Pb), and mercury (Hg). 5. Most carbonates, sulfides, phosphates, and hydroxides are insoluble, except those of alkali metals and ammonium. 6. Most oxides are insoluble, except those of alkali metals, ammonium, and some transition metals.

Determine the solubility of \(\mathrm{AgI}\)

According to rule 3, most iodides are soluble except those of silver (Ag). Since \(\mathrm{AgI}\) is a silver iodide, it is insoluble in water.

Determine the solubility of \(\mathrm{Na}_{2}\mathrm{CO}_{3}\)

According to rule 2, all alkali metal compounds are soluble. Sodium (Na) is an alkali metal, so \(\mathrm{Na}_{2}\mathrm{CO}_{3}\) is soluble in water.

Determine the solubility of \(\mathrm{BaCl}_{2}\)

According to rule 3, most chlorides are soluble, except those of Ag, Pb, and Hg. Barium (Ba) is not one of these exceptions, so \(\mathrm{BaCl}_{2}\) is soluble in water.

Determine the solubility of \(\mathrm{Al(OH)}_{3}\)

According to rule 5, most hydroxides are insoluble, except those of alkali metals and ammonium. Since aluminum (Al) is not an alkali metal or ammonium, \(\mathrm{Al(OH)}_{3}\) is insoluble in water.

Determine the solubility of \(\mathrm{Zn(CH}_{3}\mathrm{COO})_{2}\)

According to rule 1, all acetates are soluble. The anion in this compound is an acetate ion, so \(\mathrm{Zn(CH}_{3}\mathrm{COO})_{2}\) is soluble in water. Now that we have analyzed the solubility of each compound, we can conclude that: - \(\mathrm{AgI}\) is insoluble in water. - \(\mathrm{Na}_{2}\mathrm{CO}_{3}\) is soluble in water. - \(\mathrm{BaCl}_{2}\) is soluble in water. - \(\mathrm{Al(OH)}_{3}\) is insoluble in water. - \(\mathrm{Zn(CH}_{3}\mathrm{COO})_{2}\) is soluble in water.

Key concepts

Water Solubility

Water solubility refers to the ability of a compound to dissolve in water to form a homogeneous solution. This property depends on the nature of the solute and the solvent. Water, being a polar solvent, is particularly good at dissolving other polar molecules or ionic compounds. This occurs because the positive and negative charges in water molecules can interact with ions and polar molecules, breaking them into smaller parts. This process is called dissociation and allows the solute to become evenly distributed within the solvent.

Many compounds have specific rules regarding their water solubility. Understanding these rules helps to predict whether a given compound will dissolve when mixed with water. Generally, compounds containing ions with charges that can easily interact with water molecules are more likely to be soluble.

Insoluble Compounds

Insoluble compounds are substances that do not dissolve significantly in water. Certain characteristics make a compound insoluble, such as having strong ionic or covalent bonds within the compound that water molecules cannot easily break.

According to solubility rules, most carbonates, hydroxides, sulfides, and phosphates are insoluble, unless paired with alkali metals or ammonium ions. For example,

• Silver iodide (\(\mathrm{AgI}\) is an insoluble compound because it falls under the exception rule for iodides, chlorides, and bromides, which typically dissolve except when paired with silver, lead, or mercury.
• Aluminum hydroxide (\(\mathrm{Al(OH)}_3\)) is another example, as hydroxides are generally insoluble unless they are formed with alkali metals.

Insolubility can be important in various chemical applications, influencing behaviors such as precipitation reactions.

Soluble Compounds

Soluble compounds are readily dissolved in water. These compounds usually contain ions or molecules that easily interact with water molecules, facilitating dissolution. Solubility rules provide a useful guideline to predict whether a compound is soluble.

Here are some general rules:

• All nitrates, acetates, and most chlorides are soluble. An example would be zinc acetate (\(\mathrm{Zn(CH_3COO)_2}\)), which is soluble due to the presence of acetate ions.
• Compounds containing alkali metals, such as sodium carbonate (\(\mathrm{Na}_2\mathrm{CO}_3\)), are soluble because sodium is an alkali metal, and compounds with alkali metals generally dissolve in water.
• Most sulfates are soluble, but exceptions include those containing barium, lead, and calcium.

Alkali Metals

Alkali metals are elements found in Group 1 of the periodic table, which include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). These metals are characterized by having a single electron in their outermost shell, making them very reactive, especially with water.

Compounds containing alkali metals are universally soluble in water. This is because the ions formed by alkali metals have a tendency to interact strongly with water molecules, facilitating the dissolution process.

For instance, sodium carbonate (\(\mathrm{Na}_2\mathrm{CO}_3\)) is highly soluble, as it contains sodium ions. These ions weaken the electrostatic forces holding the compound together, allowing water to pull the compound apart resulting in a soluble solution. Understanding the unique properties of alkali metals can be very helpful in predicting the solubility behavior of compounds.