Question

Predict whether each of the following ionic compounds is soluble in water: a. \(\mathrm{LiCl}\) b. \(\mathrm{AgCl}\) c. \(\mathrm{BaCO}_{3}\) d. \(\mathrm{K}_{2} \mathrm{O}\) e. \(\mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{3}\)

Short answer

Soluble: \(\text{LiCl}\), \(\text{K}_{2} \text{O}\), \(\text{Fe}\text{(NO}_{3}\text{)}_{3}\); Insoluble: \(\text{AgCl}\), \(\text{BaCO}_{3}\)

Step-by-step solution

Understand Solubility Rules

Recall the basic solubility rules: Nitrates, acetates, and most alkali metal (Group 1) salts are soluble. Chlorides are soluble except for those of silver, mercury, and lead. Most carbonates are insoluble except for those of alkali metals and ammonium. Oxides are generally insoluble unless paired with Group 1 metals.

Analyze \(\text{LiCl}\)

\(\text{LiCl}\) contains lithium, an alkali metal. According to the solubility rules, salts of alkali metals are soluble.

Analyze \(\text{AgCl}\)

\(\text{AgCl}\) is a chloride. While most chlorides are soluble, silver chloride is an exception and is insoluble in water.

Analyze \(\text{BaCO}_{3}\)

Most carbonates are insoluble, except for those of alkali metals and ammonium. \(\text{BaCO}_{3}\) does not contain an alkali metal or ammonium, so it is insoluble.

Analyze \(\text{K}_{2} \text{O}\)

\(\text{K}_{2} \text{O}\) contains potassium, an alkali metal. According to the solubility rules, oxides of alkali metals are soluble.

Analyze \(\text{Fe}\text{(NO}_{3}\text{)}_{3}\)

Nitrates are always soluble, regardless of the cation. Thus, \(\text{Fe}\text{(NO}_{3}\text{)}_{3}\) is soluble in water.

Key concepts

Solubility of Ionic Compounds

In chemistry, solubility refers to the ability of a substance to dissolve in a solvent, such as water. Ionic compounds are made up of positive and negative ions. When these compounds dissolve in water, the ions separate and disperse throughout the solution. Ionic compounds have different solubility levels based on their composition and interactions between the ions and water molecules.

Understanding the solubility of ionic compounds can help predict outcomes in chemical reactions, assess compound behaviors in various environments, and even in applications like drug formulation or water treatment.

Solubility Rules

Solubility rules are guidelines that predict the solubility of different ionic compounds in water. These rules are essential for anyone studying chemistry. Here are some key solubility rules to remember:

• Nitrates (NO3-) and acetates (CH3COO-) are always soluble.
• Alkali metal salts (like Li+, Na+, K+) and ammonium (NH4+) salts are soluble.
• Most chlorides (Cl-), bromides (Br-), and iodides (I-) are soluble, with exceptions like Ag+, Pb2+, and Hg2+.
• Most carbonates (CO32-), phosphates (PO43-), sulfides (S2-), and oxides (O2-) are insoluble, except for those of alkali metals and NH4+.
• Sulfates (SO42-) are generally soluble, except for salts with Ba2+, Sr2+, and Pb2+.

By using these rules, students can determine the solubility of ionic compounds in water efficiently.

Water Solubility

Water solubility involves how well a substance can dissolve in water. Water is a polar solvent, meaning it has a positive and negative side. This polarity allows it to interact well with ionic compounds. When an ionic compound dissolves in water:

• The positive ions are attracted to the negative side of water molecules.
• The negative ions are attracted to the positive side of water molecules.
• This interaction helps break down the ionic lattice and disperse the ions throughout the water.

However, not all ionic compounds dissolve in water. The solubility rules help determine which compounds will dissolve and which will not.

Alkali Metals

Alkali metals include elements like lithium (Li), sodium (Na), and potassium (K), which belong to Group 1 of the periodic table. These elements share common properties that affect their solubility:

• They form salts that are usually soluble in water.
• Alkali metal oxides and hydroxides are typically soluble.
• Their compounds usually dissociate completely in water, releasing alkali metal ions.

For example, in the given exercise, lithium chloride (LiCl) and potassium oxide (K2O) are soluble because they contain alkali metals.

Nitrates and Acetates

Nitrates and acetates are specific types of ionic compounds known for their high solubility in water. The nitrate ion (NO3-) and acetate ion (CH3COO-) both form soluble salts regardless of the cation bound to them:

• Nitrates are always soluble, so any compound containing the nitrate ion will dissolve in water.
• Acetates are also always soluble, making any compound with the acetate ion water-soluble.

In the exercise, iron(III) nitrate (Fe(NO3)3) is an example of a nitrate that will dissolve in water.

Chlorides and Exceptions

Chlorides are commonly soluble in water, but there are notable exceptions:

• Most chloride salts (like NaCl, KCl) dissolve in water.
• However, chlorides of silver (AgCl), lead (PbCl2), and mercury (Hg2Cl2) are exceptions and are insoluble in water.

In the context of the exercise, silver chloride (AgCl) is one of these exceptions and does not dissolve in water, unlike lithium chloride (LiCl), which is soluble.

Carbonates and Oxides

Carbonates (CO32-) and oxides (O2-) generally have low solubility in water:

• Most carbonates are insoluble, except for those of alkali metals and ammonium.
• For instance, barium carbonate (BaCO3) does not dissolve in water, as seen in the exercise.
• Oxides are also typically insoluble except when combined with alkali metals.
• Potassium oxide (K2O), containing the alkali metal potassium, is an example of a soluble oxide.

These guidelines help predict whether specific carbonates and oxides will dissolve in water.