Problem 12 - Chemistry and Chemical Reactivity

Question

Which compound or compounds in each of the following groups is (are) expected to be soluble in water? (a) \(\mathrm{BaSO}_{4}, \mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}, \mathrm{BaCO}_{3}\) (b) \(\mathrm{Na}_{2} \mathrm{SO}_{4}, \mathrm{NaClO}_{4}, \mathrm{NaCH}_{3} \mathrm{CO}_{2}\) (c) \(\mathrm{AgBr}, \mathrm{KBr}, \mathrm{Al}_{2} \mathrm{Br}_{6}\)

Step-by-Step Solution

Answer

(a) Ba(NO₃)₂; (b) All are soluble; (c) KBr and Al₂Br₆.

Step 1: Understand Solubility Rules

To determine which compounds are soluble in water, we need to refer to general solubility rules. Typically, nitrates and compounds containing alkali metal ions such as sodium (Na) are soluble. Sulfates are generally soluble except for barium sulfate (BaSO₄). Carbonates are usually insoluble except for those containing alkali metals and ammonium.

Step 2: Analyze Group (a)

Group (a) includes \(\mathrm{BaSO}_{4}\), \(\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}\), and \(\mathrm{BaCO}_{3}\). \(\mathrm{BaSO}_{4}\) is insoluble in water. \(\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}\) is soluble because nitrates are always soluble. \(\mathrm{BaCO}_{3}\) is insoluble as carbonates are usually insoluble unless with alkali metals.

Step 3: Analyze Group (b)

Group (b) includes \(\mathrm{Na}_{2} \mathrm{SO}_{4}\), \(\mathrm{NaClO}_{4}\), and \(\mathrm{NaCH}_{3}\mathrm{CO}_{2}\). All sodium compounds are soluble, thus \(\mathrm{Na}_{2} \mathrm{SO}_{4}\), \(\mathrm{NaClO}_{4}\), and \(\mathrm{NaCH}_{3}\mathrm{CO}_{2}\) are soluble in water.

Step 4: Analyze Group (c)

Group (c) includes \(\mathrm{AgBr}\), \(\mathrm{KBr}\), and \(\mathrm{Al}_{2} \mathrm{Br}_{6}\). \(\mathrm{AgBr}\) is insoluble in water, \(\mathrm{KBr}\) is soluble as potassium (an alkali metal) compounds are soluble, and \(\mathrm{Al}_{2} \mathrm{Br}_{6}\) is typically soluble as it is a bromide similar to those of alkali metals.

Key Concepts

Nitrate Solubility

Nitrates are among the most soluble ionic compounds. This means that compounds containing the nitrate ion (NO₃⁻) readily dissolve in water. The solubility of nitrates is due to the strong attraction between water molecules and nitrate ions, which helps break apart the ionic bonds in the solid compound.
This characteristic makes them an exception to many general solubility rules, which is why you'll find that almost all nitrate compounds dissolve well. For example, barium nitrate, Ba(NO₃)₂, is soluble even though barium sulfate is not. Remember, if you encounter a compound with the nitrate ion, it's almost certainly going to dissolve in water.

Sulfate Solubility

Sulfates generally have a good solubility in water, but there are some important exceptions to keep in mind. Compounds like barium sulfate (BaSO₄), calcium sulfate (CaSO₄), and lead(II) sulfate (PbSO₄) are notably insoluble.

• This can be due to the way the sulfate ions bond with metal cations forming a solid structure.
• Even though most sulfates dissolve, it's the exceptions that often come into play, especially in chemical analysis and industrial applications.

Understanding these exceptions helps in determining which sulfate compounds will dissolve when mixed with water.

Carbonate Solubility

Carbonates are typically insoluble, except when they are bound with alkali metals like sodium (Na⁺) and potassium (K⁺), or ammonium (NH₄⁺). This is because carbonates tend to form stable, solid compounds that do not dissolve easily in water.
However, the presence of alkali metals or ammonium in a carbonate significantly enhances its solubility. For instance, sodium carbonate is highly soluble, while barium carbonate remains insoluble. Understanding these nuances is crucial when predicting the solubility of different carbonate compounds.

Alkali Metals

Alkali metals include elements such as lithium, sodium, and potassium. These elements are located in Group 1 of the periodic table and their ions are highly soluble in water.

• This is a general rule with very few exceptions, making alkali metal compounds (like NaCl or KBr) excellent choices for easily dissolvable ionic solutions.
• Their high solubility is due to the low charge density and high mobility of their ions in water.

This property makes alkali metals particularly important in various applications, including chemical reactions, medical solutions, and educational experiments.

Ionic Compounds

Ionic compounds are formed when metals and non-metals exchange electrons, creating charged particles called ions. These compounds often form crystalline solids with high melting points.
When dissolved in water, the ionic bonds are broken, allowing individual ions to migrate freely in solution. The solubility of ionic compounds depends on several factors, including the specific ions involved and the temperature of the solution.

• Nitrates, as previously mentioned, dissolve easily, while compounds like carbonates and sulfates may depend on the presence of certain metal ions.

Understanding the characteristics of ionic compounds is key to mastering their behavior in different chemical contexts.