Problem 34 - Chemistry and Chemical Reactivity

Question

Name two insoluble salts of each of the following ions. (a) \(\mathrm{SO}_{4}^{2-}\) (b) \(\mathrm{Ni}^{2+}\) (c) \(\mathrm{Br}^{-}\)

Step-by-Step Solution

Answer

(a) BaSO₄, PbSO₄; (b) NiCO₃, Ni(OH)₂; (c) AgBr, PbBr₂.

Step 1: Identify Insoluble Salts for (a)

The sulfate ion, \( \mathrm{SO}_{4}^{2-} \), forms several insoluble salts. Barium sulfate (\( \text{BaSO}_4 \)) and lead(II) sulfate (\( \text{PbSO}_4 \)) are both considered insoluble salts due to their low solubility in water.

Step 2: Identify Insoluble Salts for (b)

Nickel(II), \( \mathrm{Ni}^{2+} \), also forms some insoluble salts. Nickel(II) carbonate (\( \text{NiCO}_3 \)) and nickel(II) hydroxide (\( \text{Ni(OH)}_2 \)) are both known to be insoluble in water.

Step 3: Identify Insoluble Salts for (c)

For bromide ion, \( \mathrm{Br}^{-} \), identifying insoluble salts involves less common compounds, as bromides are generally soluble. Silver bromide (\( \text{AgBr} \)) and lead(II) bromide (\( \text{PbBr}_2 \)) are exceptions and are considered insoluble.

Key Concepts

Sulfate Ion Solubility

When discussing the solubility of sulfate ions, it's important to know that most sulfates are soluble in water. However, there are notable exceptions. Barium sulfate (\( \text{BaSO}_4 \)) and lead(II) sulfate (\( \text{PbSO}_4 \)) are prime examples of sulfates with low solubility. These salts do not dissolve well in water due to their strong ionic bonds and lattice structures which require a large amount of energy to break.

• Barium Sulfate (\( \text{BaSO}_4 \)): Often used in medical imaging, its low solubility makes it safe for ingestion during X-ray procedures.
• Lead(II) Sulfate (\( \text{PbSO}_4 \)): Commonly forms as a white precipitate in reactions involving sulfate ions and lead ions.

Understanding these exceptions is key in predicting reaction outcomes in chemistry, especially in qualitative analysis.

Nickel Ion Insolubility

Nickel ions, \( \mathrm{Ni}^{2+} \), are often part of insoluble salts. This is due to the nature of the nickel ion's interaction with anions, which leads to the formation of compounds that don't dissolve readily in water. Two such compounds are nickel(II) carbonate (\( \text{NiCO}_3 \)) and nickel(II) hydroxide (\( \text{Ni(OH)}_2 \)).

• Nickel(II) Carbonate (\( \text{NiCO}_3 \)): This compound is known for its green color and is used in various applications, including catalysts and pigments. It remains largely insoluble due to the strong ionic bonds present in its crystalline structure.
• Nickel(II) Hydroxide (\( \text{Ni(OH)}_2 \)): Commonly used in rechargeable battery technologies, it forms a green precipitate when nickel ions react with hydroxide ions in aqueous solutions.

The insolubility of these nickel compounds is an important consideration in areas like industrial processing and waste treatment.

Bromide Solubility Exceptions

Bromide ions (\( \mathrm{Br}^{-} \)) usually form soluble compounds with metals. However, there are exceptions which are crucial to be aware of, notably silver bromide (\( \text{AgBr} \)) and lead(II) bromide (\( \text{PbBr}_2 \)). These exceptions are significant in both scientific and practical applications.

• Silver Bromide (\( \text{AgBr} \)): Known for its light-sensitive properties, it is extensively utilized in photographic films. Its low solubility comes from the strong attraction between silver and bromide ions.
• Lead(II) Bromide (\( \text{PbBr}_2 \)): This compound can sometimes form in industrial settings and is known for its limited solubility in water compared to other bromides.

Understanding these exceptions helps in grasping how bromide chemistry can differ from general trends, aiding in fields such as photography and chemical synthesis.