Problem 134 - A Complete Resource Book in Chemistry for JEE Main

Question

Select the correct statement(s): (a) \(\mathrm{BaSO}_{4}\) is soluble in water (b) \(\mathrm{Ba}(\mathrm{OH})_{2}\) is soluble in water (c) \(\mathrm{MgSO}_{4}\) is soluble in water (d) \(\mathrm{CaF}_{3}\), is soluble in water

Step-by-Step Solution

Answer

(b) and (c) are correct.

Step 1: Analyze Solubility Rule for Sulfates

Sulfates (13;SO_4 ight) are generally soluble in water, but there are exceptions. The sulfates of barium (13;BaSO_4 ight), strontium, and lead are not soluble in water. Thus, 13;BaSO_4 ight) is not soluble in water, making statement (a) incorrect and statement (c) correct.

Step 2: Examine Barium Hydroxide Solubility

Barium hydroxide (13;Ba(OH)_2 ight) is an exception to the general rule that hydroxides are insoluble in water. 13;Ba(OH)_2 ight) is soluble in water. Therefore, statement (b) is correct.

Step 3: Evaluate Magnesium Sulfate Solubility

Magnesium sulfate (13;MgSO_4 ight) is typically soluble in water. This supports that statement (c) is correct, as we previously deduced.

Step 4: Check Solubility of Calcium Fluoride

Calcium fluoride (13;CaF_2 ight) has low solubility in water. Therefore, statement (d) is incorrect as 13;CaF_2 ight) is not considered soluble.

Key Concepts

Barium Sulfate Solubility

Barium sulfate, with the formula \( \text{BaSO}_4 \), is notorious for its extremely low solubility in water. This is due to the strong ionic bonds that hold its constituents together, making it difficult for water molecules to separate them into ions. While most sulfates are soluble, barium sulfate is one of the exceptions, along with similar compounds like lead sulfate and strontium sulfate.

• Its low solubility is a key property that finds practical application in medical and industrial fields.
• Medically, it is used as a radiocontrast agent for X-ray imaging because it is opaque to X-rays but is safe to digest due to its insolubility.

Understanding these exceptions to the solubility rules is crucial when predicting compound behavior in chemical reactions.

Barium Hydroxide Solubility

Unlike most hydroxides, barium hydroxide \( \text{Ba(OH)}_2 \) is relatively soluble in water. This is because the hydroxide ions effectively dissociate in water, which is unusual for compounds in the hydroxide family. Typically, hydroxides have low solubility, but barium hydroxide defies this convention due to the size and charge of the barium ion.

• The solubility of barium hydroxide increases as the temperature rises, making it a useful reagent in various laboratory settings.
• It is often utilized in titrations and as a precursor in the preparation of other barium compounds.

This particular exception highlights the importance of examining each compound individually rather than relying solely on generalized solubility rules.

Magnesium Sulfate Solubility

Magnesium sulfate \( \text{MgSO}_4 \) is well known for its solubility in water, which is a common characteristic of most sulfates. Its high solubility makes it practical and widely used in everyday applications such as Epsom salts.

• In agriculture, magnesium sulfate is a highly effective fertilizer that supplies essential magnesium nutrients to crops.
• Additionally, it's used in medicinal baths for muscle relaxation because it easily dissolves in bathwater, allowing magnesium to be absorbed through the skin.

Magnesium sulfate’s solubility exemplifies the typical behavior of sulfate compounds in aqueous solutions and reinforces the rule that most sulfates dissolve in water.

Calcium Fluoride Solubility

Calcium fluoride, represented as \( \text{CaF}_2 \), is known for its low solubility in water. Unlike salts that readily dissociate in water, calcium fluoride's strong ionic bonds resist dissolution, meaning only a small amount dissolves into ions. Despite being an ionic compound, it behaves differently from many other salts due to the strong attractions between the calcium and fluoride ions.

• Calcium fluoride is used in the production of glass and optics due to its low solubility.
• It doesn't interact much with water, making it stable as a lens material in humid environments.

Understanding calcium fluoride's solubility helps in predicting its lack of reactivity in aqueous environments.