Problem 63 - Chemistry: An Atoms-Focused Approach

Question

According to the solubility rules in Table \(8.4,\) which of the following compounds have limited solubility in water? (a) barium sulfate; (b) barium hydroxide; (c) lanthanum nitrate; (d) sodium acetate; (e) lead hydroxide; (f) calcium phosphate

Step-by-Step Solution

Answer

Answer: Barium sulfate (a), lead hydroxide (e), and calcium phosphate (f) have limited solubility in water.

Step 1: (a) Barium Sulfate

According to rule 3, all sulfates are soluble except barium, calcium, strontium, lead(II), and mercury(I). Barium sulfate falls under the exception, so it has limited solubility in water.

Step 2: (b) Barium Hydroxide

According to rule 4, all hydroxides are insoluble except those of alkali metals and calcium, barium, and strontium. Barium hydroxide is an exception, which means it is soluble in water, not having limited solubility.

Step 3: (c) Lanthanum Nitrate

According to rule 1, all nitrates are soluble. Lanthanum nitrate is soluble in water, not having limited solubility.

Step 4: (d) Sodium Acetate

According to rule 1, all acetates are soluble. Sodium acetate is soluble in water, not having limited solubility.

Step 5: (e) Lead Hydroxide

According to rule 4, all hydroxides are insoluble except those of alkali metals and calcium, barium, and strontium. Lead hydroxide is not an exception, so it has limited solubility in water.

Step 6: (f) Calcium Phosphate

According to rule 5, all phosphates are insoluble except those of alkali metals and ammonium. Calcium phosphate is not an exception, so it has limited solubility in water. In summary, the compounds having limited solubility in water are barium sulfate (a), lead hydroxide (e), and calcium phosphate (f).

Key Concepts

Barium Sulfate

Barium sulfate is a compound that comes into play when we discuss solubility rules, particularly because it is a common example of an insoluble sulfate. According to general solubility rules, most sulfate salts are soluble in water. However, there are important exceptions, such as barium sulfate, along with lead(II) sulfate and strontium sulfate. This compound is known for its very low solubility, which makes it practically insoluble in water.

Barium sulfate is often used in the medical field as a contrast agent for X-ray imaging and other diagnostic procedures. Its insolubility is beneficial in this context, as it passes through the digestive system without being absorbed.

When you come across sulfate compounds, remember that while most are soluble, barium sulfate is a notable exception due to its limited solubility.

Calcium Phosphate

Calcium phosphate is an intriguing compound to explore in the context of solubility. According to solubility rules, most phosphate compounds exhibit limited solubility in water. The notable exceptions to this rule are the phosphates of alkali metals and ammonium, which can dissolve more easily.

Calcium phosphate is not an exception to the rule, meaning it is largely insoluble in water. This quality is crucial to its function in biology, where it plays a key role in the formation of bones and teeth. The insolubility provides calcium phosphate with the necessary solid structure to support and protect the body.

Understanding the solubility of calcium phosphate helps in comprehending how phosphate compounds behave and interact in both chemical reactions and biological systems.

Lead Hydroxide

Lead hydroxide is a compound that fits into the specific solubility rules applied to hydroxides. Most hydroxide compounds are generally considered insoluble in water, with exceptions being hydroxides of alkali metals and some alkaline earth metals like calcium, barium, and strontium.

Lead hydroxide does not fall under these exceptions, which explains its limited solubility in water. It is crucial to understand this characteristic because it has implications in industrial applications and environmental contexts, where lead compounds need careful handling due to their potential toxicity.

Given its insolubility, lead hydroxide can form a precipitate in reactions involving lead ions in solution, which can be used to separate lead from mixtures or for monitoring its presence in water systems.