Problem 55 - A Complete Resource Book in Chemistry for JEE Main

Question

The compound insoluble in acetic acid is (a) calcium oxide (b) calcium carbonate (c) calcium oxalate (d) calcium hydroxide

Step-by-Step Solution

Answer

Calcium oxalate is insoluble in acetic acid.

Step 1: Understanding the Problem

We need to identify which of the given compounds is insoluble in acetic acid. The options are calcium oxide, calcium carbonate, calcium oxalate, and calcium hydroxide.

Step 2: Reviewing Solubility Rules

Most carbonates, oxalates, and hydroxides are insoluble in water and weak acids like acetic acid, except for those of alkali metals and ammonium. Let's focus on each compound one by one.

Step 3: Evaluating Calcium Oxide

Calcium oxide, also known as quicklime, reacts with water to form calcium hydroxide, which has some solubility in acetic acid. Therefore, calcium oxide doesn't remain insoluble.

Step 4: Evaluating Calcium Carbonate

Calcium carbonate is typically insoluble in water but can react with acetic acid to form calcium acetate, which is soluble, and carbon dioxide gas. Therefore, calcium carbonate is not insoluble in acetic acid.

Step 5: Evaluating Calcium Oxalate

Calcium oxalate is known to be insoluble in acetic acid. It does not react to form soluble products, keeping its low solubility intact.

Step 6: Evaluating Calcium Hydroxide

Calcium hydroxide is sparingly soluble in water and can also dissolve in acetic acid to form calcium acetate, which is soluble. Hence, calcium hydroxide is not the insoluble compound here.

Key Concepts

Calcium Compounds

Calcium compounds are found in abundance in nature and are critically important in various industries and biological systems. Calcium is a group 2 element in the periodic table, and it forms compounds that are utilized for different applications depending on their properties. Here are some of the common compounds:

• Calcium Oxide (CaO): Known as quicklime, it is often used in the manufacturing of cement and lime. It reacts with water to produce calcium hydroxide.
• Calcium Carbonate (CaCO₃): This is commonly found in rocks as minerals like calcite and aragonite. It's widely used as a calcium supplement and antacid.
• Calcium Oxalate (CaC₂O₄): Often found in plant tissues, it's significant in the medical field as a form found in kidney stones.
• Calcium Hydroxide (Ca(OH)₂): Known as slaked lime, it is used in food preparation, water treatment, and building materials.

When thinking about these compounds, it's essential to remember their unique properties, especially their solubility behavior in different substances, which becomes crucial for understanding their reactions in various environments.

Solubility Rules

Understanding solubility rules is fundamental to predicting how substances will interact in different solutions. Solubility rules help determine whether a compound will dissolve in a solvent, such as water or a weak acid like acetic acid.

• General Rule: Most carbonates, oxalates, and hydroxides are generally insoluble in water and weak acids, except those of alkali metals and ammonium.
• Carbonates (CO₃²⁻): Generally insoluble, except compounds with alkali metals (like sodium and potassium) and ammonium.
• Oxalates (C₂O₄²⁻): Similar to carbonates, most are insoluble, except when paired with alkali metals or ammonium.
• Hydroxides (OH⁻): Typically insoluble, except for alkali metals and calcium, strontium, and barium, which are slightly soluble.

By applying these rules, we can predict that calcium oxalate remains insoluble in acetic acid, providing an explanation for its limited reactivity and stability in this medium.

Chemical Reactions with Acids

When it comes to chemical reactions with acids, especially weak acids like acetic acid, the reactivity of a compound will depend significantly on its chemical structure and solubility.

• Reactivity with Acetic Acid: Acetic acid can react with certain calcium compounds, changing them into more soluble forms. For instance, calcium carbonate reacts with acetic acid to produce calcium acetate, water, and carbon dioxide.
• Predicting Reactions: The reaction of compounds with acetic acid follows a pattern dictated by solubility rules. Insoluble compounds like calcium oxalate do not undergo reaction, remaining stable despite the presence of the acid.
• Types of Products Formed: Reactions with acetic acid can produce a range of products depending on the compound. Carbonates generally produce carbon dioxide, while hydroxides may form water and soluble salts.

These interactions are essential in fields such as chemistry, environmental science, and industrial processes, as they determine how substances can be processed, utilized, or neutralized.