Problem 36 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

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: Understand the Reactants

Acetic acid is a weak acid, often used in vinegar. It can react with compounds to form soluble or insoluble products. Our task is to determine which of the listed compounds does not dissolve (is insoluble) in acetic acid.

Step 2: Analyze Calcium Oxide (CaO)

Calcium oxide (CaO), when reacting with acetic acid, forms calcium acetate, which is soluble in water. Therefore, calcium oxide is not the insoluble compound in acetic acid.

Step 3: Analyze Calcium Carbonate (CaCO3)

Calcium carbonate reacts with acetic acid to release carbon dioxide gas and forms calcium acetate, which is soluble in water. Thus, calcium carbonate is soluble in acetic acid.

Step 4: Analyze Calcium Oxalate (CaC2O4)

Calcium oxalate is known for being poorly soluble in weak acids like acetic acid. This makes it largely insoluble when acetic acid is the reactant under typical conditions.

Step 5: Analyze Calcium Hydroxide (Ca(OH)2)

Calcium hydroxide reacts with acetic acid to form calcium acetate, which is soluble. Therefore, calcium hydroxide is not insoluble in acetic acid.

Step 6: Conclusion: Determine the Insoluble Compound

Based on our analysis, calcium oxalate (CaC2O4) remains largely insoluble when reacting with acetic acid. Therefore, it is the compound that does not dissolve in acetic acid under typical conditions.

Key Concepts

Understanding Calcium Compounds

Calcium compounds are a group of chemical compounds derived from calcium, a common alkaline earth metal. These compounds often play significant roles in various chemical reactions due to their unique properties. Here are some common calcium compounds:

• Calcium Oxide (CaO): Also known as quicklime, it is used in various industries, including construction and steel production, for its basic properties.
• Calcium Carbonate (CaCO3): Found naturally as limestone or marble, it's used in antacids and as a calcium supplement.
• Calcium Oxalate (CaC2O4): Known for its low solubility, it's often found in kidney stones.
• Calcium Hydroxide (Ca(OH)2): Known as slaked lime, it is used in water treatment and construction.

These compounds' solubility properties significantly affect how they react with other substances, such as acids or bases. The complex interactions between calcium compounds and acids, particularly weak acids, give rise to diverse chemical reactions.

Chemical Reactions Involving Calcium Compounds

Chemical reactions involving calcium compounds exhibit a range of behaviors influenced by the surrounding conditions and reactants. When discussing these reactions with acetic acid, a weak acid, the chemistry becomes particularly interesting because of the varying solubility of calcium compounds. Acetic acid, notably their weak acid, can dissolve some calcium compounds by forming calcium acetate, a soluble salt. For instance:

• Calcium Oxide Reaction: When reacting with acetic acid, calcium oxide forms calcium acetate and dissolves easily.
• Calcium Carbonate Reaction: Calcium carbonate reacts with acetic acid to release carbon dioxide and also forms calcium acetate in solution.
• Calcium Hydroxide Reaction: Similar to the others, calcium hydroxide also produces calcium acetate when reacting with acetic acid.

However, calcium oxalate remains largely insoluble when mixed with acetic acid, demonstrating how some compounds can resist dissolution based on their chemical structure. Understanding these reactions helps in predicting and managing the behavior of calcium compounds in various applications.

Weak Acids and Their Influence on Solubility

Weak acids like acetic acid partially dissociate in solution, meaning they donate fewer hydrogen ions compared to strong acids. This reduced ability allows weak acids to perform selective reactions with compounds, impacting solubility in unique ways. Acetic acid, with its modest dissociation, can react with alkaline compounds like calcium compounds but may not fully dissolve them.

• Selective Solubility: Some calcium compounds can dissolve, such as those forming soluble ionic salts (e.g., calcium acetate).
• Limited Dissolution: Calcium oxalate showcases limited solubility owing to its stable bond structure, which even a weak acid like acetic acid cannot easily overcome.

This selective solubility is why acetic acid effectively dissolves calcium oxides and carbonates but has minimal impact on calcium oxalate. Thus, weak acids act as more selective solvents, influencing dissolution differently compared to their stronger counterparts, which fully dissociate in solutions.