The compound insoluble in acetic acid is

Options

A. Calcium oxide
B. calcium carbonate
C. calcium oxalate
D. calcium hydroxide

Answer

To determine which compound is insoluble in acetic acid, we need to analyze the solubility of the given compounds based on their lattice energy and hydration energy. Here’s a step-by-step solution:

### Step 1: Understand the Factors Affecting Solubility
Solubility of a compound is influenced by two main factors:
- **Lattice Energy (L)**: The energy required to separate the ions in a solid ionic compound.
- **Hydration Energy (H)**: The energy released when ions are surrounded by water molecules.

### Step 2: Relationship Between Lattice Energy and Hydration Energy
The solubility can be expressed as:
- Solubility ∝ Hydration Energy (H)
- Solubility ∝ 1/Lattice Energy (L)

This means that higher hydration energy and lower lattice energy will result in greater solubility.

### Step 3: Analyze the Compounds
We need to compare the compounds based on their ionic sizes and charges. The compounds mentioned are:
1. Calcium Oxide (CaO)
2. Calcium Carbonate (CaCO3)
3. Calcium Oxalate (CaC2O4)
4. Calcium Hydroxide (Ca(OH)2)

All these compounds contain calcium ions (Ca²⁺) and have different anions.

### Step 4: Determine the Charge-to-Radius Ratio (Q/R)
The charge-to-radius ratio (Q/R) is crucial for understanding solubility:
- Higher Q/R ratio indicates higher hydration energy.
- Lower Q/R ratio indicates higher lattice energy.

### Step 5: Compare the Anions
- **Oxide (O²⁻)**: Small size, high charge.
- **Carbonate (CO3²⁻)**: Larger than oxide, but still relatively small.
- **Oxalate (C2O4²⁻)**: Larger than carbonate due to more atoms.
- **Hydroxide (OH⁻)**: Smaller than carbonate but larger than oxide.

### Step 6: Identify the Largest Anion
Among the anions, the oxalate ion (C2O4²⁻) is the largest due to its structure, which consists of more atoms and a larger surface area.

### Step 7: Conclusion
Since larger anions generally lead to lower solubility due to higher lattice energy and lower hydration energy, calcium oxalate (CaC2O4) is expected to be the least soluble in acetic acid.

### Final Answer
The compound insoluble in acetic acid is **Calcium Oxalate (CaC2O4)**.

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