Arrange pH of the given compounds in decreasing order `:`

Options

A. Phenol
B. Ethyl alcohol
C. Formic acid
D. Benzoic acid

Answer

To arrange the pH of the given compounds in decreasing order, we need to analyze the stability of their conjugate bases. The more stable the conjugate base, the stronger the acid, and consequently, the higher the pH. Here’s the step-by-step solution:

### Step 1: Identify the Compounds and Their Conjugate Bases
The compounds given are:
1. Phenol (C6H5OH)
2. Ethyl alcohol (C2H5OH)
3. Formic acid (HCOOH)
4. Benzoic acid (C6H5COOH)

The conjugate bases for these compounds are:
- Phenoxide ion (C6H5O⁻) for phenol
- Ethoxide ion (C2H5O⁻) for ethyl alcohol
- Formate ion (HCOO⁻) for formic acid
- Benzoate ion (C6H5COO⁻) for benzoic acid

### Step 2: Analyze the Stability of the Conjugate Bases
- **Phenoxide ion (C6H5O⁻)**: The negative charge is stabilized by resonance with the aromatic ring.
- **Ethoxide ion (C2H5O⁻)**: The ethyl group donates electron density (inductive effect), making the negative charge less stable.
- **Formate ion (HCOO⁻)**: The negative charge is stabilized by resonance between the two oxygen atoms.
- **Benzoate ion (C6H5COO⁻)**: Similar to formate, but the presence of the phenyl group introduces a slight electron-donating effect, making it less stable than formate.

### Step 3: Order the Stability of Conjugate Bases
Based on the stability analysis:
1. Formate ion (HCOO⁻) - Most stable
2. Benzoate ion (C6H5COO⁻) - Less stable than formate
3. Phenoxide ion (C6H5O⁻) - Less stable than both formate and benzoate
4. Ethoxide ion (C2H5O⁻) - Least stable

### Step 4: Relate Stability to pH
Since a more stable conjugate base corresponds to a stronger acid (and thus a higher pH), we can arrange the pH in decreasing order as follows:
1. Formic acid (highest pH)
2. Benzoic acid
3. Phenol
4. Ethyl alcohol (lowest pH)

### Final Answer
The decreasing order of pH for the given compounds is:
**Formic acid > Benzoic acid > Phenol > Ethyl alcohol**