pH of a `0.001` M solution of hydrochloric acid will be

Options

A. `1.3`
B. `2.0`
C. `3.0`
D. `4.5`

Answer

To find the pH of a `0.001 M` solution of hydrochloric acid (HCl), we can follow these steps:

### Step 1: Understand the nature of HCl
Hydrochloric acid (HCl) is a strong acid, which means it completely dissociates in water. This means that for every mole of HCl that dissolves, it produces one mole of hydrogen ions (H⁺) and one mole of chloride ions (Cl⁻).

### Step 2: Determine the concentration of H⁺ ions
Since HCl is a strong acid and completely dissociates, the concentration of H⁺ ions in a `0.001 M` solution of HCl will also be `0.001 M`.

\[ \text{[H⁺]} = \text{[HCl]} = 0.001 \, \text{M} \]

### Step 3: Use the pH formula
The pH of a solution is calculated using the formula:

\[ \text{pH} = -\log[\text{H⁺}] \]

### Step 4: Substitute the concentration into the pH formula
Now we can substitute the concentration of H⁺ ions into the pH formula:

\[ \text{pH} = -\log(0.001) \]

### Step 5: Calculate the logarithm
The value `0.001` can be expressed as \(10^{-3}\). Therefore, we can rewrite the logarithm:

\[ \text{pH} = -\log(10^{-3}) = -(-3) = 3 \]

### Step 6: Conclusion
Thus, the pH of a `0.001 M` solution of hydrochloric acid is:

\[ \text{pH} = 3 \]