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 dissociation of HCl
Hydrochloric acid is a strong acid that completely dissociates in water:
\[ \text{HCl} \rightarrow \text{H}^+ + \text{Cl}^- \]
This means that the concentration of hydrogen ions (\( \text{H}^+ \)) in the solution will be equal to the concentration of the HCl solution.

### Step 2: Determine the concentration of \( \text{H}^+ \) ions
Given that the concentration of the HCl solution is 0.001 M, the concentration of \( \text{H}^+ \) ions will also be:
\[ [\text{H}^+] = 0.001 \, \text{M} = 10^{-3} \, \text{M} \]

### Step 3: Use the pH formula
The pH of a solution is calculated using the formula:
\[ \text{pH} = -\log[\text{H}^+] \]
Substituting the concentration of \( \text{H}^+ \) ions into the formula gives:
\[ \text{pH} = -\log(10^{-3}) \]

### Step 4: Calculate the pH
Using the properties of logarithms:
\[ \text{pH} = -(-3) \cdot \log(10) \]
Since \( \log(10) = 1 \):
\[ \text{pH} = 3 \cdot 1 = 3 \]

### Conclusion
The pH of a 0.001 M solution of hydrochloric acid is **3**.

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