Question

What is the pH of a 0.001 M hydrochloric acid (HCl) solution?

• A. \( 3 \)
• B. \( 4 \)
• C. \( 7 \)
• D. \( 10 \)

Hint:

For strong acids like HCl, the concentration of \( \text{H}^+ \) ions is equal to the concentration of the acid. For weak acids, you must account for partial dissociation.

Answer 1

The Correct Option is A

To calculate the pH of a solution, we use the formula: \[ \text{pH} = -\log [\text{H}^+] \] Where: - \( [\text{H}^+] \) is the concentration of hydrogen ions (\( \text{H}^+ \)) in the solution. Hydrochloric acid (HCl) is a strong acid, meaning it dissociates completely in water. Therefore, the concentration of \( \text{H}^+ \) ions will be equal to the concentration of the HCl solution. Given: \[ [\text{H}^+] = 0.001 \, \text{M} = 10^{-3} \, \text{M} \] Now, substitute the concentration into the pH formula: \[ \text{pH} = -\log (10^{-3}) \] \[ \text{pH} = -(-3) = 3 \] Thus, the pH of the 0.001 M hydrochloric acid solution is \( 3 \).