Question

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

• A. \( 3 \)
• B. \( 1 \)
• C. \( 7 \)
• D. \( 4 \)

Hint:

Remember: For strong acids like HCl, the concentration of \( \text{H}^+ \) ions is equal to the concentration of the acid.

Answer 1

The Correct Option is A

Step 1: Recall the formula for pH
The pH of a solution is given by the formula: \[ \text{pH} = -\log[\text{H}^+] \] where \( [\text{H}^+] \) is the concentration of hydrogen ions in the solution.
Step 2: Use the concentration of HCl
Hydrochloric acid (HCl) is a strong acid, so it dissociates completely in water: \[ \text{HCl} \rightarrow \text{H}^+ + \text{Cl}^- \] Therefore, the concentration of \( \text{H}^+ \) ions is the same as the concentration of HCl, i.e., \( 0.001 \, \text{M} \). \[ [\text{H}^+] = 0.001 \, \text{M} \]
Step 3: Calculate the pH
Now, substitute the concentration of \( \text{H}^+ \) into the pH formula: \[ \text{pH} = -\log(0.001) = 3 \]
Answer:
Therefore, the pH of the 0.001 M HCl solution is \( 3 \). So, the correct answer is option (1).