Question

100 mL of 0.01 M HCl is added to 900 mL H\(_2\)O. What is the pH of the resultant solution?

• A. 1
• B. 2.7
• C. 2.3
• D. 3

Hint:

For strong acids, pH depends only on final concentration of \(H^+\), not on dilution steps separately.

Answer 1

The Correct Option is D

Step 1: Dilution principle for strong acids.
HCl fully dissociates; dilution conserves H⁺ moles while increasing volume, lowering concentration.

Step 2: Initial moles of HCl.
Moles = 0.01 M × 0.1 L = 0.001 mol.

Step 3: Total volume after dilution.
V_total = 100 + 900 = 1000 mL = 1 L.

Step 4: Final H⁺ concentration.
[H⁺] = 0.001/1 = 10⁻³ M.

Step 5: pH determination.
pH = -log(10⁻³) = 3.

Step 6: Conclusion.
The diluted solution's pH is 3.