Following solutions were prepared by mixing different volumes of NaOH and HCl of different concentrations : pH of which one of them will be equal to 1?
- B
- A
- D
- C
Answer
(4) C
Solution
Millimoles = molarity × volume (mL); the excess acid is divided by the total volume.
A: 60 0.1 - 40 0.1 = 2 mmol in 100 mL ⇒ [H+] = 0.02 M ⇒ pH ≈ 1.7
B: 55 0.1 - 45 0.1 = 1 mmol in 100 mL ⇒ [H+] = 0.01 M ⇒ pH = 2
C: 75 0.2 - 25 0.2 = 10 mmol in 100 mL ⇒ [H+] = 0.1 M ⇒ pH = 1
D: 100 0.1 - 100 0.1 = 0 ⇒ neutral solution ⇒ pH = 7
∴ Solution C has pH = 1.
Answer: (4)