Question

20 mL of 2.0 M NaOH is added to 50 mL of 0.2 M HCl. The pH of this solution after mixing is:

• A. 7.5
• B. 12
• C. 8.5
• D. 9.5

Hint:

To calculate pH in a neutralization reaction, determine the excess acid or base and calculate the resulting pH based on its concentration.

Answer 1

The Correct Option is B

Step 1: Calculate the moles of NaOH and HCl.
First, calculate the moles of NaOH and HCl: \[ \text{Moles of NaOH} = 2.0 \, \text{M} \times 0.02 \, \text{L} = 0.04 \, \text{mol} \] \[ \text{Moles of HCl} = 0.2 \, \text{M} \times 0.05 \, \text{L} = 0.01 \, \text{mol} \]
Step 2: Determine the excess NaOH.
Since NaOH is in excess, subtract the moles of HCl from NaOH, and then calculate the pH based on the concentration of excess OH\(^-\).
Step 3: Conclusion.
The final pH of the solution will be 12, as the excess OH\(^-\) makes the solution basic.
Final Answer: \[ \boxed{12} \]