Question

What will be the $H^{+}$ ion concentration in a solution prepared by mixing 50.0mL of 0.20M NaCl, 25mL of 0.10M NaOH and 25.0mL and 0.30M HCl?

• A. 0.5M
• B. 0.05M
• C. 0.02M
• D. 0.10M

Answer 1

Answer: (B)

0.05M

Number of moles of HCl $=\frac{25.0mL}{1000mL}\times 0.30M=0.0075mol$

Number of moles of NaOH $=\frac{25.0mL}{1000mL}\times 0.10M=0.0025mol$

0.0025 moles of NaOH will neutralize 0.0025 moles of HCl.

$0.0075-0.0025=0.0050$ moles of HCl will remain.

0.0050 moles of HCl will ionize to give 0.0050 moles of $H^{+}$ ions.

Total volume $=25.0mL+25.0mL+50.0mL=100.0mL$

$\left[H^{+}\right]=\frac{0.0050mol}{100.0mL}\times 1000mL/L$

$\left[H^{+}\right]=0.050M$.

NaCl is a salt of a strong acid with a strong base. It does not hydrolyze. Hence, it will not affect $\left[H^{+}\right]$.

Therefore, the correct option is $B$.