Question

The following solutions were prepared by mixing different volumes of NaOH and HCl of different concentrations
1. 60 mL $\frac{M}{10}$ HCl + 40 mL $\frac{M}{10}$ NaOH

2. 55 mL $\frac{M}{10}$ HCl + 45 mL $\frac{M}{10}$ NaOH

3. 75 mL $\frac{M}{5}$ HCl + 25 mL $\frac{M}{5}$ NaOH

4. 100 mL $\frac{M}{10}$ HCl + 100 mL $\frac{M}{10}$ NaOH

pH of which one of them will be equal to 1?

• A. 1
• B. 2
• C. 3
• D. 4

Answer 1

The correct option is C 3

meq of HCl = $75\times \frac{1}{5}$ = 15
meq of NaOH = $25\times \frac{1}{5}$ = 5
meq of HCl in resulting solution = 10
Molarity of $[H{]}^{+}$ in resulting mixture = $\frac{10}{100}$ = $\frac{1}{10}$ = 0.1

pH = -$log[H{]}^{+}$ = -$log\left[0.1\right]$ =1.0