Question

Which of the following solutions will have $pH$ close to $1.0 ?$

• A. $100\, mL$ of $M / 10\,HCl +100\, mL$ of $M / 10\, NaOH$
• B. $55\, mL$ of $M / 10 HCl +45\, mL$ of $M / 10 \,NaOH$
• C. $10\, mL$ of $M / 10 HCl +90\, mL$ of $M / 10\, NaOH$
• D. $75\, mL$ of $M / 10 HCl +25\, mL$ of $M / 10\, NaOH$

Answer 1

Answer: (D)

(a) is exact neutralisation. Hence $p H=7$

(b) After neutralisation, $M / 10 HCl$ left $=10 \,mL$

Total volume $=100 \,mL$

Dilution $=10$ times.

$ \therefore \left[ H ^{+}\right]=10^{-2}$ or $pH =2$

(c) After neutralisation, $M / 10 NaOH$ left $=80 \,mL$

Total volume $=100 \,mL , pH >\,7$

(d) After neutralisation, $M / 10 HCl$ left $=50 \,mL$

Total volume $=100 \,mL$

Dilution $=2$ times

$\therefore \left[ H ^{+}\right]=\frac{1}{2 \times 10}=\frac{10^{-1}}{2} M$ or $pH =1.3$