Question

On adding which of the following, the pH of $20ml$ of $0.1NHCl$ will not alter ?

• A. 1 ml of 1 N HCl
• B. 20 ml of distilled water
• C. 1 ml of 0.1 N NaOH
• D. 500 ml of HCl of pH = 1

Answer 1

Answer: (D)

Milliequivalents of $20mL$ of $0.1NHCl=N_1{V}_1$

$=20\times 0.1=2$

(a) $pH$ of distilled water $=7$

$\left[H^{+}\right]=10^{-pH}=10^{-7}M$

$\therefore$ milliequivalents $=NV[$ for $HCl,N=M]$

$=10^{-7}\times 20=2.0\times 10^{-6}$

(b) Milliequivalents of $NaOH=0.1\times 1=0.1$

(c) $pH$ of $HCl=1$

$\therefore \left[H^{+}\right]=10^{-1}=0.1M$

$\therefore$ Milliequivalents $=0.1\times 500=50$

(d) Milliequivalents of $HCl=1\times 1=1$

$\because$ Milliequivalents of $500mL$ of $HCl$ having

$pH=1$ is more than that of $20mL$ of

$0.1NHCl$, therefore adding this, $pH$ of

$0.1NHCl$ solution, does not alter.