Question

The $P^H$ of $HCl$ is $1$. The amount of $NaOH$ to be added to $100ml$ of such a $HCl$ solution to get $P^H$ of $7$ is:

• A. $4g$
• B. $0.4g$
• C. $4mg$
• D. $0.4mg$

Answer 1

The correct option is B $0.4g$

$pHofHCl=1$

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

$-log\left[H{}^{+}\right]=1$

$\left[H{}^{+}\right]=0.1M$

Volume of $HCl=100ml$

$HCl+NaOH⟶NaCl+H_{2}O$

According to the equation mole of HCl reacts with 1 mole NaOH.

Hence 0.1M of HCl reacts with 0.1M of NaOH.

Amount of HCl required to prepare 0.1M of HCl is

$0.1M=\frac{weight}{36.5}\times \frac{1000}{100}$

$=0.365g$

Amount of NaOH required to prepare 0.1M of NaOH is

$0.1M=\frac{weight}{40}\times \frac{1000}{100}$

$=0.4g$