Question

$560ml$ of $HCl$ gas at STP is added to $500ml$ of $0.01NaOH$ solution. Calculate the $pH$ of resulting solution. Assume volume of solution is constant.

Answer 1

As $22400ml$ of gas equals one moles

of gas at STP

1 mole of gas (STP) $=22400ml$

$=22.4L$

$1ml=\frac{1}{22400}moles$

So for HCl

500 ml $=\frac{560}{22400}=0.025moles$

Moles of NaOH

Morality $=\frac{noofmolesofsolute}{volumeofsolution\left(inL\right)}$

$\frac{0.01\times 500}{1000}=0.005moles$

Number of $H^{+}$ ion remains

$=0.025-0.005=0.02moles$

Concentration $=\frac{0.02\times 1000}{500}=0.04$

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

$=-log\left[0.04\right]$

$=1.40$