Question

125ml of 1.00M HCl is added to 100ml of 1.00M NaOH. What is the pH of the resulting solution? (Please show your work.)

Answer 1

Millimoles of $HCl= 125\times 1.00= 125$

Millimoles of $NaOH= 100\times 1.00= 100$ Sodium hydroxide reacts with hydrochloric acid in equal amount. So, $100$ millimoles will be neutralised of both reactants.

So , $25$ millimoles of $HCl$ will remain unreacted .

So moles of $H^+$ in solution will be $25\times 10^{-3}= 0.025$

Total volume of solution $= 125+100 \ ml = 225 \ ml$

Concentration of $H^+ = \frac{0.025}{225\times 10^{-3}}=0.11\ M$

$pH$ of solutiob$=-log[H^+] = -log(0.11) = 0.95$