What will be the resultant pH, when 200 mL of an aqueous solution of `HCI(pH=2.0)` is mixed with 300 mL of an aqueous solution of `NaOH(pH=12.0)` ?

Explanation

pH of HCI solution `=2,[H_(3)O^(+)]` in solution `=10^(-2)M`
Number of moles of `[H_(3)O^(+)]` in 200 mL of HCI solution `=(10^(-2) xx 200)/(1000) =0.2 xx 10^(-2) mol`
pH of NaOH solution `=12 , [OH^(-)]` in solution `=10^(-2)M`
Number of moles of `[OH^(-)]` in 300 mL of NaOH solution `=(10^(2)xx300)/(1000) =0.3 xx 10^(-2) mol.`
Total volume of the solution after mixing `-(200 +300) =500 mL`
Number of moles of NaOH left in the solution after neutralisation by the acid
`=(0.3 xx 10^(-2) -0.2 xx 10^(-2)) =0.1 xx10^(-2) mol`