Question

Find pH of solution: 10mL 0.2M HNO₂ and 5mL of 0.2 KOH (K_a=10^-4)

Answer 1

From the chemical equation,

   HNO₂ + KOH     KNO₂ + H₂O

            5mL      5mL                 5 mL

It is evident that (10+5=15 mL) of the mixture solution contain,

(1) 10 - 5 = 5 mL of unused HNO₂

(2) 5mL of KNO₂

So number of moles of HNO₂ in 15 mL of solution = (Molarity / 1000 ) x volume of unused HNO₂

                                                                                               = ( 0.2 / 1000 ) x 5

                                                                       = 0.001 mol

Similarly number of moles of KNO₂ in 15 mL of solution = (0.2 /1000 ) x 5

                                                                                 = 0.001 mol