Answer to Question #146675 in Physical Chemistry for Sanaa

Question

Calculate the pH (give your answers to 2.d.p) of the following solution dilutions.

(a) 50 cm3 of 1.00 mol dm–3 hydrochloric acid is added to 200 cm3 of water.

(b) 100 cm3 of 1.00 mol dm–3 Ba(OH)2 is added to 400 cm3 of water at 298 K

Answer 1

a)     C₁V₁=C₂V₂

C₁=1.00moldm^-3

V₁= 50 cm³

C₂=?

V₂= (50+200) cm³

    =250 cm³

1 ×50= 250 C₂

C₂=50/250

   =0.2M

[H+] = 0.2M

pH=-log (0.2)

    =0.6990

    =0.70 (2dp)

b)     C₁=1. 00moldm^-3

V₁=100 cm³

C₂=?

V₂= (100+400) cm³

    =500 cm³

100×1=500 C₂

C₂= 100/500

C₂=0.2MBa(OH)₂

Ba(OH)_2(aq) =Ba²⁺_(aq) +2OH^-_(aq)

[OH^-]= 2×0.2= 0.4M

pOH=-log[OH^-]

       =-log [0.4]

       =0.3979

pH=14-0.3979

     =13.6021

     =13.60 (2dp)