Question

Consider a 1.55 x 10-2M solution of H2CO3 where Ka1 = 4.5 x 10-7 and Ka2 = 4.7 x 10-11. find The concentration of CO32-

i got 6.21x10^-3 for the concentration of co32- is this correct? pls solve

Answer 1

given that Ka1 = 4.5 x 10-7 and Ka2 = 4.7 x 10-11.

     H2CO3   <>   HCO3^-1 + H+

1.55 x 10-2-x.           +x.   +x

Ka1=(4.5E-7)*( 1.55 x 10-2)=x^2. (Neglect the -x )

X=8.35E-4

Plug equilibrium concentrations of part 1 into part 2 ice table

HCO3^-1<>CO3^-2 +H+

8.35E-4 . 0. 8.35E-4

8.35E-4 -x +x. 8.35E-4

Ka2=4.7 E-11(8.35E-4)/( 8.35E-4 )=x neglect the +x and -x because the ka is very small

Therefore The concentration of CO32- = 4.7 E-11