Solution :-
Carbonic acid reaction with water
H2CO3 + H2O ------ > H3O+ + HCO3-
0.105Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â
0Â Â Â Â Â Â Â Â Â Â Â
0
-x                                 Â
+x         Â
+x
0.105-x                       Â
x            Â
x
ka= [H3O+][HCO3-]/[H2CO3]
4.3*10^-7 = [x][x]/[0.105-x]
since the ka is very small so we can neglect the x from
denominator
4.3*10^-7 * 0.105 = x^2
4.515*10^-8 = x^2
taking square root of both sides
2.125*10^-4 = x= [H3O+]
formula to calculate the pH is as follows
pH= -log [H3O+]
pH= -log [2.125*10^-4]
pH= 3.67
the ka2 of the carbonic acid is not considered because it is
very small so it is negligible.
