Methyl orange became red=very acidic solution. The concentration of A2-
is very low, so it means that Ka1
is enough big (therefore the solution is acidic).
If I mark the concentration of H2
A by x, then the concentration of HA-
are both x, too.
The concentration of A2-
is very low, meaning that Ka2
is very low, too, so the amount of H+
produced can be neglected to the amount of H+
produced in the first step. The amount of HA-
that dissociated can also be neglected, so: