first construct the ICE table and then substitute the
values in the K equation and then calculate the equilibrium values
as follows
       H2X
----------------------------> HX- + H+
IÂ Â Â Â Â Â
0.125Â 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 Â Â Â Â Â Â Â
0Â Â Â Â Â Â Â Â Â
0
C      -x   +x
+x
EÂ Â
(0.125-x)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 Â Â Â Â Â Â
x        Â
x
Ka1 = [HX-] [H+] / [H2X]
=>1.75*10-5 = x2 /
(0.125-x)
=> 1.75*10-5 * (0.125-x) =
x2
=> x = 0.001479
=> 0.0015 => 1.5*10-3 M = [HX-] =
[H+]
answer => c) 1.5*10-3 M
