Determine the [oh−] of a solution that is 0.125 m in co32−.

CO3^2-  + H2O  <---> H2CO3  +  OH-
the  equilibrium  constant  expression  for  this   reaction
Kb =(HCO3-)(OH-)/CO3^-2
kb=2 .0 x  10^-4
 the  concentration  of  both HCO3-  and  OH-  can  be  presented  by  X
therefore  KB=  (x)(x)/(CO3^-2)
2.0  x 10  ^-4 =(x)(x)/0.125
multiply  both  side by  0.125
=2.5 x10^-5=(x^2)

find  square  root
x=5 x 10^-3

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