[robidf]

Hey guys,

Im having trouble with this homework problem.  We are given a 1.00M solution of (NH4)2CO3.

The equilibrium equation is shown below.

NH4 + CO3 = NH3 + HCO3

We are given Ka2 of H2CO3 is 5.6e-11.  From this Ka2, I was able to combine Ka1 of NH4 and take the inverse of Ka2 of H2CO3 to get a K value of 9.95 for the equilibrium equation.  The next part of the question asks me to show that [CO3] = .079 is consistent with the K value I calculated.  I know I must use an ICE table here but I am unable to calculate a value of .079 for CO3.

I have tried calculating the [H] and [HCO3] by using Ka1 of H2CO3 and then plugging these values into my initial values of HCO3 and H in the ICE table for HCO3= H + HCO3.  This gets me a value of 5.6e-11 for CO3 which is not consistent with the molar value they gave me.

Any help would be greatly appreciated!