Chemistry
posted by Sara .
what is the hydroniumion concentration in a 0.35m solution of NaCO3? For carbonic acid, Ka1=4.2x10^7 and Ka2=4.8x10^11. (Kw=1.0x10^14)

I'm sure you mean 0.35M solution. Do you know that 0.35M and 0.35m are not the same? This is a hydrolysis problem.
........CO3^2 + HOH ==> HCO3^ + OH^
I.......0.35M..............0.......0
C.......x.................x.......x
E.......0.35x.............x.......x
Kb for CO3^ = (Kw/k2 for H2CO3) = (x)(x)/(0.35x). Substitute and solve for x = (OH^) an convert to pH. 
Why is the last step is convert to pH? We are trying to find the hydroxideion concentration?not the pH

Nvm figured it out