[jalen]

Please indicate which step is wrong and what the correct answer should be.
The answer for pH= 4.82 and CO₃² IS 4.7 X 10^-11.
Thanks

[Borek]

Please don't post DOC files, they can be infected and most people will not want to download them.

Your calculations are hard to follow, but in the very first dissociation step concentration of H⁺ is larger then concentration of acid. It must be wrong.

See

http://www.chembuddy.com/?left=pH-calculation&right=pH-polyprotic-simplified

[AWK]

Please indicate which step is wrong and what the correct answer should be.
The answer for pH= 4.82 and CO₃² IS 4.7 X 10^-11.
Thanks

Your calculations are completely wrong. Using a quadratic equation is not neccessary in the first step, but when used it should be correctly solved.
For calculations of CO₃^2- you can use a product of K₁K₂.