Calculate the pH of a buffer solution....help

Calculate the pH of a buffer solution prepared by dissolving 4.2 g of NaHCO3 and 5.0 g of Na2CO3 in 0.20 L of water.

Calculate moles of NaHCO3 and moles of Na2CO3 used. Divide each by 0.200 L to calcualte the molar concentration of each.

Then, look up pKa for HCO3- <---> H+ + CO32-

pH = pKa + log [CO32-]/[HCO3-]

OR, look up Ka for ionization of bicarbonate. Then,

Ka = [H+][CO32-]/[HCO3-]

Plug in values and calculate [H+]

From [H+], calculate pH = - log [H+]