Question

An environmental chemist needs a carbonate buffer of pH 10.00 to study the effects of acid rain on limestone- rich soils. How many grams of Na2CO3 must she add to 1.5 L of freshly prepared 0.20 M NaHCO3 to make the buffer

Answer 1

We know the Ka and the conjugate acid-base pair. Convert pH to [H3O+], find the number of moles of carbonate and convert to mass.HCO3-(aq) + H2O(l) CO32-(aq) + H3O+(aq)Ka =[CO32-][H3O+][HCO3-]pH = 10.00; [H3O+] = 1.0 x 10-104.7 x 10-11 =[CO32-](1.0 x 10-10)[0.20][CO32-] = 0.094 Mmoles of Na2CO3 = (1.5 L)(0.094 mol/L)= 0.14 = 15 g Na2CO30.14 moles 105.99 gmol