[Barelover]

A solution contains both NaHCO3 and Na2CO3.  Titration of a 50 ml portion to a phenolpthalein end point (pKa 9.10) requires 20.10 ml of 0.1029 M HCl.  A second 50 ml aliquot requires 48.28 ml of the HCl solution when titrated to a bromocresol green end point (pKa 4.66).  What is the molar concentration of Na2CO3 and NaHCO3 in the solution???

It's a question from a past exam paper for my analytical subject.  I can't figure it out can someone please show me how to do this.

[Borek]

You need to check which protons get titrated at which pH.

[adianadiadi]

Hint: Na₂CO₃ is first converted to NaHCO₃ during titration with acid.