1st end point reaction,
NaOH+HCl→NaCl+H2ONa2CO3+HCl→NaHCO3+NaCl
∴ Milliequivalents of HCl=Milliequivalents of NaOH+Milliequivalents of Na2CO3110×17.5×10−3=nNaOH×1+nNa2CO3×1nNaOH+nNa2CO3=1.75×10−3 ...(1)
2nd end point reaction,
NaHCO3+HCl→NaCl+H2CO3
∴ Milliequivalents of HCl=Milliequivalents of NaHCO3110×1.5×10−3=nNaHCO3×1nNaHCO3=0.15×10−3≡nNa2CO3nNa2CO3=0.15×10−3wNa2CO3=0.15×10−3×106=0.0159
Weight % of Na2CO3 in the mixture=0.01590.4×100≈4%