Dear Student,
In the first titration when we use phenolphthalein , NaOH will be neutralized by HCl
so
(NV)HCl= (NV)NaOH
so milliequivalents of NaOH=(NV)NaOH = =1.75
equivalents of NaOH =
weight of NaOH = equivalents
weight of NaOH = 0.7 gm
% NaOH = = 35%
similarly in the second titration we use methyl orange
(NV)HCl=(NV)Na2CO3
(NV)Na2CO3=
so milliequivalents of Na2CO3 =0.25
equivalents of Na2CO3 =
weight of Na2CO3 in the sample = equivalents equivalent weight
(equivalent weight of Na2CO3 =
weight of Na2CO3in the mixture = 0.0265 gm
% of Na2CO3= = 13.25%
%NaOH =35%
%= 13.5%
Regards!