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Question

0.2 gm of a solution of mixture of NaOH and Na2CO2and inert impurities was first titrated with phenolphthalein and N/10 HCl 17.5 ml of HCl was required at the end point. After this methyl orange was added and 2.5 ml of same HCl was again required for next end point. Find out percentage of NaOH and Na2CO3 in the mixture.

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Solution

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 = 0.1×17.5 =1.75
equivalents of NaOH = 1.751000
weight of NaOH = equivalents ×equivalent weight
weight of NaOH = 0.7 gm
% NaOH = 0.070.2×100= 35%
similarly in the second titration we use methyl orange
(NV)HCl​=(NV)Na2CO3
(NV)Na2CO3= 2.5×0.1
so milliequivalents of Na2CO3 =0.25
equivalents of Na2CO3 = 0.251000
weight of Na2CO3 in the sample = equivalents ×equivalent weight
(equivalent weight of Na2CO3 = 0.251000×106
weight of Na2CO3in the mixture = 0.0265 gm
% of Na2CO3= 0.02650.2×100= 13.25%
%NaOH =35%
%Na2CO3= 13.5%
Regards!



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