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A mixture containing Na(2)CO(3), NaOH an...

A mixture containing `Na_(2)CO_(3)`, NaOH and inert matter weighs 0.75 g. When the aqueous solution is titrated with 0.50 N HCl, the colour of the phenolphthalein disappears when 21.00 mL of the acid has been added. Methyl orange is then added and 7.00 mL more of the acid is required to give a red colour to the solution. The % of `Na_(2)CO_(3)` is:

A

49.5

B

24.5

C

37.1

D

None of these

Text Solution

Verified by Experts

The correct Answer is:
A
Let meq of NaOH = x and meq of `Na_(2)CO_(2) = y`
Meq `NaOH + (1)/(2)` Meq `Na_(2)CO_(3)` = Meq HCl `rArr x + (y)/(2) = 0.5 xx 21 = 10.5` …(i)
and `("Meq "Na_(2)CO_(3))/(2)-= "left"` = Meq HCl `rArr (Y)/(2) = 0.5 xx 7 rArr y = 7` ….(ii)
Now, `(g_(Na_(2)CO_(3)))/(106//2) xx 1000 = Y rArr g_(Na_(2)CO_(3)) = 0.371 rArr & Na_(2)CO_(3) = (0.371)/(0.75) xx 100 = 49.5`
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