10 gm NaHCO_3(s) sample is heated in open to constant weight, the… - Vidyadip

MCQ

$10\ gm\ NaHCO_3(s)$ sample is heated in open to constant weight, the residue is titrated gainst $0.1\,M \ HCl$ in presence of phenolphathalein as an indicator, $500\ ml$ of acid was required to reach end point hence $\%$ purity of sample is ............... $\%$

A
$21$
B
$42$
C
$63$
✓
$84$

✓

Answer

Correct option: D.

$84$

d
$\mathop {2{\text{NaHC}}{{\text{O}}_3}({\text{s}})}\limits_{ + {{\text{H}}_2}{\text{O}} \uparrow } \xrightarrow{\Delta }\mathop {{\text{N}}{{\text{a}}_2}{\text{C}}{{\text{O}}_3}}\limits_{{\text{a}}\,{\text{mol}}} ({\text{s}}) + \mathop {{\text{C}}{{\text{O}}_2} \uparrow }\limits_{{\text{a}}/2\,{\text{mol}}} $

${\text{N}}{{\text{a}}_2}{\text{C}}{{\text{O}}_3} + {\text{HCl}}\xrightarrow{{{\text{HPs}}}}{\text{NaHC}}{{\text{O}}_3} + {\text{NaCl}}$

$\frac{a}{2}=0.1 \times 0.5$

$a=0.1\, \mathrm{mol}$

$w=0.1 \times 84=8.4\, \mathrm{gm}$

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