A sample of 0.3 g of urea was Kjeldahlised and the ammonia evolved was passed in to 120 mL 0.5 M HCl

Question

A sample of 0.3 g of urea was Kjeldahlised and the ammonia evolved was passed in to 120 mL 0.5 M HCl . The mass of HCl left unreacted might be\

Professor PC Thomas Classes · Answer

$\mathrm{H}_{2} \mathrm{~N} \mathrm{CONH}_{2} ightarrow 2 \mathrm{NH}_{3} ightarrow 2 \mathrm{HCl}$ $$ 60 \mathrm{~g} \quad 2 	imes 36.5=73 \mathrm{~g} $$ Mass of HCl in 120 mL 0.5 M solution $$ =\frac{0.5 	imes 120}{1000} 	imes 35.5=2.19 \mathrm{~g} . $$ Mass of HCl that can react with $\mathrm{MH}_{3}$\ liberated from 0.3 g urea $=\frac{73 	imes 0.3}{60}=0.365 \mathrm{~g}$\ Mass of unreacted $\mathrm{HCl}=2.19-0.365=1.82 \mathrm{~g}$\