Question

A mixture of $NaHC{O}_3$ and $N{a}_{2}C{O}_3$ weighs 950 gm. When the mixture is heated strongly in an open vessel, till constant weight, the mass of sample reduced by 155 gm. The correct information(s) is/ are ?

• A. The mass percent of $NaHC{O}_3$ in initial mixture = 50%
• B. The mole percent of $N{a}_{2}C{O}_3$ in initial mixture = 50%
• C. Final sample contains only $N{a}_{2}O$
• D. The loss in mass is only due to $C{O}_2$ gas evolved

Answer 1

Answer: (A)

The mass percent of $NaHC{O}_3$ in initial mixture = 50%

${Na}_2{CO}_3$ is a strong base and does not dissociate on normal heating.

$2NaH{CO}_3⟶{Na}_2{CO}_3+{CO}_2+H_{2}O$

No. of moles ${CO}_2=\frac{0.950}{22400}=4.24\times {10}^{-5}$

No. of moles of ${NaHCO}_3=4.24\times {10}^{-5}\times 22400=0.084\times {10}^{+3}=84g$

Initial ${NaHCO}_3$ mass $=155g$

$\Rightarrow$ Mass percent $=\frac{84}{155}\times 100$% $\approx 50$%