Question

Question:A pharmacist prepares an antiulcer medicine by mixing $\mathbf{286}\mathbf{}\mathbf{g}$${\mathbf{Na}}_{\mathbf{2}}{\mathbf{CO}}_{\mathbf{3}}$with water, adding $\mathbf{150}\mathbf{}\mathbf{g}$glycine, and stirring continuously at ${\mathbf{40}}^{\mathbf{\circ }}\mathbf{C}$until a firm mass results. The pharmacist heats the mass gently until all the water has been driven away. No other chemical changes occur in thisstep. Compute the mass percentage of carbon in the resulting white crystalline medicine.

Short answer

The percentage of carbon present in the white crystalline medicine is $18.1\%$.

Step-by-step solution

Given information

Mass of ${\mathrm{Na}}_2{\mathrm{CO}}_3=286\mathrm{g}$

Mass of glycine$=150\mathrm{g}$

Mass of carbon present

Molar mass of ${\mathrm{Na}}_2{\mathrm{CO}}_3=2\times 23+12+3\times 16=106\mathrm{g}$

Number of moles of${\mathrm{Na}}_2{\mathrm{CO}}_3$present in $286\mathrm{g}=\frac{286\mathrm{g}}{106{\mathrm{gmol}}^{-1}}=2.6$

Now,

$$\begin{gathered} 1\mathrm{mol}{\mathrm{Na}}_2{\mathrm{CO}}_3=12\mathrm{g}\mathrm{C} \\ 2.6\mathrm{mol}{\mathrm{Na}}_2{\mathrm{CO}}_3=2.6\times 12\mathrm{g}\mathrm{C}=31.2\mathrm{g}\mathrm{C} \end{gathered}$$

Molar mass of ${\mathrm{C}}_2{\mathrm{H}}_5{\mathrm{NO}}_2=24+5+14+32=75{\mathrm{gmol}}^{-1}$

Number of moles of ${\mathrm{C}}_2{\mathrm{H}}_5{\mathrm{NO}}_2$present in $150\mathrm{g}=\frac{150\mathrm{g}}{75{\mathrm{gmol}}^{-1}}=2$

Now,

role="math" localid="1662111128542" $$\begin{gathered} 1\mathrm{mol}{\mathrm{C}}_2{\mathrm{H}}_5{\mathrm{NO}}_2=24\mathrm{g}\mathrm{C} \\ 2\mathrm{mol}{\mathrm{C}}_2{\mathrm{H}}_5{\mathrm{NO}}_2=2\times 24\mathrm{g}\mathrm{C}=48\mathrm{g}\mathrm{C} \end{gathered}$$

The total mass of carbon present $=31.2\mathrm{g}+48\mathrm{g}=79.2\mathrm{g}$

Percentage of carbon

The total mass of ${\mathrm{Na}}_2{\mathrm{CO}}_3$ and glycine$=286\mathrm{g}+150\mathrm{g}=436\mathrm{g}$

Percentage of carbon $=\frac{79.2}{436}\times 100\%=18.1\%$