Question

Write the chemical formulas for washing soda and baking soda, and calculate the percentage of sodium by weight in each of the two.

Answer 1

Washing soda

The molecular formula for washing soda is ${\mathrm{Na}}_2{\mathrm{CO}}_3.10{\mathrm{H}}_2\mathrm{O}$

The molar mass of washing soda = 2 x Mass of Na + Mass of C + 3 x Mass of O

= 2 x 23 + 12 + 3 x 16

= 106 g

Hence, the percentage of sodium by weight can be calculated as:

$$\begin{gathered} \mathrm{Percentage}\mathrm{of}\mathrm{sodium}\mathrm{by}\mathrm{weight}=\frac{\mathrm{weight}\mathrm{of}\mathrm{sodium}\mathrm{in}\mathrm{washing}\mathrm{soda}}{\mathrm{weight}\mathrm{of}\mathrm{washing}\mathrm{soda}}\mathrm{x}100 \\ =\frac{46}{106}\mathrm{x}100 \\ =43.39\% \end{gathered}$$

Hence, the percentage of sodium by weight in washing soda is 43.39%

Baking soda

The molecular formula for baking soda is ${\mathrm{NaHCO}}_3$

The molar mass of washing soda = Mass of Na + Mass of H + Mass of C + 3 x Mass of O

= 23 + 1 + 12 + 3 x 16

= 84 g

Hence, the percentage of sodium by weight can be calculated as:

$$\begin{gathered} \mathrm{Percentage}\mathrm{of}\mathrm{sodium}\mathrm{by}\mathrm{weight}=\frac{\mathrm{weight}\mathrm{of}\mathrm{sodium}\mathrm{in}\mathrm{baking}\mathrm{soda}}{\mathrm{weight}\mathrm{of}\mathrm{baking}\mathrm{soda}}\mathrm{x}100 \\ =\frac{23}{84}\mathrm{x}100 \\ =27.38\% \end{gathered}$$

Hence, the percentage of sodium by weight in baking soda is 27.38%