18. Determine the amount of substance of sodium carbonate

According to the chemical reaction equation:

$$
\mathrm{n}\left(\mathrm{CO}_{2}\right)=\mathrm{n}\left(\mathrm{Na}_{2} \mathrm{CO}_{3}\right)=0.125 \text { mol }
$$

Determination of the amount of substance - 2 points

19. Calculate the mass of sodium carbonate

$$
m\left(\mathrm{Na}_{2} \mathrm{CO}_{3}\right)=n \cdot M=0.125 \cdot 106=13.25 \text { g }
$$

Determination of the mass of the substance - 2 points

20. Determine the mass fraction of sodium carbonate in the initial solution:

$$
\omega\left(\mathrm{Na}_{2} \mathrm{CO}_{3}\right)=\frac{m\left(\mathrm{Na}_{2} \mathrm{CO}_{3}\right) \cdot 100 \%}{m_{\mathrm{p}-\mathrm{pa}}\left(\mathrm{Na}_{2} \mathrm{CO}_{3}\right)}=\frac{13.25 \cdot 100 \%}{132.5}=10 \%
$$

Determination of the mass fraction of the substance in the solution - 2 points
Answer: $10 \%$

## TOTAL 10 points

## TASK № 2

Aluminum oxide was melted with potash. The resulting product was dissolved in hydrochloric acid and treated with excess ammonia water. The precipitate that formed was dissolved in excess sodium hydroxide solution. Write the equations for the four reactions described.

## Solution: