5. Let's determine the mass fraction of potassium sulfate in the initial solution:

$$
\omega\left(K_{2} \mathrm{SO}_{4}\right)=\frac{m\left(K_{2} \mathrm{SO}_{4}\right) \cdot 100 \%}{m_{\mathrm{p}-\mathrm{pa}}\left(K_{2} \mathrm{SO}_{4}\right)}=\frac{2.61 \cdot 100 \%}{160}=1.63 \%
$$

Determining the mass fraction of a substance in a solution - 2 points
Answer: $1.63 \%$

## TOTAL 10 points

## TASK № 2

Iron was burned in bromine. The resulting salt was added to a solution of potassium carbonate, whereupon a brown precipitate formed. This precipitate was filtered and calcined. The resulting substance was dissolved in hydriodic acid. Write the equations for the four described reactions.

## Solution: