34. Let's determine the amount of calcium carbonate substance. According to the chemical reaction equation:

$n\left(\mathrm{CaCO}_{3}\right)=\frac{1}{2} n(\mathrm{HCl})=\frac{0.822}{2}=0.411$ mol

Determination of the amount of substance - 2 points

35. Let's determine the mass of calcium carbonate $m\left(\mathrm{CaCO}_{3}\right)=n \cdot M=0.411 \cdot 100=41.1$ g

If impurities in the limestone account for $3 \%$, then the pure substance accounts for $97 \%$

Let's find the mass of the limestone $m($ limestone $)=41.1 \cdot 100 / 97=42.37$ g

Determination of the volume of the released gas - 2 points
Answer: 42.37 g

## TOTAL 10 points

## TASK № 2

To a solution of copper(II) sulfite, an excess of soda solution was added. The precipitate that formed was calcined, and the solid residue was heated in an atmosphere of excess oxygen. The resulting substance was dissolved in concentrated nitric acid. Write the equations for the four described reactions.

## Solution:

$25.2 \mathrm{CuSO}_{4}+2 \mathrm{Na}_{2} \mathrm{CO}_{3}+\mathrm{H}_{2} \mathrm{O}=(\mathrm{CuOH})_{2} \mathrm{CO}_{3}+\mathrm{CO}_{2} \uparrow+2 \mathrm{Na}_{2} \mathrm{SO}_{4}$

Formulating the reaction equation and balancing the coefficients - 4 points

26. $(\mathrm{CuOH})_{2} \mathrm{CO}_{3}=2 \mathrm{CuO}+\mathrm{H}_{2} \mathrm{O}+\mathrm{CO}_{2} \uparrow$

Formulating the reaction equation and balancing the coefficients - 4 points