18. $\mathrm{KHSO}_{4}+\mathrm{KOH}=\mathrm{K}_{2} \mathrm{SO}_{4}+\mathrm{H}_{2} \mathrm{O}$

Writing the equation of the reaction and balancing the coefficients - 4 points $19 . \mathrm{K}_{2} \mathrm{SO}_{4}+\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}=2 \mathrm{KNO}_{3}+\mathrm{BaSO}_{4} \downarrow$

Writing the equation of the reaction and balancing the coefficients - 4 points $20 . \mathrm{BaSO}_{4}+2 \mathrm{C}=\mathrm{BaS}+2 \mathrm{CO}_{2} \uparrow$

Writing the equation of the reaction and balancing the coefficients - 4 points

## TOTAL 16 points

## TASK № 3

A monobasic carboxylic acid contains $43.25 \%$ oxygen. Determine the formula of the acid

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# Solution:

22. Let's derive the general formula for a monobasic carboxylic acid:

$\mathrm{C}_{\mathrm{n}} \mathrm{H}_{2 \mathrm{n}+2} \mathrm{O}_{2}$

We will set up an equation to calculate the mass fraction of oxygen:

$\omega(O)=16 \cdot 2 /(12 n+2 n+2+16 \cdot 2)=32 /(14 n+34)$

$32 /(14 n+34)=0.4325$

Setting up the equation for the mass fraction of oxygen - 4 points

23. Determine the formula of the acid

$14 n+34=32 / 0.4325$

$14 n=42$

$\mathrm{n}=3$

The molecular formula of the acid is $\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}_{2}$ or $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{COOH}$ - propanoic acid

Establishing the molecular formula of the substance - 6 points

TOTAL 10 points

## QUESTION № 4

Substance A, upon ozonolysis, yields two compounds B and C. Compound B, upon further oxidation, is converted to acetic acid. Under the same conditions, compound C is converted to acetic acid and an acid with a molecular mass of 102. Knowing that C is a ketone that does not contain the $\mathrm{CH}_{3} \mathrm{CO}$ fragment, determine the formulas of A, B, and C.

## 18 points

## Solution: