Why is a solution of potassium hydroxide used to absorb carbon dioxide evolved during

Carbon dioxide is acidic in nature and potassium hydroxide is a strong base. Hence, carbon dioxide reacts with potassium hydroxide to form potassium carbonate and water as

$2 \mathrm{KOH}+\mathrm{CO}_{2} \longrightarrow \mathrm{K}_{2} \mathrm{CO}_{3}+\mathrm{H}_{2} \mathrm{O}$

Thus, the mass of the U-tube containing KOH increases. This increase in the mass of U-tube gives the mass of CO2 produced. From its mass, the percentage of carbon in the organic compound can be estimated.