Question

Which of the following is used to absorb carbon dioxide evolved during the estimation of carbon present in an organic compound?
A.Sodium hydroxide
B.Potassium hydroxide
C.Potassium carbonate
D.Calcium carbonate

Answer 1

Hint:
The estimation of both carbon and hydrogen is done by oxidizing the organic compound to produce carbon dioxide and water. The products are then passed through a u-tube, which absorbs or reacts with the respective compounds and helps in the estimation of weight.

Complete step by step answer:
For the quantitative and qualitative analysis of carbon in an organic compound, we use the following method –
A known mass of an organic compound is burnt in the presence of excess oxygen and copper (II) oxide. This leads to complete oxidation of the compound, which produces carbon dioxide and water.
The mass of carbon dioxide produced is calculated by passing it through a u-tube containing potassium hydroxide solution.
Carbon Dioxide is acidic in nature. It reacts with a strong base - potassium hydroxide to give a salt – potassium carbonate and water. This can be represented by the reaction –
\[2KOH+C{{O}_{2}}\to {{K}_{2}}C{{O}_{3}}+{{H}_{2}}O\]
From the above reaction, we can see that the mass of the U-tube containing KOH increases. We measure the amount of carbon dioxide from this.
The percentage of Carbon can be calculated by the following formula –
\[%C=\dfrac{\text{12 x mass of C}{{\text{O}}_{\text{2}}}\text{ formed x 100}}{\text{44 x mass of substance taken}}\]
Therefore, the answer is – option (b).

Note:
The same method can also be used for calculating the percentage of hydrogen present in the organic compound. For this, anhydrous calcium chloride is used in the u-tube.