Question

In Liebig's method for the estimation of Carbon and hydrogen, if the compound also contains nitrogen, which of the following is kept near the exit of the combustion tube?
A. Silver wire
B. ${\text{PbC}}{{\text{r}}_4}$
C. Both (a) and (b)
D. ${\text{CuO}}$ gauze

Answer 1

Hint: This question is based on the analytical study of organic compounds which includes carbon, hydrogen, oxygen, nitrogen etc using qualitative and quantitative analysis.

Complete answer:
Quantitative analysis is used to identify the number of elements or molecules produced during a chemical reaction, the organic compounds includes are carbon, hydrogen, oxygen, nitrogen and phosphorus etc while qualitative analysis is the analysis of species in the compound which is more focused on finding the elements and the ions present in the compound instead of studying as to how much they are present.
Liebig's method is basically used for the estimation of Carbon and hydrogen in which we heat a known mass of organic compound in the presence of pure oxygen after that the carbon dioxide and water formed are collected and weighed and percentages of carbon and hydrogen are calculated from the masses of carbon dioxide and water.
Suppose if the compounds also containing nitrogen, as we know that during the combustion process organic nitrogen is oxidized in its oxides form i.e. ${\text{NO,N}}{{\text{O}}_2}$ which are also absorbed in potassium hydroxide solution along with carbon dioxide.
But other than this if we place a preheated ${\text{CuO}}$ gauze near the exit of the combustion tube then we will notice that the oxides of nitrogen are reduced to nitrogen.

Hence the correct option is D.

Note: Analytical chemistry is basically the study of the separation, identification and quantification of the chemical components of natural and artificial and in that quantitative analysis part gives the indication of the identity of the chemical species in the sample while quantitative analysis identifies the amount of certain components in the substance and this separation of components is actually done prior to the analysis.