Question

Dumas method is used for estimation of:
(A) Carbon
(B) Nitrogen
(C) Oxygen
(D) Sulphur

Answer 1

Hint: We use this gas to provide an unreactive atmosphere. It is used in this way to preserve foods. It is used in the chemical industry and in the production of fertilizers. It is colourless, odourless, tasteless and constitutes the maximum percentage of earth’s atmosphere.

Complete step by step solution:
> We should first understand Dumas' method. In Dumas method, a known mass of the organic substance is heated with excess copper oxide in an atmosphere of$$C{O}_2$$.
- Let us understand this by taking an example. So, we are standing in a laboratory, and we have this unknown sample with us. Teacher assigned us a work that we have to determine the concentration of elements present in this sample. Teacher only gives this hint that this compound is made up of carbon, hydrogen and nitrogen. So, now we have to determine the concentration of carbon, hydrogen and nitrogen in this compound.
So, first we will take the weight of this compound. Then the organic substance is heated with excess copper oxide in an atmosphere of$$C{O}_2$$. Carbon, hydrogen and sulphur (if present) are oxidised to $$C{O}_2$$ , $H_{2}O$ and $S{O}_2$ respectively while nitrogen gas is set free. Any oxide of nitrogen that may form is reduced back to free nitrogen by passing over hot reduced copper gauze.
> These are the reactions that will occur:
$$C+2CuO\to C{O}_2+2Cu$$
$$2[H]+CuO\to H_{2}O+Cu$$
$$Nitrogen+CuO\to N+asmallamountofoxidesofnitrogen$$
$$Oxidesofnitrogen+Cu\to CuO+N$$
> Now, we have to determine nitrogen content in that sample. The nitrogen thus formed is collected over conc. KOH solution which absorbs all other gases that is carbon dioxide, H2O vapours, sulphur dioxide. The volume of nitrogen collected is thus noted and from this the percentage of nitrogen can be calculated.
So, from this above discussion we can now say that Dumas method is used for the estimation of nitrogen in an organic sample. Hence, option B is correct.

Note:
In Dumas method, we use different apparatus for generating different gas. We use carbon dioxide generators. It is produced by heating sodium bicarbonate or magnesium carbonate. We use a combustion tube, about 90 cm long and about 2 cm in diameter. It consists of oxidised copper gauge, which prevents backward diffusion of any gases. In this tube, a reduced copper gauge is also present which helps to reduce any oxides of nitrogen formed during combustion back to nitrogen gas. Coarse cupric oxide is also present which fills half of the tube. It consists of a long graduated tube having a reservoir and a tap at the upper end. The $$C{O}_2$$and $H_{2}O$ vapours that are produced during combustion are absorbed by KOH solution. This 40% KOH solution is present in Schiff’s nitrometer.