Principle of Dumas method

In Dumas method, an organic compound containing nitrogen is heated with excess copper oxide, so that:

• carbon is converted to $\mathrm{CO_2}$,
• hydrogen is converted to $\mathrm{H_2O}$,
• nitrogen is ultimately liberated as $\mathrm{N_2}$.

Possible impurity formed

During combustion, oxides of nitrogen such as $\mathrm{NO}$ or $\mathrm{NO_2}$ may also be formed.

Role of the heated metal/gauze

To ensure that all nitrogen oxides are converted into elemental nitrogen, the gaseous products are passed over heated copper gauze.

Copper reduces nitrogen oxides: $\mathrm{NO_x + Cu \rightarrow N_2 + CuO}$

Hence

The gas evolved is passed over copper gauze.

Checking options

• A: Copper oxide — incorrect, this is used initially for oxidation of the sample.
• B: Copper gauze — correct, it reduces nitrogen oxides to $\mathrm{N_2}$.
• C: $\mathrm{Pd}$ — incorrect.
• D: $\mathrm{Ni}$ — incorrect.

Final answer

The correct option is: $\boxed{\text{B: Copper gauze}}$

Comparison with stored answer

Stored correct answer is B, which matches the derived answer.