Question

What happens when boiling water is added to a mixture of Iron ($\mathrm{Fe}$) filings and Sulphur ($\mathrm{S}$) powder?

• A. Both $\mathrm{Fe}$ and $\mathrm{S}$dissolve to form a clear solution.
• B. $\mathrm{Fe}$ precipitates, but $\mathrm{S}$ dissolves to form a pale yellow solution.
• C. A black precipitate of $\mathrm{FeS}$ is obtained.
• D. A black suspension containing undissolved $\mathrm{Fe}$ filings and $\mathrm{S}$powder is obtained.

Answer 1

The correct option is C

A black precipitate of $\mathrm{FeS}$ is obtained.

Explanation for the correct option:

1. When we add boiling water to a mixture of Iron ($\mathrm{Fe}$) filings and Sulphur ($\mathrm{S}$) powder, a grey-black precipitate of $\mathrm{FeS}$ ( Iron sulphide) is formed.
2. The formed mixture will be homogeneous, it means that two elements mix together thoroughly and cannot be separated.
3. The reaction can be given as: $$\begin{gathered} \mathrm{Fe}\left(\mathrm{s}\right)+\mathrm{S}\left(\mathrm{s}\right)\stackrel{∆}{\to }\mathrm{FeS}\left(\mathrm{s}\right)\downarrow \\ (\mathrm{Iron}\mathrm{filings})\left(\mathrm{Sulphur}\right)(\mathrm{Grey}-\mathrm{black}\mathrm{ppt}\mathrm{of}\mathrm{Iron}\mathrm{sulphide}) \end{gathered}$$.

Explanation for the incorrect options:

1. Option (A) is incorrect because both Iron fillings and elemental Sulphur are water insoluble.
2. Option (B) is incorrect because it Iron will not precipitate out or Sulphur will form a pale yellow solution with hot water.
3. Option (C) is incorrect because a black suspension containing undissolved $\mathrm{Fe}$ filings and $\mathrm{S}$ powder is not obtained but black precipitate of Ferrous sulphide is obtained.

Therefore, among the given options, option (C) is correct. i.e., When boiling water is added to a mixture of Iron ($\mathrm{Fe}$) filings and Sulphur ($\mathrm{S}$) powder, a black precipitate of $\mathrm{FeS}$ ( Iron sulphide) is obtained.