Question

What is the role of $\mathrm{Fe}{\left(\mathrm{OH}\right)}_3$ in the contact process?

Answer 1

Contact process:

1. It is the process to manufacture Sulphuric acid by using Vanadium pentoxide or Platinised asbestos as a catalyst at a temperature range of $673-723\mathrm{K}$.
2. As part of the production of Sulfuric acid, Sulfur trioxide and oleum are also produced.

The role of $\mathrm{Fe}{\left(\mathrm{OH}\right)}_3$ in the contact process is described below:

1. During the manufacturing of Sulphur trioxide, Sulphur dioxide enters the tower to remove the soluble impurities such as Arsenic oxide.
2. Arsenic oxide is poisonous for the catalyst that decreases the rate of reaction.
3. $\mathrm{Fe}{\left(\mathrm{OH}\right)}_3$ is a positive sol and Arsenic oxide is a negative sol. It is used to remove this Arsenic impurity when the gas is passed over it.
4. The reaction is as follows: $$\begin{gathered} {\mathrm{As}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)+2\mathrm{Fe}{\left(\mathrm{OH}\right)}_3\left(\mathrm{s}\right)\to 2{\mathrm{FeAsO}}_3\left(\mathrm{s}\right)+3{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) \\ ArsenicIron\left(III\right)Iron\left(III\right) \\ trioxideHydroxidearsenite \end{gathered}$$