Question

What is the name of the compound formed between Sulphur trioxide and sulphuric acid?

Answer 1

When Sulphur trioxide$\mathbf{\left(}{\mathbf{SO}}_{\mathbf{3}}\mathbf{\right)}$ gas is dissolved in Sulphuric acid$\left(H_2{\mathrm{SO}}_4\right)$, then it forms pyrosulphuric acid$\left(H_2{S}_2{O}_7\right)$.

The common name of pyrosulphuric acid$\left(H_2{S}_2{O}_7\right)$ is oleum.

Reaction:

$$\begin{gathered} {\mathrm{SO}}_3\left(\mathrm{g}\right)+{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)\to {\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_7\left(\mathrm{aq}\right) \\ \mathrm{Sulphur}\mathrm{Sulphuric}\mathrm{Pyrosulphuric} \\ \mathrm{trioxide}\mathrm{acid}\mathrm{acid} \end{gathered}$$

Thus, the compound that is formed between Sulphur trioxide$\mathbf{\left(}{\mathbf{SO}}_{\mathbf{3}}\mathbf{\right)}$ and Sulphuric acid $\left(H_2{\mathrm{SO}}_4\right)$ is oleum or pyrosulphuric acid$\left(H_2{S}_2{O}_7\right)$.