Question

A clay mineral that is frequently used together with or in place of kaolinite is pyrophyllite ( ${\mathbf{Al}}_2{\mathbf{Si}}_4{\mathbf{O}}_{10}{\left(\mathbf{OH}\right)}_2$). Write a balanced chemical equation for the production of mullite and cristobalite on the firing of pyrophyllite.

Short answer

$\begin{array}{l}3{\mathrm{Al}}_2{\mathrm{Si}}_4{\mathrm{O}}_{10}{\left(\mathrm{OH}\right)}_2\left(\mathrm{s}\right)\to {\mathrm{Al}}_6{\mathrm{Si}}_2{\mathrm{O}}_{13}\left(\mathrm{s}\right)+10{\mathrm{SiO}}_2\left(\mathrm{s}\right)+3{\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right)\\ \mathrm{Pyrophyllite}\mathrm{mullite}\mathrm{Cristobalite}\end{array}$

Step-by-step solution

Pyrophyllite

Pyrophyllite has the same crystalline structure as talc. It is an example of infinite sheet silicate. The repeating silicate unit is ${\mathbf{Si}}_2{{\mathbf{O}}_5}^{2-}$ .

Explanation

When pyrophyllite silicate is heated then mullite and cristobalite. The balanced chemical equation of the reaction is as shown below:

$\begin{array}{l}3{\mathrm{Al}}_2{\mathrm{Si}}_4{\mathrm{O}}_{10}{\left(\mathrm{OH}\right)}_2\left(\mathrm{s}\right)\to {\mathrm{Al}}_6{\mathrm{Si}}_2{\mathrm{O}}_{13}\left(\mathrm{s}\right)+10{\mathrm{SiO}}_2\left(\mathrm{s}\right)+3{\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right)\\ \mathrm{Pyrophyllite}\mathrm{mullite}\mathrm{Cristobalite}\end{array}$