Finding moles of water evolved
Anhydrous aluminium chloride ($\ce{AlCl3}$) exists; however, it cannot be obtained by heating of the hexahydrate ($\ce{AlCl3.6H2O}$).

$$\ce{AlCl3.6H2O \rlap{\ \ \not}-&gt;[\quad] AlCl3 + 6 H2O}$$

The crystalline hexahydrate $\ce{AlCl3.6H2O}$ actually is the complex salt $\ce{[Al(H2O)6]^3+ 3 Cl-}$.

The acidic hexaaquaaluminium(3+) ion is susceptible to hydrolysis.

$$\ce{[Al(H2O)6]^3+ &lt;=&gt; Al(OH)3 + 3 H3O+}$$

Therefore, the hexahydrate $\ce{AlCl3.6H2O}$ hydrolyses upon gentle heating and releases three equivalents of water and hydrogen chloride.

$$\ce{AlCl3.6H2O -&gt; Al(OH)3 + 3 HCl + 3 H2O}$$