# How would you determine the formula and molar mass of aluminum sulfide?

Dec 3, 2016

$\text{Aluminum sulfide}$ $\equiv$ $A {l}_{2} {S}_{3}$.

#### Explanation:

So how did I know?

Aluminum commonly forms an $A {l}^{3 +}$ ion.

And sulfur (like congeneric oxygen) commonly forms a ${S}^{2 -}$ ion.

To make a neutral salt, the charge must balance hence, $A {l}_{2} {S}_{3}$.

Note that these ionic identities can be predicted by the position of these elements on the Periodic Table. How?

And as to the masses, sulfur has a mass of $32.06 \cdot g \cdot m o {l}^{-} 1$, and aluminum has a mass of $26.98 \cdot g \cdot m o {l}^{-} 1$.

And thus the molar mass of "aluminum sulfide "= (2xx26.98+3xx32.06)*g*mol^-1=??*g*mol^-1.