# What is the chemical formula of "aluminum sulfate"?

$A {l}_{2} {\left(S {O}_{4}\right)}_{3}$
The sulfate anion has a $- 2$ charge, whereas the aluminum cation has a $+ 3$ charge. The ionic compound must be electrically neutral. Thus we take 2 aluminum ions (6+ charge) and 3 sulfate ions (6-) charge, and achieve electrical neutrality. Are you happy with this treatment? What is the formula for sodium sulfate?