I need help with this question. This is what I have so far 

mass = 37.2 g AICI3 (given) 
number of ions = ? AI3+ Ions (unknown)
number of ions = ? CI- Ions (unknown) 
mass = ? g/formula unit AICI3 (unknown) 
a.

If you don't know molar mass of compound, search net for specific keyword, open Wikipedia article about it and read it..

If you know molar mass of elements (or atomic mass, or number of protons and neutrons in the case of element like Aluminium) present in compound, you can calculate approximate molar mass of compounds created with these elements. e.g. O₂ is 16 g/mol + 16 g/mol = 32 g/mol, because Oxygen has 8 protons and 8 neutrons (O-16 is the most abundant isotope of Oxygen, O-17 and O-18 are in meaningless quantity).

Edited December 26, 20196 yr by Sensei

Is this correct?

mass = 37.2 g AICI3 (given) 
number of ions = AI3+ Ions (unknown)
number of ions = CI- Ions (unknown) 
mass = g/formula unit AICI3 (unknown) 
The ratio of AI3+ Ions to CI- Ions is 1:3
Molar Mass AICI3
(1 x 26.98 g/mol AI) + (3 x 35.45 g/mol CI) = 133.33 g/mol AICI3
molar mass = 133.33 g/mol AICI3
Divide the given mass of aluminum chloride by its molar mass.
37.2 AICI3/133.33 mol = 0.279 mol AICI3