How do you find the Gram Formula Mass??

Question

I need an explaination because I don't understand.

a. Li2S
b. FeCl3
c. Ca(OH2)

Answer 1

I assume you mean molar mass - i.e. the mass of 1 mole of a molecule. To do that, you add up the molar mass of each constituent atom:

1.) Li2S = 2 atoms of Li (6.941) + 1 atom of Sulfur (32.065) = 45.947 g/mol
2.) FeCl3 = 1 atom of Iron (55.845) + 3 atoms of Chlorine (35.453) = 162.204 g/mol