Hi Emma P.,
Better check your aluminum salt formula. When you get it right, use a Periodic Table to add up all the atomic weights of all the atoms in it. That gives you the formula (= molar) mass of the salt. Use that, and the stated mass of salt, to figure the number of moles of the salt used. That number of moles, divided by the volume in L, gives you the molarity of the solution.
-- Cheers, --Mr. d.