"A 25.0% solution of Al2(SO4)3 has a density of 1.75 g/ml. What is the mass of dissolved solute in 40.0 ml of solution?"
How would one set this problem up?
Is that 25.0% solution by mass? If so, then 25.0% means we have 25.0 g Al2(SO4)3 in 100 g solution. With a density of 1.75 g/mL, this 100 g soln has a volume of 100/1.75 = 57.14 mL. Thus, 40 mL will contain,
25.0g x (40.0/57.14) = ?? g Al2(SO4)3