posted by anonymous .
i find it confusing on how to do this question..
what mass of solute is needed to prepare 400 mL of 0.850 M CuSO4 from CuSO4.5H2O
Molar mass CuSO4.5H2O = 249.69 g/mol
You want 400ml of 0.85M: 249.69 *400/1000*0.85 = 84.9g CuSO4.5H2O dissolved to total volume 400ml.
The confusing part here is that you want a solution of CusO4 but you have given CuSO4.5H2O to make it.
What to remember. 1 mol CuSO4 = 1 mol CuSO4.5H2O; therefore, you want how many mols CuSO4? That's
M x L = 0.850 x 0.400 = ?
But that's the same number of mols you want for CuSO4.5H2O also; therefore
g = mols x molar mass and
g CuSO4.5H2O = mols CuSO4 x molar mass CuSO4.5H2O