Answer to Question #137354 in General Chemistry for Selbi

Question

You are making a solution that requires 74.4 g of magnesium chloride hexahydrate (MgCl26H2O molar mass 203.30 g/mol). However, this compound is not available in your lab and you use magnesium chloride dihyderate instead (MgCl22H20 molar mass 131.24 g/mol) How much MgCl22H20 do you need to weigh out to make this solution?

Answer 1

moles of a substance are constant through out.

$moles = (mass of substance )/molar mass$

moles of magnesium chloride hexahydrate = 74.4g /203.3 = 0.365 mol

this moles is the same throughout.

mass of substance =(moles * molar mass )

mass to substance = (0.365mol * 131.24 g = 48.02 g of magnesium chloride dehydrate