Question

How many grams of Na₂SO₄ should be added to 228 g of water to make a solution with a colligative molality of 0.530 m?
(Please see Your Turn #3-3, lecture 3, slide 22 for assistance.)

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Answer 1

Na2SO4 is a strong salt : Na2SO4 = 2 Na+ + SO42- for which i = Vant'Hoff factor = 2 + 1 = 3

0.530 = moles ions/ 0.228 Kg
moles ions =0.530×0.228=0.1208

moles Na2SO4 = 0.1208/3=0.0402

mass Na2SO4 = 0.0402 x 142 g/mol=5.708 g

Thank you