Question

Calculate mulalities of 0.840M sugar?

Answer 1

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Molality (m) = moles of solute per kg of solvent (not to be confused with molarity)

1a) 4.2% (m/m) = 4.2 g KBr/100 g solution. We need moles KBr and kg of water, so we proceed as follows;

moles KBr = 4.2 g KBr x 1 mol KBr/119 g = 0.0353 moles KBr

kg water = 100 g solution - 4.2 g KBr = 95.8 g H2O = 0.0958 kg H2O

molality KBr = 0.0353 moles / 0.0958 kg = 0.368 m