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Question

You have prepared a solution by dissolving 2.709g of nickel(II) chloride tetrahydrate in 60.0mL of water. What is this solution's chloride ion concentration in molality, m? (show steps)

Answer 1

Molality (m) is moles of solute per kg of solvent.

Nickel(II) chloride tetrahydrate = NiCl₂-4H₂O

Molar mass NiCl₂-4H₂O = 201.7 g / mol

Moles NiCl₂-4H₂O present = 2.709 g x 1 mol / 201.7 g = 0.01343 moles

Moles Cl^- present = 0.01343 mols NiCl₂-4H₂O x 2 mol Cl^- per mol NiCl₂-4H₂O = 0.02686 mols Cl^-

Kg of water = 60.0 ml x 1 g / ml x 1 kg / 1000 g = 0.06 kg (assuming a density of 1.0 g / ml for water)

Molality = mols / kg = 0.02686 mols / 0.060 kg

m = 0.448 molal (3 sig. figs.)