Molality (m) is the number of moles of a substance in 1 kg of solvent This is ju

Question

Molality (m) is the number of moles of a substance in 1 kg of solvent This is just like molarity, but the solvent is measured in units of 1 kg instead of units of 1 L. For Example: I f I dissolve 0.30 moles of NaCI in 400 g of water, the molality (m) is equal to: 0.3 mol NaCl/[400 g H_2O x (1 kg H)2o/1000 g H_2O)] = 0.75 m What is the molality of a solution that is made by dissolving 4.5 g of calcium chloride in 4.75 liters of water at 80^degree C. The density of water at this temperature is 0.9718 g/ml.

Explanation / Answer

3)

mass of calcium chloride = 4.5 g

moles of calcium chloride = 4.5 / 110.984

= 0.04055

volume of solvent = 4.75 L = 4750 mL

density = 0.9718 g /ml

mass of water = 4616.05 g = 4.616 kg

molality = moles of solute / mass of solvent in kg

= 0.04055 / 4.616

= 8.78 x 10^-3 m

molality = 0.00878 m

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