Colligative Properties Dilution and Colligative Properties of Solutions

Dilution of Concentrated Solution moles before dilution = moles after dilution n = M x V Mc x Vc = Md x Vd Mc = molarity of concentrated solution Vc = volume of concentrated solution Md = molarity of dilute solution Vd = volume of dilute solution

How many mL of 12 M HCl should be added to water to prepare 400 mL of 0.5 M HCl? Given : Mc = 12 M Needed: Vc = ? Md = 0.5 M Vd = 0.4 L SOLUTION: (Mc) (Vc) = (Md) (Vd) Vc = (Md) (Vd) = (0.5 M) (0.4 L) = 0.0167 L (Mc) (12 M)

COLLIGATIVE PROPERTIES OF SOLUTIONS depend on the molality of the solution 1. Boiling point elevation – the amount by which the boiling point is elevated is determined by the equation: ∆ TB = Kb m where ∆ TB = boiling point elevation in oC Kb = molal boiling point constant (for water = 0.512 oC/m) m = molality of the solution

What is the boiling point of a solution prepared by dissolving 10 g of NaCl in 25 g of water? Given: Mole of solute = 10 g/(23+35) = 0.172 mole Mass of solvent = 0.025 kg Molality = n = 0.172 mole = 6.88 m x 2 kg 0.025 kg Solution: Solve for the boiling point elevation ∆ TB = Kb m = (0.512 oC/m) (13.76 m) = 7.05 oC 2. Solve for the final boiling point TB = 100oC + 7.05 oC = 107.05 oC

2. Freezing point depression – the amount by which the freezing point is lowered is determined by the equation: ∆ TF = Kf m where ∆ TF = freezing point depression in oC Kf = molal freezing point constant (for water = 1.86 oC/m) m = molality of the solution

What is the freezing point of a solution prepared by dissolving 10 g of NaCl in 25 g of water? Given: Mole of solute = 10 g/(23+35) = 0.172 mole Mass of solvent = 0.025 kg Molality = n = 0.172 mole = 6.88 x 2m kg 0.025 kg Solution: Solve for the freezing point depression ∆ TF = Kf m = (1.86 oC/m) (13.76 m) = 25.59 oC 2. Solve for the final freezing point TB = 0oC – 25.59 oC = - 25.59 oC

Rock salt melting snow and ice

Ethylene glycol raises the boiling point and lowers the freezing point of water

3. Vapor pressure lowering – a nonvolatile solute dissolved in a solvent lowers the equilibrium vapor pressure of the solvent

Dead Sea