Download Chapter 14 Solutions: Boiling Point Elevation, Freezing Point Depression, and Osmosis and more Study notes Chemistry in PDF only on Docsity!
Overview of Chapter 14
- Solutions
- Concentrations: Molarity Molality Mole fraction
- Colligative Properties Freezing point depression Boiling point elevation
- Osmosis
Questions to consider:
- How much salt do we need to add to ice to melt it?
- Why is it bad to drink sea water?
- How can you purify sea water?
Today’s Topics
- Boiling point elevation
- Freezing point depression
- Osmosis
Boiling Point Elevation
Elevation in BP = ∆Tbp = Kbp•m
(where Kbp is characteristic of solvent) VP solvent after adding solute VP Pure solvent BP pure solvent BP solution 1 atm P T
Change in Boiling Point
If we dissolve 62.1 g of ethylene glycol (1.00 mol) in
- g of water, what is the boiling point of the solution? Kbp = +0.512 oC/molal for water Solution
- Calculate solution molality = 4.00 m
- ∆Tbp = Kbp • m ∆Tbp = +0.512 oC/molal (4.00 molal) ∆Tbp = +2.05 oC Boiling Point = 102.05 oC
Freezing Point Depression
The freezing point of a solution is lower
than that of the pure solvent.
FP depression = ∆Tfp = Kfp•m Pure waterPure water Solution ofSolution of Ethylene glycolEthylene glycol and waterand water
Calculate the freezing point of a 4.00 molal glycol/water solution. Kfp = -1.86 oC/molal Solution ∆Tfp = KFP • m = (-1.86 oC/molal)(4.00 m)
∆Tfp = -7.44 oC
Recall that ∆Tbp = +2.05 ˚C for this solution.
Freezing Point Depression Boiling Point Elevation and
Freezing Point Depression
∆T = K•m•i
i = van’t Hoff factor = number of particles
produced per formula unit.
Compound Theoretical Value of i
Ethylene glycol 1
NaCl 2
CaCl 2 3
Q: How much NaCl must be dissolved in 4.00 kg of water to lower the freezing point to -10.00 oC? (Kfp = -1.86 oC/molal) Solution First, get the concentration from ∆Tfp = Kfp • m • i Here, i = 2 for NaCl. For every mole of NaCl salt, we get Na+^ and Cl-^ ions, so we get 2 moles of particles. -10.00 oC = (-1.86 oC/molal) • Concentration • 2 Concentration = 2.69 molal NaCl
Freezing Point Depression
Q: How much NaCl must be dissolved in 4.00 kg of water to lower the freezing point to -10.00 oC? (Kfp = -1.86 oC/molal) Solution Concentration = 2.69 molal NaCl 2.69 moles NaCl / kg water x (58.44 g/mole NaCl) = 157 g NaCl / kg water 157 g NaCl / kg water x 4 kg water = 629 g NaCl
Freezing Point Depression
Boiling and freezing point constants Osmosis
Dissolving the shell in vinegar Egg in corn syrup Egg in pure water
