http://icemeltchicago.com/chicago-ice-melt-products.php

http://group.chem.iastate.edu/Greenbowe/sections/projectfolder/flashfiles/propOfSoln/colligative.html

Colligative Properties of Solutions -properties that depend only on the concentration of solute particles, but not on the type.

The solutes in these solutions are nonvolatile, which means it has little tendency to become a gas. They stay in solution as a liquid. These tend to be ionic substances or polar covalent, like salts and sugars

In comparison: Volatiles have low boiling points and evaporate easily because they have weak, nonpolar bonding

Ex: CO2, methane CH4, diatomic gases

Molecular vs. Ionic solutes: Sugar C12H22O11 (s) is molecular. When 1 mole of itdissolves in water, one mole of particles is producedin solution:

C12H22O11 (s) C12H22O11 (aq) 1 mol 1 mol

When 1 mole of an ionic substance dissolves in water, 2 or more moles of particles are produced:

total molesNaCl (s) Na+(aq) + Cl-(aq) 1 mol NaCl 1 mol Na+ 1 mol Cl- 2CaCl2 (s) Ca2+(aq) + 2Cl-(aq)1 mol CaCl2 1 mol Ca2+ 2 mol Cl- 3

A. Boiling point elevation - The presence of a nonvolatile solute (like

sugar or salt) raises the boiling point of a solvent.

Here’s why:

The solute particles occupy sites on the surface. This prevents solvent from evaporating. The temperaturemust then be raised to bring the vapor pressure up to atmospheric pressure, which is what boiling is.

Key: = solvent = solute+

The greater the concentration of solute, the more the boiling point is raised.

1 mole of solute particles elevates the boiling pointof 1000 g of water by about ½ 0C (exact = 0.51 0C).

Ex. By about how much will each of the following solutes raise the boiling point of 1000 g of water?

a/ 342 g (1 mol) of C12H22O11 (s)?

b/ 32 g (1 mol) of CH3OH (methanol = molecular)?

c/ 58.5 g (1 mol) of NaCl?

d/ 111 g (1 mol) of CaCl2?

e/ 95.2 g (1 mol) of MgCl2?

B. Freezing point depression - The presence of a nonvolatile solute (like

sugar or salt) lowers the freezing point of a solvent.Here’s why:Normally, at freezing,the number of H2O’sjoining an ice crystal to become solid equals thenumber of H2O’s leavingthe crystal to join theliquid phase. Solute particles block liquid H20’s from joining the ice, but allow ice H20’s to join the liquid. More liquid forms,which means: it melts. To slow the rate of forming liquid,the temperature must be lowered.

liquidH2O

solidH20

= solute

The greater the concentration of solute, the more the freezing point is lowered. 1 mole of solute particles depresses the freezing pointof 1000 g of water by almost 2 0C (exact = 1.86 0C).

Ex. About much will each of the following solutes lowerthe freezing point of 1000 g of water?a/ 342 g (1 mol) of C12H22O11 (s)?b/ 58.5 g (1 mol) of NaCl?c/ 111 g (1 mol) of CaCl2?d/ 95.2 g (1 mol) of MgCl2?

Which are the best to spread on icy roads in order toprevent ice from forming?

Ex. A mixture of ethylene glycol, C2H6O2, is used as an antifreeze and a coolant in cars. A typical mixture contains about 18 moles of it in each 1000 g of solution.

a/ What is the approximate freezing point of the solution?

b/ What is the approximate boiling point of the solution?

Ex. If NaCl costs 1.5x a sugar-based ice melt product, which is a better deal? Which is better for the environment?

In sum:

boiling point

freezing point

Pure solvent:

elevated boiling point

depressed freezing point

Solution:

More moles of solute, wider range of liquid state Ionic substances produce more moles than molecular

and so they produce a wider temp. range for the liquid.

liquid

C. Osmosis – the process by which solvent moleculespass through a semipermeable membrane from a dilute solution into a more concentrated one

Semipermeable membrane – solvent can pass through it, but solute particles cannot

Solvent particles flow through themembrane from low to high concentration.

Osmotic pressure is the pressure that must beexerted in order to stop the flow of solvent.It depends only on the concentration of solute.

Ex. Fluids move into and out of cells by means of osmosis

Ex. Reverse osmosis is used to desalinate seawater.

level rises until excesspressure stops the flow

Sports drinks are designed to:1. make money; and2. replenish solutes (electrolytes) to prevent

cell damage due to osmotic pressure caused bydrinking large amts of water.

Why is salt added to boiling water?