Solutions and SolubilityChapter 8

What is a solution?

• homogeneous mixture; uniform throughout

• solvent is present in

larger amount

• solute refers to

what is dissolved

• a given solution can be made up of different amounts of solute and solvent

eg 0.10 mol/L NaCl(aq); 0.50 mol/L NaCl(aq)

Some types of Solutionssolute solvent examples

gas gas air, natural gas

gas liquid O2(aq)—fish breathe this; CO2(aq) in carbonated drinks

liquid gas water vapour in air

liquid liquid ethanol(aq)—vodka

antifreeze(aq)

liquid solid amalgam—Hg(Au)

solid liquid tea(aq)

solid solid alloys—coins

Be careful with antifreeze . . . Aqueous solutions of ethylene glycol,

CH2(OH)CH2(OH)(aq), akaantifreeze, are coloured fluorescent green. Why?Easy identification of a spill. Antifreeze has a sweet taste and can be

attractive to pets. As little as one teaspoon of antifreeze can be deadly to a cat; similarly for dogs.

Composition of dry air:

78% N2

21% O2

0.9 % Ar

CO2 0.03%

What is the solvent in air?

N2

What governs solubility?Like dissolves

like.Polar dissolves

polar; i.e.Many ionic salts are water soluble due toion-dipole attractions. For non-ionic solutes,

in water, don’t forget possibility ofhydrogen bonding.

Non-polar dissolvesnon-polar.

Important definition:

Miscible refers to liquids that are mutually soluble in any proportion.

eg. Ethanol and water are soluble in any combination.

Water Solubility of Some Ionic Solutes as a Function of

Temperature

Unsaturated, Saturated, Supersaturated Solutions

A saturated solution is formed when no more solute will dissolve in a given amount of solvent, at a certain temperature.

What will happen if additional solute is added to a saturated solution?

The “excess” solute will not dissolve. It will usually sink.

An unsaturated solution can dissolve more solute at a given temperature.

What will you observe if additional solute is added to an unsaturated solution?

It will dissolve.

A supersaturated solution contains more dissolved solute than it is “allowed” to have dissolved at a given temperature.

Let’s do the lab . . .

Homework

Brief, point-form answers to

p 357 – Learning Check 1 to 6

RQs – 1 to 9, 13, 15

Let’s look at an interesting problem . . .

In 1989, the oil tanker Exxon Valdez struck a reef in Prince William sound, Alaska. The accident released 40 million litres of crude oil, eventually covering 26,000 km2 of water.

What was the average depth of the oil slick?

What additional information is required to solve this problem?

Assume average density of crude oil to be 0.86 g/mL; 1 L = (10 cm)3

Exxon Valdez Oil Spill: Calc. average thickness of oil slick:

Voil = 40E06 L

area = 26E03 km2

oil slick as shape of a

rectangular prism:

Volume =

area * thickness

What do we need to do with the units of area and volume, above?

Get consistent units for volume and area:

Voil = 40E06 L ↓ /1000L·m-3

40E03 m3

A = 26,000 km2 * (1000 m)2/km2

= 2.6E10 m2

Volume = A * thickness thickness = V/A

= 40E03 m3/ 2.6E10 m2

= 1.5E-06 m or 1.5E-03 mm is thickness of oil slick.