Concentration II

Factors Affecting ItChapter 12

Unit 10

Solubility

Soluble / Insoluble:Ability of a solute to be dissolved in a solvent.

In reality, everything is slightly soluble.Atoms & molecules are so small (and there are so many of them), that a tiny amount will always dissolve even with insoluble substances.

Solubility of Liquids

Miscible / Immiscible:For Liquids, describes ability to mix“Like Dissolves Like”Hydrophilic & hydrophobice.g. Oil and water are immiscible.Remember, ionic & compounds with hydrogen-bonding are hydrophilic.Must have the same polarity!

Effects of T

Solubility generally increases with temperature.

Solubility of gases in liquids decreases with increasing temperature.

Effects of P

Little effect on condensed phases (solids & liquids)

Great effect on solubility of gases. Henry’s Law: P = kHC The amount of gas that can be

dissolved is directly proportional to the pressure of the gas above the solution.

P1/C1 = P2/C2

Henry’s Law in Action

Very little CO2 dissolves in 100 g H2O at 20 °C & normal pressures (PCO2~ 39 Pa)

A can of soda is pressurized with about 3 atm (300,000 Pa) of CO2.

0.45 g CO2 will dissolve in 100 g H2O at that pressure.

When you open a soda, the pressure drops and the CO2 comes bubbling out!

Describing Concentration

Dilute: (adj) A solution containing a low amount of solute.

Dilute: (v) To decrease the concentration.

Concentrated: A solution containing a high amount of solute.

Describing Concentration II

Unsaturated: A solution that can dissolve more of the solute.

Saturated: A solution that cannot dissolve any more of the solute.

A saturated solution will have some visible solute on the bottom of the container.

Describing Concentration III

Supersaturated: A solution that holds more than the maximum amount of solute.

Most often by heating a solution to dissolve excess solute, then carefully cooling.

Must be extremely clean & still. Impurities & agitation can cause the excess

solute to fall out of solution (quickly).

Dissociation

When ionic compounds dissolve in water, they dissociate into ions. Ions can conduct electricity. Called Electrolytes

Nonionic substances cannot dissociate. Do not conduct electricity Called Nonelectrolytes

Making Solutions

Volumes are not additive! 50 mL H2O + 50 mL Ethanol ≠ 100 mL In order to make solutions:1. Add solute to small amount of solvent 2. Stir to dissolve.3. Add additional solvent until the total

volume reaches the desired level.

T (°C)

g s

olu

te p

er

10

0 g

H2O

• Concentrations (g/100g H2O) under the line are considered unsaturated.

• Solutions with concentrations on the line are saturated.

• Solutions that have been carefully prepared to have concentrations above the line are supersaturated.