TuesdayMarch 22, 2011

(Solubility)

Bell RingerTuesday, 3-22-11

What is occurring at the molecular level when no

more solute will dissolve in a certain

amount of solvent at a given temperature?

Bell RingerTuesday, 3-22-11The number of molecules

leaving crystals of the solute equals the

number of molecules returning and sticking

to the crystals.dissolution = crystallization

Announcements

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Six-Week’s Assignment List Date Issued Date Due

WS - The Kinetic Molecular Theory and Nature of Gases 2/24 3/3

Quiz – Pressure Unit Conversions 3/3 3/3

WS – The Gas Laws 3/3 3/10

WS – Dalton’s Law of Partial Pressures 3/7 3/14

WS – Practice Working with Gases 3/9 3/23

WS - Solubility 3/21 3/28

CompleteWorksheet

Solubility

Solubility• If more water is added

to the saturated solution, then more sodium chloride will dissolve in it.

• At 20°C, 35.9 g of NaCl is the maximum amount that will dissolve in 100 mL of water.

• A solution that contains less solute than a saturated solution under the existing conditions is an unsaturated solution.

Solubility• When a saturated solution of a solute

whose solubility increases with temperature is cooled, the excess solute usually comes out of solution, leaving the solution saturated at the lower temperature.

• But sometimes, if the solution is left to cool undisturbed, the excess solute does not separate and a supersaturated solution is produced.

Solubility• A supersaturated solution is a

solution that contains more dissolved solute than a saturated solution contains under the same conditions.

• A supersaturated solution may remain unchanged for a long time if it is not disturbed, but once crystals begin to form, the process continues until equilibrium is reestablished at the lower temperature.

Solubility• The solubility of a substance is the

amount of that substance required to form a saturated solution with a specific amount of solvent at a specified temperature.

–Ex) the solubility of sugar is 204 g/100 g of water (at 20.°C.)

• The temperature must be specified because solubility varies with temperature.

–For gases, the pressure must also be specified.

Solubility• Solubility values can be found in

chemical handbooks and are usually given as grams of solute per 100. g of solvent or per 100. mL of solvent at a given temperature.• The rate at which a solid

dissolves is unrelated to solubility - the maximum amount of solute that dissolves and reaches equilibrium is always the same under the same conditions.

Solubility