Solubility

Today’s class:

SolubilitySaturation

Separation of mixtures

precipitate

unsaturated solution

saturated solution

remaining undissolved solute

Practice solubility / saturated solution

Solubility: Maximum concentration of a solute that can be attained in given solvent.

Saturated Solution:

Contains maximum amount of solute that can be dissolved.

Unsaturated Solution:

More solute can be dissolved in the solution.

Supersaturated Solution:

An extra amount of solute was dissolved; solution “wants” to precipitate some solute

Maximum amount of solute that can be dissolved in a given amount of solvent.

2.65 g of a solute is dissolved in 70.0 mL of water to produce a saturated solution at 20 oC. Calculate the solubility in units of g/100 mL; g/L.

m = 2.65 gv = 70 ml

1.) in g/100ml = % m/v100 mL

= msolute

vsolution

g/100ml = ?

100 mL= 2.65 g

70 ml

100 mL= 2.65 g70 ml

= 3.79 g

The solubility is 3.79 g /100 mL

2.65 g of a solute is dissolved in 70.0 mL of water to produce a saturated solution at 20 oC. Calculate the solubility in units of g/100 mL; g/L.

2.) in g/L c = msolute

vsolutionm = 2.65 gv = 70 mL

c = ? g/L = 0.07 L

= 2.65 g0.07 L

c = 37.9 g/L

The solubility is 37.9 g /L

Example 24.5 g is the maximum amount of a solute that can be dissolved in 200 mL of water at 20 oC. Calculate the solubility in units of g/100 mL; g/L.

Effect of temperature on solubility• How to make a supersaturated solution

For most salts: The warmer the water the more salt dissolves

1.) make a saturated solution at high temperature

2.) let hot, saturated solution cool supersaturated

3.) eventually excess solute will PRECIPATE (form new

crystals)

For most solids solubility increases with temperature

Temperature °C

solubility(g/100 ml of water)

Solubility of gases and temperature

The warmer the water the less Oxygen / CO2

can be dissolved

Air bubbles forming, before the water starts to boil

Solubility of most gases decreases with temperature

When oceans warm up, less CO2 can be dissolved – CO2 is released

Solubility and solvent

salt?

Solubility of a substance depends on the nature of the solvent

• salt is soluble in water

• salt is not soluble in oil

• Substances that are soluble in water are called hydrophilic

• Substances that are soluble in oil are called lipophilic

• Soap has a hydrophilic and a lipophilic part and can help oily substances dissolve in water.

SolubilitySaturation

Separation of mixtures

Separating mixtures

Most substances are not found in their pure form in nature but need to be isolated from a mixture.

Separating solid and liquid- a difference in state of matter

• Filtration

A difference in density I

• Decantation

water

oil

Example:Pouring water off rice / pasta (without using a strainer).

A difference in density II

• Centrifugation Example:Centrifugation of blood samples

Accelerates and improves sorting by density dense material collects at the bottom

A difference in speed of travel

• Chromatography

• Mixture is separated into its components using paper and a solvent.

• The different components of the mixture are transported by the solvent along the paper, but with different speeds.

Isolating a solute - evaporation

The liquid solvent is evaporated, leaving behind the solid solvent

Example:Harvesting of sea salt form the ocean.

A difference in boiling point• Distillation Example:

Distilling wine to make brandy.

Notes on separating mixtures

Homework

• Solubility: work book p. 8 # 4, 5

p. 10 # 9• Separating mixtures p. 12