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