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7-2: Concentration and Solubility
8th Grade Physical Sciences
7-2: Concentration and Solubility
Concentration • Concentration is a
measure of how much of a solute is in a solvent – i.e.: how much salt is in the water.
• Maple syrup starts as a dilute solution, when the water is evaporated, it becomes a concentrated solution – syrup!
7-2: Concentration and Solubility
Concentration • A concentrated solution has
a lot of solute dissolved in a certain amount of solvent.
• Concentrated fruit juices remove the solvent (water), leaving a lot of solute (sugars) in a small amount of solvent (water).
• “Just add water”
7-2: Concentration and Solubility
Concentration • A dilute solution only has a
little solute dissolved in a certain amount of solvent.
• If you add too much solvent (water) to the concentrated fruit juice, it becomes diluted and tastes watery.
• “Don’t add too much water”
7-2: Concentration and Solubility
Measuring Concentration
• To measure concentration, you compare the amount of solute to the total amount of the solution.
7-2: Concentration and Solubility
Measuring Concentration
• Example: 100 kg of maple tree sap has about 1 kg of sugar in it.
• The concentration is therefore: 1 kg/100 kg X 100% = 1%
7-2: Concentration and Solubility
Measuring Concentration
• After boiling the water away, maple syrup still has about 1 kg of sugar in it, but there is only 2 kg of the solution remaining.
• The concentration is therefore: 1 kg/2 kg X 100% = 50%
7-2: Concentration and Solubility
Solubility
• Solubility is a measure of how much of a solute can dissolve in a solvent – at a given temperature.
7-2: Concentration and Solubility
Solubility
• If you add solute and it dissolves, you have an unsaturated solution.
• When it no longer dissolves and just sinks to the bottom, it is called saturated.
7-2: Concentration and Solubility
Solubility
• When air is saturated with water, fog or clouds form.
7-2: Concentration and Solubility
Solubility • Too much sugar in
ice tea will cause sugar to build up at the bottom.
• The ice tea would be “saturated” with sugar.
7-2: Concentration and Solubility
How Do We Measure Solubility?
• To measure solubility, we just add a solute until it no longer dissolves.
• The amount added is the solubility.
• For sugar, 180g can be dissolved in 100g of water at 0˚C.
• That is more sugar than water!!!
7-2: Concentration and Solubility
How Do We Measure Solubility?
• Using a table of solubility, you could do an experiment to find out whether you have salt or sugar.
• Just measure the solubility and you will know which one you
have.
7-2: Concentration and Solubility
What Affects Solubility?
• Three things affect solubility:
1. Pressure
2. Temperature
3. Type of solvent
7-2: Concentration and Solubility
What Affects Solubility?
• Increasing pressure increases the solubility of a gases.
• When soda water is made, they put it under high pressure with CO2 gas.
• When you open the soda, the pressure drops and the gas comes out as bubbles.
Question? How does this affect scuba divers?
7-2: Concentration and Solubility
What Affects Solubility?
• Increasing temperature increases the solubility of solids in liquids.
• Warm water dissolves more sugar than cold water.
• BUT increasing temperature decreases the solubility of gases in liquids.
• Warm soda is flat – less fizzy than cold soda.
7-2: Concentration and Solubility
What Affects Solubility?
• Solvents affect solubility.
• Some solutes will not dissolve in water – like oil.
• The rule is like dissolves like, meaning…
1. Polar solutes will be dissolved by polar solvents.
2. Nonpolar solutes will be dissolved by nonpolar solvents.
7-2: Concentration and Solubility
What Affects Solubility?
• So oil based paints (nonpolar) can’t be cleaned with water (polar).
• You must use turpentine (nonpolar).
• Latex paint (polar) must be cleaned with water (polar).
7-2: Concentration and Solubility
Supersaturated Solutions
• Sometimes we can create a solution where more solute is dissolved than should be allowed – this is called a supersaturated solution.
• Adding even a small amount of undissolved solute will cause a chain reaction – and the extra solute will come out of the solution.
teacher folder
7-2: Concentration and Solubility Summary
• Concentrated solutions have a lot of solute dissolved.
• Dilute solutions have a little solute dissolved. • Temperature, pressure, and solvents affect how
much of a solute can dissolve. • If no more solute can dissolve, it is called a
saturated solution. • Supersaturated solutions have more than they
should have in them – and the smallest particle added can cause the extra solute to come out of the solution.
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