Lesson 13: Characteristics of Solutions
What do you know about solutions?
A solution is defined as a clear and homogeneous mixture of a solute in a solvent.
Common solutions are: salt and water, alcohol and water, or sugar and water. These mixtures are all clear and homogeneous.
The solute is the substance that dissolves; the solvent is the substance that does the dissolving.
In a mixture of salt and water, the salt is the solute and the water is the solvent.
In a mixture of alcohol and water, the alcohol is the solute and the water is the solvent.
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What do you know about solutes? Some solids when added to water do not dissolve in the water. These solids are said to be insoluble. They are known as insoluble solutes. Both iodine and chalk are insoluble solutes in water. An insoluble solute will settle out of the mixture. Insoluble solutes are usually found at the bottom of the container as a precipitate. Can you see the chalk and the iodine precipitate in the pictures to the right? A mixture containing an insoluble solute is classified as a suspension, not a solution. |
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| calcium carbonate (or chalk) and water |
iodine
and water
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When solids do dissolve in water they are said to be soluble. They are known as soluble solutes. Try saying soluble solutes out loud 10 times as fast as you can! Could you do it without slurring your words?
Substances other than water can be used as solvents. A common solvent other than water is alcohol. There are some solutes that are soluble in water and insoluble in alcohol. And, then there are some solutes that are soluble in alcohol and insoluble in water.
| Examples: | Iodine is insoluble in water but soluble in alcohol |
| (See pictures) | Salt is soluble in water but insoluble in alcohol |
Solutions are often classified as being either saturated, unsaturated or supersaturated. It is important to note that all of these solutions will still be clear and homogeneous.
Saturated solutions have the maximum amount of solute dissolved in them. No more solute can be made to dissolve.
Unsaturated solutions have less than the maximum amount of solute dissolved in them. This means that more solute could be added to the solution and the additional solute would still dissolve.
Supersaturated solutions have more than the maximum amount of solute dissolved in them. This is not normally possible. Not all substances will form supersaturated solutions. If a crystal of the solute is added to a supersaturated solution, precipitation of all of the extra solute will occur. See this!
Search the internet to do more reading about solutions.
Make a saturated solution of salt and water.
Steps:
- put 125 mL of distilled water into a glass or into a beaker
- add a quarter teaspoon of salt to the water and stir until it dissolves.
- add more salt (a quarter of a teaspoon at a time), stir until it dissolves.
- keep adding more salt, small amounts at a time until no more salt will dissolve.
- you should see a few extra grains of salt at the bottom of your glass or beaker. If your salt is very fine grind salt then maybe your mixture will look cloudy
- cover this mixture and let it stand overnight.
- did the few extra grains of salt dissolve overnight? If so, add a bit more salt and let it stand covered overnight to see if the extra salt dissolves.
When the few extra grains do not dissolve overnight, you have made a saturated solution.
But, if you notice that more salt is on the bottom of the container add a bit more water (like about 1 tablespoon of distilled water) and stir to see if the extra salt dissolves. If you add too much water you will have to continue adding salt. You want to make a saturated solution.
In your kitchen, try to dissolve the following substances in water. Record whether they are insoluble or soluble. Arrange your data in a table.
1. salt
2. sugar
3. baking soda
4. baking powder
Assignment results:
Soluble solutes:
- salt
- sugar
- baking soda
- baking powder
- vinegar
- vanilla extract
- dishwashing liquid
- hand lotion
Insoluble solutes:
- vegetable oil
- vaseline
5. vinegar
6. vanilla extract
7. vegetable oil
8. dishwashing liquid
9. vaseline
10. hand lotion
Prepare to share or submit your data table.
Share your results with another classmate. Determine whether the two of you saw the same results. For any differing cases, do a retest. Record your result.
Write a conclusion in which you list all of the soluble solutes followed by the insoluble ones.
Hand in your conclusion to your teacher either on paper or on line.
You will be given a score out of 10 based upon the accuracy of your results.