What's in a Solution?
It is easy to notice the differences between a solid, a liquid and a gas.
Can you tell the difference between a liquid and a solution? Is there one?
What is the difference between melting and dissolving?
This lesson will help you understand solubility and solutions.
Test your understanding.
Here are some important words. Which do you know something about? Which do you know all about? Which have you never seen before?
dissolve
solution
insoluble
soluble
solute
solvent
saturated
You should check again at the end of the lesson to see what you understand.
Melting and Dissolving
Two students are discussing what happens when a sugar cube is placed in a cup of tea.
One students says that the cube melts in the hot tea. The reason given is that heat melts sugar.
The other student thinks that the process is called dissolving. Sugar will dissolve in cold tea as well as hot.
Which student do you think is right? Give your reasons.
Is it a Solution?
Two beakers are on the table. One contains water, the other cola.
How could you tell which is which?
Two more beakers are on the table. One contains water, the other lemonade that has lost all of its fizz.
How could you tell which is which?
All drinks are mostly water. The differences in appearance are caused by dissolved substance like sugar and caramel. Lemonade and Coca Cola are solutions.
Activity 1 - Making a Solution.
What do you need to make a solution?
Something to dissolve - a solid.
A liquid to dissolve the solid - water.
You can try this at home or school.
Prediction
Students attempt to make solutions of the following solids:
Sugar
Sand
Salt
How successful will they be?
Click here
Another student suggested that a solution could be made using other liquids instead of water.
Can you think of any that you could use?
Water is not very good at removing (dissolving) oil and grease off your clothes. Dry cleaners use a special liquid that is good at dissolving some substances that are insoluble in water.
These smell a lot and are not good for your health.
We will mostly stick to water.
Important Words
Solvent - Any liquid used to make a solution.
Solute - Any substance that dissolves in a liquid (solvent)
Solution - This is what you make when a solvent and solute get together.
solute + solvent = solution
What are the solutes and solvents in the activity?
Activity 2 - I Want My Solid Back!
Plan experiments to separate the solids from the solutions in the last activity.
This will need two different plans as one of the solids is insoluble.
This should be easy but click here if you are not sure.
How much will dissolve?
A beaker of water will not keep dissolving sugar or salt. Put too much sugar in tea and you will be left with undissolved crystals in the bottom of the cup. There is a point at which no more solid will dissolve. The solution is then saturated. This means no more solute will dissolve.
There may be some way of getting more to dissolve.
Which of these do you think will work?
Stirring
Cooling the water
Heating the water
Adding more water
Pouring the water into a larger beaker.
Click here for the answers.
Activity 3 - Dissolving crystals
Students were given a container of blue copper sulphate crystals.
They were asked to investigate how much solid would dissolve at different temperatures.
Write a plan that they could follow. (Check back at planning an investigation if you wish)
These are their results.
Temperature (degrees Celsius)
Mass dissolved (grams)
0
14
10
17
20
21
40
29
60
40
80
55
100
75
Plot a bar chart or line graph of their results
From these results and your graph what do you think the students should conclude about the effect of temperature on how much dissolves?
Activity 4 - Particle in a Solution.
From the previous lessons you saw how particles are arranged in solids and liquids. Try to draw diagrams to show how the solvent and solute particle will be arranged in a sugar solution.
Click here for help.
You should now go back to the beginning of the lesson and make sure you understand all the important words.
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