Science Lesson Plan: Dissolving
An Investigation into Dissolving Substances in Hot and Cold Water
Feb 19, 2008
Science is about discovery and hands-on investigations are always popular with kids in the classroom. This investigation can be done as a class demonstration or in small groups. The advantage of having small groups is that the students get more involved and there are other groups' results to compare with and discuss.
Aim:
- To discover which substances will dissolve in water and which will not
- To find out if substances dissolve better in hot water or cold
- To develop recording, observation and prediction skills
- To learn about fair testing and safety issues
Materials:
- 6 clear beakers
- 6 teaspoons
- Cold water
- Hot / warm water
- 3 different substances (eg: instant coffee, sugar, hot chocolate, jello, etc)
- Measuring jug
- Paper for recording
- pencils
- paper towel for any spillages
Introductory Activity:
Introduce the lesson by talking about the process of dissolving. Ask the students if they know what this means. Provide a simple definition by giving an example, for instance, when we add sugar to a cup of tea. Explain that both water and substances (for example coffee granules) are made up of tiny shapes called molecules and that when added to each other the coffee dissolves. The students may see this as disappearing. When something dissolves in water this is called a solution. When it doesn't dissolve it is called a suspension
Have a discussion about the importance of fair testing so that the results can be compared in a meaningful way. Ask the students if it would be fair or right if different amounts of water were in each beaker or different amounts of the substances were added.
Also talk about any safety issues there may be. Are you using glass beakers? If so then there is a risk of broken glass. If water is spilled what needs to happen?
Activity:
- Have each station ready with all the equipment laid out and ready to use.
- First have the students in each group predict whether they think that any of the powders will dissolve in cold water. Have them write down their predictions.
- The students then measure and pour 150ml (5fl oz) cold water into each of three of the beakers (label these #1, #2 and #3).
- Next have them measure 1 level tsp of coffee powder and sprinkle it into beaker #1 - be careful not to stir!
- The students should make careful observations about what they see in their beaker and record what has happened on their chart.
- Repeat this process with the other two powders.
- Now ask the students to predict what the results will be if they use hot / warm water instead of the cold water.
- Repeat the experiment using warmer water this time labelling the beakers #4, #5 and #6.
- Make sure that each step is observed and recorded.
- Have each group discuss the findings that they recorded with each other and compare their results. Did they all end up with the same results? If not, why not? Were their predictions correct? Do they think the results would be different if they used water at different temperatures or different amount of the powders?
Extension:
- Try this investigation with different powders
- Demonstrate the difference between dissolving and melting. Try using a drop of heated candle wax, dropped into cold water.
- Investigate whether or not all substances need hot water to dissolve
- To help define and illustrate suspension try filtering liquid / solution through filter paper. Corn flour is a good one for this
