Teaching Sequence

Work through this resource material in the following sequence:

20 minutes – Part A: Sugar in Solution
30 minutes – Part B: Restoring Your Teeth
15 minutes – Part C: Reflecting on Learning

Part A: Sugar in Solution

This part begins with a short experiment to start students thinking about how solids can dissolve in water or other liquids. Depending on the time available to you, and your resources, you may wish to demonstrate this experiment yourself, or to run it as a class experiment where students can carry it out in groups.

If you do choose to have your students carry this experiment out themselves, please observe all relevant and sensible lab safety procedures. Students will be dealing with boiling water, which may cause grief if improperly handled.

Step 1.

Boil a jug of water, and put the boiling water into a clear beaker - anything up to 500mL should be sufficient. Ask students for predictions on what might happen to the cube once it is added to the water.

Step 2.

Add the sugar cube to the beaker, and observe the results. All going well, it ought to partially dissolve in the hot water. You may subsequently wish to stir it to help it dissolve completely.

Extension: To make this experiment slightly more complex, you might have multiple beakers at different temperatures. For instance, you might have one beaker of water at room temperature, one beaker of boiling water, and one of chilled water. This diversity would allow you to make further observations with your students - for instance, you could compare how the sugar behaves differently under different circumstances. It would be useful to be able to refer back to that observation later in the lesson, when you’re teaching about how different amounts of acid in the mouth cause different speeds of demineralisation (which is when acid in your mouth causes tooth erosion).

If you decide to use multiple beakers at different temperatures, some further preparation may be necessary before the class. For instance, if you want all students to complete their own individual experiments, you may need to chill large quantities of water, so there’s enough to go around, and prepare a standing body of water to sit at room temperature. The quantities here may also depend on the number of groups you want to have, so that each group can have the same amount of water in each beaker.

Step 3.

Once the cube is dissolved, ask students how you could get the sugar back again. The best method is to evaporate the water - you could do this over heat, if you have the time and the inclination, although demonstrating the procedure here is probably not crucial right now. The key point is to get students thinking through how to reverse that process of dissolving a substance.

Part B: Restoring Your Teeth

Step 1.

Pose the following situation to students. We know that bacterial acid can damage our teeth, ultimately causing tooth decay. When that happens, there’s a process of dissolving, not totally unlike what happened with the sugar cube. Here’s the question: if acid has damaged our teeth, what can we do to reverse that damage? What can we do to get the tooth minerals out of the saliva in our mouth and back into the teeth to restore what was lost?

Ask students to split into groups and brainstorm some possible solutions. The actual answer is quite technical, and it’s unlikely that students will identify it off their own bat. However, if they are struggling to come up with anything at all, start them off thinking about different ways of separating substances from each other.

For instance, some extraction techniques might include filtration through filter paper, evaporation by boiling, or evaporation over time by leaving a liquid in the sun. You could also use a centrifuge, which is how we separate milk and cream - obviously not a case of solids in solution, but possibly useful nonetheless as a way of thinking about techniques for separating out substances. A similar thing happens with washing machines, which end with a spin cycle that wrings most of the water out of your clothes. You could also mention electrolysis, which (for example) can be used to separate water into hydrogen and oxygen, or some sort of precipitation where you introduce a bonding substance to create a precipitate, take it out of the water, and then use a second reaction to separate the two components out again and retrieve your original substance.

There are a whole range of tricks and techniques for separating substances, meaning you can extend or shorten this part of the lesson in any way you like. It could be an opportunity to link back to previous learning, if you have dealt with filtration or any kind of separation of substances in previous classes. You could run further experiments with students, to explore these different types of extraction procedures, or send them on a research mission, to class textbooks (if you have those), or online.

Note: If your students are researching separation techniques online, make sure that they aren’t just looking up the answer on how tooth enamel is remineralised.

Step 2.

Once students have explored a string of different separation techniques, ask them to make suggestions about the most likely approach for tooth remineralisation. At the very least, they should be able to exclude some of the unlikely approaches - obviously remineralisation doesn’t involve centrifugal force, for instance.

Step 3.

At this stage, you can explain how remineralisation actually takes place. When you’re eating, the bacteria in your teeth will produce lactic acid from the sugars you consume. After you stop eating, over time, the saliva in your mouth washes the acid away, meaning you’re left with a supersaturated solution. To demonstrate a supersaturated solution to students, you might take one of your beakers of water, and dump an excessive amount of sugar into it. The water will obviously not be able to dissolve all of the sugar: some will remain in crystal form. That’s essentially what’s happening in your mouth - it’s not about getting the molecules out of the solution, it’s that once the acid is removed, there are too many molecules to be properly dissolved. That imbalance allows remineralisation to take place.

Step 4.

Display the image below (for projection on a screen or printing), as a guide to help you discuss remineralisation. This image is of a Stephan Curve, showing the pH of your mouth (typically neutral at around 7.4), and the danger point of 5.5 pH. When the mouth has a pH below 5.5, teeth will begin to demineralise. Once you stop eating, mouth pH returns to normal, and your teeth begin to remineralise.

Part C: Reflecting on Learning

In this part, students reflect on the teaching in this lesson and think about how they could utilise different techniques for teaching and communicating science to other people. If you are doing the final lesson in this unit, Communicating the Science of Tooth Decay, this reflection can serve as some of the background thinking for when students design their own teaching material. It follows on from the similar thinking done in previous lessons.

Step 1.

Students should begin by listing the components of the lesson so far. You might want to prompt them through some of this work, or draw their attention to aspects that they might otherwise overlook.

Step 2.

Once they have listed the components of the lesson, students should describe their reactions to the different parts. There is space for this work on the worksheet. Also provide students with these guiding questions:

Which parts of the lesson do you feel you learnt the most from? Why?
Which parts of the lesson do you feel you learnt the least from? Why?
Which activities do you think would be the best for younger students?
Did the information in the lesson make you want to change your behaviour in any way? Why or why not?

To support students in their thinking, you might like to share some of your own teaching strategies and experience. This time, we recommend you focus particularly on how to use learning to encourage personal change. No doubt students will have their own ideas, but you have an opportunity here to share your broader knowledge around creating interesting and engaging lessons for students.

Step 3.

Ask students to get into pairs and explain their answers to each other. Encourage them to reflect critically on their experiences and the differences or similarities between their personal responses and the wider responses of the wider class. Science communication is often about communicating with broad groups of people, and one person’s individual preferences might not reflect the best approach for a wider audience.

Step 4 (optional).

If your students are doing Communicating the Science of Tooth Decay, make sure that they retain their learnings and thoughts from this exercise - for instance, by putting their worksheets into a folder or binder somewhere. These learnings will be useful when students come to design their own teaching material in that lesson.

SugarByHalf - The Solution to Tooth Decay

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