Teaching Sequence

Work through this resource material in the following sequence:

10 minutes – Part A: Activating Prior Knowledge - Optional
25 minutes – Part B: Where’s the Acid?
20 minutes – Part C: Reflecting on Teaching

Part A: Activating Prior Knowledge - Optional

In this part, we cover some of the basic knowledge necessary for teaching this lesson. If you haven’t taught it before, we recommend using The Power of pH, which deals with this content in more depth. If your students have completed The Power of pH, you may only need a quick refresher.

Step 1.

Start by distributing the Sugar and Dental Health factsheet. Ask students to read the worksheet, particularly around the parts relating to acids and bases, and then formulate three questions relating to the information. For instance, students might ask what the key difference between acids and bases is.

Questions should be easily answerable given the information supplied in the Dental Health Factsheet. Students shouldn’t be trying to trip each other up: this activity is an opportunity to practise communicating science knowledge.

Part B: Where's the Acid?

In this section, students will carry out an experiment to test the pH of sugar. Students will also be looking to verify the accuracy of the information you provide.

Step 1.

Explain to students that the bacteria in your mouth processes sugar and turns it into lactic acid, which can cause tooth decay. Reiterate especially that sugar by itself is not acidic, and explain that you will now run an experiment to verify that claim.

Step 2.

Organise students into groups of three or four, and provide each group with three beakers, each respectively containing:

Water
Sugar solution
Soft drink

If you wanted to extend students here, you could get them to create their own sugar solution, under supervision - it will be important for each sample to have roughly the same strength. Students could also measure out their own amounts of water and soft drink, again with the caveat that each of the three beakers in each group needs to have roughly the same amount of liquid.

Step 3.

Once students are set up with their beakers, they should test the pH of each solution. You may want to use universal solution, litmus strips, red cabbage, or whatever other procedure your school is accustomed to using. Step your students through the typical procedure, and then ask them to check the pH of each solution against a pH chart.

All going well, both the water solution and the sugar solution should come out as pH neutral, around 7, while the soft drink should come out with a low pH, around 2 or 3. You may need to run this experiment beforehand to check the pH of your chosen soft drink: many of them have added acids, which will drastically lower their pH. Running the experiment beforehand will also allow you to know what the pH of your soft drink ought to be, so you can check student results.

Step 4.

At this stage, you can present students with a problem. If the sugar is only turned into an acid by the bacteria in the mouth, why does the soft drink register as acidic? The answer is probably because it has other acids added. Check the ingredients label: often soft drinks include Food Acid 330, which is citric acid (like in lemons), or Food Acid 338, which is phosphoric acid. If your chosen soft drink uses a different acid, you may want to identify it before the class starts.

At this stage, you can explain to students that soft drinks pose a double threat to your teeth: they contain acids, which can cause tooth erosion, and they often have high amounts of added sugar, which are turned into acids by the bacteria in your mouth which can cause tooth decay.

Step 5.

Finish this section by producing samples of lactic acid. You might want one sample to do a demonstration, or, depending on your resources and time, you might want to provide students with their own samples to test, again pending all relevant and sensible lab safety precautions.

Explain to students that lactic acid is produced from sugar by the bacteria in your mouth. It might be a little difficult to model that reaction directly, so you’ll just have to work with the final product. Test the pH of the lactic acid, and see how it compares to the pH of your soft drink.

Step 6.

End this part by encouraging students to review what they have and have not been able to prove.

For instance, they have been able to prove that sugar by itself is not acidic in solution, and that soft drinks often have an acidic pH. However, they have not yet proven that sugar is turned into lactic acid by bacteria in the mouth. That just isn’t an experiment that’s been tested.

You might like to extend students here by asking them how they might go about testing the transformation of sugar into lactic acid. For instance, they might take a mouth swab, put it onto an agar plate, add sugar, and then test the pH at a later time. That might be a viable approach - but it assumes that a mouth swab would pick up the bacteria, which lives on the teeth. Encourage students to offer additional suggestions, and raise problems with the ideas as much as possible, to push students to think through some of the logistical issues of creating an experiment. In particular, emphasise the limits of the findings that would result from any suggested experiment. Often students can make conclusions that are not supported by the scope of an experiment - it’s worth emphasising the limits of any experiment to counteract that tendency.

Part C: Reflecting on Teaching

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 The Power of pH.

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?
What makes a scientific experiment interesting for younger students?

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 make experiments interesting for students. 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.

Teacher Reflection

Take this opportunity to reflect on your own teaching:

What did you learn about your teaching today?
What worked well?
What didn't work so well?
What would you share?
Where to next?
How are you going to get there?

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SugarByHalf - Where's the Acid?

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