Mouthwash Experiments

mouth image by JASON WINTER from

Mouthwash is an oral solution that contains a combination of astringents, antiseptics and breath-freshening ingredients. Consumers use the oral solutions, along with brushing and flossing, to kill bacteria in their mouths and freshen their breath. If you are looking for a fun science experiment using mouthwash, you can determine which commercial mouthwash kills the most bacteria, find the ethanol content in commercial mouthwashes or create your own mouthwash.

Bacteria Experiment

To conduct an experiment to determine which commercial mouthwash kills the most bacteria, you need the following supplies: a cool cup of sterilised water, a bowl, four test tubes, a sterile eyedropper, three types of mouthwash, and four petri dishes. Place several drops of mouthwash in each of the test tubes. Leave the fourth tube empty. Put the cup of water in your mouth and swish it about. After a minute or so, spit the water into your bowl. The water in the bowl now contains the bacteria that was previously in your mouth. Using the eyedroppers take a small sample of the bacteria water and squirt it into each of the four test tubes. Wait five minutes. Remove the mouthwash/water mixture from the test tubes and spread it on a petri dish. Store the dishes upside down for 24 hours. At the end of the 24-hour period check the plates to see how many bacteria colonies have grown.

Ethanol Content

You can compare the amount of ethanol in commercial mouthwashes by using a gas chromatograph. A chromatograph separates the ingredients in a sample and provides a visual representation that shows the percentage of each component in the sample. To conduct this experiment you need: mouthwashes, 99 per cent ethanol, distilled water, 100ml flasks, pipettes and a gas chromatograph. Begin by preparing your four ethanol samples. The amount ethanol is gradually increased in each flask: the first sample contains 5 per cent ethanol, the second contains 10 per cent, the third contains 20 per cent and the last flask contains 30 per cent. Add as much water is necessary for the liquid in the flask to reach the 100ml mark. Inject 5ml of each sample to the chromatograph to be analysed. Follow by injecting the mouthwash into the chromatograph for analysing. Compare the results of the mouthwash with the results of the ethanol solutions to determine the percentages of alcohol in each mouthwash.

Creating a New Mouthwash

Create an eco-friendly mouthwash that freshens your breath, tastes good and doesn't contain alcohol. For this experiment you will need a variety of ingredients which can include: distilled water, baking soda, 3 per cent hydrogen peroxide, lemon juice, sage, thyme, rosemary and assorted mint leaves. You can also use essential oils like peppermint, spearmint and clove. The basic procedure is the same regardless of the ingredients you use. Boil water, add your fresh herbs or other ingredients, allow the mixture to cool and pour into separate bottles. If you use fresh herbs in your mouthwash recipe, strain them out before you begin the bottling process. Set up a "taste test" to determine which of the mouthwashes tastes the best.

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