Week beginning 08.06.20
For this challenge I would like you to test different liquids and record your findings in a table. They don't have ot be the same liquids I have put down on the table below - these are just examples. Remember - if a liquid has a strong colour then the PH indicator may turn that colour and it will not be a true reflection of the acidity of the liquid!
| Liquid type | Colour of the indicator strip | Acid, neutral or base |
| Vinegar | ||
| Egg white | ||
| Orange juice | ||
| Water | ||
| Milk |
Reagents and equipment
This was the equipment listed on the website - watch the video first though, you may not need all this and you could improve some. For example, when putting the solution on the filter paper you could use a paintbrush rather than a pipette.
- 300 g red cabbage;
- 1 heat-resistant glass;
- 1 coffee filter;
- 1 pipette;
- cotton wool;
- a funnel;
- a cup;
- a knife;
- a cutting board;
- 250 mL freshly-boiled water;
- 9% vinegar;
- water;
- 10% baking soda solution;
- drain cleaner (usually a 10% solution of sodium hydroxide).
Step-by-step instructions
Dice 300 g red cabbage. Transfer the cabbage to your heat-resistant glass and add 250 mL hot water. Let stand 30 minutes. Drain the solution into the second glass through the funnel with cotton wool to filter out the cabbage slices. Use the pipette to apply the solution to the coffee filter, then let the filter dry at room temperature for 30 minutes. Cut into strips. Calibrate using reagents you likely have on hand: vinegar creates an acidic medium, which turns the strip red; water creates a neutral medium, so the strip stays purple; the 10% baking soda solution creates a basic environment, which causes the stip to turn blue; drain cleaner (usually a 10% solution of sodium hydroxide) creates a strongly basic medium, which turns the strip first green, then yellow.
Process description
Red cabbage contains pigments known as anthocyanins. Anthocyanins can also be found in many fruits, vegetables, and berries, such as blueberries, red grapes, red onions, and so on. They change colors in accordance with the acidity of their environment – a property that can help you determine the pH of various substances around you! They turn red in acidic mediums such as vinegar, purple in weakly acidic and neutral mediums such as water, blue in weakly basic mediums such as a solution of baking soda, and green, then yellow in strongly basic solutions such as drain cleaner.
