How to make indicator strips at home in just 1 hour

Reagents and equipment: 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 hot water, 9% vinegar, water, 10% baking soda solution, drain cleaner (usually a 10% solution of sodium hydroxide).
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.
Red cabbage contains pigments known as anthocyanins. Anthocyanins can also be found in many fruits 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.
Safety precautions: Observe safety measures when working with heating equipment and hot liquids. When working with household chemicals, wear protective gloves, eyewear, and a mask.