Understanding Acids & Bases- Making your own indicator

Surekha Waldia
2 hours/ weekend project
Array, Array
Remember, Understand, Application

1. Make students understand that Acids are solutions that lose hydrogen ions and usually taste sour. Bases are solutions that pull hydrogen ions out of solution and onto themselves, "accepting" them, and usually feel slippery.2. To tell if something is an acid or a base, you can use a chemical called an indicator. An indicator changes color when it encounters an acid or base. 3.Indicators can be extracted from many different sources, including the pigment of many plants. In our case its red cabbage.
This activity will help students visualize how pH scale is used to measure the amount of H+ ions in a solution. Acids have a pH below 7; bases have a pH above. Strong acids have the lowest pH levels (0-4) and strong bases have the highest pH levels (10-14). Neutral solutions have a pH of 7 and they are neither acidic nor basic. Distilled water is neutral, because the H+ and OH- ions are balanced.
red cabbage
water to boil
household materials to test their pH

Make your own cabbage indicator

  • make your own pH indicator–use a blender to mix one part chopped red cabbage with two parts boiling water and use the juice to test different solutions.
  • Cook the mixture over medium heat, long enough for the water to absorb the purple pigment from the cabbage (approximately 15 minutes).
  • Strain the cabbage, reserving the liquid.
  • Acids will turn the pigments in the indicator to a reddish color; bases will turn the pigments bluish or yellow-green.
  • Consider testing:
    • Bleach
    • Cola
    • Orange Juice
    • Pickle Juice
    • Salt
    • Shampoo
    • Tomato Sauce
    • Window Cleaner
    • Turmeric powder

    Just add a dropper full of the household substances you’ve chosen to a small amount of cabbage indicator and see what happens

    Information to share with students  

1.red cabbage contains a chemical called anthocyanin that changes color depending on the acidity of its environment. In an acidic environment it is reddish-pink, in a neutral environment it is purple, and in a basic (or alkaline) environment it turns bluish-green and even yellow

Reference Links for this activity: https://www.scientificamerican.com/article/bring-science-home-cabbage-chemistry/

1. Rain water conducts electricity but distilled water does not. Why?
2. Why do acids not show acidic behavior in the absence of water?
Accurate, Clearly explained, Complete, Knowledgeable, Methodical, Precise, Informative, Satisfying

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