NATURAL pH INDICATORS
Objectives: To learn how to prepare and use natural pH indicators for the examination of the pH of solutions.
Equipment and reagents:
- red cabbage, hibiscus tea, red onion peel and/or red beets
- a small pot for making decoctions
- 4 glass beakers 250 ml
- Pasteur pipettes (7-10 pcs)
- 9 test tubes
- test tube rack
- vinegar (aqueous 9 % acetic acid solution) or any other acidic solution
- alkaline household cleaner or aqueous NaOH solution
Experimental procedure:
1. Decoction of red cabbage, hibiscus tea, red onion peel – pieces of vegetable material cooked ≈5 minutes in a small amount of water, then allow the decoction to cool without pouring it down!
2. If blueberry juice or red beet is used, no decoction shall be made, but juice diluted in water shall be used.
3. Dilute an alkaline household cleaner in one of the glass jars!
4. Pour equal volumes of prepared decoction into three test tubes!
5. Add table vinegar to the contents of one test tube, dilute alkali to the other, and leave the third for comparison!
6. Observe the colour change!
7. Repeat the experiment with another decoction or berry juice!
8. Create a table independently and mark the observations in it!
9. Conclude the discoloration of plant materials depending on the solution environment!
Precautions:
Acids and bases are chemicals that can easily damage your skin and eyes. The severity of the hazard depends on how strong the chemical is, how long contact is maintained and what actions you take after contact is made. Use personal protective equipment (PPE) as required.
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