High School (hard)

Experiment 2 –  pH measurement with plants

Danger level: Medium, corrosive substances (muriatic acid, vinegar and ammonia).

Measuring the pH (acidity) of a substance is important in many areas, from medical issues to food production. It also serves to determine whether a product is fermented, or to measure the quality of a wine. Today there are expensive devices that are used to very accurately measure the pH of a substance, but not everyone has the opportunity to buy such equipment.

In the countryside, farmers are usually able to estimate the pH of a soil by the color of some plants. Thus, estimate the acidity of the soil can be done quickly and without a comprehensive analysis, which is essential when it comes to know the time to sow plants. Furthermore, connoisseurs can recognize a good wine from observing its color. Thus, without knowing it, they determine the acidity that each wine has without need to taste it. Could a pH measurer be done using the techniques that farmers and wine tasters have developed?

In this experiment we will show you how to make a pH meter with different plants. You can test by yourself with some others that you think will work. Have fun!

Material:

• Several transparent cups
• dropper
• white vinegar
• 10 lemons
• 50g of white lime
• cleaning liquid ammonia (or pure ammonia)
• muriatic acid
• 100g of Jamaica flowers
• 1 red cabbage
• 1 beetroot
• 4 carrots
• 20 flowers of bougainvillea
• 1 blade
• 7 glass jars with lids
• foil
• sticky labels

Procedure:

1. Put the lime in a glass jar, add water, stir and cover the jar.
2. Prepare juice with the lemons, put in a glass jar and cover.
3. Cut  carrots, beets and cabbage into small pieces (but not so small).
4. Place flowers in vases and pieces of beetroot, carrots and cabbage separately. In each glass it should only be one type of plant.
5. Add water in a bowl and put it to the fire until it boils. Add boiling water to all jars with the chopped vegetables and flowers.
   Cool the extracts (what you’re doing are plant infusions).
6. Strain each of the extracts with a coffee filter or fine cloth. Pour each of the different liquids in a bottle.
7. Cover the jars, wrap in foil and store labeled solutions in the refrigerator.
8. Take the extracts from the refrigerator 30 minutes before the next part of the experiment.
9. Place some of each solution of the extracts in 5 different cups and label them.
10. In one of the glasses add 5 drops of lemon juice. Tag and observe.
11. Do the same separately with: vinegar, muriatic acid, white lime solution and cleaner with ammonia.
12. Put the glasses in a line with solutions and drops. Compare a solution that was not added with the rest. For example, you have 6 glasses with jamaica, one with muriatic acid, another with lemon, another with vinegar, one with lime, one with ammonia and one that has nothing more than jamaica. Compare the latter with others.
13. Finally, analyze the extracts to see which gives better color changes.

Questions:

Which of the extracts works best as pH meter?

How could you make a pH scale with your solutions?

What other plants do you think that could serve as indicators of pH?

Experiment 1 – Invisible Ink

Danger level: Medium: Toxic Substances

Throughout history, secret information has been transmitted. There are several ways to make invisible ink. Some need heat to display messages, others require a specific type of light, some use a magnetic field… Well, there are many types of “invisible” ink.

Here we will show you a way that needs moisture to make the message visible .

Note: The substance that we use for this experiment is poisonous. You should not ingest or put it near your mouth at any time.

Material:

• A sheet of bond paper (where you’ll write your message).
• A fine paintbrush
• A glass bottle
• Water
• 10g Cobalt chloride (CoCl2)
• sprayer

Procedure:

1. Fill the glass jar with water and add 10 grams of CoCl2. Mix until the water looks evenly red.
2. Wet the brush with a bit of ink you just made and write a message in the paper.
3. Let the sheet dry completely. If you still see a bit of red text, you need to add more water to the ink, for it is a highly concentrated solution. If this is the case, repeat step 2.
4. Fill the sprayer with water.
5. To see your text in red again, spray slighty the sheet where you’ve written the text.
6. Have fun sending hidden messages to your friends

Once you have stopped using the ink, clean the bottle you used. It could be dangerous for someone to drink.

Questions:

What happens if you saturate the mixture?
If your mixture is saturated, what color is the text when the leaf is dry?
How do you think you could use this material? What could you measure?
Do you know other invisible inks? If not, research.