Hello, today was looked at our lovely germ samples. I hope the children realized that what appears to be "nothing" actually harbors lots of germs. Attached is a photo of our collection of petri dishes and a close-up of some of them.

We also did an experiment with goldenrod paper for acids and bases. I let each child take a piece home because it's very difficult to find now that almost all paper sold now is acid-free. I told them to keep it for further experimentation at home. Here are some experiments they can do with this "acidic" paper that behaves very unusually when exposed to bases.

1. Place the paper on a table.
   
2. Place a drop of water on one of the corners of the paper. Does anything happen?
3. Fill a jar with a small amount of ammonia water. Dip a cotton ball in the ammonia water and wipe it across the top portion of the Goldenrod Paper. Save the bottom half of the paper for step 5. Does anything happen?
4. As you continue to wipe designs on the Goldenrod Paper, notice that the paper does not stay red forever. What is causing the paper to change back to yellow?
5. Use a wax candle to write a secret message (such as “Hi!” or “WOW”) across the bottom half of the paper.
6. Wipe the cotton ball with ammonia water across the secret message to see what develops.

During class we did this:

1. Place the paper on a clean, dry surface.
2. Away from the paper, spray your hand with the ammonia-water solution (if you don't have ammonia, try to find a cleaner with ammonia in it like Windex)
   
3. Gently slap your hand down on the paper... oh no! It's a bleeding handprint!
4. Your audience won't believe their eyes when you hold up the paper, dripping with your "bloody" handprint.
5. Wash your hands right away.
   

How does it work?

The ammonia on the cotton ball is a base and causes the dye in the special Goldenrod Paper to change color. You probably noticed that the red color fades over time and the paper eventually changes back to its original yellow color. Why? The carbon dioxide gas that is in the air we breathe is slightly on the acidic side of the pH scale. The carbon dioxide reacts with the ammonia on the paper to produce ammonium carbonate, which changes the pH of the paper to neutral (roughly a pH of 7) and the dye changes back to yellow. If you use a stronger base like washing soda, the red message will not disappear with just the carbon dioxide in the air. You will need to use a stronger acid like lemon juice or vinegar to change it from red to yellow. You can also use Goldenrod Paper as inexpensive pH paper to classify safe household products as being either acidic or basic.

Try all sorts of different household solutions to determine whether it is acidic (will not change), neutral (will not change) or alkaline (basic, will change).

The last experiment you can do is to dissolve baking soda in water and write a message. This time, the message will not disappear by itself. Ask the children what you could do to make it yellow again and I hope they will tell you that they need to put something acidic on it like vinegar or lemon juice.

You can change the yellow goldenrod paper into red goldenrod paper by soaking the yellow paper in a weak solution of a base, such as baking soda, and allowing it to dry. Then, you can try the hand slap experiment by putting an acidic solution on your hand instead of a basic solution and see what happens!

Here's how you could try making your own color changing paper:

Make color-changing paper similar to goldenrod paper using household tumeric powder. Although tumeric is insoluble in water, we discovered it was soluble in either ammonia or ethyl alcohol. White paper dipped in a solution of ammonia with dissolved tumeric will be dyed red which turns to yellow as the paper dries; dipped in a solution of tumeric and alcohol, the paper will remain yellow as it dries. When dry, test and observe how similar and how different the paper is from the color-changing goldenrod. Note: although this paper seems to react similar to color-changing goldenrod, the color fades much faster.

Here is some basic info on acids/bases:

For thousands of years, people have known that vinegar, lemon juice and other similar foods had a sour taste. However, it has only been in the last few hundred years that mankind has understood what makes these things taste sour. These foods taste sour, because they are acids.

The term acid, comes from the Latin word acere, which actually means sour.

In the seventeenth century, an Irish chemist named Robert Boyle first labeled substances as either acids or bases. Boyle said that:

acids taste sour, are corrosive to metals, and change litmus paper red. Strong acids can badly burn you.

bases feel slippery, and change litmus blue. Solutions containing bases are also called alkaline. Strong bases can also badly burn you.

While Boyle was able to classify acids and bases into two separate groups, he was never able to explain why these substances behave the way they do.

It was not until 200 years later that scientists began to understand why acids and bases behave the way they do. In the late 1800s, a Swedish scientist named Svante Arrhenius proposed that acids dissolve in water releasing hydrogen ions while bases dissolve in water releasing hydroxide ions. This theory helped scientists understand why many different acids were similar to one another, and why many different bases were similar to one another.

Hydrogen ions contain one hydrogen atom, while hydroxide ions contain an oxygen atom, and a hydrogen atom. When acids and bases are mixed, these ions combine forming water.

The single hydrogen atom combines with the oxygen and hydrogen atom making two hydrogen atoms, and one oxygen atom, or H2O. This process is called neutralization (both salt and water are formed). When this happens both the acids and the bases become weaker, because they have been neutralized.

In 1909, the Danish biochemist Sören Sörensen invented the pH scale for measuring acidity. The pH scale ranges from 0 to 14. Substances with a pH greater than 7 and up to 14 are bases. Substances in the middle, at pH = 7, are neutral substances, for example, pure water.

One important note! Although strong acids and strong bases can be weakened when mixed together (neutralization), the same does not apply to two of the same type!! For example, ammonia and bleach (two strong bases) mixed together can be toxic. Tell your children never to mix liquids without knowing what they are doing!

We will continue with more acid/base fun next week.