Biology: What are bones made of?

Over the last 2 weeks we have been investigating bones. We tested the effects of heat and acidic solutions on chicken bones. After placing bones in the oven, the kids observed that they became more brittle. On the other hand, bones soaking in vinegar lose their rigidity and become flexible. What do these two experiments demonstrate about the main components of bone? Bone is made up of collagen, a protein that gives bones flexibility, and calcium phosphate, a mineral that gives bone its strength. Heat destroys the protein, and vinegar dissolves the calcium phosphate through an acid-base reaction.

After these experiments, we reviewed the bones in the human skeleton and then did some comparative anatomy as we tried to identify various animal bones.

Biology: Acids and Bases

This week we started a new topic:  acids and bases.  First we used litmus paper and pH paper to classify different household liquids.  Then we boiled up some purple cabbage. Cabbage broth has the interesting property of indicating for acids and bases.

The kids added cabbage juice to the different liquids and observed the results. They recorded the color changes and using the pH values, ordered the cups according to where they fall on the scale. They observed that cabbage juice indicates strong acids with pinks, weak acids with purples, neutrals with blues, weak bases with greens, and strong bases with yellows. Finally they were given an unknown liquid, and using their cabbage-pH scale they guessed its pH.

I

Biology: Which toothpaste works best?

This week we wrapped up our unit on acids and bases by testing which toothpaste works best. The bacteria in your mouth need food to live and multiply. When you eat sugary foods and other carbohydrates, the bacteria use them as food, too. Bacteria in your mouth turn the sugars in these foods into acids that can dissolve tooth enamel (the outer layer of the tooth). Brushing your teeth can help by getting rid of the sugar, but it also functions to reduce the acid-attack on your teeth.

Using chalk to represent teeth (chalk is made of calcium carbonate which is chemically similar to teeth), the kids tested each toothpaste as follows: They set up 4 test tubes, each one with some vinegar, a piece of chalk, and some dissolved toothpaste from one of the brands being tested. Immediately after combining these materials, a balloon was placed over the opening of each test tube. Without toothpaste protection, the balloon inflated as a result of the carbon dioxide produced by the acid-base reaction. Therefore we concluded that the toothpaste that resulted in the least-inflated balloon was the MOST effective.

General Science: Plop plop fizz fizz...

This week we wrapped up our unit on acids and bases by comparing the strengths of three different brands of antacids: Tums, Gaviscon, and Rennie. We began by talking about the role hydrochloric acid plays in the stomach and how antacids treat indigestion by neutralizing this acid when it backs up up into your esophagus.

To test which brand works best the kids ground up each antacid pill into a fine powder, dissolved it in warm water, and then added it to a test tube of vinegar (our stand in for hydrochloric acid). After waiting a minute, they measured the pH. They concluded that the antacid that resulted in the pH closest to 7 was best at neutralizing the acid.

Along the way we noted several sources of error including not using pills of the same size, losing pieces of the pills as they were being ground up, and the water temperature being variable. We also made an exciting unexpected observation. Turns out that in addition to producing an acid-base reaction, adding Gaviscon solution to vinegar leaves you with an awesome slimy gel-like solid. For your average 4th grader that's up there with the inadvertent discovery of antibiotics.

Biology and General Science

This week we learned about acids and bases and three types of indicators you can use to identify them. We began by using red and blue litmus paper to test different household liquids. We were then able to classify them as acids, bases, or neutral. However while litmus paper is useful, it doesn't tell you anything about how strong or weak a base or acid is. So, for example, while baking soda and bleach, the two bases we encountered, score the same on a litmus test, baking soda tastes mildly bitter whereas tasting bleach will land you in the hospital (hypothetically speaking, of course!). We observed that in order to appreciate this without landing in the hospital, pH paper comes in real handy.