Wednesday, July 29, 2015

Acids and Bases

Acids and Bases

The Magic School Bus Young Scientist's Kit on Acids and Bases couldn't have come at a more perfect time! We just finished exploring the digestive system, which of course included a discussion on stomach acid. So what exactly IS an acid? Are there different kinds of acids? Are acids dangerous? We explored these questions and more as M worked her way through this exciting kit!

The Taste Test

What does an acid taste like? M tasted a series of (safe) liquids to determine whether they tasted sour. She labeled each liquid, then recorded her taste-test results in a table.

Yep, lemon is sour! She didn't want a second taste of that one!! LOL

Using an Indicator

M prepped a red cabbage indicator solution by ripping cabbage leaves into small pieces and putting them in a bowl with boiling water. We left the cabbage/water solution sitting for about 30 minutes while we completed other parts of the lab.

Litmus Test

While we waited for the cabbage indicator solution, M explored the acidity of various liquids using litmus paper. There are two kinds of litmus paper - red and blue. Red litmus paper stays red in an acid, and turns blue in a base. Blue litmus paper stays blue in a base, and turns red in an acid.

I drew a pH scale and explained that pure water was in the middle - neutral - at pH 7. The further you go to the left (less than 7), the more acidic a solution is, and the paper will turn red. The further you go to the right (greater than 7), the more basic a solution is, and the paper will turn blue.

M enjoyed putting drops of the liquids on the test strips with her pipette and watching the colors change. She compared the results of this test to the results of her taste test.

pH Test

Next, we used pH paper to see if we could determine how acidic or basic the solutions were. The pH paper changes color, and the color chart is used to see where the solution falls on the pH scale.

Indicator Solution

Finally, the cabbage indicator solution was ready. (We should have prepped this the night before.) This was M's favorite part because she loves pouring and measuring, and there was a more dramatic color change.

M measured the same amount of cabbage indicator solution for each cup and lined the cups in front of her test solutions.

I showed her how to use the volume markings on her pipette to suck up exactly 1mL of solution to add to the indicator in the cup.

The purple color of the cabbage indicator immediately changed color when the test solutions were added. The acid solutions turned the indicator different shades of red, the neutral solution (water) remained purple, and the basic solutions turned the indicator blue or darker purple.

This was a really fun introduction to acids and bases! There are tons of test strips left that we can use another time, and there were some additional experiments that we can attempt as a follow-up (neutralizing an acid, using an acid for cleaning or metal plating).

1 comment:

  1. Great post! This work is so much fun - thanks for sharing