Wednesday, November 16, 2011
More Cranberry Science for Children - What Makes Cranberries Red?
While the children were munching away on their sandwiches at lunch, I pulled out what's left of our bag of cranberries for the first couple, of what I hope will be a series of cranberry themed science experiments.
To begin with we reviewed what we already know about cranberries - that they float, because they have four little air pockets inside.
We talked about what happens to air as it heats up - it expands. We felt the outside of the cranberries, and decided they would not stretch like a balloon as the air expanded, but guessed that they would pop if the air inside was heated.
Then, we tested our theory by pouring boiling water over some of the cranberries, and yes indeed, they popped.
Finally, I pulled out a bowl of cranberries, that had been heated in water, popped, and then left to cool overnight in the refrigerator. The children noticed immediately, that the water was red like the cranberries.
I asked them where else in nature they have recently seen the color red. Luckily for me, they answered the way I hoped - in the fall leaves. They even remembered, that it is a pigment in the leaves that makes them appear red, though I had to help them remember its name - anthocyanin, the same pigment that gives cranberries (and purple cabbage, and poinsettias) their red color.
I reminded them too, of the experiments we've done in the past using anthocyanin to test the pH levels of various household chemicals. We decided to give it a try with the cranberry "juice", by filling four small cups with the pigment filled water, and then adding vinegar to one, baking soda to another, with lemon juice, and baking powder in the final two (you can see the actual order in the second picture below).
We didn't see much of a change with the vinegar, but the juice turned dark purple when we added the baking soda, light pink with the lemon juice, and light, fizzy purple with the baking powder.
The children guessed from the fizz when the baking soda, and even more so, when the baking powder was added, that cranberries must be acidic. They wanted to know why the baking powder had more of a reaction. I showed them on the baking powder ingredients list, that baking powder, unlike baking soda, contains both an acid and a base, and the two react together when they get wet.
Of course, once they saw the fizzing, they wanted more, so they asked if we could pour the cranberry juice cup with the baking soda, and the one with the lemon juice, together. We did, and to my surprise, not only did we get a fizzing chemical reaction, but a significant color change as well - the red disappeared entirely.
Now we just have to figure out why :)
It's great to be a homeschooler.