Saturday, January 5, 2008

The best laid plans......

Lydia over at Little Blue School gave me a great idea for a science experiment. She suggested we look at how anthrocyanins, the purple pigment in plants, can work as an acid/base indicator.

i was psyched. I worked out how to teach the children a little bit about plant pigments and a little bit about acids and bases.

The little lesson on plant pigments went well. They were fascinated by the color changes this fall so this made a lot of sense to them. However, I started boiling the purple pansies before I started teaching them about acids and bases. Bad, bad mistake. Boiling flowers take precedence over exchanges of hydrogen ions.

I gave that up as a bad idea and moved onto the experiment. It all started well, I put out 6 little cups of purple liquid full of anthrocyanins and another 6 little cups, 2 with acids, 1 with a base and 3 neutral. They started with baking soda. Going well so far, then the neutrals. Scream of delight when they saw how the vinegar turned the purple water pink.

Then mom came up with the bad idea. "Why not see if the indicator changes color if you turn it basic again by adding baking soda". Mmm, know what happens when you add a large amount of baking soda to something that already has a large amount of vinegar in it? That's correct, we have a wonderful bubbling mess.

That was the end of this experiment. All they wanted to do was alternate adding baking soda and vinegar to all the cups to see who violently they could make them overflow. Thank goodness I contained the experiment on a tray.

Here you have B&S preparing the pansies.

Watched pots never boil

Aah, nearly ready

Pansy juice all lined up with acids and bases. Thank goodness for that tray. It saved me a whole lot of cleaning.

IT WORKS!!!! The anthrocyanins change color it the presence of an acid.


Lostcheerio said...


I forgot to mention the bubbling was the best part. *cackle* And that you should lay in a large supply of vinegar, because it's sooo fun to go back and forth. For the longest time Benny would see purple flowers in someone's yard and urgently try to pick them and boil them. Hehehe. I forgot about pansies.

Shez said...

Now you tell me. LOL

Susan Z said...

You can do the acid base experiments with purple cabage. When I did it with a class at day care I just went to the produce department at a grocery store and they gave me all the outer leaves they pull off the purple cabage to make it look better. So you can get it for free!

Shez said...

Cabbage was going to be our purple of last resort. The kids love picking flowers and I never let them. They got a huge kick out of denuding my pansy plants.