Sunday, September 19, 2010

pH Indicator Solution from Fall Leaves



I hesitated to share this, because quite frankly, I think when it comes to our mystery tree, our findings from this experiment muddy the waters a little. But, there is a side that is kind of neat, and might be useful in other ways, so here goes.

I'm not sure if you remember our red cabbage indicator solution (or maybe, you've made it for yourself), but the reason red cabbage can be used to test for acids, and bases, is because of the red, anthocyanin, pigment in the cabbage.


Yes, I said anthocyanin...again.

If you've been following along with our fall science experiments, then that should be a familiar word. It's the pigment, activated in some leaves in the fall, that gives them a reddish color. So, now maybe it makes sense why we were checking to see if our leaves were acidic, or akaline (see Fall Science Part 3).

We also wondered if we could check for anthocyanin in our leaves (to basically confirm what we saw through our chromatography experiment), by mixing a solution of leaf "juice" with vinegar, or baking soda. We tore up a couple of leaves from our mystery tree, and let them soak in filtered water, for a couple of hours, and then gave it a try.

Our results were, sort of, the opposite of what I would have expected. We went from almost clear to begin with, to a dark, rusty, red with the baking soda, and a golden, orangey, yellow with the vinegar.

But, when we tested a maple leaf, that had already started to turn red, and so clearly had anthocyanin present, we saw exactly what we expected. Bluish green, with the baking soda, and pink with the vinegar.


It wasn't a total bust then, just not what we expected from our mystery tree. Still, if you've been wanting to do a pH testing experiment, and don't have any litmus paper, or red cabbage on hand, you might look around your neighborhood for an ornamental tree, with red to purple leaves, or watch for some bright red, fall foliage, and give those leaves a try.

Just remember, that while red cabbage is edible, leaf "juice" is not.

It's great to be a homeschooler.

4 comments:

Ticia said...

In a few weeks we're going to be doing a fun mystery, and I need to remember your cabbage juice pH indicators, rather than buying some.

Christy said...

I am so impressed with all that you have done and figured out with this experiment.

Phyllis said...

I love this experiment. We plan to do something similar in a couple weeks.
I didn't know the anthocyanin was activated in the fall. I thought it was always there but chlorophyl hid it and when their was less light, the chlorophyl production was reduced and the anthocyanin showed through.
Either way, amazing stuff.

Raising a Happy Child said...

This is pretty interesting. To be honest, I think Anna is too young for "science in a tube" (I know that you are doing it with older kids), but the idea intrigued me enough to try it after Japanese maples in our neighborhood turn color.