Why do Leaves Change Colours?

Today I did a science experiment with the students about why leaves change colours. First I explained to the class the scientific reason why then we did an experiment where they each ripped up leaves into small pieces and put them into jars based on their colour. I then filled each jar with rubbing alcohol and covered them. By this point I had already told the students that I was not going to tell them was was going to happen because they were going to make predictions. The answer was that the pigment from the leaves would bleed into the alcohol, dying the liquid and eventually draining the leaves of their colour. To the right is a picture of their predictions which I recorded beside their names (which have been blurred out) on a chart paper.

You can see that many of them gave the correct answer and some other answers that I thought were worth mentioning was one student said they would break into molecules, which I was very impressed that she used that word, and while doing the experiment I mentioned that one of the things that makes rubbing alcohol different from water was that it evaporates quickly, which I believe is why some students thought the leaves would dry or evaporate.

After letting the leaves soak for 40 minutes we looked at the jars and talked about how the liquid had changed colour and I managed to find a few pieces of the leaves which showed clear spots where the pigment had started to drain. I walked around with the leaves so each student could see it close up.

Now it's onto the second half of the experiment:

I gave each student a coffee filter strip and wrote their names on it and called them up to choose which colour they wanted to put their strip into. I then had them make prediction number two: what will happen to the coffee filter? Once again, to the right is their answers. The students did a good job of thinking of logical answers and even guessed at different senses (smell). I was most intrigued at the student who said the paper would stay white.

Here is what happened:

​​ The rubbing alcohol left only a line of pigment on the the paper and longer we left it in, the farther up the paper the line was pushed.

#Leaves #Science #Experiment #Preperation #Autumn