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.

13 comments:

SarahElisabeth said...

I think that you have again added an acid, lemon, to an alkali, baking soda and so produced carbon dioxide, water and a salt-sodium acetate or ethanoate. The red colour disappears as the solution is no longer acidic.

HTH-my chemistry is rusty!

Phyllis said...

Oh, that is really neat! You have me stumped as well...I am going to think about this one!

An Almost Unschooling Mom said...

SarahElisabeth - I'm thinking along those lines, except I would have expected the water to have turned back to its original red, or something like it, instead of murkyish clear. It's not an easy one to look up :)

Christy said...

Very interesting!! I can't wait to find out the reason!

Debbie said...

I can't wait to see what you figure out.

Kari said...

I chose you for the versatile blogger award! http://theheartofahomemaker.blogspot.com/2011/11/versatile-blogger-award.html

Sparklee said...

My kids would love to try this! Thanks for the great ideas!

Ticia said...

Are you using communion cups? mwa ha ha ha ha........

Christianne @ Little Page Turners said...

Love this and - more importantly - so would my little scientist! If I can't get her to drink cranberry juice, I'll have no problem getting her to experiment with it. :)

Raising a Happy Child said...

OK, I am so going to get some cranberries today to try some of this out.

An Almost Unschooling Mom said...

Ticia - I wondered if anyone would notice :)

Maureen said...

This looks fun! I'm not going to even try to solve your conundrum though, you lost me several lines before that... I'll have to sit down with your post when we do the experiment and read it slowly to allow my brain to access the far off recesses where my most of my science knowledge is stored.

Jamie Cotter said...

My husband, the scientist, says it's because the red dye in the cranberry is acidic.