Hey! Welcome to Beals Science, I'm Craig Beals. Today we're gonna make some pH
indicator out of this red cabbage. You see red cabbage is pretty fantastic, it's got
that deep red color, well it's got some compounds in it that will change color
when the acidity changes. So we're gonna explore that today and we're gonna show
you how you can do this right at home. Step one, we're gonna take our red
cabbage and we're gonna cut it up. We want little tiny pieces so that we can
extract the color. Now, kiddies at home, if you're gonna do this might want to let
an adult do the knife part. I think legally I'm obligated to say that. With
our half cabbage we can pretty well make two batches of our pH indicator. I've got my
hot water, the other thing to notice, I'm not measuring because there's really no
need to. If I find out that my indicator isn't dark enough well I just add more
red cabbage if it's too light I add more water! It's already turning blue!
Isn't that awesome! Then I let it sit for about five minutes and let it steep let
it pull all of that good purple and red color out of our cabbage. We're gonna use
a fine-mesh strainer, we just get the nice colors in the bottom. Should we taste it? Huh?
Yeah! Yeah, that's worth saving! We're going to start bleach and with vinegar
the reason is, I have a little insider information, maybe it's because I teach
chemistry for a day job, but we should see two extremes here, one of these is
basic and one of them is acidic. Let's find out!
Hmm, vinegar... Very nice! All right, children, you want to see? we get the red cabbage pH
indicator do either you know what pH is? "No". Hmm, well we're gonna have to learn that.
What about acids? "No". Bases? "No"
Vinegar?
"Cool!!!"
That's pretty good! "That's like, hot pink!"
Yeah, look at the difference! That's a big difference!
This bleach, bleach.
"Cool!"
"Ewwww..."
See it going green and then changing a red? Isn't that cool?
Now we know the BEET JUICE changes color we just got to try a whole bunch
of different stuff and find out and what colors they're gonna change to. "It's not BEET JUICE"
Oh! What is it? Ah! I have beets - we can try beets, we can make
a movie out of beats! But this is red cabbage? "Yeah". Thank you, thank you for
correcting me. I've got a whole bunch of household items here to test and what
I'm going to use is a pH probe to first, figure out the actual pH. What do you
think about vinegar? Acidic or Basic? There we go.
Two point six seven. I used the pH probe to test all sorts of stuff from
around the house until I felt like he had a pretty decent range of acids and
bases. A pretty decent range going from near zero up to 14. Well that brings up
the question, "What is pH, and what is an acid, and what is a base?" Now I'm gonna
explain acids and base and pH in 30 seconds or less! Okay? Don't tune me out!
We're gonna start a timer we're gonna learn this 30 seconds or less. Here we go!
Well first, what is pH? pH stands for power of hydrogen and if you know
anything about pH you know that there's a scale - it goes from 0 to 14 with
7 being in the middle. If I have a whole bunch of hydrogen ion, those are positive
hydrogen atoms, that means I've got something that's acidic. The more
positive hydrogen ions that I have, the more acidic it is. And, very acidic means
it has a low pH number. The opposite of that is hydroxide which is an oxygen and
a hydrogen hooked together and it has a negative charge. Now, if I have a whole
bunch of hydroxide ions, its basic and it has a high pH number. Now, what about in
the middle here? At a pH of seven well that means I have
an equal amount of positive hydrogens and an equal amount of negative
hydroxides. And, think about this, if we put those two together that's two
hydrogens and one oxygen so that's H2O, that's water, which is why water is neutral.
Thirty seconds, nailed it! Now remember the goal is to make an indicator that shows a change
in color with a change in pH. So we took a spot plate and tested each one of them
individually by putting a little bit in the spot plate and then adding some
drops of our indicator and as you can see the indicator did respond to the
changes in pH, it changed color depending on the pH. One of the things you can
notice is that the higher the number, the bluer the liquid the lower the number
the more red or pink it is. Well then, why dot we get the different colors when
the pH changes? Well, let's go back to our hydrogen ions, our acid makers, and our
hydroxide ions, are basic or alkaline makers. You see, in the red cabbage we
have something called anthocyanins, that's what gives the cabbage its color.
Let's think of that molecule as a pigment. But, there are different forms of
anthocyanins, we have some that are a little more pinkish-red and some that
are a little more blue. Now, if we put the pinkish-red and the blue together what
color do we get? We get purple! So technically, this is like purple cabbage,
not really red cabbage. If we put our cabbage juice in with something that's
acidic, all those hydrogen ions are going to start to take over one of the
forms of the anthocyanins, it's going to take over one of the colors of the
pigment that's in here, and we're not gonna see it anymore, which means the
other one is going to remain. So, if we have something that's very acidic and it
starts to take over all of the blue colors then all we're gonna see is the
pinkish-red. Now, the other side of that is if we have something that's very basic
and we have a whole bunch of negative hydroxide ions, the reddish-pinkish colors
are going to start to go away, we're not going to see them anymore. All that we
have left are the blue ones and this is why we get the changes in color, the
changes in spectrum, because of those nice little pigments inside our red
cabbage. There they are! The class of 2020, all lined up! And once I knew the pH and the color
associated with that pH I decided to line them up with the most basic on our
left and the most acidic on the right and this is what we got! With just a
little bit of experimentation we were able to make (sort of) the colors of the
rainbow, not entirely, but I bet if you really tried at home and went out and
got yourself some red cabbage and then just start mixing things with it to see how
the pH changes the color and see if you can make a rainbow that's much more
beautiful than mine. Thanks for watching and "Keep on Learning!"