Hello and welcome to chemistry in your cupboard. I'm Rosie, an educational
coordinator for the Royal Society of Chemistry, and today we're going to show
you how to make rainbows with the red cabbage indicator. A simple
experiment which you can do at home with a responsible adult. So let's get
started. You're going to need a red cabbage, some acids and alkalis that you
can find in your kitchen, a piece of paper, and a poly pocket and some paintbrushes,
kitchen roll, and some cooking equipment. Red cabbages contain anthocyanins. These
change color when they come into contact with an acid or an alkali. I'm going to use this
today to make some rainbows. One made out of drops of indicator and one made out
of homemade indicator paper. So let's start off with making the red cabbage
indicator. Ask an adult help you with this part. Take three leaves of the red
cabbage and chop them up nice and small.
Put the chopped up red cabbage into a pan, add enough water so the cabbage is
just covered. Boil the cabbage for about ten minutes. Another way to make
the indicator is by blending the leaves or leaving them to soak overnight. But if
you boil the cabbage, then you can make indicator and have cabbage for your tea.
So now the red cabbage is cool, I put a couple of pieces of kitchen roll in the
sieve and I'm going to drain the red cabbage through it to make the indicator
paper. So you can see that the red cabbage has dyed the water purple? There we
have our red cabbage indicator solution at the bottom, which is dark purple, and the
cabbage is also dying the kitchen roll purple here at the top. So I've already drawn a
rainbow onto a piece of paper and I've put it inside a poly pocket. What I'm
going to do now is use a paintbrush to drop a little bit of the red cabbage
indicator onto my rainbow. Now we're going to add some acids and alkalis that
you can find in your kitchen to the red cabbage indicator to make some of the
colors of the rainbow. First let's try an acid. Here in this egg cup I have some
lemon juice. Pop a little bit onto your paint brush and dab it into the first
line of your rainbow. Look, as I add the lemon juice to the red cabbage indicator
it turns it from purple to pink. Now let's try an alkali. In this egg cup I've
got some water mixed with washing powder. I'm going to add a little bit to the
paintbrush and dot it onto the red cabbage indicator. Cool, this time is
turning green. Let's try different alkali. Now I've mixed some bicarbonate of soda
with water and I'll put a little bit of that onto my paintbrush. Oh, this time
it's turning blue. That's because my washing powder is more alkaline than the
bicarbonate of soda. Here's my red cabbage rainbow. The red cabbage
indicator is purple, the acids like lemon juice are pink, and the alkalis like
washing powder and bicarbonate of soda are green and blue. It's super colorful
isn't it? now that my homemade indicator paper is dry I can paint a rainbow onto
the paper using the acids and alkalis that I've found in the kitchen. I'm going
to paint the first line of my rainbow with the acidic lemon juice. Look, as soon
as the paintbrush touches the paper it changes color to pink. Now let's make the
green line of the rainbow with the alkaline washing powder.
Cool, that's instantly turning the paper green. For the final line of my rainbow
I'm going to use the alkaline bicarbonate of soda.
Nice, that's changed the paper from purple to blue. So here it is, here's my
rainbow. Have a go at testing the acids and alkalis in your kitchen and show us
your results using the hashtag chemistry in your cupboard. So that was the red
cabbage indicator experiment which you can do at home with a responsible adult.
We'll be back for more experiments soon, but in the meantime subscribe to our
youtube channel for all the chemistry in your cupboard episodes. See you soon.