I'd like some way to know which liquids have lots of protons (H+)
in them BEFORE mixing them with the bicarbonate.
Ah, you want a pH indicator.
Yeah, where do I get one?
There are many different kinds of pH indicators. The best ones
are machines that use fancy electronics to measure the protons.
But they are expensive and not necessary for the simple Alchemy
we do in our "Do This!". Instead we can make a solution
that has a different color when the concentration of the protons
is different. By mixing this pH indicator with any liquid you
get a color. The color gives you a rough idea of how many protons
(H+) are free in the liquid. There are dozens of different pH
indicators.
Let's just make one. A simple one.
OK. Get some red cabbage. The stuff you eat.
Well, maybe you eat it but I don't!
It's good for you. You can get some from the store. It's called
"red cabbage" but I think it looks purple.
Hey, I found a can of "pickled cabbage". Will that do?
No, that won't work well. The reason it is "pickled"
is because it's in vinegar. That means it's already "contaminated"
with acetic acid. It wouldn't make a good pH indicator because
it already has a low pH (high amount of protons).
OK, I'll start with a piece of fresh red cabbage. Now what?
Cut a chunk of the red cabbage into very thin strips and crush
them into a paste.
This is a lot of hard work! Kitchen work! How much do I need?
That depends on how much you want. If you are only going to test
a few liquids, then prepare about a teaspoonful of paste. You
can always make more later. Once you have a teaspoonful of paste,
place it in a cup and ask an adult to pour boiling water onto
it and stir it well.
It's like making tea!
Aye, it is. Don't add a lot of water, or the indicator will be
very dilute. But add enough to give you, oh, about half a cup.
The best amount depends on the quality of the cabbage you have.
You can always make more later and try different amounts of water
and cabbage.
Let the liquid sit for a few minutes, then strain it through a
cloth to remove the pieces of cabbage paste.
I'll save the liquid in this small bottle.
Good idea. But it will only keep for a day, so use it right away.
If you want to store it longer, add a drop or two of "oil
of cloves". That will help preserve it longer.
Great. I now have a pH indicator. I'm going to test the vinegar
and lemon juice to find out which one has more H+. Ah, which
color will it turn?
Red-cabbage-indicator turns an acidic solution red and a basic
(alkaline) solution green. The more H+ in a liquid the redder
it will get. The really acidic solutions will be turned a deep
red (crimson) when you add a few drops of indicator to them. The
more H+ in the liquid the redder it gets.
So, the liquids that are turned red by this indicator will be
the best ones to use to make carbon dioxide from sodium bicarbonate.
Right. On the other hand, any liquids that turn green when you
add this indicator will not make carbon dioxide from sodium bicarbonate.
That's because they have too few H+ ions.
Fantastic. It's like a magic potion!
Well, it's really a pH indicator. When there are lots of H+ around
it, the indicator turns red. When H+ are scarce, the indicator
turns green.
How does the indicator know the number of H+ around?
That's a very good question. The hydrogen ions can temporarily
bond to the indicator. When the indicator has H+ bonded to it,
the indicator is red. When it doesn't have H+ bonded to it, the
indicator turns green. The exact (detailed) explanation is pretty
advanced. It has to do with the physics of light and colors.
That's OK. I can live with the simple explanation. I'll use this
indicator to find the most acidic liquids. I'll add a few drops
to a small amount of each liquid and the reddest one will have
the most protons for the reaction. That will be the one that gives
me the most carbon dioxide when added to the sodium bicarbonate.
Right?
Right. However, if you are going to make a careful study of this,
you should try to be accurate and specific about the tests you
do on each liquid.
How do you mean?
Well, you should carefully measure each liquid into a glass. Use
the same amount of each liquid and add the same amount of indictor
to it. That way you will have a fair comparison. You can probably
find measuring vessels around the kitchen. And an "eye dropper"
is a good way to add the indicator.
I see what you mean. It makes sense that way.
Good. Red-cabbage-indicator is easy to make. If you don't have
red cabbage you can try red rose petals or crimson hollyhocks,
but it takes a lot of flowers to make a good amount.
OK. Any suggestions of things I should test?
Well, you've already mentioned some, but don't forget that basic
(alkaline) chemicals are important to learn about too. A good
Alchemy student will test lots of things. You can create a list
of common chemicals and determine whether they are acidic or basic.
Test the pH of your drinking water by seeing what color it turns
when you add a few drops of indicator. Then dissolve an aspirin
in it and test it again. (The color might actually change while
the aspirin dissolves, so watch closely.) Or test water in which
you dissolved some washing soda. Try soaps and other cleansers.
Try to figure out which ones are safe to use on skin and which
ones are too nasty to rub on your skin.
Huh?
Compare the pH of facial soaps and laundry detergents.
Oh. I see what you mean.
Test (cleaning) ammonia. Test milk! The list is endless. And so
are the possibilities for learning something about pH.
I'll test the pH of the water in my goldfish's bowl before I've
cleaned it.
That's a good idea! The fish might change the pH of the water
as it lives in it. Test his water before and after he's been in
it a day or two.
What color would I get if I mixed an acid and a base together?
That depends on how much of each you add and how acidic and basic
they are. That brings me to another idea for a "Do This!".
Put a wee bit of washing soda into a quarter glass of water.
Then test its pH with your indicator.
It's kind of green. That means it is alkaline, right? It's low
in H+.
Right. Red-cabbage-indicator turns alkaline water green.
So washing soda is a "base"? The opposite of an acid?
Right. Washing soda collects H+. It absorbs H+ from the water. (We won't go into the details of how. That would require you to learn a lot of extra reactions.)
Washing soda makes a basic (or alkaline) solution. That's why it
is green. Now add a drop of vinegar and give it a swirl.
Hmm, I can't tell what is going on.
It helps to hold the glass against a white piece of paper and
have good light. If you still don't notice a difference add some
more vinegar and swirl it some more.
The color is changing. It's becoming less green.
That's right. As you add vinegar you are adding H+. That will
lower the pH and change the color of the liquid. If you keep adding
vinegar you will change the solution from green to red.
Oh, I get it. By adding the acid I am adding H+ and that changes
the total pH. The changing color proves it.
Exactly! This is a common way to "play" with pH. In
fact, many Alchemists use this method to get the pH exactly what
they want it to be. They mix acids and bases together until the
get the color they want. They usually start with a "reference"
solution that has a pH they know and then use acids and bases
to fiddle with it. The indicator lets them know when they have
the pH they want. The trick to this is to have accurate measuring
tools and a solution of known pH to start with. The details of
it really can't be appreciated without a properly equipped lab.
But you can use your kitchen Alchemy to get an idea of how it
is done.
Yeah, it's just a matter of adding an acid or base until you get
the color you want.
Right. The "color you want " depends upon the pH you
want. Like I've said so many times before, pH is a complex math
subject and I don't think you need to understand it now. One day
you will. But for know, you can see how to manipulate the pH of
a solution and follow that change by following the changes in
color.
I see. Is red-cabbage-indicator the pH indicator most Alchemists
use?
No, but it is a convenient one for working in the kitchen. An
Alchemist's most popular indicator is probably phenolphthalein
(pronounced "fee-nol-thal-een"). But that's a 20th century
chemical.
If I were in the 20th century, how would I make it?
Well, start with a laxative.
Laxative?! Isn't that the stuff you use for "toilet troubles"?
Yes. This takes a bit of work, but I think it's worth it. Get
a couple of "Feen-a-mint" tablets and remove the outer
sugar coating. Underneath the coat is a yellow powder. That's
what you want, so try to collect the whole yellow tablet cleanly
from the coating. Place two yellow tablets into a cup and add
a tablespoon of rubbing alcohol.
Rubbing alcohol?
Yes. It's a diluted alcohol you can get from the same place you
got the laxatives. Anyway, stir the tablets in the alcohol until
everything is dissolved. You should end up with a pale yellow
solution. Store that is a wee bottle with a stoppered top (otherwise
the alcohol will quickly evaporate).
What color does it turn an acid?
Clear. Actually it is clear when neutral too.
Clear?! That doesn't sound very interesting.
Well, it turns basic solutions a bright red.
I thought red meant "acidic".
No. That's only if you are using red-cabbage-indicator. Each indicator
behaves differently. That's why Alchemists like to have several
different indicators. It gives them more variety and lets them
see color differences better. It depends on the original color
of the solutions they are working with and exactly what they are
trying to do with it.
Any "tricks" you can do with phenolphthalein?
Yes. And it is nice that you said "tricks" because one
phenolphthalein "trick" is used by magicians.
An Alchemy magic trick. Great! What is it?
Magicians claim to turn water into wine. Of course they don't
really do that. What they really do is change the pH of a solution
containing phenolphthalein. The changing pH changes the color
of the solution from clear (water) to red (wine).
Really! How can I do it? Exactly?
Dissolve a little bit of phenolphthalein into a large amount of
water. If you don't use too much phenolphthalein the water will
appear clear. Of course, you do this trick in a clear container.
Show it to the audience. They can see it is clear and it doesn't
even have a smell.
Is it OK to taste it?
You shouldn't drink it. You may end up with "toilet troubles".
Besides, the rubbing alcohol isn't good for you either.
Anyway, it will
look like clear water. Then pick up your magic wand.
It's a special magic wand, isn't it?
Yes. Beforehand, dip the wand into a saturated solution of washing
soda. As long as the wand is not allowed to get too dry, the audience
will not see the crystals of washing soda on it. Then dip the
wand into the water and stir it while mumbling some kind of nonsense
words.
Like "phenolphthalein"!
I think "abracadabra" is the traditional mumbo-jumbo.
As you stir in the washing soda, the pH of the solution will increase
and the phenolphthalein will turn the water red. It looks like
wine.
But it won't really be wine.
Of course not. As a matter of fact it would be bad to drink it
because the pH will be so high as to be dangerous.
And ....
Don't drink it!
Right. Magicians use this trick in other ways. They just hide
the phenolphthalein and alkaline chemicals in various ways in
order to give the magic illusion. One particularly good trick
uses this Alchemy to turn a white rose red. Right before your
eyes.
Great. I can see why this phenolphthalein is useful, even though
it only turns color when basic.
Yes, its invisibility is useful. You can even use it to make invisible
ink.
All right! How?
Use phenolphthalein to write a message. Use it as an ink. You
can dip a toothpick in it to write or use an old fashion pen that
lets you put in any kind of ink you like.
Gee, I thought an old fashion pen would be a quill.
Ah, you can use a quill pen too (if you know how to make one).
Anyway, use the phenolphthalein as an ink to write a note. You
won't be able to see the note, so it isn't easy to write it.
I bet you make it visible by making it basic.
Right. Once the paper is dry you can make the message appear by
dabbing some alkaline solution on it. The writing appears as a
bright crimson red, and it disappears as soon as it dries. If
you smear it with an ammonia solution it will last only a few
hours. If you use a solution of washing soda, it lasts for a few
days. After it has faded it can be brought back by just damping
it with alkaline solution again. Sometimes, just wetting it with
water is enough. That's because the base is still there and it just
needs some water to help move the H+ around.
I see. The water helps the materials mix together well. Just like
the water you need to get baking powder to work.
Yes, precisely.
I've told you about two of the most common homemade indicators, phenolphthalein and red cabbage, but there are others around the house. Many plant juices will turn color depending upon the pH. Cherries, beets and blueberries are good examples.
Should I use the "tea-making recipe" (boiling water over the ground up bits) or use rubbing alcohol?
The "tea-making recipe" is easier but the indicators prepared with alcohol will last longer and act better.
Are there other plants to try?
Yes. The flowers of the carnation contain a pH indicator and so do the leaves of the poinsettia BUT be warned that the poinsettia is one of the most toxic plants that people keep around the house!
OK, I won't eat or drink poinsettia-indicator!
Good. Poinsettia and poinsettia-indicator should be properly labeled as very poisonous! And any indicator prepared using rubbing alcohol will be flammable as well as poisonous so always label them correctly and clearly as poison.
On the other hand, there are plenty of safer indicators to enjoy.
The spice turmeric is a yellowish powder but when added to an alkaline solution it turns red.
Wow, it seems there are plenty of indicators around that I can make and plenty of things I can test with them.
Yes, there are. Any questions or comments?
Yeah, these "Do This!"s are nice and I can even have
some fun with this stuff, but is there more I can do?
Aye! There are dozens of experiments one can do at home. Most
require only a few unusual chemicals and some equipment. You can
buy some nice chemistry kits to get you started on more experiments.
They will describe other chemical reactions and teach you more
about how reactions work. They can be a lot of fun and a learning
experience. But always follow directions and pay attention to
safety. Ask an adult to help you pick out a kit and ask them to help you with the experiments in it.