Acids and Bases
Some people drink a full glass of acid at
breakfast every morning. Do you? If you drink
orange juice, then you’re drinking acid.
When you hear acids and bases, you might
think of something dangerous or something that
only mad scientists use. This is not true. Acids
and bases are everywhere: in the food you eat, in your house, in
super markets, and even inside your body! So let’s see what acids
and bases really are.
Acid
Most things that taste sour are acids. Acids have different
strengths. The stronger the acid, the better it is at dissolving things.
For example, acid in your stomach (hydrochloric acid) is so strong
that it breaks down the food you eat. Also, you get tooth cavities
because germs feed on bits of food that you forget to brush off and
make a strong acid that melts your teeth.
Base
Bases are the opposites of acids (you will see what this means a
little later). Like acids, bases have different strengths, and stronger
bases dissolve things better than weaker ones. Strong bases are
commonly used to clean water pipes and other surfaces.
Neutral
So acids and bases are opposites of each other. What this
means is that when you mix an acid and a base that are equally
strong, they cancel each other out. This is called neutralization.
Neutralization makes something that is neither acidic nor basic; this is
called neutral. Pure water is neutral.
Experiments
Egg Experiment:
It’s time to see what happened to our eggs from
last week! Have your mentor give you and your
partner your box and observe what happened to
your egg.
Why do you think the shell
disappeared?
How would you tell if something is an acid or base? Some
weak acids like orange juice and lemonade taste sour. Some weak
bases, like soap, feel slippery to the touch. But strong acids and
bases are dangerous, so we can’t touch or taste to tell if something is
an acid or base. But don’t worry, we have something called
indicators. Indicators are chemicals that change color in acids and
bases. We will use an indicator made from red cabbage. When
red cabbage juice (indicator) is added to an acid, the liquid turns
pink. When it is added to a base, it turns blue-green. When it is
added to a neutral liquid, it does not change color. So by the color
of the indicator, you can tell if something is an acid or a base.
Neutralization Experiment:
This week during our testing for acids and bases we have acidic and
basic controls. We will start with an experiment using both of our
controls.
Materials:
Red cabbage juice
Droppers
Vinegar
Aluminum Foil (spread on desk)
Baking Soda
Cups
Method:
1. Place a small amount of baking soda in the cup and add a few
drops of cabbage juice. Note the color.
2. Do the same in another cup with the vinegar. These are your
positive controls for base (baking soda) and acid (vinegar).
3. Add a few drops of cabbage juice to water. This is your
negative control for acids and bases.
4. Now you are going to neutralize your baking soda with acid.
Add vinegar to your baking soda and cabbage juice cup until
the color of the indicator changes. How do you know when it
is neutral? How do you know when it has become acidic?
Indicator Testing Materials:
Red cabbage juice
Detergent
Vitamin C
Lime Juice
Honey
Tums
Cornstarch
Soda
Egg Whites
Droppers
Cups
Aluminum Foil (spread on desk)
Method:
1. Get a small portion of each unknown. Add a few drops of
indicator solution and note the color change, if any.
2. Fill out the chart below with as many unknowns as you can.
Unknown
Indicator Color
Acid, Base or Neutral?
Vinegar
Baking Soda
Water
Detergent
Vitamin C
Lime Juice
Honey
Tums
Cornstarch
Soda
Egg White
Questions
1. When milk rots, is it getting more acidic or basic?
2. Why is acid rain bad?
3. What would happen if you put sprinkle baking soda onto sweet
and sour pork? Why do you put baking soda into cake dough?
4. You get a heart burn when your stomach makes too much acid.
What kind of drugs can you take to cure this (acid or base)?