[Junior High School Science] Let's investigate the properties of oxygen
This is an experiment to generate oxygen.
Be careful not to get the concentration of the hydrogen peroxide solution wrong...
When I performed a demonstration experiment in elementary school,
I got the concentration wrong,
oxygen was generated with tremendous force,
and I was terrified.
Preliminary experiments are important.
It seems that 3-6% hydrogen peroxide solution is ideal, but
the reaction is too slow,
so I found it easier to work with
10% hydrogen peroxide solution,
adding 20ml to 0.2g of manganese dioxide mixed with water.
When I worked at a newly established school,
there were no L-shaped glass tubes,
so I made them myself.
You heat and bend the glass tube with a gas burner,
warm the outside of the bend to close the end of the glass tube with your finger,
and blow into the other end with your mouth to inflate it.
Science club students might be able to do it.
I hadn't made them myself since university,
so I was nervous.
I was working while thinking,
Are they going to make a part-time lecturer do this?
Now, let's begin the class.
Today, we will generate oxygen and
investigate the properties of oxygen.
First, we will generate oxygen.
Fill a water tank more than halfway with water,
and submerge four test tubes and four rubber stoppers
completely.
Confirm that the test tube is filled with water and stand one test tube upside down.
Someone, please hold it steady.
Put manganese dioxide and hydrogen peroxide solution into another test tube,
and immediately attach the rubber stopper with the L-shaped glass tube.
If hydrogen peroxide solution gets on your hands,
wash it off with water immediately.
Bubbles will come out from the tip,
so please collect the bubbles
in the upside-down test tube.
When it is about half full,
put the rubber stopper on,
and collect the second one.
Please put the rubber stopper on gently.
If you push it in tightly,
it will get stuck and you won't be able to take it off.
Please line up the test tubes containing oxygen in the test tube rack in order
so that you know which one was collected first.
It would be good to collect four, but
it is okay if you don't have four.
(After finishing collection)
Now, let's investigate the properties of oxygen.
What should you do with the first test tube?
(Don't use it)
It contains a lot of air, so we won't use it.
However,
it should also contain oxygen,
so please keep it as a spare.
Put limewater into the second test tube,
cover the mouth of the test tube with your finger,
and shake it.
What happened?
(No change)
Since the third test tube is thought to contain a lot of oxygen, please hold a white piece of paper behind it and check the color.
Next, using the third test tube,
we will investigate whether oxygen dissolves in water.
Remove the rubber stopper from the test tube,
quickly cover it with your thumb,
and mark the water level in the test tube with a pen.
Shake the test tube.
Turn the test tube upside down underwater and remove your thumb.
Again,
cover the test tube with your thumb,
and take the test tube out of the water.
Is the water level still at the pen mark?
(No change)
Insert a lit incense stick into the third test tube.
Extinguish the flame of the incense stick,
and insert it while it is just glowing red.
I will demonstrate it in front.
If it goes well, a flame will appear.
Now, I would like you to try it, and if your group has a fourth test tube, please try it with that one too.
The first and second ones
might also work well,
so you can try those too.
Now,
please write down your results and discussion.
What did you write?
I will tell you what I want you to write only for the third line of the discussion.
I want you to write, "Oxygen is a colorless gas and
is difficult to dissolve in water."
Based only on the experimental results,
it would be "does not dissolve in water," but
some of you may know that fish breathe oxygen in the water.
Oxygen dissolves in water
a little bit.
For the discussion,
please write by combining the experimental results and what you already know.
