Creating Hydrogen and Oxygen from Water

Renata blogged about the electrolysis demonstration Zach did for her class. Here are his directions for a version of that experiment that the kids can do at home.

Simple Electrolysis Experiment

This is a smaller scale experiment than what we did in class. This can be safely done at home, and will not involve the collection of the gasses.

Here are the items you will need.

1: Glass container (a jam jar works well here).
2: Two pencils
3: A piece of cardboard slightly bigger than the glass.
4: Two pieces of thin electrical wire about 8-10 inches in length.
5: Electrical tape.
6: Epsom Salt (this is NOT table salt. Ask your parents!)
7: A 9 volt battery.

Experiment steps:

1: Remove the erasers from the pencils and sharpen both ends.

2: Attach one wire (about 8-10 inches long) to each pencil by wrapping the exposed wire around one end of the pencil, and using the electrical tape to secure it.

3: Fill the glass container about 3/4 of the way with water.

4: Mix several tablespoons of the Epsom salt in with the water. You want to saturate the solution, so keep mixing until no more will dissolve. Do this about 1 tablespoon at a time.

5: Put the cardboard piece on top of the glass, and poke two holes about 2 inches apart. Push the end of each pencil that does not have the wire attached through the holes, and into the water.

6: Finally, attach the other end of the wire to the 9 volt battery with the electrical tape to help hold them in place.

At this point you will see bubbles forming at the tips of the pencils in the water. If you look closely, one will be forming bubbles more quickly than the other. This is the Hydrogen. The one with the fewer
bubbles is the Oxygen.

That's it! You have successfully split hydrogen and oxygen from water.

Cryptology - Enigma Machine

Today we learned that the Germans used a device called the Engima machine to encrypt their messages during WWII. They thought it was completely secure, but the Allies broke the code!

We watched this video about how the Engima machine works. The general idea is that when you encode a letter, it goes through three different substitution ciphers, bounces off a "reflector," and then goes back through those same three substitution ciphers again. Each substitution cipher is on a rotor. Each time you encrypt a new letter, at least one rotor moves, so you end up using a different set of substitution ciphers for each letter!

We made our own Enigma machines out of paper and tape. Here's the Enigma machine construction in progress:

Using the engima machine to decode a message:

There's a nice article here about how the Engima machine works and about some of the things that helped the Allies figure out what was going on.

Cryptology - The Alphabet Clock

In classes 3 and 4 we learned about modular arithmetic and the one-time pad.

Modular arithmetic is the sort of arithmetic you do on a clock. On a normal clock, if you start at 7 and add 11 hours you end up at 6. Mathematicians would write it like this:

7+11 = 6 mod 12

(actually, we use three horizontal lines instead of two for the equal sign, but I don't know how to make that symbol on the blog). The "mod 12'' part means that we're on a clock with 12 numbers, starting with 0 at the top (instead of 12) and continuing around to 11.

For cryptology, we use a clock with the 26 letters on it. These correspond to the numbers from 0 to 25.

On the alphabet clock,

0 and 26 both mean A

1 and 27 both mean B

25 and -1 both mean Z

and so on.

To use this clock to encrypt a message, we need some starting plaintext and a key. A key is a secret bit of information that the person sending the message and the person receiving the message both have to know in order for this to work.

Let's use CHICKEN as the plaintext and MOOFAZA as the key.

We translate the plaintext and key into numbers, using the clock. We add the first number of plaintext and the first number of key, then the second number of plaintext and the second number of key, and so on.

plaintext   CHICKEN   2    7    8    2   10  4  13
key         MOOFAZA  12   14   14    5   0   25  0
sum                  14   21   22    7   10  29 13

Then we translate the numbers back into letters. On the alphabet clock, 29 and 3 are both D.

14 21 22 7 10 29 13
O  V  W  H  K  D  N

We send the ciphertext OVWHKDN.

To decrypt the message, we need to know the ciphertext and the key. Since we added the key to get the ciphertext, we have to subtract the key to get the plaintext. Translate the ciphertext and key into numbers, and take the difference between each pair of numbers:

ciphertext OVWHKDN 14 21 22 7 10 29 13
key        MOOFAZA 12 14 14 5  0 25  0
difference          2  7  8 2 10  4 13

Finally we translate those numbers back into letters:

2 7 8 2 10 4 13
C H I C K  E  N

If the key is totally random and as long as the message, we have what's called a one-time pad. In one sense, this is the best cryptography there is: if you don't know the key, you can't figure out the message. I don't care how good your computer is - it can tell all the possible messages, but it can't tell which was the real one.

In another sense, this is horribly impractical. You have to get a gigantic list of completely random letters to your buddy, without anyone else seeing them, and you and your buddy have to always be at the same place in the gigantic list of letters. What a mess!