Number 12: The world's simplest electric motor

I saw this astonishingly simple motor described over at the fab proton's for breakfast blog and had to have a go.

All you need is:

• A small stack of 12mm diameter disk magnets (I get mine from emagnets)
• A 1.5V AA battery
• A length of stiff but bendable copper wire
• A penny 

Safety:

The magnets are very strong. Watch out they can fly together and shatter. 

What to do:


1. Stick the magnets onto the negative end of the battery.

2. Place the penny on the top of the battery.

3. Bend the wire so that it balances on the top of the penny whilst the other end only just touches magnets.

4. And watch it spin!

What's going?

When the copper wire touches the magnet a circuit is completed and electricity runs through the wire. When electricity passes through a wire it generates a magnetic field. This then interacts with the magnets at the bottom of the battery (in the same way as opposite poles of a magnet repel each other) and the who thing spins. Hey presto the world's simplest motor.

Number 11: Grape plasma

We all know about the 3 states of matter, right? There's gases, liquids and solids. Well there's actually more than that (they don't bother teaching you about them in school) and one of them is plasma. It can be made by super heating gases to the point where the electrons get stripped off leaving charged ions and free electrons. Generally you need a lot of heat, like in a star or lightning to make it. Or some clever technology, like a plasma lamps. But it turns out you can also make plasma with a grape and a microwave oven.

Safety:

1. The grapes get VERY hot so be careful when you take them out of the microwave. 
2. The process also produces ozone gas, which is poisonous and can cause breathing difficulties. It doesn't produce a lot of it, but you probably don't want to do this experiment to many times. And if you are asthmatic its probably best to just watch it on youtube. 
3. There is the potential to damage your microwave. I've never hurt mine but just be warned making  3000^oC plasma may not do it much good. So ask whoever owns the oven if its OK first.

What you'll need:

• A microwave oven
• A grape
• A knife
• Kitchen towel

What to do:

1. Cut the grape in half along its equator. Make sure you keep the two halves attached by a bit of skin.

2. Place the cut surfaces on the kitchen towel to gentle dry them.

3. Turn the grapes back over and stick them in the microwave.

4. Turn it on. 

For the sake of this video I've used 4 grapes in one go. I advice you to do it one at a time.

5. When you (carefully) take the grape out you should see that its really pretty singed around the side. Which just goes to show how hot it go.

What's going on?
I have to confess that I'm not sure about this one. And judging from discussions elsewhere on the web there's no clear answer. So if someone would like to chip in and give us an explanation I'd be glad to hear it.

Number 10: Polishing the silver

There's all sort of potions and polishes that you can buy to clean up the silver. Don't buy any of them. Because you can find everything you need to get the best cutlery sparking again in your kitchen cupboards.

What you'll need:

• Bicarbonate of soda
• Aluminium foil 
• A cup or glass
• Some tarnished silver spoon (its best if its solid silver, it will work with silver plated stuff, but you run the risk of removing the plating)

What to do:

1. Put a heaped teaspoon of bicarb into the glass.

2. Tear up 10 to 20 bits of foil and add them to the glass.

3. Put the spoon in the cup

4. Pour on hot water. Water from the hot tap will do fine. 

5.Stir and leave for 5 minutes.

6.Take the spoon out and inspect it. All the tarnish will have disappeared. 

Before

After

What's going on:

There's some pretty niffy chemistry going on here.  First lets dispel a little myth, the tarnish is not due to a reaction with silver and oxygen like a lot of people claim. Iron reacts with oxygen to make rust, but silver tarnish is something different. Silver tarnishes when it reacts with sulfur containing chemicals (usually hydrogen sulfide, which smells like rotten eggs) to produce silver sulfide. Eggs are particularly high in sulfur which is why they make your silver tarnish so quickly.

That's the easy bit. How the aluminium and bicarb work to clean the silver is a little more complicated.

Lets take a look at the chemicals that we start off with. You've got silver sulfide (the tarnish), sodium bicarbonate (the bicarbonate of soda), aluminium  hydroxide (the foil is actually covering in a layer of this, the aluminium itself is underneath and we need to get at it).

Step 1: The bicarbonate reacts with the aluminium hydroxide and turns is back to aluminium.

Step 2: The aluminium reacts with the silver sulfide to make silver and aluminium sulfide.

and that leaves you with nice clean silver.