ingridscience

Mix the baking soda and vinegar - this may be a familiar reaction to some. It makes bubbles of gas.
Tell students a chemical reaction produces the gas. Give students molecule models of the starting molecules and they figure out what the products are (tell them one product is water or H2O):
HCO3 (baking soda, or base) + H (vinegar, or acid) -> H2O (water) + CO2 (carbon dioxide gas)

The molecule models can be purchased (see resource), or made from modelling clay and toothpicks.

This chemical reaction is endothermic - it absorbs heat, so feels cold. A temperature change is an indicator that a chemical reaction is happening.
If the reaction is done in a large ziplock bag (with ~three Tbspns baking soda and ~400ml vinegar), students can feel that the reaction is cold.

The baking soda and vinegar reaction is the basis of many science activities, including setting off rockets and making food.

Add about a cup of hydrogen peroxide to the empty bottle.
Add a small squirt of dish soap, and swirl in.
Add a tablespoon of dried yeast, then rapidly swirl in.
Set the bottle upright in a tray (it will overflow).

The mixture gets warm as the chemical reaction makes heat ("exothermic"). Feel the heat underneath the tray to keep hands cleaan.
Energy transformation: chemical energy to heat energy.

The hydrogen peroxide is split into oxygen and water, catalysed (sped up) by the yeast: 2H2O2 -> O2 + 2H2O. The oxygen gas makes tiny bubbles. Molecule models can be used to show this chemical reaction.
The dish soap stabilizes the bubbles to make a foam - one end of the detergent molecule does not like water ("hydrophobic") so it inserts into the gas bubbles; the other end likes water ("hydrophilic") so sticks outside the bubbles into the surrounding water. The soap molecules surround the oxygen gas bubbles in this way and stablize them so that they last for a longer time - as a "foam".
As the oxygen is continually made the foam squeezes out of the bottle like toothpaste...for an elephant!

Foam is a kind of a mixture called a colloid - gas bubbles in a liquid.
See attached file for other colloids.

Science centre demonstration using a higher concentration of hydrogen peroxide: https://www.youtube.com/watch?v=ei5kGOW1wT8

Half fill the film canister with water, drop half an alka seltzer tablet in it, snap on the lid, turn upside down so the lid is placed on the ground, then stand back.
As the carbon dioxide gas builds up in the film canister, the pressure is eventually too great, and the lid is pushed off, shooting the canister base into the air.

The film canister can also be filled with baking soda and vinegar for the same effect (and cheaper).
Place about 1/8 tspn baking soda in a piece of toilet tissue and twist closed (to make a head of baking soda and a tail of just tissue), place in the vinegar with tail down, cap the canister then turn over to place on the ground.

Alka seltzer contains an acid and a base, which when dissolved in water, can combine to produce carbon dioxide gas and water.

Optional: model the chemical reaction using modecule models.
Give each student a model molecule of HCO3 and an H atom. These are the components of Alka seltzer/baking soda and vinegar.
When the alka seltzer gets wet, these molecules combine and rearrange to make two new new molecules. When the baking soda and vinegar are mixed the molecules react to make two new molecules. Ask students to figure out what these new molecules are, giving them the hint that one of them is water.
The products of the reaction are water (H2O) and carbon dioxide (CO2).
Carbon dioxide is a gas, and as more and more of it is made by the chemical reaction, the gas builds up in pressure until it blows the lid off the film canister.
The gas escapes by shooting out of the bottom of the film canister. This force directed downwards propels the canister upwards. (Newton's Third Law of Motion: Every action results in an equal and opposite reaction.)

Open the bottle of diet coke and place in an open space.
Move the students back.
Pour the mentos into the tube, so that they are all lined up and will fall out fast. Put a card over the top of the tube, and invert it over the coke bottle. Pull out the card and move back fast. (Alternatively, use a paper funnel to pour in the mentos - the faster you can get them in, the better.)

A giant fountain of foam is produced.

The mentos have a very bumpy surface that provides a place for bubbles of carbon dioxide to come out of solution. It does so rapidly, generating a mass of bubbles which stay around long enough to form a foam that geysers out of the bottle.

http://en.wikipedia.org/wiki/Diet_Coke_and_Mentos_eruption

Inflate the balloon and tie it off.

1. Rub it in your hair to make a charge difference between the balloon and your hair. (Electrons are transferred from your hair to the balloon.)
Hold the balloon (negatively charged) just above your head so your hair (positively charged) will be attracted to it and stand up on end.

2. Lay a tin can on the floor on its side. Rub the balloon in your hair to charge it, then hold it close to the tin can. The can will start to roll towards the balloon without touching it.
The negatively charged balloon repels the electrons of the can so that a positive charge is near the balloon. The positive charge is attracted by the negative charge of the balloon.
http://www.exploratorium.edu/science_explorer/roller.html

3. Bring the charged balloon near to a thin stream of water from a tap. The water will bend towards the balloon, as the charged molecules in the water are attracted to the negatively charged balloon.

4. Experiment with what else the charged balloon will stick to: sweater and clothing, styrofoam, the wall...
Set up as a free play activity where students investigate in their own way. They should take notes on what they find, to refer to when the group comes together to discuss what they found.

1. Blow a balloon up to different sizes and hit it with the heel of your hand to make a sound. Blow the balloon up to different sizes to make different notes.
The notes change as the balloon skin is stretched to different extents, and so vibrates at different frequencies.

2. Blow a balloon up, then release the air from it while pinching the neck. Stretch and release the neck hole to make different sounds.
As the air passes through the neck of the balloon it makes it vibrate, which produces a sound. Different sounds are made as the neck is stretched to different extents.

3. Push a hex nut into a balloon, then inflate it. Hold the neck closed then move the balloon in fast circles to make the hex nut roll around the inside of the balloon. As it reaches a certain speed it resonates the balloon skin to make a humming noise. Try other objects in place of the hex nut e.g. marble.

4. Stretch a piece of balloon over a can, and hold it on (or fasten with a rubber band), to make a simple drum. Flick or pinch and drop the drum head to make a noise - the more it is stretched the higher the sound. The vibration of the drum head causes the sound. Vary how much the skin is stretched to change the note.
Blowing onto the drum skin also makes an interesting noise.
If the drum skin breaks leaving a strand of balloon across the top of the can, this can also be plucked to make a noise - vary the tension to change the note.

Allow students to play with the molecule models.
They can build molecules from images and learn about the function of the molecules they build.
They can make up their own. I encourage them to fill all the holes on the molecules, so that their molecule is more likely to be stable. Sometimes students will make something that can be looked up and described, but often they will build larger structures that don't exist. These models have a similar appeal to lego.

A superb book discussing the function and uses of simple molecules, building into complex: Molecules by P.W. Atkins, published by Scientific American Library.

Ideas for chemical reactions to demonstrate with these molecule models attached.