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Mini Explosions

Sun, 17/01/2010 - 19:14 — admin
Introduction
Public summary: 

Make an impressive explosion with kitchen ingredients and find out more about what makes things go with a bang.

Exploding film canisters with lemon juice and bicarb.
Useful information
Kit List: 

Lemon Juice (and maybe vinegar)
Bicarb
A couple of washing up bowls
Teaspoon or similar for scooping bicarb
Clear plastic box with the hinged lid
Green tray to catch any leakage from clear plastic box (doesn't live in blue box)
(All of this lives in a large blue box with white lid)

Frequency of use: 
5
Explanation
Explanation: 

Initially, mix lemon juice (about 1/4 fill the cannister) and bicarb (1/4 of a teaspoon) in the film cannister with the lid off, so that the kids can see it frothing up.

Ask them where they think the bubbles are coming from/ what's in the bubbles (space for a bit of a discussion of different gases here, many of them will have heard of CO2).

Get them to think about what lemon juice is like (sour), and what else is sour (vinegar, other citrus juice..) any acid can let out the gas that's "trapped" in the powder. Possibly also discuss use of bicarb in baking... heating it up releases gas, which puts bubbles in your cakes.

The bubbles should froth well over the top of the cannister, point out that if the lid were on the gas wouldn't be able to get out. Ask them to predict what will happen if you put a lid on (does the gas have anywhere else to go...)

Now try it and see if they're right!

There are 2 slightly different approaches:

Method 1

Put some lemon juice in the cannister, put a piece of tissue paper over the top of the cannister with bicarb on top of that, push the lid on so it hold the tissue paper. The bicarb is now held at the top of the pot away from the lemon juice.
Put the cannister upside down in the clear plastic tank and shut the lid (it's often a good idea to have the lid partially shut before you invert the cannister to reduce the risk of it getting off you). The bicarb and lemon juice will mix and the pot will explode upwards.

Method 2

Put some lemon juice in the cannister, press bicarb into the well in the centre of the lid. The bicarb is now held at the top of the pot away from the lemon juice.
Put the cannister upside down in the clear plastic tank and shut the lid (it's often a good idea to have the lid partially shut before you invert the cannister to reduce the risk of it getting off you). The bicarb and lemon juice will mix and the pot will explode upwards.

It's usually a good idea to try both methods and see which one works better for you and the type of film cannister you happen to have.

Some film cannisters explode better than others, so it is worth trying different ones to make sure you are using the right lid. The oval ones work really well.

Other things to think about: vinegar (acetic acid) is a stronger acid than lemon juice (citric acid); if using vinegar expect this reaction to be quite quick...

Risk Assessment
Date risk assesment last checked: 
Thu, 22/12/2011
Risk assesment checked by: 
hannah2809
Date risk assesment double checked: 
Fri, 20/01/2012
Risk assesment double-checked by: 
Catherine
Risk Assessment: 
DESCRIPTION Lemon juice and bicarbonate mixed in a film cannister. Top pressed on. Explodes off in box.
RISKS

1. Slip hazard
2. Explosions could get out of box, (or occur before the cannister has been put in the box) and get into eyes

Irritant to eyes
Irritant in cuts

ACTION TO BE TAKEN TO MINIMISE RISKS

1. Clear up spills if on a slippery floor. Do experiment outside if possible

2. Do experiment in a clear lidded fish tank so kids are not peering over the top to see what is happening.
Ensure the top of the tank is not at eye level (it is possible for a small volume of the reagents to be propelled through the crack between the top of the tank and the lid). Run a length of clear plastic tape along the hinged side (which should be closest to your audience) to prevent splattering.

It is important to keep the kids under control. Try to keep control over at least one of the reagents, so the kids can't just do it themselves
Don't let the kids peer over the top
We have eyewash in with the expt - the demonstrator must ensure he or she knows where it is.
Tissue paper may be used as a "fuse" to increase the time taken for the reactants to come into contact with each other - this gives more time to get the cannister into the tank. Lemon juice is usually better than vinegar, as it reacts more slowly, so again, there is more time to get the canister into the tank. In addition, eye protection should be provided for demonstrators to minimise possible risk of solution splashing into demonstrator's eyes.

ACTION TO BE TAKEN IN THE EVENT OF AN ACCIDENT 1. Call first aider in case of injury
2. Call first aider. Use eyewash to wash out of eyes if trained and confident to do so, if solution or reactants have entered eyes.
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