HELP! REQUIRED FOR 12 JULY 2010

[Zaahira Mahomed]

Doing a project on reaction rates and factors that affect them.
Doing the cornflour bomb.
Cornflour is sprayed into the flame of a candle burning inside a large tin can with the lid on. The resulting small explosion caused by rapid combustion of the cornflour blows the lid off the tin. The reaction dramatically illustrates the conversion of the chemical energy stored in foodsuffs into heat and other forms of energy. It can also be used to show the effect of surface area on the rate of chemical reaction.

Read our standard health & safety guidance

Lesson organisation
This is a brief demonstration, taking about 5 minutes – but of course may have to be repeated on demand!

Apparatus and chemicals
Safety screen
Eye protection for teacher

Large coffee tin (500 g catering size) with metal lid (see notes 1 and 2)
Glass funnel, small (2 – 3 cm diameter)
Rubber bung (13 mm), one hole
Candle, short piece, or nightlight
Pipette filler, rubber bulb (about 50 – 100 cm3) type
Rubber tubing, short lengths, to join pipette filler to funnel stem
Wooden splint and matches to light candle

Cornflour, dry, a few grams required for each demonstration (see note 3)

Technical notes
1 The apparatus needs to be assembled as shown in the diagram below before the lesson. Make a neat hole in the side of the coffee tin, near the base, of suitable size to take the one-holed rubber bung. Insert the funnel into the hole in the bung so that the stem protrudes outwards from the narrow end of the bung. Fit the bung carrying the funnel into the hole from inside the can, so that it is pointing slightly upwards - see diagram. Connect the pipette filler bulb to the funnel stem using short a lengths of glass and rubber tubing. Place a short length of candle (or a nightlight) inside the coffee tin and stick it down with a little molten wax.



2 This apparatus can be improvised in a number of ways, but it is important that the resulting apparatus can blow a cloud of cornflour into the candle flame when the pipette filler is squeezed. An alternative arrangement is to place a small crucible inside the can, to contain the cornflour, and replace the funnel with a glass tube bent at right-angles, so that it's tip is directed downwards into the crucible. Some prior experimentation and adjustment may be needed to ensure the demonstration works well.

3 As an alternative to cornflour, other similar, oxidisable, fine powders can be used, eg custard powder, icing sugar or lycopodium powder (Note: lycopodium powder is a form of pollen, which may cause sensitisation or hay fever-like symptoms in susceptible individuals. If the demonstration works well, very little lycopdium powder should enter the air in the room). The powder usually needs to be dried in an oven at about 80oC.

Procedure
HEALTH & SAFETY: The experiment must be conducted behind firmly fixed safety screens close to the can. The class should be seated sufficiently far back from the demonstration to avoid any risk of being hit by the flying tin lid.

1 Place a few grams of cornflour in the funnel. This may be more easily done before finally putting the funnel in place inside the can, and connecting it to the pipette bulb.

2 Light the candle and quickly fit the tin lid. Quickly (before the candle goes out) give the pipette filler a rapid squeeze to blow the fine cornflour powder into the candle flame, keeping your head well back. The resulting rapid combustion of the finely-divided cornflour blows the lid off the tin.

I've completed my project and would just like to clarify a few things..
What are my independent, dependent and controlled variables?
How do I structure my conclusion?
How do I allow factors to influence my project, therby influencing the rate of reaction?

Thank you so much..

[deleted-71417]

Hi,

I suggest you read the variables page of the Science Buddies Project Guide for help on figuring out dependent and independent variables:
https://www.sciencebuddies.org/science- ... bles.shtml

The page on conlusions may also be helpful to you:
https://www.sciencebuddies.org/science- ... ions.shtml

Here is the top level link to the project guide:
https://www.sciencebuddies.org/science- ... ndex.shtml

I hopr this helps get you started.

Barrett Tomlinson