What it shows
Catalysts speed up a reaction without being used up. Yeast and raw potato contain catalase, an enzyme that breaks hydrogen peroxide into water and oxygen, and the volume of oxygen collected measures how fast it works.
The science
Hydrogen peroxide breaks down slowly on its own: 2 H2O2 gives 2 H2O + O2. A catalyst gives an easier path, so the reaction goes faster but the catalyst is unchanged at the end. Catalase in yeast and fresh potato is an enzyme, a biological catalyst. Boiling destroys the enzyme because heat changes its shape, so boiled potato should do almost nothing. Measuring oxygen volume against time shows the rate for each catalyst.
Materials
Cost: under Rs 200. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Hydrogen peroxide 3 per cent, 150 ml (pharmacy)
- A pinch of dry yeast, 2 g of raw potato paste, 2 g of carrot paste and 2 g of boiled potato paste
- A plastic bottle of 250 ml with a one-hole cork or clay seal
- A pipe or a clean straw pipe and an inverted bottle full of water in a bowl
- A measuring cylinder or syringe
- A stopwatch
- A small spoon for each catalyst
Safety
For this project: An adult must supervise. Wear goggles because hydrogen peroxide irritates eyes. Do not seal the reaction bottle completely or it may burst, and do not drink or taste anything. Wash hands afterwards.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Fill the collecting bottle with water, cover its mouth with a card, turn it upside down in a bowl of water and remove the card. It should stay full.
Put 20 ml of hydrogen peroxide in the reaction bottle. Fit the cork and delivery pipe, with the pipe end under the upturned bottle.
Open the bottle, add a pinch of yeast, replace the cork quickly and start the stopwatch.
Read the volume of gas collected every 15 seconds for two minutes. Write the numbers in a table.
Rinse the bottle, refill the collecting bottle and repeat with raw potato paste, then carrot paste and then boiled potato paste. Use the same volume of peroxide and about the same mass of catalyst every time.
Run one test with no catalyst as a control to see how slow the reaction is on its own.
Plot volume of oxygen against time for all catalysts on one graph.
Compare the slopes at the start of each line: a steeper slope means a faster reaction.
What you should see
A set of curves showing yeast and raw potato producing oxygen fast, carrot slower, and boiled potato and the no-catalyst control giving almost none.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What is a catalyst?
A substance that speeds up a reaction and is not used up in it.
2Why does boiled potato not work?
Heat destroys the catalase enzyme by changing its shape.
3How can you test for oxygen?
It relights a glowing splint, which an adult can show in the lab.
4Why keep the volumes and masses the same?
Otherwise the comparison between catalysts is not fair.
Take it further
Test the effect of temperature on yeast by chilling or warming the peroxide to 10, 30 and 50 degrees C.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
Science projects
Safe Chemistry Projects for School
Experiments and models with kitchen materials and proper safety
Science projects
Science Projects for Class 9 and 10
Models and experiments for high-school physics, chemistry and biology