D Preliminary Work
What are you going to change?
I am going to change the amount of yeast.
What are you going to measure?
I am going to measure how much gas is given off.
What do you need to find out before you plan your method?
I need to find out:
What apparatus I need.
How long the experiment will take.
How violent the reaction is.
How to take accurate measurements.
Preliminary Results
Apparatus
Measuring Cylinder
Filter Paper
2 Boiling Tubes
Thermometer
Spatula
2 Stands
Bung with long flexible tube
Palette
Stopwatch
Syringe
Plastic Knife
Beakers
A Tub
Item to be Changed
Amount of yeast
Method
- Fill a tub with water.
- Put a measured amount of yeast in a boiling tube.
- Set two stands up, one to hold the measuring cylinder and one to hold the test tube.
- Fill a measuring cylinder with water and cover the top with your hand. Turn it upside down and lower it in the tub of water.
- Use one stand to hold the measuring cylinder in place
- Set the bung and rubber tube up.
- Direct the rubber tube to go under the water and into the measuring cylinder.
- Set up the other stand so it holds the test tube with the bung on.
- Take the bung off, put a measured amount of Hydrogen Peroxide in.
- Put the bung back on.
- Observe, record and time all the reaction.
Your experiment should look something like this
Safety
Always wear goggles.
Always wear lab coats.
Never sit down whilst doing the experiment.
Making it fair
An experiment must always be fair otherwise it will not represent the results in a suitable way.
This is achieved by keeping everything uniform apart from the variable that you wish to investigate.
Table to put the valid results in:
Analysis
Graph: See graph.
The graph clearly shows that the bigger amount of yeast you put in the Hydrogen Peroxide, the more oxygen is let off. This is because of the reaction theory (the rate of a reaction depends on how often and how hard the reacting particles collide with each other. The particles have to collide to react). If the solution is made more concentrated it means there are more particles of reactant knocking about between the molecules which make the collisions between the important particles more likely.
There is a pattern on my graph, and this is, as the concentration of the solution increases, the amount of oxygen given off increases.
This graph above indicates that there was an overall increase in oxygen given off during the experiment.
If I were to repeat the experiment ideally, if possible, I would use a machine to cut the yeast allowing perfect sizes, dimensions, weights and surface areas enabling a perfectly fair experiment.
There were a couple of anomalous results, but overall there was a pretty sound pattern. Human error may well have caused this.
Evaluation
I am pleased with my experiment and its achievements.
I kept to my method
From my results I have found that the higher the concentration of Hydrogen Peroxide, the quicker the rate of the reaction, thus more oxygen being produced.
I have succeeded in what I had planned to do, which was to find out how the amount of yeast in Hydrogen Peroxide affects the amount of oxygen produced in the reaction. The results I got were not a surprise and were what I had expected and predicted from the start. I did get one result that was anomalous, but I put this down to the lack of my accuracy. The results I got were what I expected, so I am happy with them.
The experiment could have been made more accurate by using other methods of measuring yeast and Hydrogen Peroxide. More accurate measurements of Hydrogen Peroxide could have been perfected by not using measuring cylinders, which were only to either 0.5cm² or 1cm² degree of accuracy. This is not very accurate. I would probably use a gas syringe, which measures much more accurately, which may well have solved this problem. Another inaccuracy was when we cleaned out the test tubes; they could have still contained some Hydrogen Peroxide and/or yeast. This would give that test either an advantage or a disadvantage. I know that the temperature can affect the rate of a reaction. The temperature was not the same from one experiment to the other, as the first time the test tubes would have been room temperature whereas after a bit of washing out they would be cooler due to the water. So this may have changed the results slightly. The more different concentrations of yeast would prove the whole experiment was correct without a doubt. Even more repeats could be done for each amount of yeast, enabling more accurate averages.
