The variable that I am going to use is concentration as this is the most practical out of the four variables. The collision theory explains how concentration affects the rate of reaction and therefore the amount of oxygen produced:
For a reaction to occur the reactant particles must collide. Only a certain fraction of the total collisions cause chemical change; these are called successful collisions. The successful collisions have sufficient energy (activation energy) at the moment of impact to break the existing bonds and form new bonds, resulting in the products of the reaction. Increasing the concentration of the reactants brings about more collisions and therefore more successful collisions as there are more reactant particles per unit volume therefore increasing the rate of reaction.
I must first work out how to find out the percentage of the concentration of yeast solution whilst diluting it.
The initial percentage of concentration in the yeast solution is 2% so to calculate the percentage of the concentration whilst diluting it I must use this formula:
Concentration of yeast = Volume of yeast solution ÷ Volume of yeast and volume of water × 2% so:
5ml (yeast) ÷ 5ml (yeast) + 0ml (water) × 2% = 2%
4ml (yeast) ÷ 4ml (yeast) + 1ml (water) × 2% = 1.6%
3ml (yeast) ÷ 3ml (yeast) + 2ml (water) × 2% = 1.2%
2ml (yeast) ÷ 2ml (yeast) + 3ml (water) × 2% = 0.8%
1ml (yeast) ÷ 1ml (yeast) + 4ml (water) × 2% = 0.4%
These will be the 5 concentrations I will be using.
Also I must insure that all other variables remain constant throughout, the variables (other than concentration) that could effect my investigation the most would be temperature and the concentration of the Hydrogen Peroxide. I will make sure that the temperature doesn’t affect the results by insuring that all windows and doors stay closed throughout the investigation. Also I will be using the same burette that contains Hydrogen Peroxide each time so that the concentration of it remains the same throughout the investigation.
My predictions
I predict that as the concentration of the Yeast solution decreases the amount of oxygen produced will also decrease. I believe this as if the concentration of a solution is decreased there are less reactant particles per unit volume. This decreases the probability of reactant particles colliding with each other.
I predict that if I half the amount of concentration in the Yeast solution the amount of oxygen produced will also half. I believe this will happen as there will be half the reactant particles per unit volume then the probability of reactant particles colliding with each other will decrease by 50%.
In this second preliminary investigation yeast solution was used as it is easier to adjust the concentration. The hydrogen peroxide stayed constant throughout with five ml being added every time. I decided to use a gas syringe to record the results, by using a stop watch from the moment the hydrogen peroxide was added I could get an accurate reading on the gas syringe after ten seconds. This would show me how much oxygen had been released in the ten second time span. My results were as followed:
I will repeat each of the conditions to insure that there are no outliers and if the results don’t match I will have to do the investigation a third time
For my final method this is the apparatus I will use:
- 12 boiling tubes – To sufficiently hold the Yeast solution and Hydrogen Peroxide
- Boiling tube rack – To sufficiently hold the boiling tubes upright
- Gas syringe – Measures the amount of oxygen produced
- Burette – Accurately measures out amount of Yeast solution and Hydrogen Peroxide
- Stopwatch – Accurately measures 10 seconds
- Yeast solution (measured from burette for an accurate measurement)
- Distilled water (measured from burette for an accurate measurement)
- Hydrogen Peroxide (measured from burette for an accurate measurement)
These are the steps that I will need to follow whilst doing the investigation:
- Take the boiling tubes and place under the burettes, fill the first of the boiling tubes with 5ml of yeast solution and 0ml of distilled water.
- Place the boiling tube into the boiling tube rack.
- Place a different boiling tube under the burette containing Hydrogen Peroxide and fill it up with 5ml of Hydrogen Peroxide.
- Next take out the yeast solution and quickly and sufficiently add the 5ml of Hydrogen Peroxide then as soon as it is all in push on the stopper of the gas syringe over the boiling tube.
- Immediately start the stopwatch.
- Once the stopwatch has reached 10 seconds take a reading from the gas syringe.
- Place the reading into your table.
Repeat this process for all of the remaining concentrations and you will have a full table of results.
Here is a diagram of the experiment:
Results
These results show me that as the variable concentration decreases the amount of oxygen produced also decreases. I have no anomalous results in my results this shows reliability and accuracy in them. Also most of my results lie on the line of best fit thus proving the accuracy and reliability of them further. At first as the concentration was decreasing the oxygen produced went down consistently by around 4/5 cm3, then at the change from 0.8% concentration to 0.4% concentration it went down by 8 cm3.
In my analysis of the results I must look back at my predications and test them against my results:
My predictions
I predicted that as the concentration of the Yeast solution decreases the amount of oxygen produced will also decrease. This has occurred as you can see from my results that as the concentration went down the subsequently so did the amount of oxygen produced. This is because as if the concentration of a solution is decreased there are less reactant particles per unit volume. This decreases the probability of reactant particles colliding with each other.
I predicted that if I half the amount of concentration in the Yeast solution the amount of oxygen produced will also half. This has occurred as you can see from my results at 1.6% concentration the amount of oxygen produced was on average 21.0 cm3, and at 0.8% concentration the amount of oxygen produced was on average 11.5 cm3. This is very close to half the amount of oxygen being produced so I can therefore perceive my prediction as being accurate. This happened because there will be half the reactant particles per unit volume then the probability of reactant particles colliding with each other will decrease by 50%.
Overall I must look back briefly at the collision theory to show why the amount of oxygen produced decreased when the concentration did scientifically:
For a reaction to occur the reactant particles must collide. Only a certain fraction of the total collisions cause chemical change; these are called successful collisions. The successful collisions have sufficient energy (activation energy) at the moment of impact to break the existing bonds and form new bonds, resulting in the products of the reaction. Increasing the concentration of the reactants brings about more collisions and therefore more successful collisions as there are more reactant particles per unit volume therefore increasing the rate of reaction. This theory has been shown to be true in my results.
Evaluation
The results of my experiment where overall very accurate, you can tell this by the fact that I have very small error bars signalling that my results varied minimally. Also you can see that my results are accurate as most of them lie on the line of best fit. Also the reliability of my results can’t be questioned as I repeated the experiment three times and all results where close in individual repeats. No outliers have occurred which means I controlled the other variables sufficiently.
Although I conducted the experiment as accurately as I could there was a few sources of error in the method that I used. Firstly, some help from my partner was needed to start the stopwatch as quickly as possible – this caused a small delay as it is very difficult to start the stopwatch instantly as the hydrogen peroxide is poured in. This small delay could differ from test to test causing a small difference in the data that I was receiving. However I did two tests and the averages where taken and there were no major differences within the two tests. I am happy that I used a gas syringe as it took the measurements very accurately and helped me achieve results without having to predict what the oxygen produced was.
If I where to do this test again I would use more than 10 seconds after the hydrogen peroxide was poured in. I would push this up to 20 seconds to get a more accurate showing of the oxygen produced.
Using my graph, with lines of best fit, I can draw a conclusion from my experiment. The concentration to amount of oxygen produced graph has a positive correlation – as the concentration is increased so does the rate of reaction and therefore oxygen produced.
I believe there was a sufficient range of readings to justify my predictions and conclusions as you can see a clear consistent line of best fit. Taking all into consideration I believe that the conclusions I took from this experiment are accurate and precise and have been proven so by my results.