Apparatus:
- Yeast (20g)
- Sugar (8 g)
-
Water (52 g= 52 cm3)
- Termometer (0-110 ºC ±0.05 ºC)
- Weighting machine (±0.05 g)
- Razor blade
-
Boiling tubes (20.0±0.5 cm3)
- Stand, bosses and clamps
- Manometer tube
- Clip
- Clock (±0.1 s)
- Pipettes (2.00±0.05 ml)
SAFETY:
Precaution, razor blade is a sharp apparatus.
Method:
- Prepare solutions acorrding to data in Table 1 so in each case you have 20 g of solution.
- Construct the apparatus shown on the Drawing 1 using manometer and boiling tube.
-
As only the influence of yeast concentration is measured, place each solution with different yeast concentration in boiling tube.
- Shake the tube with solution before each measurement in order to have equal distribution in boiling tube.
- Dive the boiling tube in beaker with hot water and keep the temperature stable.
- As reaction starts, time how long does it take for the fluid to rise through the distance of 5 cm in the manometer tube.
- Open the clip at the top of boiling tube and repeat the test in the same yeast concentration, shaking the tube again before the measurement.
- Do the same test with different yeast concentration.
Drawing 1: The apparatus used in the experiment.
The reaction in the experiment has followed the equation:
C6H12O6 → 2C2H5OH + 2CO2
At first, the adequate solutions were made. The amount of sugar (2.00 g) was kept the same during all the measurements, only the amount of yeast and water was changed so that the total mass of solution was 20.00 g.
Water was measured in cylinders in cm3 so I needed to calculate the mass not volume. Since the density of water is 1g cm-3 the mass of water will numericaly be the same as the volume, just the unit will be changed.
Eg. 16.00 cm3 *1g cm-3= 16.00 g
Higher yeast concentrations were created by increasing the amount of yeast in the solution and decreasing the amount of water.
After creating necessary solutions, the experiment was carried and the measurements were recorded in Table2.
Having measured the time for each reaction only three times, the ucertainity was calculated using the equation:
uncertainty=
Rounded to 1 decimal place
Having all needed results and values, I calculated the values for the rates of reaction using the equation:
Rate of reaction=
The uncertainty for the rate of reaction was calculated using the equation:
Uncertainity=
I decided to round the results to 2 decimal place.
Rounded to 2 decimal place
Later on, the graph was plotted.
Graph1: The rate of cellular respiration in different yeast concentration.
Conclusion:
Using the solutions with the range of yeast concentration from 10% to 40%, I am allowed to say that the experiment confirms the hypothesis.
The rate of cellular repiration was established by CO2 released. The time was measured in which each solution (with different yeast cncentration) releases the same amount of CO2.
The average time taken for the fermentation to occur changes with the yeast concentration. The higher the yeast concentration, the less time is needed. The reaction happens the faster in 40% concentration and is equal to 8 seconds, while the slowest reaction occurs in 10% concentration, being equal to 23.5 seconds. What is more, the uncertainty for the 40% yeast concentration solution is the highest of all due to big dispersion in measurements.
So as for the rate of reaction, it increases almost linearly between the 10 to 40% yeast concentration. The value of rate of reaction for 20% yeast concentration does not fit perfectly to the other datas. The rate of fermentation will increase proportionally as yeast concentration increases.
I was not able to create wider range of solutions with higher yeast concentrations, because of too big amount of yeast in 20g solution; different proportions of substances should be made to wider the range. It was also impossible to create 100% yeast solution, since in each solution created the mass of sugar was kept constant, so that the maximum percentage solution for the fermentation to occur was 90%.
It also show how big influence on the rate of reaction has the yeast concentration.
Comparing my results with the literature () where claimed that the rate of fermentation increases with increasing yeast concentration but levels out at some point, the results I obtained were correct (in the range 10 to 40 % yeast concentration).
In the experiment there were errors due to:
- Significant uncertainities of the equipments which might later influence the measurements and results
- too few measurements made so that the not fitting ones could be eliminated, which in fact influenced the results obtained the most
- Imprecise clock
- Human reaction [±0.2 s] in measuring time could affected the measurements, but it was a small influence
To improve the experiment and get more accurate and precise result, I could have:
- Make more measurements to reduce the uncertainty
- Use wider range of concentrations to be able to determine the optimum yeast concentrations during the experiment
- Use mass concentration measuring equipment provided by more specialised laboratory
- Use the clock with measures time with more decimal places to reduce the uncertainty
-
Use the Carbon Dioxide Detector to confirm the same amount of CO2 released in each fermentation reaction
References:
D.A. Clare "Analytical biochemistry"
M. Kent "Advanced Biology"
Odnieść się do wszystkich błędów
Użycie co2 detektora
Opisanie dokładnie grafu
Inne improvements
Wytłumaczyć czemu nie wider range
Bo trzebaby było zmienić objętości bo w podanych reakcja przemieszczzała się do manometer tube; wtedy wszystko od nowa
Wytłumaczyć uncertainitys of fequipment
Nie mówić że eliminated
Imprecise clock też nie powinno
Jak poprawić human reaction
LITERATURA od razy jak pisze o rate