dcp and ce lab report 13 ibdp

Anastasia Chrysilla Candidate number: 001863-‐003

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Qualitat ive Data Col lection

0.0M 0.5M

1.0M 1.5M

2.0M

At first, when the yeast was mixed with glucose solution, the solution was semi-transparent. After it was left for 43 hours, the yeast and glucose solution became cloudy white. The solution of

yeast mixed with 2.0M glucose concentrations had the thickest color, while the solution of yeast mixed with 0.0M glucose concentrations (only distilled water) had the faintest color.


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Quantitat ive Data Col lection Below is shown data collection table

Table 1. In it ia l Percentage Absorbance of Yeast and Glucose Solut ion

Init ial %Absorbance (±0.001au)

Glucose concentration

/ Molar Trial 1 Trial 2 Trial 3 Trial 4 Trial 5

Average % Absorbance of al l tr ials

0.0 0.378 0.458 0.356 0.480 0.496 0.434 0.5 0.380 0.321 0.362 0.396 0.390 0.370 1.0 0.238 0.274 0.263 0.276 0.301 0.270 1.5 0.206 0.182 0.189 0.216 0.305 0.220 2.0 0.170 0.165 0.164 0.159 0.165 0.165

Table 2. F inal Percentage Absorbance of Yeast and Glucose Solut ion

Final %Absorbance after 43 hours (±0.001au)


/ Molar Trial 1 Trial 2 Trial 3 Trial 4 Trial 5

Average % Absorbance of al l tr ials

0.0 0.410 0.500 0.368 0.544 0.530 0.470 0.5 0.484 0.354 0.388 0.426 0.414 0.413 1.0 0.302 0.338 0.338 0.353 0.382 0.343 1.5 0.258 0.217 0.219 0.249 0.336 0.256 2.0 0.233 0.217 0.223 0.212 0.209 0.219

Data Processing In table 1 and table 2 above, average percentage absorbance (APA) of all trials will be

used as initial and final value of average absorbance of yeast and glucose solution respectively. In order to determine optimum glucose concentration for yeast fermentation, the percentage

change in APA after yeast and glucose solution was mixed and left for 43 hours was calculated. The biggest percentage change in APA will show that within the given length of time, yeast


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fermented the most thus indicates that it was the optimum glucose concentration for yeast fermentation. Below is shown the calculation.

% Change in Average Percentage Absorbance (±0.002) after 43 hours=

𝐹𝑖𝑛𝑎𝑙 𝐴𝑣𝑒𝑟𝑎𝑔𝑒 %𝐴𝑏𝑠𝑜𝑟𝑏𝑎𝑛𝑐𝑒 − 𝐼𝑛𝑖𝑡𝑖𝑎𝑙 𝐴𝑣𝑒𝑟𝑎𝑔𝑒 %𝐴𝑏𝑠𝑜𝑟𝑏𝑎𝑛𝑐𝑒𝐼𝑛𝑖𝑡𝑖𝑎𝑙 𝐴𝑣𝑒𝑟𝑎𝑔𝑒 %𝐴𝑏𝑠𝑜𝑟𝑏𝑎𝑛𝑐𝑒 × 100%

For example, referring back to table 1 and 2, percentage change in APA when yeast was mixed with 0.5M glucose solutions was calculated

0.413− 0.3700.370 ×100% = 11.622%

The same calculation was done for all APA in five different glucose concentrations. The overall result is shown below

Table 3. Percentage Change in Average Percentage Absorbance after 43 hours

Percentage Change in Average %Absorbance Wednesday - Friday

Glucose concentration / Molar

Average %Absorbance

(±0.001 au) % Change in Average

Percentage Absorbance (±0.002 au) Init ial Final

0.0 0.434 0.470 8.295% 0.5 0.370 0.413 11.622% 1.0 0.270 0.343 27.037% 1.5 0.220 0.256 16.364% 2.0 0.165 0.219 32.727%

In Table 1, Table 2, and Table 3, the uncertainty of APA is ±0.001 au, which is the

smallest measurement unit of spectrophotometer, while percentage change in APA has uncertainty of ±0.002 au – the sum of uncertainties for initial and final average percentage absorbance.


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According to text book Chemistry for IB Diploma (2011), the formula to calculate percentage uncertainty is as shown below:

𝑃𝑒𝑟𝑐𝑒𝑛𝑡𝑎𝑔𝑒 𝑢𝑛𝑐𝑒𝑟𝑡𝑎𝑖𝑛𝑡𝑦 =𝐴𝑏𝑠𝑜𝑙𝑢𝑡𝑒 𝑢𝑛𝑐𝑒𝑟𝑡𝑎𝑖𝑛𝑡𝑦𝐸𝑥𝑝𝑒𝑟𝑖𝑚𝑒𝑛𝑡𝑎𝑙 𝑣𝑎𝑙𝑢𝑒 ×100%

The way to calculate percentage uncertainty of percentage change in APA is shown below. The

experimental value used is the APA and percentage change in APA in 0.5M glucose concentration solutions.

%Uncertainty of %Change in APA = %Uncertainty of %Change in APA + %Uncertainty in APA

= !.!!" !.!"#!!.!"#

+ !.!!" !.!"#

× 100

= 4.921% The calculation above is applied to calculate Percentage Uncertainty of %Change in APA in five different glucose concentrations. The end result table is shown as below

Table 4. End Calculat ion Result of Percentage Change in APA

Percentage Change in Average %Absorbance Wednesday - Friday


/ Molar

Average %Absorbance

(±0.001) % Change in Average

Percentage Absorbance (±0.002)

Percentage Uncertainty of %Change in Average

Absorbance Init ial Final 0.0 0.434 0.470 8.295% 5.786% 0.5 0.370 0.413 11.622% 4.921% 1.0 0.270 0.343 27.037% 3.110% 1.5 0.220 0.256 16.364% 6.010% 2.0 0.165 0.219 32.727% 4.310%

From Table 4, a graph is generated as shown on the next page,


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Graph 1. Percentage change in APA after 43 hours in di f ferent g lucose concentrat ion

The error bars show percentage uncertainty of percentage change in APA. R2 value equal to one shows that the trend line fits the experimental points perfectly.

From graph 1, there is a positive correlation between glucose concentrations with the percentage change in APA. It can be deduced that the optimum glucose concentration is 2.0M as shown by biggest percentage change in APA due to faster fermentation of yeast.

Conclusion

Yeast+glucose %absorbance decreases coz after time yeast fermentation releases a substance that has different absorbance wavelength with its initial state (?) *I have to find the literature source: TURBIDITY*

y = 0.6087x4 -‐ 2.3351x3 + 2.6792x2 -‐ 0.7654x + 0.0829 R² = 1

0.000%

5.000%

10.000%

15.000%

20.000%

25.000%

30.000%

35.000%

40.000%

0.0 0.5 1.0 1.5 2.0 2.5

Percentage Change in Avg %Absorbance (±0.002)

Glucose Concentration /Molar

Percentage Change in Average %Absorbance

Percentage Change in Avg %Absorbance Poly. (Percentage Change in Avg %Absorbance)


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Evaluation From graph 1, it can be seen that some error bars are quite wide. For instance, the

highest percentage uncertainty shown as error bar is 6.010%. This show that some errors must have occurred during the investigation, such as:

Find factors affecting yeast glucose fermentation

Scienti f ic error

− To improve the accuracy and validity of the result, more trials (5 to 10 trials for each glucose concentration) should be done.

− Wider range (0.5ml to 5.0ml) of glucose concentration should be used to improve the accuracy and validity of the result.

Systematic error − When the yeast and glucose solution was left for 43 hours, it was left indoor yet it was not

placed in a closed isolated room thus air pressure and temperature may affect yeast fermentation. Improvements: Place the yeast+glucose solution in a closed room with no air conditioner to minimize change in air pressure, air movement, and temperature.

− The readings of each trial in every different glucose concentration were not taken at the same time. For example, five readings on percentage change in APA (one for each trial) of

yeast and 0.5M glucose concentrations were not taken at the same time. Improvements: All trials must be conducted at the same time.

− Between trials, yeast was kept heated with water bath. The temperature may have affected the experimental result of some trials.

Improvements: Trials must be done at the same time so the yeast would have the same length of heating time.


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Random error − The condition of the yeast was not known. It may have died by the time the measurements

after 43 hours was taken.

Human error

− The test tube used in spectrophotometer was washed with distilled water between each measurement thus without proper drying distilled water left on the test tube may have interfered with percentage absorbance result.

Improvements: Dry each test tubes, with paper towel or use different test tube for each

trials in different glucose concentration.

dcp and ce lab report 13 ibdp

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