Prediction:
If the concentration of bile increases, then the time for the colour of phenolphthalein to change would decrease. . If the concentration of bile decreases, then the time for the colour change of the indicator would increase.
Materials: - 10mL distilled water - 5 corks
- 10mL bile - 5 test tubes
- 40mL half & half cream - 1 test tube rack
- 50mL NaCO3 - 1 bottle phenolphthalein
- 10mL lipase - 1 grease pencil
- Stopwatches
Procedure: 1) Using the grease pencil, label the test tubes 1 through 5.
2) Place test tubes in the test tube rack,
3) Take the test tube labelled 1 and measure 8mL of cream, 10mL NaCO3, and
2mL lipase into the test tube.
4) Add 4mL of distilled water into test tube 1.
5) Then, add 8 drops of phenolphthalein into test tube 1.
6) Place a cork on the test tube.
7) Begin to gently shake the test tube, while starting the time on the
Stopwatch.
8) After the pink colour fades, stop the time on the stopwatch.
9) Record the time observed from step 8.
10) Repeat step 3 for the test tube labelled 2.
11) Add 3mL of distilled water and 1mL of bile into test tube 2.
12) Repeat steps 5- 9.
13) Repeat step 3 for the test tube labelled 3.
14) Add 2mL of distilled water and 2mL of bile into test tube 3.
15) Repeat steps 5- 9.
16) Repeat step 3 for the test tube labelled 4.
17) Add 1mL of distilled water and 3mL of bile into test tube 4.
18) Repeat steps 5- 9.
19) Repeat step 3 for the test tube labelled 5.
20) Add 4mL of bile into test tube 5.
21) Repeat steps 5- 9.
22) Repeat all steps (1- 21) in order to have 3 replicates of this lab.
Table #1: Time Intervals Recorded for the Change of Color of the Indicator of Different Test Tubes. The time interval for three replicates is recorded.
Analysis/Discussion:
First thing to be noticed is that the time interval for replicate #1, test tube #1 seems to be out of place when compared to the rest of replicate #one.
In replicate #one and replicate #three, test tube #5s are clearly the least time within their respective replicates. According to the procedure, test tube # 5 has the highest bile concentration and according to the hypothesis, it should have the least time. The observations from test tube # 5, both replicate #1 and #3 confirm that. However, in replicate #2, test tube #4, instead of test tube #5 has the lowest time interval for the dissipate of the pink color. According to the procedure, test tube #4 has the second highest bile concentration, the results in replicate #2 is still reasonable. Replicate #1 and #2, test tube #1s, clearly has the longest time interval for the pink color to dissipate in their respective replicates. According to the procedure, test tube #1s has the lowest bile concentration and according to the prediction, they should have the highest time interval. Observations from replicate #1 and #2 confirm the predictions. According to the procedure, test tube # 3 of all replicates should have a medium bile concentration (2ml bile: 2ml water) and test tube #4 of all replicates should have a higher concentration that test tube #3 (3ml bile: 1 ml water). Based upon the hypothesis, because test tube #4 has a higher bile concentration than test tube #3, test tube #4 should have a shorter time interval than test tube #3. However, in replicate #1, test tube #3 and #4 displayed a contrary behaviour to the hypothesis. Nevertheless, replicate #2 and #3, test tube #3 and #4 respectively displayed the hypothesized predictions.
Conclusion:
There are assumptions in this lab such as that each substance used in the procedure will react the same way every time; and the condition in which the individual trials were performed is uniform throughout the experiment.
Although there are observations that were not predicted by the hypothesis, however majority of the observations do support the hypothesis. In conclusion: if the concentration of bile were high, the lipase activity would be faster than that of a lower concentration of bile. Therefore, a higher concentration of bile would result in a lesser time interval required to dissipate of the indicator color than that of a lower bile concentration solution.
Evaluation:
There are many errors contributing to the incoherence of the observation collected:
- The time interval to dissipate the pink color, in other words the time when the test tube becomes not pink is very dependent upon a person’s judgement or physical conditions (color blindness perhaps). In order to record the time elapsed during each individual experiment, one person must make an interpretation/judgement on when to stop the time based upon his/her ideas. Because of this interpretation, there could be differences of opinions on the time interval between the partners, resulting in an inaccurate recording of time elapsed.
- A minor source of error could be changes in the substances/materials exposed to air in respect to elapsing time. For instance, some cream is known to change in physical properties (states) when the ambient temperature increases. Assume that the cream used in the experiment was taken out of the refrigerator at a certain temperature, and trial one was carried out immediately, followed by trial 2 and so on. By the time trial #5 is complete, the cream has endured time (which allowed for slight differences of cream) that is not included in trial #1, producing a different cream used in trial #1. The result is some minor difference between trials.
- The procedure is judged adequate because it is simply to follow and straight forward.
- Possible improvements for this lab could be that one test use fresh and another test uses an old cream. The purpose of this set of experiment is to test whether slight differences in creams cause any significant differences in the time elapsed.
