- Close the tap and run some distilled water into the top of the burette, then swish the burette up and down to let the water clean all the inside of the burette. Open the tap, let the water drain out.
- Attach the burette to the retort stand and take care that the burette is upright and stable.
- Close the tap and use the funnel to put 25 ml of ethanol into the burette.
- Remove the funnel, make sure that there is no air bubble inside the burette. Measure the temperature of ethanol by the thermometer.
- Put the conical flask under the burette, adjust the height of the burette so that the tip of the burette is just above the lip of the conical flask.
- Open the tap and immediately start the stop watch.
- Stop the watch when 25 ml of ethanol is fully released from the burette.
- Continue to open the tap and collect the remained ethanol in the burette.
- Repeat step 1 to 8 four more times.
- Then change ethanol with methanol, propan-1-ol, butan-1-ol and octan-1-ol. Experiment step 1 – 9 with each alcohol.
- Range and repetitions of experiment:
-
There are 5 different ranges (The lowest value: 0.789 g ml-1 & the highest value: 0.826 g ml-1, Please refer to Data Collection and Processing -> Processed data).
- The initial procedure is repeated 5 times and thus 25 results are recorded.
- The volume of each alcohol sample remains constant for every test at 25 ml. Different volumes of the alcohol sample may cause inaccuracies in terms of measuring the time taken to release. For instance, larger volume of the same alcohol sample certainly takes longer time to be released.
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The temperature of each alcohol sample need to remain constant for every test at 20 oC (293 K). The analysis, written by Weirauch, D. A., Jr. (1998, December) [3], of the high-temperature spreading kinetics for liquids affecting density shows that they can be modified with a constant shift factor. Therefore, higher temperature of the same alcohol sample may reduce the time taken for the alcohol to be released.
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The burettes and funnels are rinsed carefully with distilled water prior to the experiment to ensure that inside the burettes do not contain any unnecessary substances/ions. If present, they may react with the alcohols to form products which have different liquid density, as opposed to original liquid densities of the alcohols at 20 oC (293 K).
- The same burette is used for every measurement. This is because burettes from the same manufacturer cannot be guaranteed to have the same radius of the tips (possessing relatively small values). The use of different burettes can result differences in the time taken for the alcohol to be released.
DATA COLLECTION AND PROCESSING
Table 2.1 shows the collected raw data table.
- Calculating the mean time taken to release 25 ml of alcohol from a burette:
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Mean time taken / s = (1st + 2nd + 3rd + 4th + 5th trial data) ÷ 5.
Table 2.2 shows the processed mean time taken
to release 25 ml of alcohol from a burette.
- Presentation of processed data:
Graph 2.1 shows the relationship between the liquid density and the mean time taken to release 25 ml of each alcohol from a burette.
- Treatment of uncertainties:
- I try to read off carefully volume of the burette from the bottom of the meniscus with my eye level at the meniscus in order to make sure that the volume of each alcohol sample used is only 25 ml.
CONCLUSION AND EVALUATION
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According to the presented graph of the mean time taken to release 25 ml of different alcohols, there is a very strong positive correlation between the liquid density and the mean time taken to release 25 ml of alcohol from a burette as a very good line of best fit can be observed. (Please refer to Data Collection and Processing -> Presentation of processed data -> Image 2.1).
- The results demonstrate that, the higher the liquid density is, the longer time taken for 25 ml of the alcohol to be released from the burette.
- The conclusion totally agrees with my hypothesis.
- Evaluation of procedures:
- Safety in the laboratory is highly maintained (by wearing goggles, lab coat and being careful with glass apparatus to avoid any poisonous alcohols that may splash).
- Standard ranges and repetitions are met, a very strong positive correlation between the liquid density and the mean time taken to release 25 ml of alcohol from a burette is observed.
- Quantitative investigation, with repeats strongly supporting each other, successfully proves that the expectations based on scientific knowledge are totally correct.
- Several inevitable uncertainties occur throughout the whole experiment which may account for inaccuracies in the collected data.
- The concentrations of the alcohols vary from 94.0 % to 99.5 %. The differences in concentration of each alcohol affect the reliability of the data, since 25 ml of pure alcohols (or 5 alcohols with the same concentration) may take different time to be released from the burette.
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Although there is a very strong positive correlation between the liquid density and the mean time taken to release 25 ml of alcohol from a burette, the independent variables (liquid density) do not increase constantly due to the limited number of available alcohols (Please refer to Data Collection and Processing -> Presentation of processed data -> Image 2.1).
- The entire procedures, although are simple, take a long time to finish because of the 50 ml burette need to take at least 3 times to add 5 alcohol samples (5 repetitions for each alcohol), 25 ml each. Overall there are 15 times to add 25 alcohol samples since I decide to investigate 5 different alcohols. The more time I need to add more alcohols into the burette, the more likely inaccuracies to occur.
- Improving the investigation:
-
The procedures can be partially replaced by computer data logging suggested by Laurence Rogers (1995) [5] to prevent uncertainties from human errors when stopping the watch. The experiment can be programmed to collect the data (Time taken for 25 ml of the alcohol to be released from the burette) automatically.
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More alcohols with liquid densities within the ranges (The lowest value: 0.789 g ml-1 & the highest value: 0.826 g ml-1) can be tested to fill the 2 gaps between methanol and propan-1-ol, butan-1-ol and octan-1-ol in the presented graph. For instance, penta-1-ol has the liquid density of 0.815 g ml-1 at 20 oC (293 K) [6].
- Pure alcohols should be bought in the same concentration to ensure the reliability of the collected data. Otherwise, diluting the alcohols to the same concentration can be less expensive, yet time consuming.
- A larger burette, for instance, with measuring volume of 75 ml (only 2 times to add 5 alcohol samples, 25 ml each) will reduce the times need to pour more alcohols into the burette to 10. Not only this change in equipment may save time of experimenting, but also minimise the uncertainties.
Bibliography
[1] Weinberg, F. (1984, December). Fluid flow from a low to a higher density liquid. Metallurgical and Materials Transactions B, 15(4), 681. Abstract retrieved March 8, 2009, from Springer Link. Web site: http://www.springerlink.com/content/n84726w432072592/
[2] Department of Chemistry. (2006, August 25). Biological effects of Methanol and Larger Alcohols. In Ethanol. Retrieved March 8, 2009, from Imperial College London. Web site:
http://www.ch.ic.ac.uk/rzepa/mim/environmental/html/ethanol_text.htm
[3] Weirauch, D. A., Jr. (1998, December). Predicting the spreading kinetics of high-temperature liquids on solid surfaces (Vol. 12). Alcoa Technical Center. Retrieved March 8, 2009. doi:10.1557/JMR.1998.0478
[4] Process Calculator. (2009). SG. In Liquid Density. Retrieved March 8, 2009, from Radix Business Models Pvt Ltd. Web site: http://www.processcalculator.com/Liquid_Density.aspx
[5] Rogers, L. (1995, May). Sensors and The Data-Logger. In Hardware and software. Retrieved March 9, 2009, from School of Education, University of Leicester Web site: http://www.le.ac.uk/se/lto/logging/test1.html
[6] Process Calculator. (2009). SG. In Liquid Density. Retrieved March 8, 2009, from Radix Business Models Pvt Ltd. Web site: http://www.processcalculator.com/Liquid_Density.aspx
