1x 20 cent coin
1x Beaker (250cm3)
1x Hot plate (± 0.05oC)
1x Pipette
1x Thermometer (± 0.5oC)
1x Water bath (± 0.05oC)
Water (250cm3)
Figure III: Diagram of Apparatus
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Set the water bath to 10.0oC
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Set the hot plate to 10.0oC
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Pour approximately 250cm3 of water into a 250cm3 beaker
- Place beaker into the water bath and let it sit for about 15 minutes to adjust to the temperature
- Place the 20 cent coin on the hot plate
- After 15 minutes, check the temperature using the thermometer
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If it has reached 10.0oC, draw water from the beaker into the pipette
- Working quickly, hold the pipette close to the coin and carefully start to drop droplets of water onto the coin, one at a time, counting each drop
- When the water on the coin breaks up and overflows, stop dropping droplets
- Record the number of drops that the coin could hold (exclude the drop that made the water overflow) and any qualitative observations
- Repeat the experiment for this temperature 4 more times
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Repeat the experiment using the following temperatures: 20.0oC, 30.0oC, 40.0oC and 50.0oC
Figure IV: Quantitative data collected from experiment
Figure IV: Qualitative data collected from experiment
Figure VI: Calculated values obtained from experiment
The water temperature at 10.0 oC is used as a sample calculation
Average number of drops the coin could hold for this temperature:
The results collected from the experiment show a trend. As the temperature increased, the number of drops of water the coin could hold decreased and hence had less surface tension. In Figure VII, the line of best fit is a curve, showing a decreasing curve, with a wide gradient. However, larger temperatures should also be tested to provide greater evidence for this. The results gained support the hypothesis posed, that increasing temperature reduces the capacity of surface tension. The qualitative observations also show this decreasing capability as the surface tension has a less square shape and a smaller height.
Water molecules contain two hydrogen atoms and one oxygen atom. The bond between these atoms involves unequal sharing, that is, polar covalent bonds. This results in the water molecule having an unequal charge distribution, with hydrogen having a partial positive charge and oxygen having a partial negative charge. This creates hydrogen bonds as the positive and negative ends of the molecule attract each other. The surface tension of water is caused by these strong cohesive intermolecular forces that water has. On the surface of the water, this attraction is particularly strong as the water molecules have nothing above them to be attracted to, resulting in them pulling harder on the sides. This creates surface tension. In the experiment, it can be seen that the water with higher temperatures have a lower surface tension. Temperature affects surface tension as it increases the kinetic energy of the molecules, resulting in a reduction in surface tension capability as the bonds are broken. The experimental results obtained support the properties of water and surface tension.
The data obtained from this experiment is valid and reliable as each temperature was repeated five times as well as controlling the controlled variables. The result values were also quite similar. There was no great deviation and the results fell within acceptable differences. The advantage in this experiment was the counting of the droplets, which had clear distinctions. However, there were a few limitations in this experiment.
There were possible sources of random error. One possible source of error was an inconsistent experimental technique. As this experiment requires precision of individual technique, especially with the dropping of droplets, this could possibly be the largest source of random error. However, this was minimised through the repeated trials. Temperature fluctuation is also another source of possible error. While the water bath and hot plate can control the temperature, the water in the pipette could fluctuate. But this can be reduced by quickly performing the experiment for each trial. Also, there were possible systematic errors in this experiment. If the equipment was calibrated incorrectly, it would affect the values.
Further improvements could also be proposed for this experiment. A trial run for each temperature can be performed in order to gauge an approximation for the surface tension which would ensure that the first result does have a great difference between the others. More repeats, such as 10 trials, would be also beneficial to the nature of this experiment.