Apparatus
The followings are the apparatus I need for my experiments:
(own choice – not necessary)
Safety Aspects
The chemical used in this experiment is potassium manganate (VII), which is a very strong oxidizing agent. If it is in contact with the skin, oxidization will take place and the skin will turn brown. Eventually, the skin will be pealed off of course. So if any potassium manganate (VII) spillage should be treated with a large amount of water. For safety precautions, Goggle has to be worn all the time while doing the experiment. While doing the experiment we should also be aware of the hot water and Bunsen burner.
Method
- Collect all the apparatus needed
- Boil the water in the kettle
- Fill the beaker with 200mL of boiled water
- Check the temperature of the water and see whether that is the temperature you want
- If the temperature is too high, then pour some of the hot water out and add some cold water. If the temperature is too low, then place the beaker on the tripod and turn on the gas tap, to heat up the water by using the Bunsen burner
- When the temperature of the water is reached, then add a small amount of potassium manganate (VII) crystals in the water and start the timer
- Observe the diffusion takes place while the purple colour of the crystals diffused in the water
- When the water turn all purple stop the timer and record the result
- Do a few more experiment at different temperatures of water to find out how the temperature of the water affects the diffusion rate
Trial
The trial is to check will the experiment work. So time won’t be wasted during the experiment. During the trial, I used the highest and lowest temperature of water that I may use for this experiment.
Modification
In the trial the glass rod was used to place the potassium manganate crystal in the same place. However the crystal stuck to the glass rod instead, so the glass rod will not be used when doing the experiment. I have used 91, 42 and 33 degrees as the temperature of the water. The 91 degrees water was fine, but the 33 and 42 degrees water appeared to be taking too long for the purple colour to spread. That may take an hour or so to spread and I will not have that much time for doing my experiment, so I will have to use the water of 50 degrees or higher for my experiment.
Results
These are the results I collected :
Analysis
The graph shows how is the diffusion rate affected by the temperature of the water, and the results tell us that as the temperature increases , the time for the purple colour to spread is shorter. The time and temperature of the water are inversely proportional. On the graph, the best fit line is steep at first, this tells that there is a stronger affect in lower temperature range. The curve on the graph will eventually flatten. The rate of diffusion increases rapidly, as the temperature increases at the same time. All the above means that the diffusion speeds up as the increasing of temperature. This result has agreed with my prediction.
The diffusion rate increased as the temperature increased the heat of the water makes the crystals, which are solids. The heat of the water converted the heat energy into kinetic energy and makes the particles of the crystals vibrate more rapidly, so that it breaks down more easily and it collides with the particles of the crystals faster. Therefore the purple colour also spreads faster as the temperature of the water gets higher.
Evaluation
The results obtained from the experiment turned out quite good, except from
one anomalous result. That is the one at of 53 °C and takes 165 seconds for the purple colour to spread. The result is slightly out of the best fit line on the graph. Either the amount of water or the amount of potassium manganate used caused this error. Due to the limit of time, I didn’t have a chance to re-do the experiment. If I can do this experiment again, I would measure the amount of water and potassium manganate more carefully. I would also have to repeat each experiment two to three times to enhance accuracy. A thermostat can also be use to get a more accurate and exact temperature of the water
For further investigations, another solid substance can be used, such as iodine. We can use other substances and see whether temperature also affect the rate of diffusion of these substance. But we have to always remember to repeat the experiment at least 3 times, no matter what substances we will use.