Diffusion is the movement of molecules moving from a region of high concentration to a region of low concentration. If a drop of food colouring is dropped in increasing temperatures of water, then it will spread faster throughout the water because an increase in temperature means an increase in the molecules kinetic energy (Andrew, 344). The molecules will move faster and diffusion will occur faster in less time.
Independent: Different temperatures of water
Dependent: Rate of diffusion in seconds
Surface area and amount of water
It is very crucial that the surface area and amount of water is kept the same. Large surface area will increase the rate of diffusion as the molecules will have more space to spread over. All tests will be done in 200ml test tubes.
Amount of food colouring
The amount of food colouring should be kept the same for adequate results. An increase in the amount of food colouring will result in a decrease in the rate of diffusion because there will be more molecules to spread evenly throughout the water and thus will take more time. One drop of food colouring will be used for all trials.
Concentration of the food colouring
The concentration of the food colouring should be kept the same. If there is an increase in the concentration then there will be more molecules in the same amount of volume and that will result in a decrease in the rate of diffusion. More molecules will have to move from region of high concentration to a region of low concentration and thus take more time. To keep this variable controlled, food colouring of the same type and brand will be used.
5 X 200ml test tubes
Queens liquid green food colouring
Adtemp 419 hypothermia thermometer digital thermometer (±0.001 °C)
Cornea Pc-100 hot plate
100ml of ice cubes
Insulated gloves must be worn when dealing with boiling water and hot plate
1) The amount of water was controlled by using a 500ml beaker to measure 100ml of water.
2) The 500ml beaker was put on the hot plate.
3) A digital thermometer (±0.001 °C) was used to check the temperature until it reached 100 °C (±0.001 °C).
4) When the temperature was 100 C° (±0.001 °C), the boiling water was poured in a 200ml test tube to keep the surface area controlled.
5) An eye dropper was then used to extract the green food colouring. Same brand was used for all trials to keep the concentration of the food colouring the same.
6) The amount of food colouring was controlled by dropping only one drop of food colouring in the test tube and as soon as the food colouring was dropped in the test tube, the stop watch was started.
7) The stop watch (±0.5s) was stopped when the food coloring dissolved and spread evenly throughout the water.
8) The time was recorded.
9) Steps 1 to 8 were repeated with water temperatures of 80°C, 60°C, 40°C, 20°C and 0°C
i) For 0C°, ice cubes were put in the 500ml beaker and steps from 2 to 8 were repeated.
10) After the first trial was done with various water temperatures, the second and third trials were carried out.
The raw data table was processed into processed data by finding the average rate of diffusion in seconds. The processed data table is a better representation of the data because each trial for each water temperature had a different result. By finding the average it is easier to see the data and make assumptions based on it rather than looking at the raw data with many trials. The first differences were also calculated for the average to show the rate at which the points are decreasing.
The graph showed the average rate of diffusion in various temperatures of water. The relation between the average diffusion and temperature of water is a decreasing function. As the temperature of water increased, the rate of diffusion in seconds decreased.
The standard deviation was calculated for water temperature of 100°C.
Standard Deviation Formula:
1. The mean of the average rate of diffusion was found.
2. The calculated data for each trial was subtracted from the mean to obtain a list of deviations.
3. The differences were subtracted.
4. The squared differences were added.
5. The sum was divided by the total number of data values represented by ‘n’ values minus 1 (n-1)
6. The calculated data was square rooted to find the standard deviation.
1. Mean = (127.4 + 130.7 + 126.8) / 3
2. 127.4 – 128.3 = -0.9
130.7 – 128.3 = 2.4
126.8 – 128.3 = -1.5
3. (-0.9)2 = 0.81
(2.4) 2 = 5.76
(-1.5) 2 = 2.25
4. Sum of the squared differences = 0.81 + 5.76 + 2.25
5. n – 1
= 3 – 1
= 2 8.82/2 = 4.41
6. Standard deviation = Square root of 4.41
The standard deviation was rounded according to the average rate of diffusion calculated. There is a value of 1 significant digit out of the values of 127.4, 130.7 and 126.8, so the standard deviation will be rounded to 1 significant digit. The standard deviation for water temperature of 100°C is 2.
The aim of this experiment was to assess the effects of various temperatures of water on the rate of diffusion. The hypothesis was proven to be correct. When the food colour was dropped in increasing temperatures of water, the rate of diffusing decreased. When the water temperature increases, the molecules kinetic energy also increases, causing them to move from region of high concentration to a region of low concentration faster in less time. (Andrew, 344) This lab also helped explain the importance of diffusion in living cells. Diffusion is essential in cells for bringing inside nutrients. When cells lack something, they have a lower concentration inside, compared to the outside surrounding. So by diffusion, the missing nutrients flow inside from high region of concentration to the inside of the cell that has a low region of concentration (Campbell, 2005).
Limitations and suggestions for improvements
Methods for improvement
The temperature of the food colouring was not known. The temperature should be constant because if the temperature of the food colouring is high or low then it will affect the temperature of the water and affect the rate of diffusion.
This limitation could be improved by simply storing the food colouring before doing the experiment in a room temperature area for a day.
For 100°C, the water was measured before boiling it. The water should be measured after boiling it because water evaporates when boiled. The control variable, same amount of water, can fluctuate.
This limitation can be improved by boiling more than needed so if water does evaporate, the needed amount can still be collected. A 500ml beaker can be used to measure the water.
The temperature of the surrounding where the experiment was taking place was not controlled. For example if the temperature of the surrounding is too cold then the hot water can quickly lose its heat.
A precise digital thermometer such as Calicos can be used to make sure the room’s temperature is between 22 to 23 C°.
1. Campbell, Neil A., and Jane B. Reece. Biology. San Francisco: Pearson, Benjamin, Cummings, 2005. Print.
2. Ruth Richardes. “Movement of Materials across Cell Membrane.” http://highered.mcgraw-hill.com/sites/dl/free/0072439440/60317/exercise3.pdfPaul 67-54.
3. Campbell, Andrew A, and David M. Biology Course Companion. Oxford University Pres. New York, 2006. Print