Does a difference in solute concentration affect the rate of osmosis?

Hypothesis
The rate of osmosis will vary in accordance to the level of solute concentration in a solution. Water will diffuse at a higher rate in highly-concentrated solutions than in lowly-concentrated solutions (1).

Materials
Distilled water
Molasses
4 dialysis bags
Funnel

Rubber bands
1 Stop watch
Paper towel
Pipettes
Temperature probe
1-scale

Procedure
One end of each of the four dialysis bags were tied to form bags
Each dialysis tube was filled with a different concentration of molasses and water. For example, 2ml of molasses was dissolved in 6ml of water in the first dialysis bag (marked ‘1’), which was equivalent to roughly one pipette and three pipettes respectively
The other end of each dialysis tube was tied to prevent molasses or water from pouring out
After this, the external surfaces of the bags were rinsed to remove the glued molasses from the tubes in order to prevent any alteration of results
Keep track of the dialysis bags- this was done by means of the paper towel, which was split into four sections marked ‘1’ ‘2’ ‘3’ and ‘4’
Each dialysis bag was simultaneously inserted into a separate 200 ml beaker filled with water at room temperature, and the mass of the dialysis bags measured after every five minutes
 The changes in mass were calculated and recorded in a graph

An independent variable refers to the variable being manipulated when testing the results of the experiment (1). The independent variable in the present experiment, therefore, was the molasses (solute) solution, while the dependent variable was the change in the mass for each bag, since it was the measurable variable in the experiment. The experiment involved a number of controls, which included the interval between measurement of the mass change, the temperature probe, the scale, the used pipettes, the type of molasses, the room temperature in the used beakers, as well as the temperature in the used water, which were all kept constant all through the experiment.

Observations
There were changes in the weights of the dialysis bags between the intervals of measurement


Results

Dialysis bag/Solute Concentration
Initial mass of concentration
5 Minutes
10 Minutes
15 Minutes
20 minutes

Bag 1 (6ml water, 2ml molasses)
14.74
15.51
16.2
16.64
17.66

change in mass (in grams)

0.77
1.54
1.9
2.92

Bag 2 (4ml water, 4ml molasses)
17.25
17.65
19.27
20.03
20.19

change in mass (in grams)

0.4
2.02
2.78
3.75

Bag 3 (2ml water, 6ml molasses)
23.18
24.76
26.25
27.27
28.12

change in mass (in grams)

1.58
3.07
4.09
5.12

Bag 4 (0 ml water, 8 ml molasses
17.49
18.89
20.03
20.95
22.07

change in mass (in grams)

1.4
2.54
3.46
4.58





\
Discussion
Besides other aspects, different levels of solute concentration in a solution affect the rate of osmosis. The dialysis tube with more water experienced the lowest amount of change in mass. This proves the actuality of diffusion, which is the movement of water molecules from high concentration to low concentration (2). The results, however, make it difficult to deduce that the solution with least water will have the highest osmosis rate as predicted, because rather than the dialysis bag with the least amount of water (0ml of water, 8ml molasses) experiencing the highest change in volume, it was the bag that contained 2ml water: 6ml molasses that experienced the highest change in volume. There are various errors that could have affected the results of this experiment. First, although the temperature of the water in the dialysis bags was maintained at room temperature, the water in the beaker was not measured using the temperature probe. Also, an error could have been caused by the air bubbles in the pipettes used to measure the molasses. It was difficult to maintain a constant measure of molasses as pipettes were used as the apparatus for measurement.  

Conclusion
The results show that water moved from the beakers to the dialysis bags depending on the concentration of the solution in the bags. The conclusion is that the experiment actually accepted the hypothesis; that is, difference in concentration of solute does have an effect on osmosis rate.

References
James Perry, Joy B. Perry, David Morton, 2012. Laboratory Manual for Non-Majors Biology, Boston: Cengage Learning.
Cecie Starr, Lisa Starr, Christine Evers, 2014. Biology: Concepts and applications, Boston: Cengage Learning.