Procedure
Firstly we took the pieces of string and we used them to seal one end of the dialysis tubing then we took small pieces of paper and wrote respective letter on them (A, B, C and D) for identification purposes then filled the bags with their respective water-sucrose solutions (A 10ml of 1% sucrose, B 10ml 1% sucrose, C 10ml 25% sucrose and D 10 ml 50% sucrose). And we checked for leaks then we took firstly the 1000ml beaker and we filled it with 50% sucrose solution and dipped bag A in it started the timer and waited three minutes, we did the same thing with all the bags except we filled the large bowl with 1% sucrose solution and submerged bags B, C and D, we also noted the change in mass.
Data collection and processing
We then collected the data in a table:
Table 1 change in mass after 10 min intervals
After collecting the data we needed to see the change in % for that we use this simple equation:
Example:
Table 2 Δ mass (%)
Figure 1 change of % of mass over time
Conclusion and evaluation
These are the results: Bag A decreased in mass about 33.03 %, Bag B increased in mass about 3.7%, Bag C increased in mass about 16.32% and Bag D increased in mass about 42.33%.
The results I have acquired were expected, as Bag A contained 1% sucrose solution inside the dialysis tube and 50% sucrose outside, so naturally it would result in the movement of the water molecules from inside the bag out to try and achieve equilibrium, which caused it to decrease in mass. Bag B, which I thought would maintain its mass actually increased in mass, which could be attributed to a leak or the fact that the sucrose concentration differs due to bags C and D, as they were both of a higher concentration which means that the water would move inside the bags altering the concentration and affecting bag B.
In this lab we were tasked to prove that osmosis exists and is not just a claim, which we have achieved, my hypothesis was partially correct but that is due to Bag B’s increase in mass, which could be attributed to the sources of error in this lab.
The lab contained many error sources, such as the solution itself where it was mixed with tap water which would affect the pH of the solution. Another error sources was the human factor as when we were supposed to tie the other end we were supposed to try and get rid of all the air bubbles, and that was because we needed to keep the bag fully submerged to ensure the largest surface area for increase rate of osmosis. Also the surface area between the tubes varied which would also affect the rate of osmosis another sources of error was the lack of replicates, which would give as a more definitive answer, and point out more sources of error.
The lab had both strengths and weaknesses, the strengths of this lab were mainly in it being an easy way to investigate osmosis and show how it works. But it has many weaknesses, such as the insecure tying of strings, the inability to measure the surface area and volume of the tube to have a universal length and volume for all the tubes was a weakness. Time management was also a weakness as we could not complete the entire procedure. The fact that the dialysis tubes were partially permeable was a good thing except for the fact that their permeability was controlled by their size and volume not by choice of molecules, (as in cell membranes which only allows certain molecules through).
To improve the lab, we can instead of tying the tubes with strings seal them by heat sealers as it is a better method than the strings, because they don´t need to be tied, which would give us a uniform shape and control the surface area. Another advantage with this method is that it isn´t as time consuming as tying the tubes with strings and it is easier to get hold of a common surface area and volume for all the tubes to be used this way, as we can measure a length of dialysis tube and seal it. We can use deionized water for all the solutions we will mix, to give it a pH of 7 and making it not affect the rate of osmosis, and as sugar is neutral, and that helps maintain a controlled setting. We can repeat the experiment more than one time to get more replicates and an average change in percent. We could also have the bags B, C and D in separate container with the same concentration of sucrose solution outside the cell just to maintain that one bag’s concentration does not affect the other. If the experiment doesn´t necessarily need to involve dialysis tube, it is better to thin vegetable slices, for example potatoes (1 cm in thickness), as it is a better way to observe osmosis with less error sources, and instead of using sugar solution, we can use salt solution and submerge the potato slice in it, as the salt levels in the cells is fixed. And as the potato will not leak or puncture, and there is smaller risk of them letting in other molecules than water, and less risk for big loss of mass that may affect the results.