Introduction Osmosis is a key for every living organism on Earth, from humans to plants. In this lab we examined the processes of osmosis and diffusion. Osmosis is a specialized type of diffusion; “it is the process of water moving across a semi-permeable membrane, in response to a concentration gradient” (Readel, 2000). Fluid passes both in and out of the semi permeable membrane in osmosis, but usually there is a “net flow in one direction or another, depending on which side of the membrane has a higher concentration of solutes” (Smith, 2013). There are different factors that can affect the rate of osmosis such as temperature. In one experiment, my group and I used dialysis tubing to simulate a cell membrane. This tubing was filled with molasses and was immersed in water; cold, warm and hot. The bags were removed at regular intervals and measured for the amount of osmosis that occurred. We observed that the bags in the hot water experienced the highest amount of osmosis. In warmer temperatures the water particles tend to diffuse from high to low concentration, thus trying to dilute the solute concentration from the solution outside. From these observations and conclusion, my group and I hypothesized for our own experiment the level of solute concentration will affect the rate of osmosis. Diffusion is the process of “any substance moving from a region of high concentration to a region of lower concentration” (Readel, 2000). Therefore we predicted that the higher concentration of solute a solution had would yield a higher rate of osmosis. Methods In order to determine if our prediction was correct, our group designed an experiment using five different amounts of standard sodium chloride (NaCl) with distilled water in order to create five different concentrations of NaCl solution. We then used five dialysis tubes to simulate the cell membrane; each tube was filled with 8 mL of distilled water with a transfer pipette (containing approximately 2 ml when full), and each tube weighed at about 10 grams. Our first solution consisted of only distilled water in a beaker, followed by four concentrated solutions each in its own beaker. Those solutions consisted of 5 g/L, 10 g/L, 15 g/L, and 20 g/L of NaCl solution. Then we placed one bag in each beaker of solution respectively. After exactly 5 minutes, we removed each bag, pat each bag dry and weigh them. We recorded the results and then returned each bag to its appropriate container of solution for another 5 minute interval. We repeated these measurements at 0, 5, 10, 15 and 20 minutes. Results The results of our experiment are depicted in our graph. This graph shows the weight of each dialysis tube gradually increasing every five minute interval. In order to find the weight gain from each dialysis tube, we subtracted the weight at the time interval minus the initial weight. The weight difference is subtle at the beginning of the experiment with a difference of less than one gram. Then it slightly increases between the 10 and 15 minute interval with a weight difference of more than one gram. Towards the end of the whole experiment some of the dialysis tubes begin to decrease in weight, specifically for the solutions that contained 5 and 10 g/L of NaCl. Discussion/ Conclusions Based on the result of our experiment, it showed that the solution with the 10 g/L of NaCl had the largest weight. It is clear that our data does not support our hypothesis; however we do not reject our hypothesis. We believe it was based on the several experimental errors that occurred throughout out the experiment that provided the result. One factor that significantly affected our results was the dilution of our salt solution. The 80 g/L of NaCl solution we created did not dissolve completely with the distilled water; most of the salt had settled at the bottom of the container. Therefore for each of our five different concentrations of salt solutions, we believe that each solution we made could have been significantly less than what we had intended. Another human error that had occurred was differentiating between each dialysis tube. After taking out all the tubes at once from their beakers, we lost sight of which tube belonged to which beaker and believe that we might have placed back some of the tubes incorrectly. One other human error that we believe significantly affected our results was the procedure in drying the dialysis tubes after removing them from their beaker. We noticed at the end of the experiment we had been placing the tubes on a wet paper towel; this could have probably allowed the dialysis tubes to absorb more water therefore potentially adding more weight to the tubes. Finally, our group noticed that our dialysis tubes were leaking. We believe this would explain why in our data at the last 20 minutes of the experiment some the dialysis tubes began to decrease in weight.
If we were to do this experiment again, my group and I would have revised our procedures and corrected our mistakes in order to receive the result we were expected based on our hypothesis and prediction. We would label each dialysis bag with the salt concentration that we placed them in. Our NaCl solution would be completely dissolved in the distilled water before creating our five different concentrated solutions, and finally made sure to have used a dry paper towel every time we removed the dialysis tube from their beakers, avoiding any water outside of the beakers to be added to the tubes. We understand how and why each step needs to be performed in a particular way in order to avoid other variables and human errors that can negatively affect our data results. We learned for this lab that salt concentration does affect the rate of osmosis. Although we cannot state that the higher the solute concentration indicates a higher rate of osmosis with this lab, but based on the results we have gathered we can tell it does in fact increases.

Work Cited Readel, Karin (2000). Osmosis: Effects of Temperature and Solute Concentration
Science 100, An Interdisciplinary Study. UMBC Baltimore, MD

Smith, S. E. (2013, March 15). What is osmosis?. Retrieved from http://www.wisegeek.org/what-is-osmosis.htm