Diffusion and Osmosis
The aim of this lab is to understand the physical processes that are observed in chemistry and biology. The effects of the steepness of a concentration gradient are the key research points for osmosis and diffusion. The dialysis bags were filled with various concentrations of sucrose and placed in beaker solutions. Solution A contains 20% glucose, 1% starch, 0.5% egg albumin, 1% NaCI. The bags were weighed in order to define the changes in the weight, which were caused by water diffusion. The bags with high sucrose concentration gained weight faster in comparison with low concentration bags.
The role of diffusion and osmosis in nature can not be overestimated, as these processes are used by various organisms for various aims. Molecules of the substances become evenly distributed if they contact the molecules of other substances, especially if they are in a liquid or gaseous state. The random motion of molecules lets substances diffuse into each other, hence the aim of this report is to formulate the basic rules of diffusion and osmosis by stimulating molecules of various substances to diffuse.
Materials and Methods
Dialysis tubing, rubber bands, wax pencil, graduated cylinder, 2 beakers, pipettes, test tube rack, 8 test tubes, Solution A, distilled H2O, Lugol’s iodine (I2KI), AgNO3, Biuret reagent, Benedict’s reagent, Water bath (50°C)
Dialysis tubing was filled with solution A and sealed. The mass of the bag was determined and recorded. Then, the tubing was placed in a beaker of distilled water for 45 minutes. Then, the mass was determined again, and the solution from the tubing was added to 8 test tubes for testing the solution for starch, chloride, Benedict’s test for reducing sugars, and Biuret test for protein
It was revealed that the chloride test was the only positive, and the mass change is 3.43 grams. Considering the results of all the tests, the average mass changes are 3.11 grams. Moreover, the weight gain was faster if the solution was more concentrated.
|Inside Dialysis tubing||Outside Dialysis tubing|
|[Total Solute] in %||22,5||0|
|[Water] in %||77,5||100|
|Bag Mass (grams)||22,57||26|
The experimental bags gained weight due to the water diffused into the solution through the diffusion tubings. Moreover, the more concentrated solutions were subjected to greater diffusion. As for the tests for starch, sucrose, Cl- and protein, most tests revealed that only Cl- test is positive, while the other results (with positive glucose and negative Cl- tests) may be regarded as test errors. (1)
Estimating the Solute Concentration of Potato Cells
The process of osmosis is closely associated with gaining the concentration equilibrium in nature. Molecules are subjected to it when the solvent is able to cross the semi-permeable membrane in order to make the solution less concentrated, while the solvent is unable to go through such a membrane.
Potato cores will be cut from a single potato and then trimmed to the same size. Each core will be weighed and placed in one of seven different sucrose solutions to determine the effect of solute concentration on cell mass and/or volume. Data will be used to estimate the solute concentration (osmolality) of potato cells.
Materials and Methods
1 large potato, sucrose solutions (0.1, 0.2, 0.3, 0.4, 0.5, 0.6 molars), 7 beakers or disposable cups, distilled water, cork borer, forceps, wax marker, balance, razor blade, metric ruler, Petri dish, caliper.
Beakers with distilled water (with various sucrose solution concentrations) were marked 0 through 6. Seven cores of a single potato of 4 cm on average were cut from a single potato. All the cores were placed in a corresponding beaker. The mass , as well as length and volume of each core, had been previously measured. Then, the cores were left for incubation for 60 minutes. After this, the cores were measured again (weight and size)
The results of the test are offered in the spreadsheet of the experiment. To define which solution is isotonic, the volumes of the cores should be compared. If the changes in volumes are close to 0%, the concentration is considered isotonic. The test revealed that various concentrations might be isotonic (0; 0.1; 0.2; 0.4 mol).
The graph (Figure 1) represents the average data of core Vol change in beakers. Beaker 1 – the least concentrated solution, beaker 7 – the most concentrated. The hypertonic solutions are those that make the core grow in mass and volume. As a rule, these are less concentrated glucose solutions, as the principle of osmosis is to equal the concentration of solutions through a semi-permeable membrane. (2) As the potato is regarded as a concentrated environment, solvent from less concentrated solutions penetrates the more concentrated environment. (3)
The experiment revealed that the higher solution discrepancies perform higher osmosis rates, as the less concentrated solutions tend to become more concentrated and vice versa until the equilibrium is reached.
- Godard, B. 2004. Kinds of Osmosis. Journal of Canadian Studies 38.1: 65
- Ozaki, L. 2002. Rejection of Organix Compounds by ultra-low-pressure Reverse Osmosis Membrane. Water Res. 36:123-130
- Potera, C. 2005. Reverse Osmosis Moves Forward. Environmental Health Perspectives 113: 25.