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Osmosis/ Diffusion Lab

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Introduction

Riley Lambertsen Osmosis/Diffusion Lab Date: 11/20/08 Design: Research Question: How will a hypotonic solution (distilled water) affect osmosis and diffusion of a solution of starch and glucose in a dialysis (semi- permeable) membrane? Hypothesis: In a hypotonic solution, water concentration is greater outside the membrane than inside. Therefore, water will flow into the bag and the mass of the bag will increase. Glucose will diffuse out of the bag because it is a small molecule and the concentration of glucose is lower outside the bag than inside. Benedict's solution will determine if this occurs. Starch is a large molecule and will remain in the bag regardless of the concentration gradient. This is due to the fact that the starch molecules are too large to pass through the pores of the dialysis membrane. Iodine will determine if this is true. Relevant Variables: Independent variable- diffusion of water, starch, and glucose. Dependent variables- mass and color changes. Other relevant variables- concentration, size of molecules, pore size of dialysis membrane, temperature, security of bag closure. ...read more.

Middle

Test the water in the beaker for glucose by adding 15 drops of Benedict's solution. Heat the water for the Benedicts test. If the water turns bright orange, then glucose molecules are present. 11. Record your results in the data table. Sufficient Data: 7 � 1 Data Collection and Processing: Data Collection Table: Mass of Dialysis Membrane and Color Change Tests Before Weight (gm) After Weight (gm) Color Change w/ Iodine Color Change w/ Benedicts. Sample 1 42.63 44.40 None Bright orange Sample 2 36.87 37.86 None Bright orange Sample 3 40.46 41.37 None Bright orange Sample 4 33.34 34.96 None Bright orange Sample 5 40.61 42.58 None Bright orange Sample 6 30.81 32.19 None Bright orange Sample 7 42.00 43.30 None Bright orange Differences Between Before and After Weight of Bag Mass Gained(gm) Sample 1 1.77 Sample 2 0.99 Sample 3 0.91 Sample 4 1.62 Sample 5 1.97 Sample 6 1.38 Sample 7 1.30 Data Processing: Standard Deviation of "Mass Gained": X M X- M (X- M) ...read more.

Conclusion

Because it did not, we know that the starch is still in the membrane and couldn't diffuse through. Then 15 drops of Benedict's solution was added and the water was boiled. The beaker turned bright orange, indicating that glucose was present and had diffused through the membrane. Thus, I accept my hypothesis on the basis of my data. Evaluation of procedure: The experiment itself was fairly simple, and didn't have any major problems. The only areas that could really be improved were the starting mass of the solution- filled membrane, and the timing of the lab. If complete specificity was wanted then the amount of hypotonic solution could also be predetermined and regulated. Improving Procedure: The starting masses of the solution- filled membranes were all different. This was due to unspecific measurements and simply judging "how much". As well, the trials were not all conducted for the same period of time. There was a margin of error of about � 2 minutes. To remedy these problems, a regulated amount of solution and a better timer could be used. Also the amount of hypotonic solution should be regulated to decrease the percent error. ...read more.

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