Control of Variables: using distilled water, using one solution source of starch and glucose, constant temperature, using only one type of dialysis membrane, securely tying the bag.
Materials: ~20 cm dialysis tubing, ~40ml starch solution, ~ 75 ml distilled water, 200 ml beaker, scale, benedicts solution, iodine, hot plate, funnel, string.
Procedure:
- Open the dialysis tubing by running cool tap water over one edge and rubbing layers together with fingers.
- Tie off one end securely with a piece of string. (draw a pic)
- Place funnel in the open end of bag.
- Fill the bag ~ 2/3 full with the sugar starch solution.
- Tie off the top of the bag with a piece of string. Try to omit large air bubbles at top.
- Weigh the bag.
- Put the bag into the beaker and poor just enough distilled water to cover the bag. It should resemble the following:
- Wait 30 minutes and then reweigh the bag as shown.
- Test the water in the beaker for starch by adding 4 drops of iodine. If the water turns dark purple, then starch molecules are present.
- 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.
- 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
Differences Between Before and After Weight of Bag
Data Processing:
Standard Deviation of “Mass Gained”:
Standard deviation formula….. S = √{ ∑( X- M)2 / n}
X= data points
M= mean
n= number of trials
S = √{ ∑( X- M)2 / n}
S = √{ (0.1225 + 0.1849 + 0.2601 + 0.0400 + 0.3025 + 0.0016 + 0.0144)/ 7}
S = √{0.926/ 7}
S = √{0.1322857143}
S = 0.3637110313
S ~ 0.36.
Data Presenting/ Graph:
Conclusion and Evaluation:
Conclusion: This lab worked out quite well. The weights of the dialysis membranes filled with solution showed a significant difference between the before and after. The actual mass of the bag increased, which alludes to osmosis having happened because the hypotonic solution tried to reach an isotonic state with the solution. Also, two quick tests explained what occurred with the glucose and starch. 4 drops of iodine to the water did not show a visible color change. If starch was present, the water would have turned dark purple. 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.