How will you experimentally determine if dialysis occurred in the experiment? Ad

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How will you experimentally determine if dialysis occurred in the experiment?

Add 450-500mL of distilled water to a clean 600 mL beaker, It must be distilled water, not tap water. Remove the remaining strip of tubing from the water and separate the tubing walls. Hold the tubing by both ends to prevent spillage and insert the glass funnel into one end of the tubing. Add 10 mL of 10% NaCl solution, 10mL of 10% fructose solution and 10mL of starch solution to the tubing. Insert a glass stirring rod into the holes in the tubing. Gently rinse the outside of the tubing over the sink with distilled water from a wash bottle to remove any contaminating material. Suspend the tubing in the 600mL beaker of water as you did in Part I. Add additional water if necessary to cover the solution in the tubing. Immediately after suspending the tubing in the water use a 10mL beaker to remove some (approximately 5 mL) of the water from the 600mL beaker. Take a sample of water from the middle of the beaker, don't just skim off the top. Pour a little into each of the three test tubes labeled 1-3. To test tube #1 add 5-6 drops of 0.1M AgNO_3 (silver nitrate). AgNO_3 will stain your skin and clothes so use caution and wear gloves. The appearance of a white precipitate confirms the presence of CI^- ions. To test tube #2 add about 40 drops of Benedict's reagent and heat briefly in a boiling water bath. The appearance of a dark red/orange precipitate confirms the presence of fructose. You should, however, record any color changes observed when doing the tests. To test tube #3 add 5-6 drops of I_2/KI reagent. The appearance of a blue/black color confirms the presence of starch. Pour out the three test tubes into the appropriate waste container. Wash them out with soap and water. You will need them again so make sure they are clean. Wait about 15 minutes and repeat this process. Remove about 5mL of the water and perform the 3 tests again. Record the time and results of each test. Repeat this process again at the 30 minute, 45 minute and 60 minute interval. You should end up with 5 sets of data: at time-zero, 15 minutes, 30 minutes, 45 minutes and 60 minutes. After taking the sample at 60 minutes and doing the tests, you may discard the solutions in the beaker and tubing in the sink. The solutions in the test tubes must be discarded into the appropriate waste container. The used tubing can be discarded in the trash.

Explanation / Answer

Ans. During the process of dialysis, the solutes (NaCl, Fructose and Starch) diffuse across the dialysis membrane (the membrane of dialysis tube/ tubing) in the surrounding aqueous solution/solvent (distilled water in the beaker) to establish the equilibrium. Therefore, the solutes diffuse out from tubing into water taken in beaker.

Note that the distilled water lacks solute initially. During dialysis, NaCl, Fructose and starch diffuse into it.

So, presence of NaCl, Fructose or Starch in the distilled water after time of experiment indicates that dialysis has occurred- i.e. solutes have moves from tubing to distilled water in beaker.

The method of detecting the presence of NaCl, Fructose and Starch is mentioned in #5, #6 and #7 respectively. A positive test of these solutes in water sample collect from beaker after certain intervals confirms the process of dialysis. The distilled water gives negative result for all solutes at the beginning of experiment.

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