Dialysis Lab Instructions And Report

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Montclair State University *

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270

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Chemistry

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Dec 6, 2023

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Macromolecules and Small Molecules: Using Dialysis to Determine whether Molecules are Large or Small; Understanding Equilibrium Materials:  a piece of dialysis tubing and clamps  600ml or 1 liter beaker filled with distilled water  One half the class will use a mix of [blue dextran] and [vitamin B-12]  The other half of the class will use a mix of [starch} and [iodine] Blue dextran/B12 Groups : Wear gloves. Obtain about 1 ml each of the colored solutions of blue dextran and vitamin B12. Close one end of the dialysis tubing with a clamp as explained by the instructor. Using a P1000 micropipettor, add the blue dextran and Vitamin B12 to the dialysis tubing. Squeeze out most of the air, leaving a small pocket of air above the purple solution. Close the open end of the tubing using another clamp. Observe the color of the solution in the bag, and take a picture of it with your cell phone, against a white background. Starch-iodine Groups : Wear gloves. CAREFUL: Iodine solution stains! Obtain about 1 ml each of the solutions of starch and iodine. In a clean plastic tube, mix the two solutions and observe the color change. Close one end of the dialysis tubing with a clamp as explained by the instructor. Using a P1000 micropipettor, transfer the starch – iodine mixture to the dialysis tubing. Squeeze out most of the air, leaving a small pocket of air above the purple solution. Close the open end of the tubing using another clamp. Observe the color of the solution in the bag, and take a picture of it with your cell phone, against a white background. All Groups : Rinse the outside of the dialysis bag under distilled water and place it in the beaker filled with water. Remove gloves and wash hands. Observe what happens over the course of the lab period and describe it in your laboratory notebooks. Leave your dialysis overnight, so at end of lab period cover your beaker with aluminum foil, place a name label on the beaker and move it to the side bench. Include the names of all the members of the group. All members of your group need to return to the lab on the next weekday, record your observations of your own experiment and an opposing group, carefully noting the color inside and outside the dialysis tubing (lift the bag up to see the inside, take a picture as above). Osmosis: Movement of water across membranes from higher to lower concentration.

Materials:  100 ml cylinders  Sucrose solutions (5% and 10%)  H 2 O Dialysis tubes will contain 5-10 ml of either water, 10% sucrose or 5% sucrose. The 100 ml graduated cylinders will contain either water, 10% sucrose or 5% sucrose. Weigh each dialysis tube and then place into the corresponding solution for 20- 30 minutes. After the 30 minutes, take the dialysis bags out of the solutions, dab dry and weigh. Record the weights on the following table. A B C D Solution in Bag 10 ml 10% Sucrose 10 ml Water 10 ml 5% Sucrose 10 ml 5% Sucrose Solution in Cylinder 90 ml Water 90 ml 10% Sucrose 90 ml water 90 ml 5% Sucrose Weight Before Weight After % Change in weight % Change in weight =[(Mass After - Mass Before) ÷ Mass Before] x 100% Interpreting the results: I. For the dialysis experiment: In a brief paragraph, interpret your experimental observations and the experiment of another group, keeping in mind the key concepts of semipermeable membrane, large molecules and small molecules. For the Osmosis experiment: In a few sentences, explain why the weight of the dialysis tubes either increased or decreased due to the movement of water molecules. II. Respond to the following numbered questions after your observation of the two experimental groups. 1) “Permeable” means porous and “semi-permeable” means partly porous. How do the results you have observed with blue dextran and vitamin B12 show that your dialysis tubing is “semi-permeable” ? 2) If dialysis tubing containing water was placed into a beaker filled with a solution of vitamin B12, describe carefully what you would expect to happen and what you would see in terms of the colors of the contents of the tubing and the solution in the beaker.

3) Starch is a large polymer. A concentrated solution of starch is a milky white color. Iodine consists of small molecules and a solution of it is orange. When iodine is in contact with starch, it binds to the starch creating a dark blue colored complex. Describe what you would expect to occur if you placed starch solution inside a dialysis bag and placed the bag in a beaker full of iodine solution. 4) Artificial dialysis treatment of the blood is frequently used for people with kidney failure. These patients would otherwise accumulate high levels of toxins in their blood that the kidneys normally filter out and remove. How does your simple dialysis experiment help you understand the purpose of dialysis treatments for humans? Hint: urea is a small molecule which builds up in the blood from the metabolism of excess proteins. Blood of course also contains large molecules (proteins) and entire cells (red and white blood cells etc). 5) Two of the symptoms of lactose intolerance are bloating and diarrhea. What role does osmosis play in the latter symptom? A detailed article about “hemodialysis” in humans can be found here: http://en.wikipedia.org/wiki/Hemodialysis The less frequently used technique of “peritoneal dialysis” is described here: http://en.wikipedia.org/wiki/Peritoneal_dialysis I would not expect you to know all the details discussed, but recommend you look at the articles to gain an overview of each technique.

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