Osmosis w/Dialysis Tubing (Lisa Hellinger)
Research Question and Hypothesis:
How does solute concentration effect the movement of water across a semipermeable membrane?
Standards:
NGSS Science & Engineering Standards
Developing and Using Models
Modeling in 9–12 builds on K–8 experiences and progresses to using, synthesizing, and developing models to predict and show how relationships among variables between systems and their components in the natural and designed worlds.
Develop a model based on evidence to illustrate the relationships between systems or components of a system. (HS-LS2-5)
Constructing Explanations and Designing Solutions
Constructing explanations and designing solutions in 9– 12 builds on K–8 experiences and progresses to explanations and designs that are supported by multiple and independent student-generated sources of evidence consistent with scientific ideas, principles, and theories.
NGSS Cross-cutting Concept Standards
Structure and Function
Investigating or designing new systems or structures requires a detailed examination of the properties of different materials, the structures of different components, and connections of components to reveal its function and/or solve a problem. (HS-LS1-1)
Systems and System Models
Models (e.g., physical, mathematical, computer models) can be used to simulate systems and interactions including: energy, matter, and information flows—within and between systems at different scales. (HS-LS1-2), (HS-LS1-4)
Stability and Change
Much of science deals with constructing explanations of how things change and how they remain stable. (HS-LS2-6),(HS- LS2-7)
NGSS Disciplinary Core Idea Standards
Structure and Function
Investigating or designing new systems or structures. Within cells, special structures are responsible for particular functions, and the cell membrane forms the boundary that controls what enters and leaves the cell. (MS-LS1-2)
Experimental Design:
In this lab activity, you will investigate the passage of materials through a semipermeable membrane by passive transport. The membrane you will use, dialysis tubing, is semipermeable because it has submicroscopic holes through it. Six dialysis bags will be filled with various concentrations of a sucrose solution. Each bag will be massed and then placed in cups of distilled water for 30 minutes. After 30 minutes the bags will be massed again.
Independent variable:
The independent variable is the concentration of the sucrose solution.
Dependent variables:
The dependent variable is the percent change in mass of the dialysis bags in grams.
Series:
We will study the mass of dialysis bags (dependent variable) as a function of time (independent variable) at various solute concentrations (series).
Constants and Controls:
Temperature is held constant. Sucrose is the only solute and water is the only solvent. All bags are made with the same dialysis tubing. The bag that contains distilled water is the control.
Materials:
8 inch strips of dialysis tubing - 6/group
6 plastic cups/group
6 sucrose solutions (1M, .8M, .6M, .4M, .2M, 0M)
Add food coloring and make note of colors and molarity
1 small funnel/group
1 graduated cylinder/group
scissors
calculators
distilled water
paper towels
balance
Procedures:
Complete the following steps for each sucrose solution. It is important to budget your time so that you finish. Your bags must be prepared and ready to submerged by 8:20 because they must sit for 30 minutes. You then need time to dry and mass them again before you leave. You may finish answering the questions at home, but the data must be collected today.
Wash your hands with soap and water to remove oil that may interfere with the dialysis tubing by clogging its microscopic pores.
Obtain six pieces of dialysis tubing that have been soaked in water. The tubing should be soft and pliable. Tie a knot at one end of each piece of dialysis tubing. This will form a bag.
Roll the other end of the tubing between your thumb and index finger to open it.
Using a small funnel and graduated cylinder, measure out 15mL of one of the colored sucrose solutions. Using the same funnel pour the solution into the bag you prepared.
Smooth out the top of the bag, running it between your thumb and index finger to expel the air. Tie off the open end of the bag. Leave enough room in the bag to allow for expansion - about 4 cm. It is very important to leave this extra room.
Cut the ends of the bag close to the knot.
Dry the bag very well with paper towels. Take care to dry the knotted ends well. Determine its mass and set aside on a paper towel until other bags have been prepared.
Rinse your funnel and graduated cylinder with water before preparing the next dialysis bag.
Repeat steps 3-7 with each of the different colored solutions.
Immerse each dialysis bag in separate cups of distilled water at the same time. Make sure that the portion of the bag that contains the sucrose solution is completely covered by the water in the cup at all times. Wait 30 minutes before continuing to the next step.
While waiting create a table of your design that includes: initial mass, final mass, change in mass, group’s percent change in mass, class average percent change in mass. Insert your table at the beginning of the analysis section.
After 30 minutes, remove all bags from the cups (at the same time) and dry them very well with paper towels. Again, take care to dry the knotted ends well.
Mass the bags and record the final masses in your data table.
Determine the change in the mass of each bag.
Calculate the percent change in mass. Use the following formula: % change in mass = (final - initial)/initial x 100%. Record in your data table.
Obtain and record the class averages for percent change in mass in your data table.
Sample data and graphs:
Analysis & Conclusions:
Water moves from areas of low solute concentration to areas of high solute concentration or water moves from areas of high water potential to low water potential.
Real Life Application:
"Reverse Osmosis works by using a high pressure pump to increase the pressure on the salt side of the RO and force the water across the semi-permeable RO membrane, leaving almost all (around 95% to 99%) of dissolved salts behind in the reject stream. The amount of pressure required depends on the salt concentration of the feed water. The more concentrated the feed water, the more pressure is required to overcome the osmotic pressure. The desalinated water that is demineralized or deionized, is called permeate (or product) water. The water stream that carries the concentrated contaminants that did not pass through the RO membrane is called the reject (or concentrate) stream" (Purtec Industrial Water, 2017).
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