Publication No. 10333
Student Laboratory Kit
Materials Included In Kit
Iodine solution, IKI, 100 mL
Additional Materials Required
Water, distilled or deionized, 200 mL
Silver nitrate solution is corrosive and can cause burns; avoid contact with eyes and skin. Iodine and salt solutions are irritating to eyes and skin. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Please review current Safety Data Sheets for additional safety, handling and disposal information.
Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Silver nitrate can be disposed of following Flinn Suggested Disposal Method #11. All other materials can be disposed of following Flinn Suggested Disposal Method #26b.
Correlation to Next Generation Science Standards (NGSS)†
Science & Engineering PracticesDeveloping and using models
Analyzing and interpreting data
Disciplinary Core IdeasMS-PS1.A: Structure and Properties of Matter
MS-PS1.B: Chemical Reactions
MS-LS1.A: Structure and Function
HS-PS1.A: Structure and Properties of Matter
HS-PS1.B: Chemical Reactions
Crosscutting ConceptsStructure and function
MS-PS1-2. Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.
Chart I. Starch/Salt Tests
Chart II. Testing Beaker Water
Answers to Questions
How do the membranes around cells help to regulate the internal makeup of the cell? How does a semipermeable membrane work? What is diffusion?
Diffusion (the random movement of molecules) is one of the key processes involved in the movement of materials throughout living systems. Diffusion can be effectively demonstrated by observing the action of a drop of dye in a glass of water. The water molecules in the water are in constant, random motion. If a drop of blue food dye is added to the glass, the dye begins to slowly diffuse throughout the water. The individual dye molecules disperse and, compelled by collisions with the moving water molecules, eventually become evenly distributed throughout the glass. The water in the glass would now appear to be a uniform shade of lighter blue. The movement of individual molecules in this system is indeed random. The net movement of the dye molecules is directional, in the sense that they (initially) move from a region where they are highly concentrated (the dye droplet) to where they are less concentrated (the surrounding water). Thus diffusion (the term usually refers to the net movement of molecules) is said to occur down a concentration gradient—from a region of high concentration to a region of lower concentration. When the dye has become evenly distributed, and the dye and the water are at equilibrium, the net movement of the dye molecules appears to have stopped. It is important, however, to realize that the random movement of individual dye and water molecules continues even when “equilibrium” is reached.
Dialysis tubing will be used in this laboratory to simulate a cell membrane. It is made of a selectively permeable cellulose tube perforated with microscopic pores. The pores are small enough such that the tubing can be used to model the behavior of the cell membrane with respect to the sizes of molecules that will (or will not) diffuse through them.
Iodine solution, IKI, 9–10 drops
Silver nitrate solution is corrosive and can cause burns; it will stain skin and clothing; avoid all contact with eyes and skin. Iodine and salt solutions are irritating to eyes and skin. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory.
Test tube 1—5 mL water + 3 drops iodine solution
Test tube 1—5 mL beaker water + 3 drops of iodine solution
Record the test results in Chart II on the Dialysis Worksheet.
Student Worksheet PDF