Diffusion and osmosis lab

Outline of the day 1.Turn in your lab reports at the front –More than 10 minutes late = bad 2.Any questions on last week’s lab? 3.Quiz 4.Introduction to the lab 5.Lab! 6.Check out Get a stamp Make sure I mark you down for attendance

Quiz Ends 10 minutes after it’s started –Ends at: ____

Lab this week! Exploring diffusion and osmosis –Effect of molecular weight on diffusion Using agar plates! –Effect of temperature on rates of diffusion Demonstration! –Using osmosis to determine solute concentration Using dialysis tubing

Diffusion “The movement of molecules or ions from areas of their higher concentration to areas of their lower concentration. Over time, the random movement of molecules will result in the even distribution of the material?” – Krogh, 2005 The “random movement of molecules or other particles, resulting in even distribution of the particles when no barriers are present” –Purves et al., 1995

Diffusion Start with a gradient of molecules End with equal concentrations on both sides Image pd by LadyofHats Mariana Ruiz Villarreal -

An animation of diffusion ml

Molecular weight Sum of the mass of all atoms in the molecule Three molecules –Silver Nitrate (AgNO 3 ) Mol. Weight: 170 –Iodine potassium iodide (IKI) Mol. Weight: 293 –Methylene Blue Mol. Weight: 373 C 16 H 18 N 3 ClS AgNO3 image PD by Benjah-bmm27 from mb image PD by Calvero at

Osmosis Diffusion of water across a semi- permeable membrane –Water moves down its concentration gradient, just like any other molecule Pure water (distilled water) No net movement of water in or out 100% water Concentration gradient: Cell with pure water inside These solutions are isotonic to each other Image pd by LadyofHats Mariana Ruiz Villarreal - other art by Marc Perkins

Osmosis Diffusion of water across a semi- permeable membrane –Water moves down its concentration gradient, just like any other molecule Pure water (distilled water) Water moves into the cell by osmosis 100% water 90% water Concentration gradient: Cell with 10% NaCl solution The cell is hypertonic to the surrounding solution Image pd by LadyofHats Mariana Ruiz Villarreal - other art by Marc Perkins

Applying osmosis We’ve got “urine” of an unknown concentration You need to figure out what concentration it is, using osmosis –Dialysis tubing is a semi-permeable membrane Water can cross it, but ions and large molecules cannot. Methods note: –Wet the string before weighing the bag

Before you leave Clean up your work area –Wash glassware and store upside down Show me your lab report so I can stamp it –Need to have all data fields filled in –Complete at home and then turn in at the beginning of next lab Remember that we’ll have a quiz at the beginning of the next class –6-7 questions on today’s lab –3-4 questions on the lab we’ll do next week

Notes for the instructor: Add any relevant cleanup instructions to the final slide (that slide is a generic one I’m adding to each presentation).

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History August 2007: Marc Perkins released first version. (If you modify these slides and redistribute them, add your information to the list)