Labs 6 & 7 Diffusion and Osmosis Diffusion • dialysis tubing filled with 0.15mg/ml KMnO4 • tubing placed into a beaker of water • one beaker kept at into room temp water, the other placed into ice cold water bath Diffusion 0.06 0.05 Absorbance (545nm) • KMnO4 particles should diffuse out of the dialysis bag and into the surround beaker water • take a sample of water from each beaker at defined times and measure its absorbance at Abs 545nm 0.04 0.03 Room temperature 0.02 ice cold 0.01 0 0 5 10 20 40 60 Time (minutes) – detecting the presence of KMnO4 particles • because you did a standard curve – you could plot this as concentration vs. time • diffusion should be higher at room temperature vs. cold 15 bath temp room temp Time (minutes) ice cold Abs 545 0 0 0 5 0.025 0.01 10 0.045 0.015 15 0.048 0.024 20 0.041 0.034 40 0.039 0.036 60 0.034 0.035 KMnO4 Standard Curve and Unknown Sample # Abs545nm 1 2 3 4 5 6 7 8 9 10 Column3 Column4 Column5 slope = 0.284 – 0.044 0.0156-0.002 slope = 17.554 molar absorptivity = 17.554 [KMnO4] mg/ml 0.992 0.5 0.284 0.13 0.075 0.044 slope unknown 1 0.5 0.25 0.125 0.0625 0.03125 0.015625 0.0078125 0.00390625 0.001953125 KMnO4 Standard Curve 1.6 1.4 0.108 unknown 17.55412522 0.108 Absorbance 545nm Column1 Column2 1mg/ml KMnO4 1.2 1 0.8 0.6 0.4 0.2 0 concentration 0.006152444 mg/ml KMnO4 concentration (mg/ml) Diffusion KMnO4 concentration (mg/ml) • you have already calculated the molar absorptivity for KMnO4 (see spec lab) • but you did a standard curve and you could recalculate it • for each absorbance value – divide by the molar absorptivity to get the concentration • the units are the same as the standard – which was mg/ml • plotting concentration vs. time looks just like absorbance vs. time 0.003 0.0025 0.002 0.0015 room temperature 0.001 ice cold 0.0005 0 0 5 10 15 20 40 60 Time (minutes) Time (minutes) 0 5 10 15 20 40 60 room temp ice cold mg/ml 0 0 0.00142418 0.00057 0.00256352 0.000855 0.00273442 0.001367 0.00233565 0.001937 0.00222172 0.002051 0.00193688 0.001994 Diffusion • place a crystal of KMnO4 in a petri dish of water and measure its spread through the water over time – diffusion results in the increasing diameter of the KMnO4 “cloud” in the water • place a drop of NaOH in an agar dish and measure its diffusion through the agar – agar is a colloid and will slow the diffusion of NaOH vs. water • same concept at the dialysis tubing study – high concentration to low concentration Osmometer • based on saturated sucrose solutions • submerged in pure water – i.e. hypotonic solution (high [water], low [solute]) – low osmotic pressure – water will move from high [water] to low [water] – volume of the sucrose solution increases – sucrose solution moves up the tube • SO: water movement into the osmometer pushes the sucrose solution up – you measured distance over time as a way of measuring osmotic pressure • many osmometers are attached to pressure transducers that measure the pressure physically “pushing” the sucrose solution up Osmometer • measured the distance the red sucrose solution travelled up the pipette and plotted it versus time • the slope of the graph is essentially the osmotic pressure of the water (or sucrose solution) – i.e. the driving pressure that causes water to move Potatoes and Turgidity • immersed pieces of potato in increasing molarities of sucrose – 0.0M sucrose = pure water – up to 1.0M sucrose • each sucrose solution has a defined number of sucrose particles and free water molecules – the higher the concentration – the higher the osmotic pressure of the solution • the osmotic pressure of the potato is defined also – it has to be compared to the OP of the surrounding sucrose solution in order to figure out which way water will flow – hypotonic solutions – water flows out of solution into cells – hypertonic solutions – water flows into solutions from the cells • increased water movement into the potato slices will increase its weight Potatoes and Turgidity Change in Mass Over Time @ Various Sucrose Concentrations – i.e. where the line crosses the 0 axis 0.4M Sucrose 0.6M Sucrose 0.8M Sucrose 1.0M Sucrose 1.3 1.1 Potato Mass (g) 0.9 0.7 0.5 0.3 0.1 -0.1 0 5 10 15 20 25 30 -0.3 -0.5 Time (min.) Total Percent Change in Mass vs. Sucrose Concentration 40 y = -43.459x + 26.688 R² = 0.9479 30 % Change • graphing the weight change vs. time can show you the rate of osmosis • graphing the final weight change vs. sucrose molarity tells you what [concen.] is isotonic 0.0M Sucrose 20 10 0 0.0 0.2 0.4 0.6 -10 -20 [Sucrose] (M) 0.8 1.0 1.2 • go to this website and try the self quizzes at the ends of the exercises: http://www.phschool.com/science/biology_ place/labbench/lab1/intro.html