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Labs 6 & 7 Diffusion and Osmosis

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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

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Diffusion 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 – 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 bath temp room tempice cold Time (minutes)Abs

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KMnO4 Standard Curve and Unknown Column1Column2Column3Column4Column5 1mg/ml KMnO4 Sample #Abs545nm [KMnO4] mg/ml unknown slope unknown0.108 concentration mg/ml slope = – slope = molar absorptivity =

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Diffusion you have already calculated the molar absorptivity for KMnO4 (see spec lab) but you did a standard curve and you could re- calculate 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 room tempice cold Time (minutes)mg/ml

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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

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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

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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

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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

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Potatoes and Turgidity 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 – i.e. where the line crosses the 0 axis

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go to this website and try the self quizzes at the ends of the exercises: place/labbench/lab1/intro.html

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