Diffusion of sodium chloride through dialysis tubing using conductivity sensor
Seung Soo (Jason) Lee002213-065Internal Assessment – Investigating the Relationship between Concentration ofGlucose and Rate of Diffusion of Sodium ChlorideResearch Question:How will changing the percentage of glucose concentration affect the rate of diffusion of sodiumchloride across a visking tubing – down a concentration gradient – measured using a conductivity probe?Introduction:Diffusion is a passive process in which molecules spread, from areas of high concentration to areas oflow concentration, until equilibrium is reached. For instance, sodium chloride molecules inside a viskingtubing will diffuse out from the area of high concentration to an area of low concentration. There areseveral factors that can affect this rate of diffusion. Such factors include the concentration gradient, thesurface area of visking tubing, and temperature. 1In this experiment, glucose solution will be poured into the visking tubing in addition to the sodiumchloride solution to observe the effect of glucose concentration on the rate of diffusion of sodiumchloride. The rate of diffusion will be measured using Logger Pro and a conductivity probe: theconductivity of the water as sodium chloride diffuses out will be measured by the probe for 60 seconds.After the collection of data, the rate of diffusion can be calculated by finding the slope of conductivity vs.time graph, since rate of diffusion is change in conductivity over time. If the change in conductivity issignificant the rate of diffusion is high and if the change is small the rate is low. Rate of Diffusion =1 Bailey, Regina. "Diffusion and Passive Transport." About. N.p., n.d. Web. 12 Dec 2010.<http://biology.about.com/od/cellularprocesses/ss/diffusion.htm>.
Seung Soo (Jason) Lee002213-065Hypothesis:Visking tubing is a semi-permeable membrane that allows for molecules to diffuse in or out, dependingon the concentration gradient. As mentioned in the introduction, the only factors that can affect therate of diffusion across a visking tubing are the concentration gradient, surface area, and temperature.Although glucose molecules are larger than sodium chloride molecules, they will not clog the viskingtubing; there will still be thousands of pores through which the sodium chloride will be able to diffuseout. Therefore, as long as there is a greater concentration of sodium chloride inside the visking tubingthan outside, the molecules will continue to diffuse out unperturbedly until equilibrium is reached, nomatter how high the concentration of glucose is inside the visking tubing. Effect of Glucose Concentration on Rate of Diffusion of Sodium Chloride Average Rate of Diffusion, ΔμScm-1s-1 0 1 2 3 4 5 6 7 8 9 10 Concentration of Glucose, %Figure 1: Prediction of the Effect of Glucose Concentration on Rate of Diffusion of Sodium ChlorideThe figure above demonstrates no change in the rate of diffusion of sodium chloride as the glucoseconcentration increases. As such, the hypothesis is that the concentration of glucose solution inside thevisking tubing will have no effect on the rate of diffusion of sodium chloride.
Seung Soo (Jason) Lee002213-065Variables: Variable Description Units / range Method of Measuring / Manipulating Independent Concentration of % The independent variable will be manipulated by a process of glucose serial dilution, from 10% concentration to 5%, 5% to 2.5%, 2.5% to 1.25%, and 1.25% to 0.625%. Dependent Rate of diffusion of ΔμScm-1s-1 This will be measured with a conductivity probe. The sodium chloride conductivity probe measures the amount of electricity, and because sodium chloride contains charged ions, the ( ) conductivity probe can accurately determine the amount of sodium chloride that is diffusing out. Therefore, the rate of diffusion can be measured using a conductivity probe. The conductivity will be measured from 0-60 seconds, and the rate of diffusion can be calculated by finding the slope of the conductivity vs. time graph. The uncertainty can be considered negligible. Controlled Concentration of % The concentration of sodium chloride will be kept constant at sodium chloride 10% concentration, and this will be insured by using the same solution for every trial. Volume of water cm3 Volume of water inside the visking tubing is set at 10mL of inside & outside sodium chloride solution and 5mL of glucose solution. the visking tubing Volume is measured accurately using a burette and a pipette. Volume of water inside the beaker (where the diffusion will take place) is set at 200cm3. Volume is measured accurately using the increment on the beaker. Range of μm The range of conductivity is kept constant at the 2000μm conductivity range on the conductivity probe Rate of stirring Increments on The rate of stirring is set at the first increment on the the magnetic magnetic stirrer for every trial. stirrer Temperature °C Temperature is kept constant by conducting the experiment at room temperature (about 25 °C) for every triplicate trial. Surface area / cm2 / cm3 The same visking tubing is used for every triplicate trial to volume ratio of ensure that the width of the visking tubing is constant. In visking tubing addition, the visking tubing is cut into same lengths – 15cm – to keep the surface area / volume ratio constant.Table 1: List of Variables
Seung Soo (Jason) Lee002213-065Apparatus and Materials: Electronic balance (±0.001g) Spatula 50 cm3 burette (±0.05 cm3) Glucose 10 cm3 pipette (±0.02 cm3) Distilled water Five 50 cm3 beakers for serial dilution Scissors 2 large beakers Magnetic & plastic stirrer Visking tubing Conductivity probe Sodium Chloride Logger ProProcedures:Preparation of 10% sodium chloride solution 1. 25g of sodium chloride and 250cm3 of distilled water are poured into a large beaker. 2. The beaker is stirred several times using a plastic stirrer until a homogenous solution is made.Preparation of glucose solution of various concentrations (serial dilution) 15 cm3 distilled water 15 cm3 15 cm3 15 cm3 15 cm3 10% 5% 2.5% 1.25% 0.625% Figure 2: Serial Dilution of Glucose Solution
Seung Soo (Jason) Lee002213-065 3. 3g of glucose and 30cm3 of distilled water is poured into a small beaker. 4. The beaker is stirred several times using a plastic stirrer until a homogenous solution is made, thus creating 10% glucose solution. 5. 15 cm3 of the obtained solution is transferred into another small beaker using the 50cm3 burette and another 15 cm3 of distilled water is added using the same sized burette. The beaker is then stirred using a stirrer until a homogenous solution is made, thus creating 5% glucose solution. 6. Step 5 is repeated 3 more times to obtain 2.5%, 1.25%, and 0.625% glucose solutions. The burette is washed every time a new serial dilution is performed.Conducting the experiment Conductivity probe Visking tubing Magnet Magnetic Stirrer Figure 3: Diagram of the Apparatus for Gathering Data 7. 16 visking tubing of about 15cm in length are prepared. A knot is tied on one end of each of the visking tubing’s. 8. Logger Pro is turned on, and the conductivity probe is connected to Logger Pro. The range is set at 2000μm. 9. 15 cm3 of sodium chloride solution is poured into a visking tubing using the 50cm3 burette. A large beaker is filled up to the 200cm3, then placed on top of the magnetic stirrer. The magnetic stirrer is turned on to the first increment only. The visking tubing is put inside the beaker to start the diffusion process, and the rate is measured using the conductivity probe and Logger Pro for 60 seconds. (This step gathers data for the control) 10. 10 cm3 of sodium chloride solution is poured into a visking tubing using the 50cm3 burette. 5cm3 of 10% glucose solution is added into the same visking tubing using the 10cm3 pipette. 11. Visking tubing is placed inside a large beaker filled up to 200cm3 with distilled water, and the beaker is put on top of the magnetic stirrer running at first-increment speed. 12. The rate of diffusion is measured using conductivity probe and Logger Pro for 60 seconds. 13. Steps 10-12 are repeated triplicate trials for all five concentrations of glucose.
Seung Soo (Jason) Lee002213-065Data Collection:Qualitative Data: To the naked eye, the change in concentration of glucose solutions did not seem to make a significant difference in the diffusion of sodium chloride. The presence of visking tubing seemed to get in the way of the magnetic stirrer at times, causing a slight disruption in the stirring.Quantitative Data:*** Refer to the Appendix for a complete table of raw data from Logger Pro.
Seung Soo (Jason) Lee002213-065Data Processing: Glucose Rate of Diffusion of Sodium Chloride / ΔμScm-1s-1Concentration /% Trial 1 Trial 2 Trial 3 10.000 10.41 10.02 10.45 5.000 10.66 9.987 (16.90)2 2.500 10.47 9.237 (12.61) 1.250 10.14 9.92 (14.16) 0.625 (15.04) 10.09 10.50Table 2: Rate of Diffusion of Sodium Chloride for All Trials3 Glucose Calculation Average Rate of Diffusion Concentration / % (±Standard Deviation)4 / ΔμScm- 1 -1 s 10.000 10.29 ± 0.24 5.000 10.32 ± 0.48 2.500 9.85 ± 0.87 1.250 10.03 ± 0.16 0.625 10.30 ± 0.29Control (no glucose added): 10.08 ΔμScm-1s-1Table 3: Calculation of Average Rates of Diffusion2 Values in parentheses were excluded as outliers due to their extreme deviation from the norm.3 The rate of diffusion was determined by finding the slope of conductivity vs. time graph using linearregression on Logger Pro software.4 The processing of standard deviation is shown in table 4
Seung Soo (Jason) Lee002213-065Data Presentation: LEGEND Red Lines: 10% glucose concentration (Run 1) Blue Lines: 5% glucose concentration (Latest 3) Green Lines: 2.5% glucose concentration (Run 3) Orange Lines:1.25% glucose concentration (Run 4) Purple Lines: 0.625% glucose concentration (Latest 6)Figure 4: Graph of Raw Data from Logger Pro55 Slopes of lines that have values closest to the average slope value for each concentration of glucose are shown in boxes.
Seung Soo (Jason) Lee002213-065 Effect of Glucose Concentration / % on the Rate of Diffusion of Sodium Chloride / ΔμScm-1s-1 12 Average Rate of Diffusion, ΔμScm-1s-1 11 10 y = 0.022x + 10.074 R² = 0.1931 9 8 0 2 4 6 8 10 Concentration of Glucose, %Figure 5: Graph of Average Rate of Diffusion against Concentration of Glucose6 76 Vertical error bars represent standard deviation for triplicate trials.7 Horizontal error bars represent absolute uncertainty for concentration of glucose. (Difficult to see on graph because error is minute)
Seung Soo (Jason) Lee002213-065Uncertainties:Standard Deviation: Glucose Rate of Diffusion of Sodium Chloride / ΔμScm-1 s-1 Average / ΔμScm-1s-1 Concentration / % (±Standard Deviation) Trial 1 Trial 2 Trial 3 10.000 10.41 10.02 10.45 10.29 ± 0.24 5.000 10.66 9.987 ( – )8 10.32 ± 0.48 2.500 10.47 9.237 (–) 9.85 ± 0.87 1.250 10.14 9.92 (–) 10.03 ± 0.16 0.625 (–) 10.09 10.50 10.30 ± 0.29Table 4: Standard Deviation at Different Concentrations of GlucoseExample of Standard Deviation Calculation:[Glucose Concentration] = 10% ≒ 0.237557 ≒ 0.24Same calculations were done for 5%, 2.5%, 1.25%, and 0.625% glucose concentrations.8 Data marked with (-) represent outliers.
Seung Soo (Jason) Lee002213-065Uncertainty due to dilution of glucose solution:*Uncertainty due to 50cm3 burette = ±0.05 cm3Concentration of Uncertainties Glucose / % Volume of Volume of distilled Total percentage Absolute uncertainty glucose solution water added / cm3 error for for concentration of added / cm3 concentration of glucose / % glucose / % 10.000 – – – – 3 3 5.000 15.00 ± 0.05cm = 15.00 ± 0.05cm = ±0.6 0.030 15.00 ± 0.3% 15.00 ± 0.3% 2.500 15.00 ± 0.05cm3 = 15.00 ± 0.05cm3 = ±0.6 0.015 15.00 ± 0.3% 15.00 ± 0.3% 1.250 15.00 ± 0.05cm3 = 15.00 ± 0.05cm3 = ±0.6 0.008 15.00 ± 0.3% 15.00 ± 0.3% 0.625 15.00 ± 0.05cm3 = 15.00 ± 0.05cm3 = ±0.6 0.004 15.00 ± 0.3% 15.00 ± 0.3%Table 5: Uncertainty Table for Concentration of Glucose Solution Glucose Concentration Average Rate of Diffusion (±Standard (±Uncertainty) / % Deviation) / ΔμScm-1s-1 10.000 10.29 ± 0.24 5.000 ± 0.003 10.32 ± 0.48 2.500 ± 0.015 9.85 ± 0.87 1.250 ± 0.008 10.03 ± 0.16 0.625 ± 0.004 10.30 ± 0.29 Table 6: Combined Uncertainties of Independent & Dependent Variables
Seung Soo (Jason) Lee002213-065Conclusion / Evaluation: The relationship between the concentration of glucose solution and the rate of diffusion can beseen in Figure 5. As the linear regression shows, there is hardly any relationship between theconcentration and rate of diffusion. The slight rise in the slope and the slight variation among the datapoints can be concluded as outcome of experimental error. Therefore, the data supports the hypothesis;the concentration of glucose solution inside the visking tubing indeed had no effect on the rate ofdiffusion of sodium chloride. The general trend of all 15 trials in the experiment seems to be similar. As can be seen in figure4, most trials display more or less the same rate of change in conductivity over time, with the exceptionof a few that deviate. These deviations (the top four lines on the graph in figure 4) were consideredoutliers and rejected during data processing. These outliers were due to experimental error during theexperiment, which will be discussed later. The results are reliable because the uncertainties are fairly low. The uncertainties in theindependent variable – percentage of glucose concentration – are minimal and almost negligible. Thiscan be seen through the miniscule horizontal error bars in the graph in figure 5. The uncertainties in thedependent variable – the average rate of diffusion – determined by the standard deviation of the ratesof diffusion, are small in relation to the actual average rates. These uncertainties are displayed on thegraph in figure 5 through vertical error bars. The one vertical error bar that is abnormally large – thestandard deviation for 2.5% glucose concentration – is due to the fact that only two trials were takeninto account for the average. Such magnitude in uncertainty can be improved by increasing the numberof trials. Furthermore, because the results correspond with the accepted scientific theory – that theconcentration of glucose does not affect the rate of diffusion of sodium chloride across a visking tubing– the results can be concluded as reliable. The only glaring problem in the procedures was that, in the process of diffusion of sodiumchloride across the visking tubing, the conductivity probe and the visking tubing itself got in the way ofthe magnetic stirrer, causing the stirrer to stop spinning at times. This problem could have caused adeficiency during the process of sodium chloride spreading throughout the distilled water. As a result, itcould have caused a discrepancy in the conductivity reading measured by Logger Pro. Nonetheless, thestoppage of the stirrer was only for a couple of seconds, and it could not have impacted the experimentsignificantly enough to cause a glaring error in the results. Still, the problem could be the cause of thehigh number of outliers and the sizeable standard deviation. The investigation would be much improvedif the apparatus could be improved to eliminate this issue.
Seung Soo (Jason) Lee002213-065Improving the Investigation: Error Impact ImprovementThe serial dilution was Some of the water molecules The entire experiment could beconducted over a evaporated. As a result, there was not conducted in one day; in one timeperiod of two days, due enough glucose solution left at the far period, without any rest within theto time constraints ends of the serial dilution. Although experiment. This way, the effects of the evaporation caused minimal the evaporation of water would be difference of less than 1 cm3, it still minimized. increased error.Occasionally, the The conductivity probe and the visking The conductivity probe and theconductivity probe and tubing disrupted the rotational motion visking tubing could each be held inthe visking tubing got in of the magnetic stirrer. As a result, the place, so that it does not drift intothe way of the sodium chloride diffusing out of the the rotational motion of themagnetic stirrer. visking tubing may not have been magnetic stirrer. In this case, completely dissolved and distributed another human helper would be evenly throughout the beaker with required. Another way of improving distilled water. Therefore, error in the this error would be to use a larger measurement of conductivity, and beaker; placing the conductivity thus the rate of diffusion, could have probe and the visking tubing at the been increased. far ends of a larger beaker would lessen the chances of them bumping into the magnetic stirrer.50 cm3 burettes were The large burette – relatively large in A smaller burette could be used;used to transfer 15 cm3 comparison to amount necessary – perhaps a 20 cm3 burette, tosolutions increased the percentage uncertainty. decrease the percentage uncertainty.Table 7: Ways to Improve the Investigation