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Factors affecting the rate of Diffusion.

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Factors affecting the rate of Diffusion Aim The aim of this experiment is to investigate the factors affecting the rate of diffusion. Introduction In this experiment, agar will be used. It will be the inert medium that we are using to investigate diffusion through. Agar is extracted from seaweed and after dissolving it in hot water it cools to form a 'solid' jelly. The agar that will be used will be made alkaline by adding small amounts of sodium hydroxide and has had the indicator phenolphthalein added to it to give it a pink colour as it is in alkaline conditions. The H+ from the hydrochloric acid will diffuse through the agar and the indicator will go colourless. Method The apparatus will be as follows: 1/2 a petridish of pink agar at a depth of 1cm A supply of 2M HCl A supply of distilled water A cork borer of 4mm depth and 10mm depth A test tube A stop watch A petridish of agar Distilled water Different concentrations of HCl will be made using distilled water to dilute the HCl using a pipette, as it is very accurate. The concentrations will be 2M, 1.5M, 1M, 0.75M, 0.5M and 0.2M. The total volume will always be 10cm3. The first concentration will be put into a test tube. ...read more.


To make different concentrations of HCl acid, the following measurements of acid and distilled water will be used: Concentration in molars Volume of HCl in cm3 Volume of distilled water in cm3 Total Volume in cm3 2M 10 0 10 1.5M 7.5 2.5 10 1M 5 5 10 0.75M 3.75 6.25 10 0.5M 2.5 7.5 10 0.2M 1 9 10 Time taken for acid to diffuse into agar Dependent The time taken for the acid to diffuse into the agar will depend upon the concentration of hydrochloric acid. Size of agar piece Controlled If the size of the agar piece is large, then the time taken for the HCl to diffuse into it will be more than if it were a small piece. A 4mm diameter cork borer will be used to keep the size equal. Temperature Controlled The particles gain more kinetic energy with a higher temperature meaning more collisions, and so the rate of diffusion is faster. The room temperature will be monitored in case there are any drastic changes. Stirring/Shaking Controlled If the test tube is shaken or stirred, the time taken for the acid to diffuse into the agar will decrease. To keep this constant, the test tube will not be shaken. Apparatus used Controlled If different apparatus is used, the results would be different. ...read more.


There could be three main reasons other than the inaccuracies above that there were anomalies. Firstly, the pipette was not accurate enough; it was accurate to within 0.05ml. Secondly, in the agar, there were actual dips on the surface meaning some pieces were larger than others. Lastly, sometimes the agar floated meaning HCl was not diffusing in from some sides, meaning some took longer. As far as the reliability was concerned, there were two inaccuracies with the equipment. The pipette could only measure to within 0.05ml. Also, the stopwatch could only measure approximately to the nearest 2seconds because of human reaction time. This is because, when the endpoint is nearing, it is hard to judge whether the solution is colourless or not. If I were to guestimate the percentage, I would say that it is approximately 10%. On the graph, there are error bars to show where the results could have lied. From these results, an alternative line of best fit has been drawn. An alternative method for this experiment would be to instead of adding agar to the HCl, the HCl would be added to the agar. The agar would be put at the bottom of a beaker, and using a pipette, 20cm3 of HCl would be added right above the centre of the agar piece. The time taken for the agar to turn colourless would be taken. ...read more.

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