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Diffusion in Agar Block

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Introduction

Biology Experiment - Agar Block Aim: To check how the surface area to volume ratio affects the rate of diffusion in an agar block. Theory: Diffusion: Diffusion is defined as the movement of particles from a region of higher concentration to a region of lower concentration. This can be seen in a cell where gases diffuse through the cell membrane. The rate of diffusion is said to be dependant upon the various factors listed below- * Size of molecules that have to diffuse * Concentration Gradient * The distance across which diffusion occurs * Number of pores/openings * Surface Area and Concentration This rate of diffusion is measured by considering the time taken for changes to physical changes to occur. For example if a red substance is diffusing out of a transparent substance the colour fades as more of the red substance diffuses out. Hypothesis: It is logical to hypothesize that the agar blocks with the largest surface area to volume ratio will take the least amount of time to diffuse i.e. it should have the fastest rate of diffusion. This is because if the agar has a larger surface area more of the agar is in contact with the hydrochloric acid and so diffusion takes less time. The hypothesis also states that in cases where the volume of the agar block is changed while surface area remains constant the rate of diffusion should not be affected as the reaction only occurs at the surface so the volume of the agar does not affect the rate of diffusion. ...read more.

Middle

1 6 : 24.4 0.245 : 1 238.14 6 26.0 : 6 4.33 : 1 6 : 26.0 0.231: 1 222.72 Beaker Volume of HCl (cm3) Dimensions (cm) Surface Area (cm2) Volume of Agar Block (cm3) Time Taken (s)(+/-0.01) Length Width Height 7 25 3 2 1 22 6 303.11 8 25 5 1.2 1 24.4 6 270.56 9 25 6 1 1 26 6 255.59 Beaker Surface Area: Volume Simplified Ratio Volume: Surface Area Simplified Ratio Time Taken (s)(+/-0.01) 7 22.0 : 6 3.67 : 1 6 : 22.0 0.273 : 1 303.11 8 24.4 : 6 4.07 : 1 6 : 24.4 0.245 : 1 270.56 9 26.0 : 6 4.33 : 1 6 : 26.0 0.231: 1 255.59 Average Readings for Testing of Surface Area Volume Of HCl (cm3) Dimensions (cm)(+/-0.05) Surface Area (cm2) Volume of Agar Block (cm3) Time Taken (s)(+/-0.01) Length Width Height 25 3 2 1 22 6 275.40 25 5 1.2 1 24.4 6 245.95 25 6 1 1 26 6 231.41 Surface Area: Volume Simplified Ratio Volume: Surface Area Simplified Ratio Time Taken (s)(+/-0.01) 22.0 : 6 3.67 : 1 6 : 22.0 0.273 : 1 275.40 24.4 : 6 4.07 : 1 6 : 24.4 0.245 : 1 245.95 26.0 : 6 4.33 : 1 6 : 26.0 0.231: 1 231.41 Testing for Volume by keeping Surface Area Constant Beaker Volume of HCl (cm3) Dimensions (cm)(+/-0.05) Surface Area (cm2) Volume of Agar Block (cm3) Time Taken (s)(+/-0.01) Length Width Height 7 25 1 2 1 10 2 208.44 8 25 1.5 1.4 1 10 2.1 211.12 9 25 3 0.5 1 10 1.5 205.76 Beaker Surface Area: Volume Simplified Ratio Volume: Surface Area Simplified Ratio Time Taken (s)(+/-0.01) ...read more.

Conclusion

* There is also a chance of parallax errors occurring while measuring the volume of Hydrochloric Acid and while cutting the agar pieces into shape. * The stopwatch may not have been started at the exact moment; this error can be large if only one person is conducting the entire experiment. The stopwatch may also not have been stopped at the exact moment and this adds to the error. * The volume of Hydrochloric Acid added may not have been exactly the same. Fair Test: * Keep the blank white paper behind the beaker at all times during the experiment as it is only then that detection of the changes in colour can be made. * Do not leave the agar out open in the air. Always shut the lid of the Petri dish after removing the agar. * All the equipment must be clean; the deposition of dust and dirt may affect the rate of diffusion. * Do not move or shake the beaker while the experiment is taking place. * The concentration of acid and that of the colouring agent (phenolphthalein) is the same through out the experiment. * Conduct the experiment in atmospheric conditions and do not change any elements such as temperature etc. Safe Test: * Be careful with equipment such as the beaker so that you do not end up dropping it. * Do not cut yourself with the scalpel. * Do not touch any of the chemicals with open wounds as open wounds are prone to infection. * Do not ingest any of the chemicals and make sure you wash your hands after handling the agar etc. as they may cause itching. ...read more.

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