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Agar Diffusion Investigation

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Biology Coursework Plan Introduction Having considered the phenomena of diffusion and osmosis I have been told to do a piece of coursework to investigate the rate of diffusion when using different concentrations of acid. I have been told to use Agar. Agar is extracted from sea weed and after dissolving in hot water it cools to form a 'solid' jelly although 99% of this is water. The agar is an inert medium that I am going to use to investigate the rate of diffusion. The agar I will be given has been made alkaline by adding a small amount of NaOH and has the indicator (phenolphthalein) incorporated which is pink in alkaline conditions. As the H+ ions from the acid diffuse in the indicator within the agar will become colourless. ...read more.


* Ensure a good supply of paper towels is available in the event of a spillage and be sure to wipe up any spillages immediately before they escalate. Preliminary Variables I am going to investigate what variables I am going to change during my preliminary investigation. During my preliminary investigation I am going to investigate how both concentration and volume of HCl effect the time taken to turn the phenolphthalein colourless. I am also going to investigate what amount of Agar jelly solution should be used. I am going to use a cork borer and a straw to cut pieces of the agar jelly solution and compare results between the two. Preliminary Investigation Method To being with obtain one test tube rack and one stopwatch. ...read more.


Now return the six test tubes to the test tube rack and repeat the experiment only this time varying volume of HCl used instead. Once all six test tubes have their appropriate agar jelly solution added, add 15ml, 10ml and 5ml of 0.5M HCl to the test tubes one by one and start the stop watch, adding the different volumes of HCl to one of the different sized agar solutions each: As before wait until the agar has turned completely colourless in the first test tube then record the time taken and repeat the process for the next test tube. Preliminary Investigation Results Concentration Cork Borer Sized Agar (Time Taken - Seconds) Straw Sized Agar (Time Taken - Seconds) 1M 0.5M 0.2M Volume 15ml 10ml 5ml ?? ?? ?? ?? Dean Lancaster Page 1 26/04/2007 ...read more.

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This is an reasonable piece of work. The student has a clear idea of what needs to be done, however a little more attention needs to be paid to making the plan as effective as possible.

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Marked by teacher Kate Gardiner 17/10/2013

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