Factors affecting the rate of Diffusion.

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Factors affecting the rate of Diffusion


The aim of this experiment is to investigate the factors affecting the rate of diffusion.


        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.


The apparatus will be as follows:

½ 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. Using a cork borer, 4mm of agar will be taken and dropped into the test tube making sure that all of it is covered by the HCl solution. A stopwatch will then be used to find the time taken for the agar to turn colourless when all the HCl has diffused into it. This will then be repeated with the different concentrations and then repeated again for accuracy.  

Preliminary work

        10cm3 of 0.2M HCl was taken and put into a two test tubes. A 0.2M concentration was used, as this will take the most amount of time to diffuse into the agar. Two cork borers were then taken, one of 4mm diameter and the other of 10mm diameter. Using the cork borers, 2 pieces of agar were taken and put into separate test tubes. The time taken for the HCl to diffuse into the agar was taken. For the 4mm diameter piece, the agar turned colourless in 4minutes and 26 seconds. The 10mm piece on the other hand took 31mintutes and 37 seconds. I have decided to use the 4mm diameter cork borer as it took only 4minutes. I am not going to use the 10mm diameter cork borer as it took over half an hour and I could not do twelve of them measurements in one hour.  

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        When the experiment is performed, safety goggles must be worn as something might come in contact with your eyes when shaking the solution or pouring it etc. If anything is spilled, it must be wiped up immediately as it might be harmful to other people unaware of what it is.


        I predict that as the concentration of hydrochloric acid increases, the time taken for the acid to diffuse into the agar decreases and the rate (1000/time in seconds). This is due to there being more particles to move randomly. Each particle has the ...

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