Agar Diffusion Experiment

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. The acid I will be given will be 1M Hydrochloric Acid (HCl). I will be given one Petri dish of pre-prepared pink agar poured to an approximate depth of 1cm.

Safety

It is important to remember safety whenever working in a laboratory particularly when handling corrosive solutions such as acids and bases.

To this extent it is essential to always where safety goggles when doing any experiment. In order to ensure the safety of myself, and my friends I am going to take the following safety precautions during my experiment:

* Ensure safety goggles are worn at all times during the experiment.

Diffusion In Agar Jelly

* Always ensure any beakers containing HCl are kept in away from the edge of the table.

* Always wash hands after handling corrosive materials.

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* 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. Now take six test tubes and use the cork borer and a scalpel (if necessary) to lift three pieces of agar jelly solution. Drop the three cork borer size agar solution pieces into the first three test tubes. Take a straw and use it to cut a further three pieces of agar jelly solution using the same method as before. Drop the three straw size agar solution pieces into the final three test tubes. Now add 5ml 1M, 0.5M and 0.2M HCl to the test tubes one by one and start the stopwatch; adding the different concentrations of HCl to one of the different sized agar solutions each:

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.

Once all of the test tubes have been timed, dispose of the HCl and agar jelly in the appropriate way and clean out all 6 test tubes thoroughly. 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.