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An investigation into a factor affecting the rate of diffusion of hydrochloric acid into Agar gelatine.

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By Sian Burnell An investigation into a factor affecting the rate of diffusion of hydrochloric acid into Agar gelatine We carried out an experiment to investigate the rate if diffusion using hydrochloric acid and a petri dish of agar gelatine impregnated with universal indicator. In our preliminary work we did three experiments each one slightly different to the one before. In the first, we used five different concentrations of acid put into wells in the agar with a size 6 bore and measured how much of the Agar had turned pink at certain intervals. After starting the experiment we found that no definable pattern had occurred. These were the results we found Concentration (Moles) Time (secs) 30 60 90 120 150 Diffusion into agar (mm) 0 0 0 0 0 0 0.1 0.5 1 1 1.5 1.5 0.5 1 2 3 3 3 1 3 5 6 6 6 2 1 2 3 3 3 Due to these results having no definable pattern we tried another experiment. In this one we picked a set time and measured how much diffusion had occurred around the wells. ...read more.


We couldn't do anything for temperature, as we were to assume the temperature was constant throughout. It is because of these factors that we carry out preliminary work so we can find out what factors are best to investigate and which need to be kept the same throughout. As I have mentioned we have decided to investigate the concentration due to the results from our preliminary work. Due to the fact that the higher the concentration the quicker the reaction we believe that this sort of graph will occur. In this sort of experiment the reason the reaction will be quicker when the acid is stronger in concentration is because of the collision theory. When the concentration is stronger there are more molecules of acid to collide and react with each other resulting in a much quicker rate of diffusion, obviously when the concentration is lower the affects are reversed. For the main experiment we used: * Three petri dishes of agar gelatine impregnated with universal indicator * Hydrochloric acid of five different concentrations * A pipette * A ruler * Stop clock * Borer size 11 Firstly we put five holes in each petri dish of gelatine, we then filled them to the top with hydrochloric acid. ...read more.


Also the experiment was done on two separate days therefore temperature may have been a factor or it is possible for the acids to have been mixed when people have not washed the pipettes efficiently. I can see that the experiment showed to a high degree what I had expected Apart from the fact that I wouldn't have expected the time to be so long. I think that the Anomalous results could be due to, perhaps the temperature or the Accuracy of the measuring. The measuring can affect the time because even though the diffusion was measured regularly it could have reached 5mm before we measured it. Also the rulers weren't very accurate. To lessen these inaccuracies a water bath may have been used to keep the temperature constant. To keep the measuring more Accurate we could have done with rulers to a hundredth of a centimetre not just A tenth. About the timing of the timing of the measuring there is only one possible solution I can think of and that is to cut blocks where the space around the well is 5mm that way we could see when the 5mm of gelatine had turned pink. ...read more.

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