Once Again there was no definable pattern with this experiments we tried another one more experiment. In this one we timed how long it took for the hydrochloric Acid to diffuse through 5mm of gelatine, around the wells. These were the results we obtained.
Even though this experiment took a very long time there was a clear pattern so this was the method we decided to use in our main experiment.
The rate of diffusion can be affected by the concentration of the hydrochloric acid, the size of the well that the Acid is put into and the temperature. We found that the higher the concentration the quicker the universal indicator will make the gelatine turn pink. We also found that the smaller the well the quicker the rate of diffusion, and with both of these facts vice versa. Temperature is also a factor that could affect the rate of diffusion because if the temperature was higher the diffusion is likely to occur quicker compared to when the temperature was lower. 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. Each one of these we did one at a time due to not being able to time fairly more than one experiment at a time. As soon As the wells were filled up we set the stop clock going. We would regularly measure the amount of diffusion until it got to 5mm. Once At this level the stop clock would be stopped and the time recorded. Then another well would be filled up.
After completed the lengthy experiment these were the results we found.
I can see that my prediction and preliminary graph showed a definite pattern. The only reason they weren’t totally correct was due to the two anomalous results I came up with. The anomalous results that occurred could be due to a number of things, firstly we used 3 petri dishes and in them the agar gelatine may not have always been the same thickness as the others. 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.
