Ensuring a Fair Test
As mentioned above, I want the most accurate and precise results possible, and there are various things I can do to ensure this. The first is to make sure that only one variable is changed each time. For this experiment, the controlled variable will be the temperature All other things will be kept the same; amount of hydrochloric acid (15 cm³), amount of potassium carbonate (10g), concentration of hydrochloric acid (1 mol), form of potassium carbonate (powder), thermometer (as different ones may have slight inaccuracies), and the conical flask. These precautions will ensure that the differences in results are due only to temperature, and no other factors. For example, using a different concentration of hydrochloric acid each time would mean the results for temperature would be influenced by this other factor.
Range and Extent
Even in the most carefully controlled environments, freak results can occur. To prevent against this, I will repeat every experiment three times. If the results are similar, then they are most likely accurate. However, if I get a result which does not fit, I will repeat the experiment however many times necessary to get concurring results.
As my hypothesis stated that a ten degree increase would result in a double in the rate of reaction, having experiments at ten degree intervals makes good sense. I also want a wide range of results, and so will measure at 10°C, 20°C, 30°C, 40°C, 50°C, 60°C and 70°C. By this time, I will have thorough results that provide good conclusions.
Alterations to Method
After performing some preliminary tests, I found I had far too much potassium carbonate, and not enough hydrochloric acid. After experimenting with different mixtures, I decided to use 40 cm³ of hydrochloric acid, still 1 mol, and 1g of potassium carbonate. I also decided not to stir the mixtures, as it is difficult to control, and often causes the results to happen very quickly, even at low temperatures.
Results Table
Graph
Conclusion
My results show that increasing the temperature of a reaction, and so increasing the amount of energy, causes a rise in the rate of reaction. This is due to collision theory. This states that for a reaction to occur, the particles must collide with sufficient energy to react, and this is the activation energy. By heating the mixture, I am increasing the amount of energy the particles have, and so increasing the number of successful collisions. Heat also causes particles to move faster, so increasing the temperature increases the probability of a collision, thus causing a higher rate of reaction. My results also show that a ten degree increase in temperature causes a double in the rate of reaction. For the majority of results, this is true, and those which it is not are very close to been true. My results agree with my hypothesis; a rise in temperature does cause an increase in rate of reaction, and a 10° does lead to an approximate double in rate of reaction.
Evaluation
I feel the experiment went very well. I produced good results, and only had three anomalies (highlighted in red). They supported my hypothesis, which was based on sound scientific knowledge. I also feel I achieved a high level of accuracy in my experiment. I was able to measure time to a hundredth of a second, although with human reactions, its more likely that I did it a half of a second, which is why I rounded all my results to the nearest second. I also did not feel it was necessary to have any more detailed results, as I cannot plot graphs that accurately, and my interpretations are not that precise. I was able to measure temperature to the nearest degree, and I would have liked to have had more accurate control over this, and this perhaps could have been achieved using digital apparatus. I was able to measure the mass of the potassium carbonate to a hundredth of a gram, which I think was easily sufficient. I could measure the amount of hydrochloric acid to the nearest millilitre, which was acceptable, but could again have been improved. I think my results are very reliable. By repeating them three times each, it meant that the odds of all results been anomalies is minute, and means that they can be trusted. The maximum difference in any two results in the same class, excluding anomalies, is just 5 seconds, and this was on the longest experiment, so it had even less of an effect. There are some results which do not follow the pattern, and these have been highlighted effects. Although I cannot say exactly why these occurred, there are various possibilities. The hydrochloric acid could have been diluted; someone may have splashed some water into it, or an acid of higher concentration. There may also have been a bad batch of potassium carbonate. Human errors do occur, and it is probably more likely that in these results I confused one acid for another. I think the biggest problem I encountered was putting the potassium carbonate into the hydrochloric acid. All I was able to do was to drop it in, and this obviously was not accurate. Some stuck to the sides, sometimes it spread evenly, others it seemed to stay together. I could not mix it, as there was no accurate way to do this, and I feel this is the biggest weakness in the experiment. A way of guiding the potassium carbonate in would have helped, and perhaps some form of mechanical or electronic mixing to ensure it is fair every time. I think I had sufficient evidence to support my hypothesis; the results clearly show that increasing the temperature increases the rate of reaction. As the graph curves upwards, and gets higher quicker and quicker, it shows that increasing the temperature by a certain amount does cause the rate of reaction to double, and in this experiment it was around 10°C. To expand this experiment, and to further support my hypothesis, I would like to take intermediate results i.e. at 15°C, 25°C and so on. This would allow deeper analysis of the results, and to provide even more proof that the hypothesis is correct. It may also allow us to find out the exact temperature increment required to double the rate of reaction, which would be interesting and useful to know and understand. Investigating different concentrations of acid would also be an interesting expansion, and would allow us to find optimum conditions for increasing the rate of reaction, and possibly finding a link between rate of reaction and acid concentration.
