Fair Test
This experiment will be a fair test because I am only varying one factor, which is the temperature of the experiment. I am not going to vary the concentration of hydrochloric acid. This is important so I can make a concise and fair analysis and conclusion. If any of the fixed variables were altered during the experiment, then it would no longer be a fair test. Water is the control for my experiment.
Precision
There are a few things in this experiments that will limit the precision. The clock watch is accurate to 100th of a second, but that is too accurate for our purpose. We are measuring the rate by human eye. Everyone’s eye is different, so it is quite a guess when you think that all of the magnesium has reacted. This makes the experiment only accurate to about 1 second at fast speed, and 3 seconds if the experiment is slow. This experiment has quite a few limiting factors. The major inaccuracy is the use of the human eye to say, “stop”. In this experiment, I will be using the method of averages to decrease the error rate. I will perform a repeat for each data value. Then I will be using the average for each data point to get a more accurate result.
Preliminary results
The experiment was carried out once in a way that the experiment could be experimented upon. It was decided that the temperature did not seem to fluctuate much so would be hard to measure. The results did seem to fit with my hypothesis but these are not results.
Method
For this experiment the following pieces of equipment are needed:
- 2x 80 ml beakers.
- 1x measuring cylinder
- 150 ml of 2.0 concentration acid
- 150 ml of water
- 18 cm of magnesium ribbon
Set the apparatus up as follows:
Results
These are the results that I collected:
These results as a table are not easy to understand but a graph of these results can be seen on a separate graph.
Analysis
The graph very definitely shows a trend, and a curve can be drawn that supports a negative correlation, (as X gets bigger, Y gets lower), meaning that as the concentration of HCL increases the time taken for the magnesium to dissolve is decreased (higher rate of reaction). As the concentration decreases the rate of reaction decreases. This agrees with what I said in my hypothesis, that concentration makes the rate of reaction increase. The reason for this increase in rate of reaction is that the higher the concentration the more particles there are for the magnesium to react with.
Evaluation
This experiment has problems with it that are due mainly to human factors, it is very difficult to measure the exact time it takes for the magnesium to dissolve. This is because at the higher rates of reaction the magnesium splits into small pieces that differ in times of dissolving. It can be un-accurate when the magnesium sticks to the side or only floats on the surface as less of the magnesium comes into contact with the acid. My results seem to be accurate because there are few anomalies, perhaps because the fact that I repeated the experiment and took and average deleted rogue results. I feel that my results are accurate enough for the trend of the graph to be accurately taken into account. I would have preferred to take many more results, but I had to repeat some of the experiments more than twice, due to things like, the change in temperature of the equipment.
Accuracy
This experiment was limited by several factors. Firstly, the human eye judged the time at which the experiment finished. The eye is not way near the most accurate means of judging when it has finished. This will lead to a huge inaccuracy in the results is you do not judge the point of finish as roughly the same for each experiment. If it not accurately judged, you will get unreliable results. The measuring cylinders were only accurate to 1cm³. This means that the volumes of hydrochloric acid and water will vary slightly from each data point to the next. The ruler for measuring out the 5cm strips of magnesium is only accurate to ½mm. These will not really have any effect on the result readings. The main accuracy problem is that the human eye did all of the judgement on when the experiment had finished.
Further Work / Extension
To extend my knowledge in this subject, I could do another investigation into the effect of temperature on the rate of reaction. I predict that the temperature of hydrochloric acid is directly proportional to the rate of reaction. I could carry out this experiment by doing different temperatures.
Suitability of method
This experiment was very suitable for the investigation. It got me all the information that I needed, without any problems, and the information was clear to interoperate and understand. It was an easy experiment to carry out.
Improvements
I could improvement this experiment by using a different method of measuring the finish time in a different method. I could collect all the hydrogen gas produced in a gas syringe, and when a certain volume of hydrogen is collected, I could stop the clock. I don’t have to finish the experiment, by only get to a certain volume of gas collected. This would eliminate the inaccuracy of the eye determining the finish point by a huge amount. This would improve the accuracy of my experiment.
