Preliminary Experiment:
To determine how much acid and magnesium should be used for the final experiment I will conduct a preliminary experiment using different amounts of each.
Plan for Preliminary:
I will use volumes of acid, in intervals of 10ml, ranging from 20 to 40ml, and lengths of magnesium ribbon, in intervals of 0.5cm, from 1cm to 3cm.
Method for Preliminary:
Measure required volume of hydrochloric acid using measuring cylinder and pour into beaker
Add required length of magnesium to acid
Time and record how long the reaction takes
Repeat for each result.
Equipment for preliminary:
Measuring cylinder
Beaker
Hydrochloric acid
Magnesium ribbon
Stopwatch
Ruler
Scissors
Results from Preliminary:
With these results in mind I have chosen to use a volume of 30ml of acid and 1.5cm lengths of magnesium ribbon to make the best compromise between speed, as I have to do the experiment in a set time, and having results that have reasonable differences in repetition and averages so a clear pattern will form and make anomalies easier to see, therefore allowing reliable conclusions to be drawn from them.
Plan:
Method:
Measure 30ml of hydrochloric acid using measuring cylinder and pour into beaker
Add 1.5cm length of magnesium ribbon to acid
Time and record how long the reaction takes
Repeat 3 times for each molarity
Equipment List:
Measuring cylinder
Beaker
Hydrochloric acid solutions of different molarities
Magnesium ribbon cut to 1.5cm lengths
Stopwatch
Ruler
Scissors
For the experiment I will use 30ml of acid for each reading, repeating the readings 3 times for each of the 7 molarities I will use and will measure the time in seconds of the reaction between the acid and a 1.5cm ribbon of magnesium. The molarity of the acid ranges from 0.5m to 2.0m.
To make the test fair all the input variables, except for the molarity of the acid, will be kept the same. The input variables for the experiment are: the amount of acid used, I will keep this the same by carefully measuring 30ml of acid for each reading. The temperature of the acid, this will be the same as the acid is stored at room temperature therefore the acid will be at room temperature. The length of magnesium ribbon, this will be kept the same by carefully measuring the ribbon using a ruler then cutting it to length. The concentration of the acid, this will be changed to see how it affects the reaction rate.
To make the experiment safe safety goggles will be worn at all times and funnels will b used when pouring acid from bottles to the measuring cylinder to minimise spillages.
The experiment will enable me to prove my prediction correct as by recording the time of the reaction in different concentrations of acid then analysing the results to find a correlation between time and molarity I will be able to see if my theory was correct.
Results from Final Experiment:
Analysis:
My results show that there is a clear pattern, being the higher the concentration of acid the faster the reaction rate. This proves my prediction correct. Although there was a clearly anomalous result, the first reading for the 1.5m solution, the averages for all the solutions fell into a clear pattern that can be seen on the graph as a downwards curve.
The reason the results showed this pattern is that in the higher concentrations of acid there are a larger number of acid particles moving around so this increases the chance of an acid particle colliding with a magnesium particle, which therefore increases the rate of reaction. This proves that the theory in my prediction was correct.
I have drawn a graph showing 1/time, this a rate graph, and although my results didn’t line up very well on the line of best fit it allows me to make predictions about other molarities before I test them, for example, using my 1/time graph I would predict that the 1/time result for a 2.5m solution of acid would be 0.059 seconds.
Evaluation:
The experiment was successful as it determined how concentration of acid affects the reaction rate of hydrochloric acid and magnesium, the question asked in the aim. The plan was a good one and I did not have to change anything during the experiment to make it work better. To improve the reliability of my results I could have used more concentrations of acid to see if the pattern carried on as it did previously or changed, I could have repeated the readings more times to make them more accurate.
My results were good. They were reliable as the repeat readings were very close to one another with the exception of the first reading for the 1.5m solution and the last reading for the 1.25m solution. The second result for the 0.5m solution was almost forty seconds lower than the other results but as the readings were so high the percentage of error was relatively small. The results were consistent with my prediction and quite consistent within themselves, which indicates that they are fairly reliable. The results lined up very well on the graph with a very close curved line of best fit that all the results fall directly onto or very close to with only two off the line and only 1 second away. This backs up the consistency and reliability of the results, which makes my evidence good enough to support a firm conclusion.
There was only one result, the first reading for the 1.5m solution, that I considered far enough away from the other results to be considered unreliable. I put this inaccuracy down to human error, probably a mis measurement of acid or magnesium or failure to wash the beaker out properly after the previous experiment.
To improve my knowledge of reaction rates I could and how concentration affects them I could conduct experiments using different metals and different acids. I could also use a larger range of concentrations to extend my results and give me more evidence. Using smaller gaps between concentrations would also further my evidence as it would improve my rate graph allowing me to draw a more accurate line of best fit therefore allowing me to make more accurate estimates for results of concentrations not yet tested.
