How the concentration of an acid affects the rate of reaction.

Chemistry coursework

How the concentration of an acid affects the rate of reaction

Prediction

For a reaction to take place there must be enough energy for the particles to collide & react. So as the concentration increases so will the rate of reaction because there are more acid particles in the solution for the magnesium to collide & react with. Therefore I think the rate of reaction will speed up as the concentration gets higher, for instance 1M will react twice as fast as 0.5m.

Plan

I will set up the apparatus as shown in the diagram below. I will be reacting magnesium with sulphuric acid to test if the concentration of an acid affects the reaction time. I will use molars between 0M & 1M for my initial trial run. I will measure the rate of reaction using a conical cylinder with a rubber bung & a gas syringe. I will then time how long it takes to fill up to 100cc of gas. I will repeat each concentration 3 times then take a average so I get more accurate results, I will repeat any anomaly’s I get so I will get my final results as accurate as possible. I will use five different concentrations so I can gather a good range of data.

Fair test

I will have only one variable so I can relate all changes in the experiment to that one thing – in this test I am changing the concentration of the acid. However I must also monitor several other things that could alter my results.

Surface area- this would speed up the reaction rate by increasing the chance of a collision if the size is made bigger or decrease the chance if the size is made smaller. So I will use the same magnesium ribbon through out the experiment.

Temperature – if the temperature is increased the amount of collisions will be higher & more violent because the higher the temperature the more energy the particles have. I will aim to keep my experiments all at room temperature at all times.
Catalyst – I will not be using a catalyst as ...

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Surface area- this would speed up the reaction rate by increasing the chance of a collision if the size is made bigger or decrease the chance if the size is made smaller. So I will use the same magnesium ribbon through out the experiment.

Temperature – if the temperature is increased the amount of collisions will be higher & more violent because the higher the temperature the more energy the particles have. I will aim to keep my experiments all at room temperature at all times.
Catalyst – I will not be using a catalyst as it increases the speed of a reaction by adding a chemical that will change the speed of a reaction but not change its self.
I will also use the same balance to weigh the magnesium so it will hold the same margin of error on each piece of magnesium I use.

Diagram

Trial run

These preliminary tests helped us to determine the concentrations we will use in the actual test. They did this in two ways:

They show us not to go in margins below 0.25M or else the results would be too slow.
We had initially planned to use 0.25g of magnesium ribbon in each test we did but found that a more suitable amount was 0.12g for the reason that each test would take too long.

Results

Experiment results

Rates of reactions

On the first table any anomalies were repeated. We used the experiment results average column to work out the rates of reaction table – we did this by taking the amount of acid used and dividing it by the average time for that reaction to occur- volume/time (100/time). We used the rates of reaction table to plot they graph.

Conclusion

As the rate of reaction increased so did the concentration of the acid. The graph shows a simple trend in the data by having a line of best fit that is an upward curve showing that the rate of reaction is affected by the concentration of acid. This has happened because when the concentration has increased there are more acid particles for the magnesium particles to collide with causing the reaction to take place faster. I used my results to calculate the rate of reaction volume/time (100/time). I believe that my graph supports my qualitative prediction that as the concentration of acid increases so does the rate of reaction. My graph shows an uneven numerical increase – it doesn’t follow a numerical order it just has an upward increase that has unevenly plotted points. This shows there is an optimum point at which the magnesium & sulphuric acid reacts at by having irregular gaps it shows that it must speed up when it reaches a certain concentration of acid. I think this concentration is between 1.25M & 1.5M because this is where the graph is steepest. However my quantitative prediction wasn’t correct, the rate of reaction in 1M wasn’t double that of 0.5M- for my prediction to of been correct 1M needed to equal 1.34 seconds on the rate of reaction table but it equaled 1.94 seconds.

Evaluating

I believe that the procedure I used & the evidence I obtained were got in a good way because although I had several anomaly’s it worked well & the experiment was successful; it showed I correctly worked out my qualitative prediction. My line of best fit was a smooth curve going through three of the five points; however I had two results that didn’t quite fit – one above the line, one below. I think a reasonable explanation for this is that it was human error – such as placing the bung in the flask after different amounts of time or having to begin using a different coil of magnesium ribbon part way through the experiment. I could improve the accuracy of the results by using the sane coil of ribbon, having an electronic gas syringe that could collect gas as soon as the magnesium was added or doing more tests with more concentrations & repeat them more times- however the amount of tests I did with repeats does offer a reliable source of information. Another way in which I could improve this experiment is to do this test in a different way, I could measure the amount of gas formed every 10 seconds for a minute then take a average for each concentration to see how many CC’s of gas were formed per 10 seconds, I could do that & see which test had the most reliable results with least anomaly’s.