Find out the effect of acid concentration on the rate of reaction

* Once the magnesium has completely disappeared stop the stopwatch and record the time

* Repeat the process until I have sufficient results

I feel that this experiment is easy to set-up and is cheap as the equipment required is neither expensive nor hard to use. Below is a clearly labelled diagram of what the experiment will look like once completely set-up:

Throughout the experiment I will be constantly changing two variables and these are acid concentration and water concentration as these are the two main factors in influencing the rate of reaction.

While I am changing two variables I am keeping the length of magnesium the same throughout as I am trying to determine the rate of reaction between hydrochloric acid and magnesium which therefore means the magnesium needs to be a consistent size otherwise the experiment would be rendered unfair.

It is extremely essential that I control each variable appropriately and that the test is fair otherwise my results will have anomalies and will make the investigation unreliable.

In this investigation I am not going to have a limit on how long each test can last for as it is not important and there is no way I can predetermine the time it will take to do each of the tests.

Due to the drastic effect of anomalies and the importance of reliable and correct data I feel it is apparent that I need to do each test five times and then work out an average of all the results from the five tests which I can then display in a graph. This will mean in total I will have done twenty-five tests at the end of the experiment which is a sufficient amount in order to make the results extremely reliable and correct.

I feel in any experiments you do you need a wide range of results as it makes it easier to find out any patterns and evaluate afterwards as you will have stronger evidence.

I predict that the most concentrated acid will give the fastest rate of reaction because from my scientific understanding I know that for a reaction to occur, two or more molecules of different elements or compounds, for example Mg and HCl have to collide. From the previous statement it suggests that the more molecules present the more susceptible a reaction will occur. Consequently as there are more collisions, the reaction will go faster and the rate of reaction will be higher. To help me develop my prediction I have used various sentences from the webpage, www.chem4kids.com/files/react_rates.html.

Now that I have developed a prediction based on theoretical knowledge and information from other sources I now have the ability to develop a graph displaying the likelihood of the results. The graph is below:

The reason why I felt that the rate of reaction is proportional to the acid concentration is that from my understanding I feel the higher the acid concentration the faster the rate of reaction, which I have backed up with scientific evidence previously. Towards the end there is a slight bend, the reason why I have incorporated this is that I feel that it would begin to gradually level off to 0.01 seconds as I feel it would be incorrect to suggest that with a acid concentration of fifty millilitres it will take 0.01 seconds to react with the acid when at forty millilitres it takes 250 seconds.

Now that I have a solid understanding of what I am going to do in the investigation and have a rather strong prediction with accompanying evidence I am now ready to begin. The results I have retrieved are below:

Acid/Water (ml)

Time

(S)

Time

2

(S)

Time

3

(S)

Time

4

(S)

Time

5

(S)

Average (S)

50/0

79.8

75.0

66.6

73.8

74.4

73.92

40/10

94.2

68.4

91.8

26.6

85.2

93.24

30/20

420.6

306.0

273.0

80.6

249.6

285.96

20/30

687.0

727.8

634.8

739.8

787.8

715.44

0/40

901.8

975.6

987.6

918.6

969.0

950.52

Now that I have retrieved the results successfully I am now going to display the results graphically in a graph to interpret, determine any patterns and anomalies etc. The graph is displayed below:

Now that I have completed the practical aspect of the investigation I can now safely say that overall it has been successful and everything has gone according to plan.

As you can see from my graph it is apparent that the results partially agree with my prediction as there is a positive correlation between the time and acid concentration and they increase at a relatively proportional rate. From this graph I have discovered that there is a relatively high possibility there is a few anomalies, or the test was not done correctly. This could be due to a multitude of reasons, from starting the stopwatch slightly later to not having the magnesium exactly 1cm. So to combat this problem I have drawn a line of best fit onto the graph which is an additional line that goes through the middle of all the results to give me an average. From my line of best fit it is now apparent that the more acid, the quicker the reaction time which means in scientific terms, the higher the acid concentration, the faster the reaction rate which is exactly what I predicted in my prediction.

Towards the end of the normal-line there is a curve, this again could be due to the line levelling of to 0.01 seconds as I suggested earlier.

I felt that the experiment was quite accurate, but due to the nature of the investigation it is clear that it is almost impossible to get completely accurate results, for example when I attempt to time the reaction rate it is extremely probable that I will not begin the stopwatch at exactly the same time as the magnesium impacts with the acid and water. Due to the problems that could arise, I have insured that I have done numerous tests so that I can get an average, which is susceptible to be more accurate then the results from a few tests.

To make the experiment more accurate I feel the only solution would be to dramatically increase the number of tests I undertake and get averages from them.

I felt that it is possible, looking at the shape of the line that there may be one or two anomalies in the data, but they are not dramatically different in comparison with other results, therefore I feel it is solely due to human error and slight inaccuracies.

I think that the methodology I used was suitable for the experiment as everything went well enough for me to retrieve quite accurate and reliable results, while also making sure the test is as fair as possible.

I feel that the data was originally not entirely accurate and reliable as there are no repeated results, which is what you would expect to find in accurate data, but to solve this problem as best as possible I have used the averages in the graphs.

To extend the original problem I am going to do another test where I will replace the magnesium with another element, which is going to be the highly reactive potassium (K) and see how that makes a difference to the reaction rate. After completing this, if the shape of the line followed a similar pattern to the previous tests then this would dramatically support my evidence and prediction. The chemical equation is below

2K + 2HCl -> 2KCl + H2

The results I have retrieved from the tests are below:

Acid/Water (ml)

Time

(S)

Time

2

(S)

Time

3

(S)

Time

4

(S)

Time

5

(S)

Average (S)

50/0

48.4

53.5

66.6

28.7

50.4

49.52

40/10

57.7

39.2

57.6

97.6

55.1

61.44

30/20

383.8

247.7

233.4

51.0

213.8

245.94

20/30

646.9

692.2

605.7

707.4

752.5

680.94

0/40

868.9

938.7

947.4

888.7

935.0

915.74

To make the data easier to analyse and interpret, I am going to place the data into a graph which is located below:

From the graph it is evident that there is a positive correlation and that the rate of reaction increases at a relatively proportional rate to the acid concentration which is exactly what occurred in the previous experiment. The only major difference is that the overall reaction time is significantly quicker, which is almost certainly due to the fact that potassium is higher then magnesium in the reactivity series. This helps me significantly prove the below statement.

From this investigation I have found out that the higher the acid concentration the quicker the reaction rate as there is more acid particles to collide with the magnesium, which I have thoroughly backed up in numerous ways.

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