Investigate one of the factors that effects the rate of reaction between Magnesium and Hydrochloric Acid.

Chemistry Coursework - GCSE Assessment

Question:

Investigate one of the factors that effects

the rate of reaction between

Magnesium and Hydrochloric Acid.

Planning

In this piece of course work, I will be testing the reaction times of Magnesium in Hydrochloric Acid. I have a wide range of different experiments, and variables which I could choose from. These are:

Temperature of Hydrochloric Acid,
Volume of Hydrochloric Acid,
Concentration of Hydrochloric Acid,
Mass of Magnesium,
Surface area of Magnesium, and
If there is a presence of a catalyst.

From these variable, I have decided to choose 'Concentration of Hydrochloric Acid'. This set of experiments can be achieved using the equipment I have available to me, and it should give me a clear indication of the different reaction times.

I have decided not to do the other variables, for the following reasons:

It would be too difficult to keep the temperature constant with the equipment available to me. To do this I would have needed to use a constant temperature water bath or some similar equipment.
Changing the volume of hydrochloric acid could have been achieved, even using the limited equipment I had available, but I considered that changing the concentration would produce a more in-depth analysis of the way the reaction takes place;
Changing the mass of the magnesium, could also have been achieved, but this would lead to changing the surface area too. This would have made the experiment unfair.
Changing the surface area of the magnesium would also have been too difficult for me to do, using the equipment available to me. This is because we give the magnesium in strips, and so changing the surface area would also change the mass, or be difficult to measure using the equipment, and so change more than one variable, and therefore make my experiment unfair.
Adding of a catalyst, might have been possible, but catalysts are reaction specific, and therefore I would need to make sure that the catalyst I would have chosen could actually do the job I would want it to do.

The methods I will use to keep all of these variables the same, are:

I will keep the temperature the same, by measuring the temperature before each experiment, to make sure that the temperature is approximately 24 oC. This will allow me to keep this variable constant.
I will keep the volume of Hydrochloric acid the same, by using the same measuring cylinder to measure all of the amounts. This should keep this variable constant, but I would have liked to have used burettes, so that my measurements could have been even more accurate.
I will keep the mass of the magnesium the same, by taking the magnesium off a role, with the same thickness, widths, and I will be cutting it using the same ruler, to get exactly 2cm each time. This should also keep the surface area of the magnesium the same. This will allow me to keep this variable constant.
I will make sure not to use a catalyst, by not getting one out, and by not having one on my table, which could contaminate my whole experiment. This will allow me to keep this variable constant.

Now I have determined what experiment I will be doing, I will describe how I will set it up, and carry it out, so that someone else can check my results to see if the results I obtained are correct.

Because we are only supplied with 1M and 2M Hydrochloric Acid, to get a more varied set of results I have decided to mix the acids together to get the right concentrations. This will also allow me to keep the volumes the same, at 10ml. Below, I will describe how I have managed to make the different concentrations:

0.5M = 5 ml of Water +

5 ml of 1M Hydrochloric Acid

1.0M = 10 ml of 1M Hydrochloric Acid

1.2M = 4 ml of Water +

6 ml of 2M Hydrochloric Acid

1.5M = 5 ml of 1M Hydrochloric Acid +

5 ml of 2M Hydrochloric Acid

1.6M = 2 ml of Water +

8 ml of 2M Hydrochloric Acid

2.0M = 10 ml of 2M Hydrochloric Acid

By using these amounts of the different acids and water, the different concentrations can be formed. This allows me to change the concentrations, but keep all of the other variables the same, mainly the volume of the ...

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0.5M = 5 ml of Water +

5 ml of 1M Hydrochloric Acid

1.0M = 10 ml of 1M Hydrochloric Acid

1.2M = 4 ml of Water +

6 ml of 2M Hydrochloric Acid

1.5M = 5 ml of 1M Hydrochloric Acid +

5 ml of 2M Hydrochloric Acid

1.6M = 2 ml of Water +

8 ml of 2M Hydrochloric Acid

2.0M = 10 ml of 2M Hydrochloric Acid

I have decided to make six separate experiments, one for each different concentration, so that there is a wide range of results for me to analyse and evaluate. For these six experiments, I will repeat each one four times, to make sure that my answers are accurate, and so that I will be able to see if I have any anomalous results. This will also allow me to get an average on which I can draw a graph.

Apparatus

24 X Pieces of 2cm Magnesium Ribbon,
6 X Boiling tubes,
3 X Measuring cylinders,
1 X Container of 1M Hydrochloric Acid,
1 X Container of 2M Hydrochloric Acid,
1 X Boiling tube Holder,
1 X Thermometer,
1 X Stop Watch,
1 X Beaker, and
1 X Pipette.

Safety

To keep my experiment as safe as I can, I will be:

Wearing safety goggles, to keep the acid away from my eyes;
Using a Boiling tube rack, to keep the boiling tubes from rolling off the table;
Rinsing out the boiling tubes after each experiment, so that they don't get knocked over and spill acid on to myself, or others;

I will be trying to be safe generally, by not acting immaturely, which should keep myself, and others, as safe as possible.

Prediction

Due to my own knowledge, which I have learned from previous work on reactivity of chemicals, and further research which I carried out on my own, I predict that the higher the concentration is, the faster the reaction time will be.

I also predict that the end temperature each time should be about the same; and only being different because of the length of time the experiment took to complete. So, theoretically, the end temperature should be lower, the lower the concentration is.

Finally, I predict that hydrogen gas will bubble off because of Magnesium's position in the Reactivity Series.

I predict this because, when the acid is stronger, the magnesium will react quicker. However the total energy produced should stay the same, because the total energy released from a reaction will always be the same, just that the time it takes may vary.

Also, I predict that the end temperature will be lower with weaker solutions, because the energy created by the Magnesium, to turn the water warmer, will be more spread out. Over a period of time the temperature should go back to the starting temperature, or never leave it if the experiment takes a very long time.

Finally, the magnesium should produce hydrogen gas, when reacted with Hydrochloric Acid, because:

Magnesium + Hydrochloric Acid = Hydrogen + Magnesium Chloride

Mg + 2 HCl = H2 + MgCl2

From the above equation, it would not be possible to achieve a different result, and therefore Hydrogen is the only gas that can be produced when Magnesium reacts with Hydrochloric Acid.

Aims

From the research I have done in to chemical reactions, I aim to be able to get precise, clear, reliable results for which I can the evaluate. I plan to do this by recording my results accurately, and clearly in tables and on graphs.

I will make sure the readings I get are also accurate, and not too precise for the equipment I have available to me. I plan to do this by rounding my results up or down ( depending on whether the figure is above, or below half way ). This should make my results more reliable.

Method

I will Collect all of the apparatus listed above, and set it out as shown in the diagram.
For the first set of results I hope to obtain, I will add 5ml of water, (from the beaker half full of water, using one of the pipettes, so that we can get a more accurate result ), to 5ml of 1M Hydrochloric Acid. I will measure the amounts in separate measuring cylinders, which should produce a suitable level of accuracy This should produce 0.5M Hydrochloric Acid.
I will make sure that the temperature of the acid is approximately 24oC, by placing the thermometer in to the acid, where I will leave it until the end of the experiment, so that I can record the end temperature.
Next, I will clear any time from the stop watch's memory, and pick up one of the 2cm strips of magnesium.
Finally, I will drop the magnesium in to the 0.5M Hydrochloric Acid, and as soon as it touches the acid, I will start the stop watch. Once all of the Magnesium has gone/reacted, I will record the time in the table below. I will also take the final temperature, and write it down in the same table of results.
I will then rinse out the boiling tube and dry it, and repeat the experiment another three times, using the same boiling tube, and the same concentration. This is so that the different concentrations can be kept in different boiling tubes. After each experiment, I will right down the times, and the final temperatures.
Once I have the times for this concentration, I will then go on to using the next concentration ( See above for details on how to make the different concentrations ). I will carry out all of the experiments the same way, only changing the concentration, and the boiling tubes after I have carried out that experiment four times. After each experiment, I will right down the final time and temperature in the table of results.

I will start doing the experiments with the lowest concentration first, and one I have repeated them four times, then I will go on to the next higher concentration. This will produce a systematic set of results, and show that the way I will carry out my experiments will be very accurate, and reliable.

Obtaining

I carried out my experiments exactly the same way it says in my method, in the previous section. I did this because my method would, and did produced a safe, fair, and reliable set of experiments and results.

I made sure to be safe while doing my experiments, by following the safety protocols explained in the previous section.

I produce a fair, and reliable set of results, by making sure that I followed my method, and by keeping all of the variables the same ( See previous section ).

I produced exact measurements, by following my method, and by using the equipment I had available to me as accurately as I could, by using pipettes to pour liquids, one ruler to measure the two cm pieces of magnesium, a digital stop watch, and mercury thermometer.

I decided to do six separate experiments, as explained in the previous experiment, and to repeat each experiment four times.

I decided to repeat each experiment four times, so that I could get accurate results, and so that I could spot anomalous results. Also, when I received any anomalous results, I repeated them again, to make sure which answers were correct and which are anomalous.

Also, I can now make an average of all six experiments, so that I will be able to produce graphs to represent the data I received.

Below is a table of result, with all of the primary results I received during my experiments. I have included an average to go with the actual results I collected. I have not included any of the repeated results to replace the anomalous ones.

Table of Results

From these results it appears to me that the whole of the set of results for the 0.5 M acid are anomalous, due to the exceptionally long time each experiment took compared to stronger solutions. I will therefore discount these from my graphs and conclusions.

From the other results I can clearly see that one of the times for using 2 M acid, is anomalous. Due to this fact, I have decided to repeat this experiment again, to see what the answer should be.

The new answer I recorded, is 12 seconds, with a temperature of 32 oC.

This shows that my result was anomalous, and the line in the table for 2.0 M hydrochloric Acid, should now read:

I will now do the rest my coursework, using these new results, because they are more accurate than the line I was previously going to use.

I have prepared a graph to illustrate my results. This is a:

Line Graph to show time taken for a piece of Magnesium to react with different concentrations of Hydrochloric Acid.

This graph shows that the time for the reaction increases as the strength of the solution decreases, and that the slope of the graph is gradually decreasing, but is not approaching zero for the range of values I am using.

Analysing

From the results which I obtained from my experiments, and showed in the previous part of this piece of coursework, I will try to explain what happened, and why.

Original Prediction

I predicted that:

the higher the concentration is, the faster the reaction time will be,

the end temperature each time should be about the same,
hydrogen gas will bubble off because of Magnesium's position in the Reactivity Series, and

the end temperature will be lower with weaker solutions.

From the results I learned from my experiments, I have proved that the higher the concentration was, the faster the reaction time was. I know this, because there is a general trend on both my graphs and table, of the length of time decreasing, as the concentration increases.

I have also proved that there was a temperature increase during these experiments, because the end temperature was always higher than the starting temperature, by approximately the same amount. This proves that this set of experiments are exothermic. This can be demonstrated as a result of Collision Theory.

Heat is generated as molecules collide, which increases the temperature. However heat is lost through radiation and conduction from the equipment, by bubbling off of the Hydrogen gas and by forming molecules of a stable compound (Magnesium Chloride). As the reaction proceeds there is less Hydrochloric Acid and Magnesium remaining, so the rate of heat generation slows down.

The end temperature was not necessarily lower when I used weaker solutions, but the actual temperature rise in each case was relatively small and could have been influenced by external factors. There was no consistent relationship between the concentration of the acid and the final temperature.

Finally, I proved that hydrogen gas did bubble off, due to Magnesium being higher up the Reactivity Series than Hydrogen. I tested the gas given off with a lighted splint (to produce a popping sound), which proved it was Hydrogen. There was no other gas it could be as a result of the chemical equation given earlier.

This set of experiments have proved that all of my main predictions were correct, and only my final prediction was not proved. However, I had no previous information on which to base this prediction.

Evaluation

From my analysis of the results I obtained and the Table and Graph I produced from them, I can see that my experiment was generally successful. The method I used produced a realistic set of results, which were consistent with each other.

The results appear to be accurate, except for those for the 0.5 M solution and one of the 2 M solution results, which I corrected. It was possible that the strength of the solution was not measured accurately, and this may have been the cause of the anomalous results. The final set of results for the range 1.0 M to 2.0 M are therefore accurate.

The method I used to carry out the experiments was a good one, as it was safe, accurate and reliable. The concentrations of the solutions were neither too strong nor too weak. The volumes of materials were not too big or too small to be safe to work with. However the actual volumes of chemicals used were small, which may have caused the results to be less accurate than I believed them to be. The times taken were not too short or too long for the experiments to be carried out during a normal practical period.

The experiments could have been improved by using more accurate equipment, but this was not available to me. This could have been by using burettes to measure the liquids; a digital scale for measuring the mass of the magnesium; a sensor to measure when the magnesium had reacted; electrical stopwatches to measure time, and electrical thermometers to measure the beginning and end temperatures.

I didn't have any of this equipment available to me, so I couldn't use it, but if I did this experiment again, I would try and make sure I used the better equipment I described above.

From the final set of results I used, and the graph I produced, I think that my experiments were reliable. I therefore consider that my experiments proved that my predictions were generally correct, and that I can draw firm conclusions from them. I also think that my predictions will hold for experiments outside the range that I evaluated, but that there may be limits at which errors are introduced.

As an extension to this piece of work I think that it would be useful to carry out the same experiment using a far wider range of strengths of the Hydrochloric Acid solution. This would prove whether the same effects are found outside my tested range, or whether there is a point at which the experimental results break down because the solution is either too strong or too weak to produce meaningful results.

By Andrew McLennan 11 B 07 / 02 / 2000