The final variable is concentration and my one of choice because of its wide enough range of available concentrations to test, easy to carry out the experiments and to get accurate results in the time allocated.
Basic Method-Epsom Salts:
- 1. Place the magnesium into dilute, cold sulphuric acid; Hydrogen should be given off. When the reaction stops excess magnisium should remain.
- Remove excess magnesium using a filter. The remaining substance is the magnesium sulphate solution.
- Gently Heat the magnesium sulphate solution to evaporate off any excess water. The result is a saturated solution. Dip cold stirring rod into the solution and crystals should form around the rod.
- When cooled this solution should crystallize.
- Pour off the remaining solution leaving just the crystals between pieces of filter paper.
Method:
For this experiment the following specifications will be used and will remain constant throughout the experiment.
- Magnesium strips
- Reading hydrogen levels every 5 seconds
- Temperature
- 0.1g of magnesium.
- 50ml of sulphuric acid
To do this experiment, one must set up the equipment as shown in the diagram below with the equipment listed and labeled.
This practical has to be done accurately and efficiently to record the best set of results possible. To do this you must set up the experiment as accurately as possible and record results every 5 seconds.
Apparatus:
- Conical flask
- Cork
- Small measuring cylinder
- Plastic tub
- Large measuring cylinder
- Sulphuric acid
- Magnesium
- Flask
- Test tube stand (optional)
- Water
- Stopwatch
- Goggles
- Two clamps with stands
- Delivery tube for conical flask with side arm
- Electronic weighing scales
Apparatus setup and procedure
- Measure out the required concentration in ratio with water with 50ml of solution.
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Once you have measured these concentrations in to your 5 measuring cylinders, fill your 200ml measuring cylinder with water completely so that there are NO air bubbles left in the top; and invert it into your tub of water fixed by the clamp stand.
- Measure out the Magnesium strips to 0.1g exactly and place it into the conical flask before pouring the concentration of Sulphuric acid to the solution.
- Now place your conical flask with side arm with the 1g of magnisium inside and clamp it to a clamp stand and feed the side arm into the water and positions it so the end of the funnel is inside the 200ml measuring cylinder once again ensuring no air bubbles are released into the measuring cylinder prior to the experiment..
- Draw up some rough results tables and make sure before starting the experiment to have someone to record the results with a stopwatch, someone to observe the experiment and to call out the results shown, also someone will have to put the solution of H2SO4 and H20 into the conical flask and place the bung.
- Once all is ready place the H2SO4 solution in the conical flask with the magnisium and place the bung on immediately, record the results shown every 5 seconds for 40 seconds. Repeat each concentration 3 times. Making sure that all the Hydrogen bubbles are released into the measuring cylinder and not the tub to obtain the most accurate results as possible.
Variables:
- Concentration of the Sulphuric acid solution: As the concentration gets higher, the more lightly particle collision is going to occur simply because there are more of them.
- Gas released: Hydrogen
Constants:
- 0.1g of magnesium
- Magnesium ribbon (Low surface area): The smaller the piece of magnesium e.g. powder; the larger the surface area. The larger the surface are; the faster the rate of reaction. With a higher concentration of Sulphuric acid, a high surface area would make the reaction to fast to be monitored accurately so ribbon is being used.
- 50ml sulphuric acid
- Constant temperature: The temperature will be kept as constant as possible considering the experiment location. This is to keep my results as accurate as possible, the higher the temperature the more energy the particles carry making them move a lot faster in their container; This faster movement causes collision of particles to occur more frequently, increasing the rate of reaction.
- Intervals between recording results: 5 seconds
Fair test:
In order to see that this experiment is a fair test the ‘constant’ factors shown above will have to remain so. If they are not the experiment will be more prone to anomalies. As well as this the other factors that can affect the rate of reaction must be kept constant. These are surface area, temperature, and a catalyst. I will also have to make sure the cork and the side arm are firmly put in their positions to ensure that all the hydrogen released from the reaction is collected in to the large measuring cylinder.
Preliminary Trials:
Before starting the main experiment I carried out a set of preliminary trials to ensure all the correct equipment and the right concentrations and amount of solutions where selected for the main experiment. The areas that where needed to be decided upon where the surface area of magnisium. The amount of the Sulphuric acid solution that was to be used. The mass of magnisium to use in the experiment. The initial choices and there changes are shown here:
- The surface area:
- Was originally powder form
- Changed to ribbon form, because of the reaction was too fast to monitor with the higher concentrations of sulphuric acid.
- The amount of sulphuric solution used:
- Was originally 50ml sulphuric solution
- Now changed to 20ml because the 50ml was too much for 0.1g of magnisium to react with.
- The mass of magnisium to be used:
- Originally 0.2g of magnisium
- Changed to 0.1g because 0.2 was more than enough for the reaction to sustain a good set or results
Evaluation of Preliminary trials:
A number of mistakes were made here, mostly concerning the speed of the reaction and the over use of some of the chemicals in the experiment. I am more sure of the new measurements of chemicals and there reliability but think that it may be a good decision to measure out the amounts in moles to compare the results achieved with the official mole results, problem being this would prove difficult with such a large variation in concentration and I am not running the reaction to its full extent but over 40 seconds.
I am sure that the new variations of chemicals used after the preliminary tests will offer a more accurate set of readings than the prior set.
Prediction:
I predict that the higher the concentration of the sulphuric acid the more Hydrogen is released and so the faster the rate of reaction.
Quantitative prediction:
I predict that the following formula will apply to this experiment:
Research:
This section aims to provide a more detailed scientific theory, including analysis of the molecular scale concerning all aspects of this experiment. The theory shown here will mainly be used as proof that the prediction above is accurate, but it can also be referred to throughout the rest of the this write up to explain anomalies or points of interest.
Magnesium + Sulphuric acid ➔ Magnesium sulphate + Hydrogen
Mg (s) + H2SO4 (aq) ➔ MgSO4 (aq) + H2 (g)
As you can see from the formula above, Hydrogen is released as a result of sulphuric acid and magnesium reacts to make magnesium sulphate (Epsom salts). The speed (or ‘rate’) at which this hydrogen is released determines the rate of the entire reaction. The fundamental question for this experiment is to discover whether increasing the surrounding concentration of the sulphuric acid speeds up the progression of the reaction.
The way in which the four factors (shown in bold below) could affect the rate of reaction is described in basic here, along with an explanation of a molecular scale (shown in blue):
- Temperature:
- The sulphuric acid can be heated to a specific temperature before the magnesium is added; thus altering the rate of the reaction.
- Different temperatures can be achieved using a Bunsen burner.
- When a reaction has a higher temperature, the molecules within the reaction receive more energy. With more energy molecules move faster, and so the rate of the reaction between the molecules or two or more different substances increases.
- Surface Area (of the magnesium):
- Using various forms of magnesium can change its surface area. There are four typical forms of magnesium:
- Nuggets (spherical, approximately 1 cm in diameter)
- Ribbon (approximately 3cm strips)
- Turning (2mm shavings)
- Powder
- The more surface area a substance like magnesium has the more molecules of that substance are open to the reaction at any one time. With more reactant molecules available, the faster the rate of reaction.
- Concentration (of the sulphuric acid)
- Sulphuric acid can be diluted to varying specification to create five different concentrations measured here in mol (m):
- 0.5m
- 1.0m
- 1.5m
- 2.0m
- 2.5m
- If a substance has a high concentration level, then it will contain more molecules of the chemical, For example, if a liquid chemical is diluted with water, it will have a lower concentration level than the same chemical that is not diluted. With more molecules of a certain chemical, there will be a higher opportunity of the two reactant molecules meeting, so increasing the rate of reaction.
- A catalyst:
- There are four different types of catalyst that can be used in this experiment:
- Manganese Dioxide (MnO2)
- Potassium Dichromate (K2Cr2O7)
- Potassium Permanganate (KMnO4)
- A catalyst is a substance added to a reaction to speed it up. For example, an enzyme is a catalyst, and can be added to certain biological reactions to increase the breakdown of certain food molecules.
Prediction conclusion:
Having researched the way in which various factors (including concentration of sulphuric acid) can affect the rate of a reaction, I can safely say that a reaction with a higher concentration with a higher concentration of a reactant substance will have a faster rate than a reaction with a lower concentration.
Results:
Graphs:
Below are the graphs corresponding to the results table above. And as above they descend from highest to lowest concentration. All anomalies are circled in red.
Results observations:
There are many anomalous results that can be seen from these results (circled in red), there also seems to be a very large difference in one run of results from the others in the 40% concentration results, where run-3 has a much higher hydrogen production rate than the other runs. There are many minor anomalies in all the graphs but other major ones can be seen in the end of run-2 in the 80% concentration results where the rate of reaction is a lot slower in the last 20 seconds of the experiment.
Also in the beginning of run-2 of the 100% concentration experiment the production is considerably higher.
Other important anomalies can only be seen when a mean graph is put together. We can see that there are some anomalies over all half way into the 100% concentration reading and at the beginning of the 80% concentration experiment. But perhaps a more significant anomaly is the 20% concentration line, where when put into a mean average the reading goes down! I can still draw a line of best fit none the less but it shows that the practical needs to be refined. We can see clearly from these graphs that as the concentration increases so does the rate of reaction. From the relatively straight lines of best fit we can tell that the rate of reaction is continuous with each different concentration.
Scientific Model:
From these results we can tell that as the concentration of H2SO4; when increased in the solution of 20ml H2SO4 and H20 (Sulphuric acid and water –a neutral chemical in this experiment-) the higher the rate of impact between H2SO4 and Mg; and so higher the rate of reaction. Proving the prediction on the basis that the higher the concentration of a reactant is the higher the rate of reaction (Increase in H2SO4 concentration = Increase in the rate of reaction), by literally increasing the ratio of the reactant substance the rate of reaction is increased dramatically and the faster the products are released.
Test of scientific model:
The proof of this scientific model is seen in the way that the lines of best fit are straight showing that the concentration of a reactant is equally relational to the rate of reaction. We can also prove this by seeing that the higher the concentration of H2SO4 the higher the overall rate of reaction is (see the mean average graph). This shows us that the scientific model is accurate.
Evaluations:
The results from my experiment were a relative success, although there were some major anomalies, the individual concentration graphs and the mean average graph gave me enough information to come to some sort of a conclusion on whether my chosen factor has a bearing on the rate of reaction of magnesium and sulphuric acid to produce Epsom salts.
The evidence I can give this can prove my prediction and the scientific model.
On the whole the experiment was a success and mostly encountered anomalies that although quite large are not on such a large scale to stop me from reaching a good accurate conclusion.
The worst anomaly in the whole experiment was on the 40% concentration experiment, although this anomaly can only be seen to its full extent in its individual graph:
The large difference between Run-3 and the other runs is vast, this is lightly to be the result of human error like many of the other anomalies, most lightly reason being that the concentration of H2SO4 or the mass of Mg used in that run. This highlights that there is problems with the procedure and the accuracy of me and my groups experiment.
The anomalies that are present in the experiment are overall minor but the reasons for there occurrence are relatively small in most cases apart from the result shown in run-3 of the 40% test. The main reasons can be split up into two main categories, procedure failure and equipment failure. I will not highlight the main problems:
Procedure failure:
- Considering that the levels of hydrogen being released where measured by eye via the measuring cylinder, leaving huge space for human error, there could have been some serious cases of misjudgment. This would make the results and the graphs slightly inaccurate.
- The results may have been written or copied down inaccurately, giving a false set, resulting from minor to severe anomalies.
- The magnesium may and lightly to of been weighted incorrectly, creating a higher or lower rate of reaction compared to the amount being tested. (this could have been the cause of the large anomalous results in the 40% concentration test)
- The sulphuric acid was measured out in a rush and some confusion could have been caused and the wrong ration of H2SO4 and H20 may have been put into the measuring cylinder, resulting in anomalies.
- The measurement of hydrogen might not have been accurate to the time intervals.
- The measuring cylinder may not have been completely full of water, creating an overall inaccurate run.
Equipment Failure:
- There may have been a very small leak or an opening in stopper or in the side arm tubing, this would cause the results to be inaccurate.
- The electronic scales may have been giving false measurements but this could also be due to human error or recording of the measurements given by the scales.
- For the lower concentration (lower rate of reaction) runs. The large measuring cylinder used for collecting the results, may have been to large to get an accurate reading because of such small increases in hydrogen volume, it may have been wiser to use a smaller measuring cylinder for the lower concentrations, but this was only to be discovered after the experiment was completed.
Extended investigation:
Research:
There are a number of ways that I could extend and improve this investigation, the one bellow should generate considerably more accurate results and cut down on the floors in procedure and equipment failure in the tests. This involves removing the large measuring cylinder, and the tub of water and replacing it with a ‘gas syringe’. This piece of equipment is made for measuring volumes of gas and so is perfect for such an experiment where we are measuring the amount of gas given off by a reaction.
Diagram:
The advantages for using this piece of equipment are:
- The measurements are more accurate and than guesswork by eye.
- Likely hood of it leakage or incorrect reading reduced.
- Less equipment is used. (taking away the measuring cylinder with and the tub of water)
I would also change the measurements of the chemicals to be moles so we can get accurate calculations and so we can tell if the experiment ran accurately by the amount of produce Hydrogen and MgSO4 are left at the end of the experiment.
Revised Method and apparatus list:
Apparatus:
- Conical flask with side arm
- Cork
- Scales
- Small measuring cylinder
- Magnesium ribbon
- Sulphuric acid
- Two clamp stands
- Stop watch
- Gas syringe
- Goggles
Method:
Set up apparatus as before BUT instead of preparing water with the upturned measuring cylinder, attach the gas syringe to the clamp stand and secure the end of the side arms delivery tube to it. Then continue the procedure as normal recording the results from the readings on the side of the gas syringe.
Diagram:
Conclusion:
The experiment went well, at the end of the experiment, i am able to conclude that from the results given from the practical and from the research taken that my prediction is accurate. As the concentration of H2SO4 is increased so does the rate of reaction equally until either of the reactants are used up to the point that the concentration (of sulphuric acid) or the surface area (of the Magnisium because of the lack of molecules after most of them have reacted) .
The conclusion states the facts originally shown in the prediction and those backed up in the observations in the scientific model after the experiment. The anomalies that occurred did not have any crucial bearing on the experiment as it does not require accuracy to a finite level as long as the results are moderately accurate I can come to a conclusion.