In my investigation I will be using molar quantities. A mole is a number, which is 6.023 x 1023. One mole of atoms or molecules of any substance will have a mass in grams equal to the relative formula mass (Ar or Mr) for that substance. The formula for finding the number of moles in a given mass is shown below:
Mass in g (of element or compound)
NUMBER OF MOLES =
Mr (of element or compound)
PLAN
In this investigation I will be investigating the best way to produce Epsom salts in terms of quantity and money spent. In this investigation three different experiments will be carried out to determine the best method of producing Epsom salts. The first test will be to determine whether I should use magnesium or magnesium carbonate to produce Epsom salts in my investigation. The second test I will do is to try and determine which form of the magnesium/magnesium carbonate I will be using e.g. ribbons powder, turnings. The final and main experiment will be to use different concentrations to find out which gives the best result. The lower the concentration the less sulphuric acid used which means less money spent. So I will be looking to find the method for making the best Epsom salts in terms of cost, quantity and time by looking at the rate of reaction. The four different concentrations of sulphuric acid I will be using are 25%, 50%, 75% and 100%. I will be using molar quantities in this investigation so 25% concentration = 0.25M, 50% concentration = 0.5M, 75% concentration = 0.75M and 100% concentration = 1M.
(An explanation to what a mole is can found in ‘background information’). The total volume will be 40cm3 altogether. The exact measurement, in terms of volume, that I will be using is:
0.25 M - 10cm2 acid/ 30cm3 water
0.5 M - 20cm2 acid/ 20cm3 water
0.75 M - 30cm2 acid/ 10cm3 water
1 M - 40cm2 acid
I will be doing every experiment twice to reduce the chance of getting anomalous results. The reactions that will be taking place in the investigation to produce Epsom salts is shown below:
Magnesium + Sulphuric Magnesium + Hydrogen
acid sulphate
Mg(s) + H2SO4(aq) MgSO4(aq) + H2(g)
OR (depending on the findings made during the test run 1 –see plan)
Magnesium + Sulphuric Magnesium + Water + Carbon
carbonate acid sulphate dioxide
MgCO3(s) + H2SO4(aq) MgSO4(aq) + H2O(l) + CO2(g)
In the reaction hydrogen / and carbon dioxide is given off as a by - product so I will be collecting the gas given off in the reaction as a measurement of the rate of reaction. The rate of reaction depends on how often and how hard the reacting particles collide with each other. As I have stated earlier, the factor I will be experimenting with is the concentration of acid. A factor means anything that will influence the outcome of the activity. The other factors in this experiment are the temperature of the water, room temperature, temperature of H2SO4, surface area of the H2SO4, amount of Mg / MgCO3 used, amount of H2SO4 used, the overall volume, type of magnesium used and size of the delivery tube. All these factors must be constant and controlled during the experiment. Below I have explained how this will be done:
Volume of substrate - using a measuring cylinder will ensure this factor can kept constant. In this experiment the volume that will be used is 10cm3
Temperature (of water, H2SO4 and room temperature) – temperature is very important because faster collisions occur when increasing the temperature, which means a faster reaction. So the temperature must remain constant.
Before doing the experiment the water and H2SO4 will be kept out in the room so it will be at a constant room temperature when doing the experiment. The room temperature will be controlled by shutting all the windows, door and covering air vents, as well as turning off heaters and radiators. This will ensure that the room temperature remains constant.
The magnesium / magnesium carbonate (surface area, amount and type) – I am unsure of the outcome of changing the surface area and will make a decision on what to use in test 1. After determining which type to use (Mg/MgCO3) in test 2 I will find out the best type to use (ribbons, turnings, powder) and then we will use the chosen one throughout the experiment the same amount will be used because we will measure the Mg/MgCO3 using a weighing scale and use the same amount throughout the whole investigation
Size of delivery tube - If the delivery tube is larger and is a bigger tube, more gas is collected quickly. This is because more gas can travel through faster than if it were a smaller tube because of the larger volume inside of the tube. In a smaller tube less gas would be collected in the same time. This is again, because there is less space inside the tube and less gas can travel through in the same time. That is why it is important to use the same delivery tube throughout the investigation.
Safety Precautions
Safety is essential in this investigation and precautions will be highly imperative. The following things need to be done – safety goggles must be worn, ties tucked in, hair tied back, all bags and coats be placed in the corer of the room, sensible behaviour by all students, aisles must be clear (tucked-in chairs) and care must be taken when carrying around and handling the H2SO4. The magnesium must also be kept away from naked flames because at a high temperature it is reactive. This should be all right because there is no need for the use of fire in this investigation. As stated in ‘background information’ sulphuric acid is very corrosive, which is why safety goggles are essential for this experiment.
EQUIPMENT
- The following pieces of equipment are vital for the investigation and next to them I have explained their purposes:
Conical flask - this will contain the reaction between the magnesium/magnesium carbonate and the sulphuric acid.
Bung - this is the cover of the conical flask. This stops the H2 gas from escaping and makes it go through the delivery tube instead.
Delivery tube - the gas will travel through this from the conical flask to the measuring cylinder.
Two medium sized measuring cylinders - one will be in the water tub and one is for collecting the gas and the other for accurately measuring out the correct moles of sulphuric acid and the correct volumes.
Water tub- this contains water and the measuring cylinder that is collecting the gas
Weighing scale - this will be to weigh the correct amounts of Mg/MgCO3
Stopwatch - for timing; to indicate when each reading should be taken down.
Retort stand - this will contain the clamp, which will hold the measuring cylinder straight
Clamp - this will be attached to the retort stand and will hold the measuring cylinder in position
Safety goggles - for safety purposes this will need to be worn because we are working with acid
Pencil case - contains pen, pencil, ruler, rubber sharpener and calculator for recording results.
HYPOTHESIS Based on the research I have obtained and through my own scientific knowledge, I have made predictions for the investigation I am about to carry out.
Test 1
I think that magnesium will be better than magnesium carbonate because in magnesium carbonate CO2 gas is given off as a by-product as well as H2O. Because there is a lot of by-product the reaction will be very fast. So it will react violently as soon as there is contact with the sulphuric acid, which means in the time it is placed inside and the lid is placed on a lot of gas has escaped. Whereas, with Magnesium only H2 is given off as a by-product so it would be slower and results can be recorded more easily and accurately (because we do not have to record the results very quickly).
Test 2
After determining that we are using magnesium, in this test we are trying to determine in which form we should use it. The two forms of magnesium we can use are either ribbons or turnings. I predict that we will find that the best form to use is the turnings because it has less surface area than the ribbons. This is because the rate of reaction is higher when there is more surface area or is a smaller particle size. The reason for this is because it increases collisions. If it was a solid like a ribbon there would be less area available for the acid to react with, so there will be less useful collisions. Whereas if it is broken up into smaller pieces like turnings, the surface area has increased and there is more area available for the acid to react with and there is going to be more useful collisions.
Test 3
I predict in this test I will find the higher the concentration the faster the rate of reaction. I am very sure of this prediction because if a solution is concentrated there are more particles of reactant knocking about between the water molecules, which make collision between the important particles (the magnesium particles and sulphuric acid particles) more likely. So the lower the concentration the lower the amount of gas produced. An important point to make is that since the lower concentrations will produce a lower amount of H2 gas, we should measure it over a larger time-range than we first thought.
METHOD
The method for test 3 is: first fill up the water tub with water until it is nearly full. Place the medium sized measuring cylinder upside down in the tub, making sure the measuring cylinder is completely filled with water and there is no air in it. Then place the delivery tube, coming from the conical flask, under the measuring cylinder. Using the other measuring cylinder measure out the correct concentration of acid and mix with water, making sure the volume of the acid is a total of 40cm3. Pour the acid into the conical flask. Then place the magnesium/magnesium carbonate into the acid and immediately place the bung on the top of the conical flask and start the stopwatch. By looking at the measurements on the side of the measuring cylinder, record the volume of gas produced every 20 seconds for 2 minutes (120 seconds). The whole experiment is then done again, so in total there will be two sets of results for each concentration. This is so that later in the analysis; using the two results I can find the average results for each concentration and use that in my graph. This means the chance of getting anomalous results is reduced. After the completion of the second test we then examined the results we got from our first run and the results from the second to make sure they were similar. If we found there were anomalies we then did that particular run a third time to get more reliable results. For test 1 we are trying to determine whether to use Mg or MgCO3, the method for this test is exactly the same as for test 3, except the same concentration of acid is used throughout the test (it is controlled). The magnesium is first put in and the results recorded and then the magnesium carbonate is put in and the results are recorded. For test 2, where we are trying to find out if it would be better to use ribbons, turnings or powder (ribbons and turnings for magnesium and turnings and powder for magnesium carbonate). Again, the concentration will be controlled and will be the same throughout the experiment and the rest of the experiment is the same as well, apart from the form of the Mg/MgCO3 reacting with the sulphuric acid. Results are recorded after this test and a decision should be made on which form of Mg/MgCO3 should be used. A diagram of how the experiment should look once set-up is on the separate piece of paper labelled ‘figure 1’.
RESULTS & ANALYSIS
Test1
We have not collected any results for this test because after doing two runs, one for each magnesium, it was very clear to us that there was no need to complete the recording of results, because by then we knew what to use.
We decided to use 0.1g of Mg and MgCO3 for this test. We first did the magnesium and the rate of reaction was at a steady pace and wasn’t really too fast or too slow but at a good rate. We then did the magnesium carbonate and the rate of reaction was very slow. This surprised me because in my hypothesis I stated that we would use magnesium instead of magnesium carbonate, but I had said that I would do that because MgCO3 would collect gas too quickly, because CO2 is being given off as a by-product in addition to H2O, which I though meant would mean a more violent reaction. But this experiment totally contradicts my prediction and is the total opposite of my prediction.
After finding out that too little gas was produced for MgCO3, which means we had to use more mass for higher rate of reaction, we had made our decision. We would be wasting money on using more mass of MgCO3 whereas we can use less mass of Mg where there is a faster reaction, so in terms of costs we have come to the conclusion that it would be sensible for business reasons to use Mg.
Test 2
Looking at figure 2 (The table of results is shown in the separate piece of paper labelled ‘figure 2’)
These tables show the results we found for trying to find out the type (form) of the magnesium that we should use in our final experiment, test 3.
Table 1
This table shows the results when using magnesium turnings. We have done this experiment twice. That is why there are two runs. We have done this so we can reduce the chance of getting anomalous results. When looking at the two runs, no anomalous pieces of data sticks out.
Table 2
This table shows the results when using magnesium ribbons. We have also done this experiment twice, which is the reason for two runs. We have done this so we can reduce the chance of getting anomalous results. When looking at the two runs, no anomalous pieces of data sticks out.
After comparing the data found in both runs for each form of magnesium we have decided to use magnesium turnings in our final experiment (test 3). The reason we have chose it is because with the same amount of mass as ribbons more gas is produced, which means a faster rate of reaction. This means that if we use turnings instead of ribbons Epsom salts are produced faster. This is what I have predicted in my hypothesis, so I am pleased to see it working out. The reason that turnings react faster than ribbons is because there is more surface area and there are more particles available to react, which means there are going to be more useful collisions.
Test 3
Looking at figure 3 (The table of results is shown in the separate piece of paper labelled ‘figure 3’)
These tables show the results we found for the final experiment, in which we are trying to find out the effect of varying the concentrations on the production of Epsom salts.
Table 1
This table shows the amount of gas produced every 20 seconds for 2 minutes. The results are for four different concentrations of sulphuric acid; 1 mole, 0.75 moles, 0.5 moles and 0.25 moles. We have done each concentration twice. That is why there are two runs for each concentration. We have done this so we can reduce the chance of getting anomalous results. When looking at the table, no visible anomalous pieces of data stick out at the moment.
Table 2
The averages are shown in this table. The way to work out the average is by adding the results together and then dividing it by the number of results there was.
E.g. for working out the average for 1 mole concentration of sulphuric acid after 20 seconds: 38 + 36
2 = 37
So 37 will be used in the graph and for analysis.
After looking through the average table of results all results seem fine and there doesn’t seem to be any pieces of anomalous data.
Table 3
In this table I have shown the total amount of gas collected after 2 minutes for each concentration. When looking at this data there are no anomalous pieces of data and it seems to be correct when thinking about it in terms of the particle theory. Higher concentration means more reactant particles available, which means there is more of a chance of collisions and more of a chance of gas being produced. Which is what you can see when looking at the table. The higher the concentration of sulphuric acid there is you can see there is more gas produced.
After looking through all the results for test 3, I have found that the results match my hypothesis where I predicted that I would find the higher the concentration the faster the rate of reaction, which is what I have found. I am very pleased that this prediction is correct and there doesn’t seem to be any anomalous results but after drawing the graph any anomalous results will be clearer.
Looking at figure 4: Graph showing amount of gas produced every 20 seconds, for different concentrations
The graph confirms my hypothesis being correct and this is how I expected the graph to look. An important note to make is that if I carried on taking down results it wouldn’t carry on increasing, it would reach a constant amount. When looking at the graph for anomalous results, the curve 0.25 molar concentration of H2SO4 is a lot lower than I would have expected. The result that sticks out the most out of there the one for 20 seconds (, which I have circled in red). The whole line has to be pulled down because of that particular result. This is because the line of best fit needed to be lowered because the particular result had slightly poor correlation towards the other results for that concentration. This anomalous result could have been received due to one or more of the factors I mentioned in the ‘plan’ not being constant at that precise time (20 seconds). (See ‘evaluation’ for my attempted explanation to why we received this anomalous result.)
But apart from that the graph looks as I had expected it to look and from looking at the graph I can say the experiment was successful in proving my predictions.
EVALUATION
At the end of the experiment I have found out that 1M of H2SO4 would probably be the best concentration to use because it produces the most gas in the quickest amount of time. My experiment went well and apart from a minor problem with the 0.25 molar concentration there were no anomalies. So if I were to do the test again there wont be any real changes I would make as it worked very well. The only thing I would change, if I were allowed to do it again is to use a gas syringe. I realise that some people would disagree that this would help and would argue that this would be no more accurate than using a measuring cylinder, but I belie using a gas syringe results can be carried out to a higher degree of accuracy and can be more accurate than a measuring cylinder. I also that this costs money but it may help to produce more Epsom salts and effectively save money.
As I mentioned earlier there was a slight problem with the 0.25 molar concentration. I have made a list of things that could have gone wrong at the time we were doing that particular test:
The lid of the conical flask/the bung - the lid may not have been airtight and some of the gas could have escaped. Also in the time it took us to place in the magnesium and place the lid on some gas may have been lost
The temperature- although I said all windows, doors and air vents must be covered I did not ensure this was done and while we were doing the tests for the 0.25 molar concentration a draught could have got into the room, decreasing the temperature and slowing down the reaction and therefore less hydrogen gas could have been produced.
Turnings- the turnings are quite small so by accident we may not have emptied the whole 0.1g into the sulphuric acid and left some behind. This could have affected the results because it would lower the volume of hydrogen gas been produced, as there would have been less magnesium for the acid to react with.
Concentration- the concentration may not have been exact to the point of being a molar quantity. Slight mistakes in measurement could have been made during the 0.25 molar concentration test, which explains the slightly anomalous results. This could have been slightly more water being added when diluting the 1M concentration to 0.25 M which meant we had effectively used a concentration lower than 0.25M.
After considering all this, if I were to do the experiment again I would definitely do it more carefully and carry out measurements to a higher degree of accuracy. This would involve using more accurate measuring devices. I realise this may cost more money and could even go over the budget, but I think if it helps to produce more Epsom salts than it is worth it as we can effectively earn more money from it. As I mentioned before, I believe the use of a gas syringe could be helpful in being more accurate. I also believe the use of a more scientific and precise weighing scale that measures down to milligrams would greatly help us. Also I believe the use of a more naturally flexible delivery tube could help a lot because the one we used in the experiment didn’t bend very well and could have prevented the hydrogen gas from flowing through it freely, which could have caused a slower reaction.