To show the effect of a catalyst on activation energy a dotted line is drawn to show how much energy is required if a catalyst was added. As is obvious by the graph the activation energy decreases by a considerable amount.
PREDICTION AND HYPOTHESIS
I predict (using information earlier in this section) that as you increase the temperature the rate of reaction will increase. This is because the heat energy, which is supplied to the atoms, is converted into kinetic energy and therefore the atoms move and collide with each other causing reactions. If you add more heat energy (i.e. increasing the temperature) then the atoms will have more kinetic energy and therefore move faster. If they are moving faster the rate of reaction increases because the atoms will collide more often and more and the reaction will speed up. This also means that there will be more successful collisions, as the atoms are colliding with a greater force.
Another prediction that I have thought of is that even though an increase in temperature will affect the rate at which the reaction takes place, but at the end of it the same amount of hydrogen will be formed. This is because no matter which temperature the solution is at the same amount of hydrochloric acid and magnesium is being used. The only difference is that at a higher temperature this maximum amount of hydrogen that can be formed, from the amount of hydrochloric acid and magnesium added, will be obtained quicker. The graph below shows this.
As you can see line x is the maximum amount of hydrogen that is formed as there is no more magnesium to react with the hydrochloric acid. This is the end point of the reaction and at a higher temperature this point is achieved faster as the rate of reaction is quicker.
This graph illustrates my prediction and hypothesis number 2.
My 3rd prediction, which is mentioned in the corresponding hypothesis, is that the temperature of the solution will increase, as it is an exothermic reaction. This means that will give out heat during the reaction. I will therefore measure the temperature of the solution to prove this.
From my prediction I can conclude and make myself a set of hypothesis:
- As the temperature increases as will the rate of reaction.
- At all temperatures the same amount of gas will be formed
- The temperature of the solution will increase as the reaction is taking place
- If any of the other variables mentioned are changed it will affect the rate of reaction.
To prove hypothesis number 4, I will attempt to do experiments in which I keep the temperature and change the other variables. This will also prove that they are variables and that I have not made a mistake by including them in my list of variables.
Another prediction which I can make concerns volumes, and the maximum amount of hydrogen which can be formed using the mass of magnesium and volume of Hydrochloric acid used.
The mass of 80mm of magnesium is 0.071g. First I have to find out the number of moles of magnesium.
Moles of Mg used = Mass
R.A.M
= 0.071g
24
= 2.95x10-3
Because from the equation we can see that there is the same number of moles for Mg and H2, they both have 1 mole, the figure is the same for the moles of H2. 2.95x10-3.
1 mole oh hydrogen takes up 24000cm3 in volume. Therefore, 0.00295 will occupy:
24000 x 0.00295
= 70.8cm3
This means that no matter what the temperature, the maximum amount of hydrogen which can be formed from the reaction can be 70.8 cm3
APPARATUS AND ITS SET UP
The following apparatus will be needed for the experiment:
- Conical flask: this will contain the hydrochloric acid and the magnesium
- Gas syringe: this will be used to measure the amount of hydrogen produced
- Thermometer: to measure the temperature of the solution
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50cm3 measuring cylinder. To measure the amount of acid, as accurately as possible.
- Bung with hole: this will be used to stop any gas from escaping through the top of the conical flask. The hole is so I can insert a thermometer to measure the temperature of the solution inside.
- Water Bath: this is so I can heat the hydrochloric acid to the desired temperature and keep it constant throughout the experiment. If I used a Bunsen burner it would be impossible to keep the temperature constantly at a certain point.
- Rubber tubing: to connect the conical flask with the gas syringe
- Timer: to measure the elapsed time.
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Hydrochloric acid: 50cm3 for each experiment
- Magnesium: 80mm for each experiment
- Goggles: as a safety precaution.
- Clamp stand: to hold the gas syringe in a constant position, therefore stopping any errors in the reading of it.
The apparatus should be set up as shown on the other side of the paper.
SAFETY AND FAIR TESTING
Because of the nature of this experiment safety precautions must be taken. The use of goggles must be taken at all time, due to the corrosive nature and of the temperature of the acid. The utmost attention must be constantly paid towards the apparatus as a crack or leak in the conical flask might lead to very unwanted results. As in all experiments the apparatus must be handled with care as any faulty equipment might be dangerous and might lead to a set of incorrect results.
Keeping the experiment a fair test is a vital procedure, as this will give me reliable results. The most obvious variables that I must keep constant are the 5 mentioned in the scientific theory. The 6th, temperature, will obviously not be kept constant, as that is what I am investigating.
The magnesium which I use is normally left in the air before I use it, and tends to have formed a layer of oxide, a black substance, around it. I will use sand paper to remove the oxide. If the oxide is not removed it will be an unfair test, because the reaction will take longer, as the oxygen layer acts as a shield, and it will take a while before it dissolves, and magnesium and hydrochloric particles react.
The other 5 and the ways in which I am going to keep them constant are:
- Concentration of hydrochloric acid: I will make sure that I use a constant molar of acid and to make sure that the conical flask is dry before putting any acid in as any water in the acid would lower the concentration.
- Surface area: To keep this constant I must use the same strip of magnesium and keep it at the same length throughout the investigation.
- Volume of acid: will measure the volume of acid using precise measuring tools. There must also be no extra acid left in the conical flask between the interval of two experiments as this would lead to a false amount of acid in the flask.
- Catalyst: I will add no catalyst to the acid.
- Pressure: before each experiment I will open all the holes into the flask ensuring that the pressure level is kept the same.
A factor that is not included in the variables but that I will keep the same is the working condition in which the experiment will take place in.
METHOD AND PROCEDURE
The following procedure must be followed to ensure a reliable set of results:
- Set up the apparatus as shown in the diagram on the previous page
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Measure out 50cm3 of 0.5m hydrochloric acid. I have chosen this amount as preliminary tests show this amount to be suitable to what I am doing. Any more acid would prove to be a problem, as too much hydrogen would be formed then 100cm3, the maximum range of the gas syringe.
- Measure 8cm of magnesium. This measurement was also chosen from a preliminary experiment. Also one must sand off the black oxide which layers magnesium when it is left in air for too long.
- Pour the hydrochloric acid into the conical flask.
- Put the flask into the water bath and wait as the hydrochloric acid heats up to the appropriate temperature.
- Add the magnesium to the acid close the bung and begin measuring the experiment
- Using the gas syringe to measure the amount of gas produced every quarter of a minute.
- Repeat this procedure at either a different temperature or the same one.
I will make measurements at the following temperatures: 10°C, 20°C, 30°C, 40°C, 50°C, and 60°C. I will repeat each temperature at least once and then find an average. I will measure 5 temperatures to see if there is any proportional relationship between any of my factors.
My decisions on the range and on the number of readings that I will take have been premeditated from results of preliminary experiment. I found that using only 25cm3 of 1.0M of acid and 5cm of magnesium was insufficient, as all the magnesium had reacted within 45 seconds. This would be too small a time to see any change on a graph and comparison between thee graphs would be virtually impossible. I therefore, need to use a lower concentration of acid, as there will be fewer collisions, making the experiment react slower, giving me enough time to collect a suitable amount of data. And I will also change the amount of acid from 23cm3 to 50cm3 as this means that there are more particles to collide with, and the experiment may take longer.
My choice for going up only to 60°C is due to the fact that after that point the hydrochloric acid begins to evaporate. This was found during a preliminary experiment where after 50cm3 of hydrochloric acid was heated to 70°C only 45cm3remained when poured into a measuring cylinder. And if I do lose any acid before the experiment one of my variables, which is the volume of hydrochloric acid, will change and therefore lead to an unfair test.
Another matter, which was uncovered during the preliminary testing, was that sometimes not all the magnesium was immersed into the acid at once as it was too long (i.e. it was stuck vertically to the flask and only a little bit was immersed at first). This gives drastic changes in the results. Therefore, the magnesium must be coiled up before it is placed into the acids so that all of it is immersed.
BIBLIOGRAPHY
I have you the following sources to help for the planning of this report.
Nigel D. Purchon PURCHON.COM
Lawrie Ryan CHEMISTRY FOR YOU
ANALYSIS
WHAT I HAVE SEEN
Looking at the results table the obvious connection with temperature and the rate of reaction is there, as the temperature increases so does the rate of reaction. So going back to my prediction I can say that I was accurate in the fact that I had predicted that as the temperature increases the rate of reaction also increases. That evidence is clearly shown in the graph of the rate of reaction.
Just to make things easier on the explanation I will create a list of things which the results show mw. This will make reference to each point easier.
- The rate of reaction increased as the temperature increased.
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The amount of hydrogen gas formed at the end of the experiment increases as the temperature increases, after my prediction stated that the number should be the same. Also after my prediction said that the total volume of hydrogen that could possibly be formed would be 70.8cm3, three of my experiments were higher.
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The reaction at the beginning of the 200C experiment was slower than the reaction at the beginning of the reaction for 100C.
- The repeat of a temperature does not always match well with the first attempt.
You can say that the rate of reaction will obviously be faster as the temperature increases because the total volume of gas formed will increase. This is not true because I am not measuring the rate of reaction through dividing the total volume of gas formed by the 300, the total time. But instead I am dividing the volume of gas formed by the time the gas took to reach its completion point. For example, at 500C the total amount of gas formed may be 72.00cm3, however it may have taken 300 seconds (5 minutes). And in an experiment where the temperature was only 300C may have produced only 59cm3 of gas but may have only taken 105 seconds. If we use my formula we find out that the rate of reaction for 500C is 0.24 cm3/s, where as for 300C the rate of reaction is 0.59cm3/s. So we see that actually the rat of reaction was actual quicker when the temperature is at 300C.
However, this does not happen in my experiment and the rates of reaction increase as the temperature increases. However, something which I had predicted does not represent itself in my results.
My prediction was, that even though the rate of reaction would increase the final volume of gas collected would be the same for all temperatures. This would be because of what I explained earlier, that if the reaction took less time to accomplish the rate of reaction would be faster. Therefore, I have myself proved my prediction wrong.
I was unable to prove my prediction that as the reaction takes place the temperature will increase as this is an exothermic reaction. This was due to an error in reading which could not be fixed.
My fourth prediction, that if you change any of the factors mentioned in the variables list you will get an unfair test, was not proven. This was due to problems with time. However, some of my colleagues did test the variables which I mentioned and they did get changes in the rates of reaction by increasing or decreasing the variable.
WHAT THE GRAPHS SHOW US
What I have explained before is all shown on the graph. What we need to understand is where and how it is like that
The first thing that is to be explained about the graphs is how it shows us that the rate of reaction is faster. It would be obvious, if someone was to be asked that question that they would look at the rate of reaction graph. However, if that information was not present, and if you did not know how to work out the rate of reaction the graph which shows the volumes of hydrogen produced is sufficient. What we know is that on the x axis we have the time, and on the y axis the amount of hydrogen formed. So the rate of reaction would be faster when the volume of gas formed is higher and the time taken to reach this, lower. This can be seen by the gradients of each curve. The higher the gradient the higher the rate of reaction. So therefore from that graph, knowing the rate of reaction is quickest on the steepest gradient, you can find out that when the temperature was 60oC the reaction was fastest
This happens because of both the collision/kinetic theory and because of activation energy.
As the temperature of the hydrochloric acid increases the atoms inside move faster as they receive more energy from the extra heat provided. This means that the particles move faster, and they collide more often. What it also means is that more collisions are successful as the particles impact with a greater force and more bonds are broken.
To show how I calculated the rate of reaction graph I have included a table.
EXPLAINING WHAT HAPPENED
Please note that the number of the finding corresponds with the number of my list of findings, on the last page.
Finding 1). The rate of reaction increased because the atoms are gaining more energy. The atoms gain kinetic energy from the heat which is produced. So if you increased the temperature you therefore, are increasing the heat energy supplied to the atoms. This in turn increases the kinetic energy and the atoms move faster. If the atoms are moving faster they collide more often with each other and therefore, increase the rate at which they react.
Another factor is activation energy. This is the energy needed at which two atoms can collide with each other with sufficient force to break bonds. The higher the temperature the more energy is supplied to each atom. Therefore, the greater chance that when the two atoms collide they will have enough energy to break the bonds and create a reaction
Finding 2). As I mentioned earlier this went against what I had said in my prediction. Because I had said that the final amount of Hydrogen formed should not be over 70.8cm3 and this should be the final amount of gas formed for each experiment. However, while doing the experiment itself I found the answer to this problem.
If you look at the diagram of the apparatus you will see that the pipe leading to the gas syringe from the chronicle flask is ascending. We also know that hot air rises. Therefore, the hotter the hydrochloric acid, the hotter the air in the flask and the hotter the gas the leaves the reaction will be. So the air will rise more and the gas formed will rise more. So if the temperature was higher the more gas actually rises and therefore, the gas syringe indicates more. Also at a higher temperature the normal air rises more, and so that may have collected in the gas syringe.
Another reason may be that as the atoms were moving slower as the temperature decreased, therefore, many atoms may have just never come in contact. Or maybe it is because of the fact that the reaction is exothermic and as the experiment goes on the solution losses temperature and therefore, here is not sufficient activation energy for the atoms to react. In the higher temperatures the temperature would have decreased faster because the reaction is giving out energy faster, but by the time the temperature has decreased to a level where there is not enough energy a lot more gas would have been formed.
The reason that the final amount of gas formed in the reaction for 600C, 500C and 400C is higher than 70.8cm3, can be explained by the evaporation of water. Because the acid is diluted it contains a significant volume of water mixed with it. Therefore, at higher temperatures this water may have evaporated, causing two unwanted occurrences. Firstly, this means that the water which evaporated made it seem as though more H2 was being formed, and so steam was also being collected in the syringe, and that the experiment was not fair. And because the water had evaporated it would have caused an increase in concentration, automatically adjusting one of my variables which were meant to stay the same.
Finding 3). This could be due to a technical problem, the gas syringe may not have worked properly, or the tube may have been blocked. If my memory serves me correctly I distinctly remember doing both the first and second attempts of the 200C investigation on the same day, and not doing any other temperatures. This could easily mean that part of the apparatus was faulty.
Finding 4). The fact that neither temperatures match up is confusing but not unexplainable. The important number to keep in mind with the experiment is the final volume of gas formed, and those normally stay to within 3cm3 of each other. What happens during the reaction is a different matter. It could be that the hydrochloric acid was not measured accurately enough, or the temperature of the solution may have been a degree off. Apart from that the results do seem to be accurate enough.
That means that I can have one conclusion on the investigating the effects of temperature on the rate of reaction between hydrochloric acid and magnesium:
An increase in the temperature = an increase in the rate of reaction.
However, this is too simple. And below is another more reasoned conclusion.
An increase in the temperature =
An increase in the level of energy supplied to atoms =
An increase in the kinetic energy in the particles =
Particles moving faster and colliding more often, and with a greater force =
More successful collisions = more collisions and more breaking and forming of bonds =
A greater rate of reaction.
EVALUATION
ERRORS AND THE WAYS TO FIX THEM
Looking at my result I can say that they are sufficient enough to draw up the conclusion which I have made. And that they do not seem to bring out any extremely anomalous results
However, one point which must be touched upon is the difference between the readings taken on the first and second attempts of a temperature. There may be many different factors affecting the reliability of these readings.
One may be that when the temperature of the water bath is set it is set around 5 degrees warmer than the actual temperature. This is so that the Hydrochloric acid heats up quicker and so that it stays constant as the water become cooler. In some cases the water may have become hotter than intended and the reaction may have taken faster as the solution may have heated up during the actual experiment.
I also noticed that the volume of the acid decreases as it is heated. This maybe due to the fact that hydrogen from the liquid evaporates from the solution. This may have thrown off the accuracy of the investigation.
However, the chance that hydrogen evaporated is not as likely, as water. Because the Hydrochloric acid has been diluted there is a significant amount of water, making the HCl less concentrated. However, at the higher temperatures the water might have evaporated, and caused the concentration of the acid to increase.
To solve this problem I two thing must be done. The hydrochloric acid must be accurately measured at the correct temperature, so to stop any extra energy being given off. To stop gas from leaving the hydrochloric acid the solution must be put in a container exactly the same volume as the acid. This means that there is no where for the gas to leave the solution, and drift about. Also to stop gas from leaving the hydrochloric acid there should be a slide to stop gas from going into the gas syringe. This is the same for the evaporation of the water.
We can see from the graph, other problems. One of them is the fact that during the investigation for 200C we see a set of anomalous results which do not fit the line of best fit. We need to know why this happens, and improve our reliability. And bellow in the, next heading, I have tried to show ways of improving reliability
INCREASING RELIABILITY
As we can see from the graphs there are a few anomalous results, and some of the 2nd tries do not match the first, and to fix these we need to know why these may be happening, and to then, give ways to improve the reliability had these experiments been done again.
- It is very difficult to get the water bath to the exact temperature, so this can vary and effect the movement of particles in the reaction. To improve this we can get more accurate water baths, and spend more time exacting their temperatures. Also because the AC was on the water bath may have kept cooling down after it reached the desired temperature.
- During one experiment the syringe began sticking, and the pressure of the hydrogen was not enough to move the syringe. We fixed that by cleaning the syringe thoroughly. However, there is still a possibility that the syringe was faulty and gave inaccurate readings. To improve the syringe’s reliability we must only ensure that it stays clean, and slides freely.
- The flask was not fool proof, and there may have easily been a leak in the tube, or where the tube meets the flask or the syringe. To increase the reliability of this the tubing should be sealed tight, and should be enforced with air proof seals.
- The gas syringe may not have been perpendicular to the clamp stand. This means that it may have been sloping either downwards or upwards. If the gas were to push the tube only a slightly, the force of gravity may have pulled it down even further.
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When the experiment was started the bung had to be taken off to put in a piece of magnesium. The bung had to then be placed back on very fast, as to let no gas escape. However, gas particles move faster than the human hand, and may have escaped before the bung was placed back on. This may explain why the rate of reactions, for the first few seconds of the 500C and 200C experiments were slower than the first few seconds of the 40oC and 10oC experiments respectively.
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Another reliability flaw, that wasn’t actually a problem but, as I said, a flaw in reliability. It was that not all the hydrogen formed may have been collected, or that more was collected in the 60oC experiment than in the 109C. Firstly, in the conical flask there is an empty space around 50cm3 which is not taken up by the solution. This means that there is a possibility that 50cm3 of gas may have not been collected. This would be ok had this happened to all the experiments. However, this would not happen because on when you have a higher temperature the gas is hotter. And we know that hot air rises, so in the higher temperature experiments the more of the hydrogen which was left in the conical flask may have risen and gone into the syringe. However, at 100C the hydrogen may have not risen at all, and so nearly 50cm3 of gas may have not been recorded.
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When it come to reliability one of the major concerns is measurement. In the experiment we used a measuring cylinder to measure out 50cm3. A burette would have been a better choice of apparatus to choose. This is because a burette’s base has a smaller surface area than a measuring cylinder, and therefore, is more sensitive to small changes in the volume. When I measured out the magnesium I used a ruler. This was the only way I could think of, although I must admit that I was not happy with the method. However this was the best way. If we had to use weight then to get the exact weight you would have to keep adding pieces of magnesium if the piece you had already chosen was too light. This would then increase surface are, and would falter the experiment further. What would have been most reliable would have been to use a combination of weight and length. This way, a person could cut the piece to a certain length and then weigh it. The weight can then be checked each time the magnesium is cut, so you can get a better measurement of the magnesium.
- When you start the experiment there is air in the flask. . So when the hydrogen gas began releasing from the reaction it may have bumped into air molecules and moved them into the syringe. This means that you now have both the hydrogen which you want to record, and an amount of air molecules, which include oxygen, carbon dioxide, nitrogen, and noble gasses. So you now have more gas than you actually want, and so the reading on the syringe is higher than it should be. A way to solve this problem would be to suck all the air out of the flask before the experiment starts to create a vacuum. However, this may have added effects on the experiment that are not wanted
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To increase reliability of the results you may have taken more readings at 50C, 150C and 250C. You could also have it had even smaller intervals, like 230C, 23.50C and 240C. However I feel that it would firstly be very hard to have the Hydrochloric acid reach each temperature with the accuracy needed, and I also feel that the difference between each temperature would be too insignificant to come to a firm conclusion. The only way you could test the difference with readings of such small intervals would be if around 40 reading were taken. And would take a very long time.
Apart from this fact I think that the evidence gained is suitable to form a substantial conclusion of the reaction between Hydrochloric acid and Magnesium.
OTHER LINKED INVESTIGATIONS
Other investigations which could be done, related to this one, could be to keep temperature the same and change the variables mentioned in my prediction. Those are:
- Concentration of the acid
- Volume of acid
- Surface area of the magnesium
- Using a catalyst
You could also change the substances, and test to see how the reactivity of different metals.
You could also test the problems which have gone wrong and see if they really were a problem, and did affect the experiment. One which I would like to test is whether no hydrogen is present in the conical flask even after it seems that the experiment is over. One way of doing this is to somehow block the syringe after the hydrogen has been collected, perhaps pinching the tube. And then collecting the gas in a test tube. Once that has been done you can test for the hydrogen by putting a lit splint over the test tube. When the hydrogen is released a squeaky pop can be heard, telling you that hydrogen is present
I have found that the experiment did go as planned and that my prediction did support my results.