Preliminary work 2
This method is similar to preliminary work 1 however I have decided to experiment in different temperatures to see whether it makes a difference to my results. Basically I have collected hydrogen in different temperatures of water in the beaker surrounding the magnesium and hydrochloric acid reaction.
In this experiment I have used a magnesium strip again wieghing 0.05g, 25cm3 of hydrochloric acid and a water bath at three different temperatures 66 oC, 44 oC and 22 oC. The equipment I have used is a stop clock, bowl of water, measuring cylinder, bung, delivery tube, beaker and a test tube.
Here are the results: -
From the results above I have found out that the rate of reaction decreases as the temperature drops, which means that temperature may have a effect on my results. Also by using a reasonable choice of temperatures I have tried to see whether this allows a pattern.
During preliminary work 2 I have had several problems, they were that I couldn’t keep control of the temperature as it wouldn’t stay constant and got colder and also was difficult to keep topping up. Most importantly I had noticed that the reaction was excothermic, which means that the reaction got hot its self, which made it even more difficult to control the temperature.
However I found out a way to keep my temperature surrounding the reaction constant; by using a electronic water bath with a themometer, but the problem is that i have not got this equipment and will be hard to provide me with one.
The problem with using a upside down measuring cylinder:
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It is hard to fill a measuring cylinder of H20 and keep it full once it is turned upside down.
- Measuring cylinder isn’t very accurate
- Does water pressure have any affect on my results?
Taking all the above in account I have decided to use a different method which does not involve using a measuring cylinder as it causes too much hassle and difficulty, aslo I have decided that I am going to keep my reaction in room temperature as it is the easiest to control and does not make a big effect on my results.
Preliminary work 3
This method is also collecting hydrogen and it works by the strip of magnesium and hydrochloric acid reacting and the hydrogen produced being pushed through the delivery tube, which is then measured in the graduated gas syringe. I have decided to use the gas syringe rather than the measuring cylinder because it is easier to handle and measure. And I have decided to do my experiment at room temperature as it is easy to control and will not drop at all.
Similarly to preliminary work 1 and 2 I have used a magnesium strip again weighing 0.05g and 25cm3 of hydrochloric acid, the equipment I have used are stop clock, conical flask, bung, delivery tube, graduated gas syringe and 2 pairs of clamps and stands.
The results above seem to be reliable and accurate due to the equipment and materials I have used. I have not had any major errors or difficulty during my experiment, therefore I feel that this is the right method for me to used in investigation.
Investigation
I have used my preliminary work to design the best method/experiment for my investigation and I am going to use preliminary work 3. Now I have decided to change the concentration of the acid to see what the outcome will be.
I am still going to use a strip of magnesium weighing 0.05g, 25cm3 of solution which has water and hydrochloric acid in. In school I am allowed to use a maximum of 2.0 molar of concentration due to health and safety reasons. So I have decided to go up ½ a molar for each experiment, however for the last experiment I am going to use 0.25M, which is not ½ a molar, but it should work o-k as it should be similar to 0.5 but a bit slower. This means I will have to do five experiments and I think my concentration levels are at a sensible range and are fair because they go up equally ½ molar at a time, which may allow a pattern (except 0.25M). Also I used 05M and it worked o-k in a previous preliminary work.
I am going to make my solution of water and hydrochloric acid at the same volume of 25cm3 and so I will have to calculate and measure out accurate amounts of hydrochloric acid and water. The table below shows the proportion of acid and water I am going to use in percentages.
So for example 75% of 25cm3 is 18.75cm3
I am going to repeat this experiment 3 times as I feel it is needed to get reliable results.
My prediction is that the higher the concentration of acid, the quicker the hydrogen is going to be collected.
(Table no.5)
Anomalies
Conclusion - (see graph number one)
My graph shows that the more concentrated the acid added to the reaction the quicker the hydrogen is collected. On my graph, the size of error bars are fairly small which show that there were not big differences in my results, however the experiment with 0.5 molar of the concentration has the longest error bar, which tells us that there were differences in my results and errors occurred, which may have made my results undependable. I am fairly confident with the reliability of my conclusion as I feel I have done the experiment a number of times to get trustworthy results and used equipment that were easy to handle which means that I could do the experiments without any major errors or difficulty. Also my result match my line of best fit, which makes my confidence in reliability stronger.
Calculating rate
I am now going to find out the rate of the reaction.
Conclusion – (see graph number two)
My graph shows that the rate increases as the concentration increases. I am again fairly confident with my results because I think they are reliable as I used a calculator to work out the rate and I rounded it to a reasonable number, so I don’t think their should not be any major errors in my conclusion. Also my results seem to again match my line of best fit showing a curved line hitting all my results as expected, which assures that my results are reliable.
Statistics
I am trying to find out whether there is a pattern between the rate and concentration in my experiment. I am going to see whether the rate doubles if I double the concentration, so if I use 0.25 molar which has a rate of 0.0041, the rate for 0.5 molar should be 0.082 as it is doubled like the concentration, but in my experiment it has not doubled as it is 0.012. To make my prediction of no pattern occurring dependable, I am going to use two more examples. So the rate of 0.5 molar is 0.012, so if I double the concentration which will be 1.0 molar the concentration should double and should be 0.024 but it isn’t as it is 0,041. 1.0 molar has a rate of 0.041 so if I double the concentration the rate should double and be 0.082, but it isn’t as it is 0.16. This shows that there is no pattern in my experiment. However in graph number 2, I have noticed an exponential pattern, which means that as the concentration increases the steeper the graph gets.
Explanation
Concluding that the rate increased as the concentration increased, I have found an explanation to why this must have happened.
This has happened because hydrochloric acid and magnesium particles collided to cause a reaction (which means that in the solution, particles that have reacted quite fast) however the particles can react in two different ways, elastic collision and inelastic collision.
Elastic collision is when two particles collide into each other but do not react due to the lack of energy they have. On the other hand some particles collide and react as they have enough energy, which then forms a new product; this is an inelastic collision. For a collision to be successful and for a definite reaction to occur, a particle of magnesium and a particle of acid will have to collide with the SUFFICIENT ENERGY, which is called the ACTIVATION energy.
Infrequent collisions may happen as the dilute solution will not have many acid particles in it which means that it will take longer for a magnesium particle to find an acid particle and collide. Also because the water in the solution blocks the magnesium and acid from colliding and so can prevent the reaction, this is because, in a dilute solution if there is more water than acid it will be hard for one particle to get to another, as the water will get in the way, so the rate will decrease. However the rate increases if there is more particles of acid and less water in the solution, as the magnesium will be able to find the acid faster and there will be more chances of successful collisions.
Evaluation
I have identified my anomalous result that are highlighted in table no.5 and the reasons for the anomalous results accruing is because of the apparatus I used, It was impossible to put the bung in quick enough and it was unavoidable that some gas escaped, which means that some hydrogen must have got out, meaning that I will have got mistaken results which affects my whole investigation. Also the gas syringe moves out slightly as pressure changes when the bung is put in, therefore made errors in my results. To improve this I can use an ignition tube, which will prevent any hydrogen being let out. This works by the bung already being fit into the conical flask and all you have to do is tip the conical flask so that the ignition tube, containing the magnesium, falls over, the magnesium falls out and the experiment is started without the hassle of opening and closing the bung.
Another thing I have done wrong was that when I used the 0.05g of magnesium I only measured 4cm off and I measured the mass once. I then assumed the mass would remain constant every time I measured 4cm. To improve this I should have weighed the magnesium each time by using an electronic balance which is unfailing at measuring light weights.
A further error I had made was that I used a measuring cylinder to measure the acid when I had known that it would not give me accurate measurements, which would have gave me errors in my experiment. To atone this mistake I should have used a pipette as it would have give me the correct measurements and made my results extra reliable due to the ease of reading and measuring the acid.
If I had done all the alternatives I have mentioned above, I would have been confident that my experiment is errorless and reliable. This is because they are bound to give accurate measurements of magnesium, acid and keep all the gas in during the experiment.
