Then, repeat the experiment using more and more concentrated HCL.
I will be measuring the amount of Hydrogen produced in this experiment. As more Hydrogen is produced the further the syringe will move outwards.
Variables
Controlled: My controlled variables are the temperature of the acid, the size of the surface area of the magnesium, the volume of the acid/water solution and the length of the magnesium strip. I will not stir the HCL, partly so the rate is not affected and also because if I did the hydrogen would escape anyway.
Fair test
I will use the same length of magnesium for each experiment so each time only the concentration of the acid changes not the magnesium, which could speed up (more) or slow down (less) the reaction. Also less hydrogen will be produced.
I will clean out the flask after each experiment because there will be the remains of the last experiment or other substances in the flask that could distort the experiment. There could be some stronger acid left in the conical flask than the acid I’m about to use so there will be a slightly faster reaction. There may also be bits of Mg left over so that in my next experiment there will be too much Mg, thus not being a fair test.
I will open the syringe and dismantle it from the flask and tube to let the Hydrogen escape so the next experiment is not distorted because there’d be hydrogen already there.
I will clean the Magnesium every time because it may have a coat of dirt and substances that may also distort the experiment. The HCL will not be able to get to the Mg until the dirt has been corroded away by the acid, increasing the time taken for the reaction.
I will use distilled water because there are no impurities in it that may affect my results. If I use tap water, which is impure because of the hard water that we have in Hull then the particles of Mg and other minerals could speed up the experiment because there will be more Mg.
I will use the same amount of HCL each time because it could speed up the reaction.
The temperature will need to be the same each time because the collision theory tells us that the temperature give the particles more energy and the reaction rates may be affected.
I will push the syringe in so that when I start the experiment the reading isn’t higher than it should be.
I will keep the surface area of mg the same because it may speed up the reaction if the area is increase.
The temperature will stay the same; I will be working at room temperature so the rate of reaction will not be affected by the particles being given more energy.
The consistency of the Mg will be kept the same i.e. if in one experiment I use a strip of Mg and in the next experiment some powder then the collision theory tells us that this will change the rate of reaction. I will use strips each time.
I’ll use the same size apparatus each time because if I use a smaller syringe then it later it may not be big enough to contain all of the hydrogen produced and then the end may fall out and I wouldn’t be able to measure all of the hydrogen
Safety
Hydrochloric acid is an irritant it is corrosive and dangerous. You must wear safety goggles and lab Coats at all times because it can burn, especially one’s eyes.
The moving part of the syringe is attached to the main part by a piece of string so that if too much hydrogen is produced and it is pushed out it will not fall out and break on the floor.
The Magnesium is flammable so do not light it.
Reliability
The Mg will be cleaned, and I will be conducting a fair test as mentioned above. I will also use the same apparatus each time and repeat each experiment 3 times to get an average.
Accuracy
I will measure all liquids by looking at eye level at the point of graduation of the meniscus. I will stir the mixture before I add the Mg so the two liquids can mix evenly before hand. I will measure the HCL in a measuring tube before hand. I will be measuring the hydrogen to a half of a millimetre e.g. 22.5 mm. I will measure the Mg using a 300mm ruler to the nearest millimetre.
Problems to be solved
At first I used 10cm of Mg but when I added the HCL the reaction went too quickly for me to take accurate readings and also after 30 seconds the end of the syringe had to be taken out so I could not take any readings. To solve this I will use 5cm of Mg. The reaction will not be too fast for me to take readings every 5 seconds.
When I tried using 5cm of Mg and measuring the hydrogen after every 30 seconds I found that the reaction was almost over by that time so I decided to record the readings every 5 seconds to get more results. This worked well.
I need to take into account that if the syringe won’t go all the way in then at the end I need to take away the amount that it started at. This is usually a few ml but is still important.
What I have changed
I will use 5cm of Mg
I will take readings every 5 seconds.
I think my preliminary experiments have helped a lot because I now know what measurements and amounts to use in my experiments
Concentration of acid 2 mols
These is tables show how I will change the concentration of the acid in my experiment.
Concentration of acid 1mol
Apparatus
100ml gas syringe
250ml conical flask
Stopwatch
Delivery tube
50ml Measuring cylinder
100ml glass beaker
Magnesium ribbon
Distilled water
HCL-50ml
Retort stand
Clamps
Method
I will use the same apparatus as in the preliminary experiments but obviously I will make the stated changes to the concentration of HCL and amount of Mg. I will use the same method as in the preliminary experiment, timing the reaction every 5 seconds. I will change the concentration by adding water to the HCL as shown in the table below.
Range of measurements
I will use concentrations of HCL from 0.8 to 1.6.
These are the changes I will make to the concentration.
These are the changes I will make to the concentration.
Results
All of the experiments started with the hydrogen at 0cm3.
These are my second set of results:
Again, all of the experiments started with the hydrogen at 0cm3.
These are my third set of results
All of the experiments started with the hydrogen at 0cm3.
These are my averages
The Rate of reaction results
Analysis
Conclusion
From my results I conclude that as the concentration of HCL increases the rate of reaction increases. This fits my prediction because I said that this would happen. This is very clear, as the rate of reaction is faster for the higher concentrations and with all of my results the greater the concentration the faster it takes for the reaction to finish.
However, the rate of reaction is not directly proportional to the concentration. In my prediction I wrote that this would happen and this doesn’t fit. If I look at my rate of reaction results then I can see that the rate was not directly proportional. The rate never doubles at all because the average rate at 0.8 is 0.2853 and the average rate at concentration 1.6 (double 0.8) is 2.49, which is more than 8 times more so a lot more than double. It is, in fact more than eight times greater. Also on my rate of reaction graph the results do not go in a straight line. I also said in my prediction that twice the Hydrochloric acid used, twice the amount of hydrogen will be produced in the same amount of time. This didn’t happen because in my averages table at 5 seconds for concentration 1.6 the amount of H produced was 15.3 mm3 and at the same time for concentration 0.8 there was only 1.3 mm3 produced, not double like I said. This trend continued through out the experiment.
I do conclude that the amount of H produced was proportional to the concentration, but as I have mentioned not proportional.
I think that more rate of reaction increased as the HCL concentration increased because, going back to the collision theory, as the concentration increased there were more particles to collide with the Mg. There were more particles, mols per litre, so more collisions and therefore a greater chance of collisions and so a faster rate of reaction occurred. There were more particles to collide with the Mg particles so there was a faster rate of reaction each time I increased the rate of reaction.
Evaluation
Accuracy of measurements
I think that my measurements were accurate because I measured the amount of H produced in mm3 and not just cm3. I also measured the acid accurately because I measure how much I had by looking at the meniscus at the point of graduation. I measured the Mg to the nearest millimetre so each experiment I had the right amount of mg. I measured the gas to the nearest millimetre as well. All of my apparatus was accurate because they, if they had measurements on, were all to the nearest mm.
How could it be improved?
I could have measured the temperature of the acid at all times so that the rate was not affected. The temperature could have changed because I didn’t do the experiment all on one day so the particles could have been given more energy.
I could have got more results; I wanted to use more concentrations as well as the ones I used but they were not available. I may have got better, or even more predictable results had I done this. Only once did the concentration of the acid double, from 0.8 to 1.6 and I could have had, maybe 1 to 2 mol or even going up to three mols and then the acid concentration would have doubles more than just once, perhaps giving me more reliable results. I thought that I got reliable results because I did lots of repeats.
Anomalous results
There were some anomalous results: For my first set of results at 1mol acid after 5 seconds the amount of hydrogen was 9ml but with the other two repeats they are 4 and 3.5, two very close results. The 4 and 3.5 seem more reliable because they are repeats and they are very similar.
With my third set of results at 1.6mol acid after 5 seconds the amount of hydrogen was only 11ml but the other two were 17 and 18 so these two seem more reliable. With my first experiment with 0.8mol acid the hydrogen produced was 0ml and with the other repeats 2ml of hydrogen had been produced.
With my second set of results at 1.6mol acid the amount of hydrogen produced was 17ml after 5second but then the rate of reaction speeded up dramatically to 33,44,45 and then it levelled out at 46ml. This was a lot quicker than the other two experiments form 5 to 15 seconds. This could be due to the water not being stirred enough so that the mg went from an area of HCL evenly mixed but then going to an area where the water has not mixed yet, thus having a larger concentration, with more particles and therefore a quicker rate of reaction.
Perhaps the most anomalous result was in my third set of results at 1.2molacid after 10 second there was 21ml of H2 produced but then after 15 seconds it went down to 18. This is not possible, unless somehow the hydrogen escaped but it could just be down to human error. I could have misread the syringe.
At 1.4mol acid after 10 second on my third set of results, the hydrogen produced went from 18 t o40ml and then to 51ml. The reaction stopped. This could be due to the syringe jumping. The corresponding results were a lot slower.
Some of these could be due to the syringe jumping. After I took results sometimes the amount of hydrogen was not as much as you might think but then as soon as you have taken the result the syringe jumps forward. It doesn’t tend to move smoothly and continuously.
Procedure
How could I improve it?
I could have done regulated stirring before I added the Mg then the HCL would be evenly spread and diluted. I could have used more concentrations of acid to get more results and hence, more reliable results. I could have found a way of ensuring the syringe would move smoothly and constantly and not jumping as it did. I could perhaps use a lubricant to solve this and reduce the amount of (hopefully) all anomalous results.
Any problems
I don’t think that there were any problems with the procedure and nothing went wrong. There were, obviously anomalous results but no consistent problems that changed my experiment or prevented me form carrying out the task.
Reliability of measurements
I think that my results were reliable because I got repeats and from my results I can tell that this helped. I did get some anomalous results but because I got averages they were evened out. From my repeats I could see what the results should have been if I did get an anomalous result. I conducted a fair test and also took into account the need for accuracy. For example I looked at the point of graduation of the meniscus and I measured everything to the nearest millimetre.
Suitability of procedure
I think that my procedure was suitable although it could have been improved. When I put the Mg into the flask I couldn’t start the stopwatch quick enough. This meant that the reaction stated just before my experiment started so I could have got inaccurate results but if I did this every time then all of the experiments were all affected and not just some of them. It is, however unlikely that I spent the same amount of milliseconds putting the bung in and starting the stopwatch. I could have asked someone to start it for me. This was the only fault I could find.
Sufficient evidence
I think that I could have got more evidence by conducting more experiments because I would have liked to use more concentrations, thus getting more result and more to compare and analyse. I don’t think that I did get quite enough because I am not entirely happy with my results as they did not fit my prediction, although I know that this is not essential. I concluded that the rate to reaction was not directly proportional to the concentration but I am not entirely convinced. I didn’t get many chances to prove this.
Improvements and further work
I could do more experiments, e.g. more concentrations, or I could even change the experiment by using a different acid or metal to see if anything changes or if I get better results.