Gas Syringe Method
Equipment
Conical Flask, Bung, Connecting Pipe, Gas Syringe, Hydrochloric Acid, Magnesium Ribbon, Clamp, Stand.
For this method we set up the equipment as follows;
The first to do is to gather together all equipment, then once that is done get the conical flask and put the bung into the top of it. Then connect the pipe from the bung to the gas syringe, making sure that it is air tight. Then once everything is set up get the stop clock ready, measure out the 50ml of hydrochloric acid and pour it into the conical flask and again the same as the burette method simultaneously put the magnesium into the conical flask, put the bung into the top of the flask and start the timer. We took down measurements in 5 second intervals. The gas syringe has a volume of 100ml³.
Results
Burette Method
50ml Hydrochloric Acid 2Molar and 10cm of Magnesium Ribbon
This is another disadvantage of the gas burette method because it will only measure up to 50ml³ we will not be able to get the full reading for the experiment. Another disadvantage is that the burette method changes readings in stages going from 9 to 17 instantly as soon as an air bubble reaches the surface; this can make the experiment inaccurate because if you about to take a reading and an air bubble comes to the top and the reading drops then it will not be scientifically accurate.
Gas Syringe Method
50ml Hydrochloric Acid 2Molar and 10cm of Magnesium Ribbon
This is another example of an advantage of the gas syringe method as it can hold up to 100ml³ of gas. Another advantage of the gas syringe method is the accuracy that this method allows us to have because the gas is constantly passing into the gas syringe the reading is steadily and constantly going up so when the time comes you can take an accurate reading.
How did the preliminary Experiments help with my decisions for the actual experiment?
The preliminary experiments helped me to make a lot of decisions and the most important decision of all which was with which method I would carry out the actual experiment? I have decided to do the experiment using the gas syringe method; I made this decision using several things from the preliminary experiments the first was the fact that the gas syringe method was quiet a lot more accurate than the burette method. This means that it would be a good idea to use this method because it is more accurate when taking down the results and so should therefore give us a more accurate rate of reaction. Other things that pushed me towards making the decision to use the gas syringe method was that it was a lot easier to take down the results because the readings on the side of the gas syringe can be set to any angle whereas the readings on the side of the burette will always have to be upside down and so this makes it a lot harder to try and read out the readings when the time comes.
Equipment
Conical Flask, Bung, Connecting Pipe, Gas Syringe, Hydrochloric Acid, Magnesium Ribbon, Clamp, Stand, Measuring tube and Stop clock.
The accuracy of the conical flask will go up in sets of 25ml, but we will first use the measuring tube to measure out the quantities of both the acid and the water we will use to dilute the acid. The measuring tube is accurate down to 1ml. The accuracy of the gas syringe is also down to 1ml but this is down to 1ml³.
Risk Assessment
The acid that we are using in this experiment is of 2 molar strength, which is strong enough to at least cause irritation to the skin if spilled on it, the hydrochloric acid would also cause irritation to the eyes and mouth if ever spilled into those. Another risk is that magnesium is flammable especially if in powder form, but we are using it in a ribbon form and we are not using any flames in any part of the experiment. The gas which is given off from the reaction between Hydrochloric acid and Magnesium ribbon is Hydrogen which is a flammable gas.
We will reduce the risk of these hazards by wearing protective eyewear for example laboratory goggles, we will also measure out the hydrochloric acid pouring away from the body, over the sink. We will not be using flames in our experiment so the risk is reduced from the hydrogen and magnesium but still other experiments could be using flames so we will still have to be careful and make sure to stay away from any other experiments using flames.
Method
Above is a labeled diagram of my equipment which has been set up.
The first thing that we shall do is to prepare our work area where we will be doing the experiment, clear anything that could cause an obstruction or any risk. The next thing to do is to simply gather together, and not set up, all equipment that we shall need. When getting the hydrochloric acid we shall take one container full and if we need anymore we merely ask for some more, and we shall only get the magnesium ribbon when we need it, this is not only for safety reasons but also we shall be able to measure out the desired amount there and then. Next we will set up the equipment that we have just gathered together, as the diagram above shows.
Once this is done we will take the measuring tube and measure out our first strength of hydrochloric acid, once measured out accurately we shall then put it into the conical flask. Then we shall measure out the 10cm of magnesium ribbon and gently fold it into a smaller shape. Then this is where a moment of inaccuracy could enter into the experiment we now have to put the magnesium ribbon into the conical flask, whilst at the same time put the bunk into the top and start the stop watch, but this is impossible so we just have to do it as fast as we can whilst still being safe in what we are doing.
Once we have done this we then record results every 5 seconds until the experiment runs out of either hydrochloric acid or magnesium ribbon and so cannot carry on. I will take measurements ranging from 1ml³ to 100ml³, as this is the largest amount of gas that the gas syringe will hold. I will check that my results are reliable by firstly checking that everything went as predicted in which the weakest solution took the longest time in order to give off all the gas and that the strongest solution would finish reacting the quickest.
Another way which we will check that the results are reliable will be to check the results against the preliminary experiment. I shall make sure that my results are accurate by keeping some aspects of the experiment the same. The things that are going to be kept the same are the amount of hydrochloric acid and water, there will always be 50ml no matter what the concentration, The length of the magnesium ribbon will not change either; there will always be 10cm of that and the temperature at which the experiment will take place will always be near enough the same because we shall carry it out at room temperature and although we cannot always control this we will always do the experiment in the same room as to try to lessen this possible change. We will change however the concentration of the hydrochloric acid.
Results
One of the key calculations that I used was the calculation of how to work out the rates of reactions which was, you have to take the amount of gas given off after the first 5 seconds and divide it by 5.
For Example: At 2 Molarity strength of hydrochloric acid set of results; 1.
The volume of gas was 64cm², divide this by 5 which was the amount of time that elapsed for this much gas to be given off and you get 12.8cm²/second. Now to carry on working this out for the rest of this set you have to find the difference between 64cm² which was the amount given off after 5 seconds and the amount of gas released after 10 seconds which was 88cm², the difference is 24cm² and so we again divide that by 5 and we then get 4.4cm²/second which is the correct rate of reaction for this time period.
Conclusion
The most obvious trend that I can see is that the higher the strength of the hydrochloric acid then the larger the rates of reaction will. This is proven in the first and last sets of results, which are for hydrochloric acid strengths of 2molar and 0.4molar. The highest rate of reaction for any set of result in the 2molar is 14cm²/second whereas the highest rate of reaction for hydrochloric acid strength of 0.4 is 1cm²/second which is a difference in rates of reaction of 13cm²/second. Another pattern that I saw was that no matter the strength of the hydrochloric acid the volume of gas will always increase and never decrease, it may stay exactly the same for a few seconds but it should still increase. This will always happen because this particular experiment is an irreversible reaction. This means that once the magnesium has reacted with the hydrochloric acid and the gas is given off then there is no way to get the magnesium back. My results are agree totally with my original predictions, which was that the 2molar experiments would react a quicker than the hydrochloric acid that was 0.4molar. My prediction also said that as the hydrochloric acid became nearer and nearer to 0.4molar then the reaction would take place slower and slower. The only abnormality that there was in the whole experiment was with hydrochloric acid strength of 1.2molar, results set 3 the first rate of reaction result was 7cm²/second, which was a 4 cm²/second increase on the other 2 sets of results.
Evaluation
I think my results were very accurate as the results for the gas given off was accurate down to the nearest cm² thanks to the gas syringe and the rates of reaction results were accurate down to the nearest tenth of a cm²/second and that was down to how I worked out those particular results. I had one odd results which didn’t match my prediction and that was set of results 3 for with a molar strength of 1.2molar. This result was 7cm²/second over the other 2 sets of results. One explanation for this odd result could possibly be that we put the bung into the top of the conical flask too late and didn’t start the stop clock at the same time. My results I think are very accurate because the volume of gas measured from the gas syringe and taken down were accurate to the nearest cm² and the rates of reaction was accurate down to the nearest tenth of a cm²/second. I think that my results are good enough and accurate enough to give a firm conclusion that the stronger the molarity of the hydrochloric acid is then the faster the magnesium ribbon is going to dissolve. I think this because my results show it, the starting strength which was 2molar took less than half a minute whereas the finishing strength which was 0.4molar took 5 and a half minutes, this was the longest results set out of all strengths of hydrochloric acid. There are a few ways in which I could make my reaction more accurate and reliable and the most obvious would be that I would have to find a way to hang the magnesium above the hydrochloric acid so that as soon s the bung goes in the acid drops and the stop clock starts, this would therefore eliminate any possible abnormalities. I think a way in which I could make this experiment last longer and to give extra evidence would be to do the same experiment only using smaller gaps in strengths of the hydrochloric acid, in other words do the experiment again only use hydrochloric acid of 2molar, 1.8molar, 1.6molar, 1.4molar…and so on until you got down to 0.2molar. This would give you a much more wider set of results especially if you did all of those strengths 3 times as we have done in this experiment. That is another way of making the experiment more accurate, by repeating it more than 3 times to so that we had enough sets of results for each strength to rule out any abnormalities.
By Joey