3. Surface area. The acid particles can only collide with the exposed magnesium atoms that are in the outer layer of the ribbon when a big piece of ribbon is used. When it is powdered, more atoms are exposed. Small particle have a large surface area in relation to their volume. So there is a greater chance of an acid particle colliding with a metal atom, thus the greater the chance of more successful collisions.
4. Some reactions can be speeded up by adding a catalyst. In the presence of a catalyst, a collision needs less energy to be successful. The result is that more collision can be successful and thus the greater the rate of reaction. They also give a surface for the molecules to attach to , thereby increasing their chances of bumping into each other.
Method:
Apparatus: - a) 100ml measuring cylinder
b) 10ml measuring cylinder
c) Test tube
d) Stopwatch
e) Magnesium ribbon
f) Hydrochloric acid
g) Safety goggles
h) Water tub
i) Retort stand
j) Glass tube for collected acid
k) Pencil for winding magnesium
Diagram:
Instructions:
1. Firstly you have to set up the equipment.
2. Fill up the water tub to about three thirds with water or whatever amount you want as long as the gas doesn’t escape.
3. Place the 100ml measuring cylinder sideways in the tub then gently tip the open end up so the gas in it escapes. Make sure there is no gas in the cylinder.
4. Hold the measuring cylinder in a upside down position near the middle of the tub and hold it there with a retort stand.
5. Get the test tube and using one of your hands, carefully lift the measuring cylinder and place the end of the collect tube under it.
6. Using a retort stand, hold the test tube above the water.
7. Get your magnesium strip and coil it around your pencil.
8. Remove the bun from your test tube and place the magnesium in it.
9. Get you and your partner ready and when you start to pour the acid in, tell him to record the readings at the appropriate times. Replace the bun as soon as all the acid is in the test tube.
10. Read the amount of gas produced at the appropriate times in the measuring cylinder. The times are as follows: every 30s for 0.75 and 1m, every 20s for 1.25m, every 10s for 1.5 m and every 5s for 1.75 and 2m.
11. Make sure you get at least five readings for every experiment. Get your results and fill them into a table. Using this table, create the needed graphs.
12. Repeat the experiment at least twice for every concentration of acid.
13. Write up your conclusion and evaluation after studying your graphs and your results.
To make our investigation a fair test, I will have to make sure that I keep the following factors the same:
- Starting temperature of the acid
- Volume of acid used
- Surface area and shape of the magnesium ribbon
- Clean, uncontaminated equipment
- Use the same stopwatch every time
These will be needed to be the same every time other wise we could end up getting odd and unreliable results.
The factors that follow will be the ones that are changed in every experiment:
- Concentration of the acid
This will help the investigation as it tells me if the rate of reaction depends on the concentration of the acid.
Safety:
The things that I will need to do to keep myself; others and the experiment safe are listed below:
- Make sure every person around are wearing their safety goggles
- Care when using glass equipment because if broken, many sharp pieces are scattered around and could cut someone
- Disposal of the acid is done with precaution
- Tie long hair back and tuck in shirts
- Clear work area from cutter
- Make sure everyone knows what you are doing
- Tell the teacher in case of an accident
Obtaining evidence:
The times for when the amount of gas has to be read are above in the method. We had taken nine results for both experiments with 1m. We got ten results for both our 0.75m experiments to. For 1.25, we got seven results both times. 1.5m consisted of twelve results each time. 1.75m took ten results both times to. And finally, 2m took eight results both times. Our measurements were pretty precise, as we could plot decent graphs from them. We used the 100ml measuring cylinder to record the amount of gas collected and a stopwatch to see when we had to record the results. Because the measuring cylinder we used went up in only 1cm at a time, we couldn’t get very precise readings. To make our results as accurate as we could, we had two people checking the amount of gas collected so if a person missed the amount, the other could tell it. This way, we had less confusion in the group and everyone got to be part of the experiment.
Results:
0.75m:
1m:
1.25m:
1.5m:
1.75m:
2m:
Time taken:
Conclusion:
1 over time table:
I found out that my predication was true. The stronger the concentration of the acid, the faster the rate of reaction was. This can be seen in my results where 0.75m took 270 seconds whereas 2m took a mere 45 seconds. This can also be seen in my second graph, the gradient gets steeper the higher the concentration of the acid. This is because the ions are closer together in a concentrated solution. The closer together they are, the more often the ions collide. The more often they collide, the higher the chance of a reaction between the magnesium and the hydrochloric acid. Also because there are more particles in the solution which would increase the likelihood that they would hit the magnesium so the reaction rate would increase. The graph gives us a good device to prove that if you double the concentration the rate of reaction increases. If you increase the number of particles in the solution it is more likely that they will collide more often. I had repeated all the experiments twice so that I can get accurate and reliable results. I therefore conclude that the initial rate of reaction increases as the concentration of the acid increases. As I had said before, my prediction fits with results as the stronger the concentration of the acid, the faster the rate of reaction. Also, after looking at my first graph, you can see that no matter what the concentration was, all the experiments started off with a high rate of reaction. It was the stronger acids that didn’t level of as they had a constant high rate of reaction whereas the weaker acids decreased. All the experiments were exothermic. This means that they gave of heat as a product. This could be due to the friction created between the particles when they had collided and reacted. The temperature rose quicker with the stronger acids. Also, all the final readings for the amount of gas produced should have been the same according to theory. We all used 5cm of magnesium every time and the gas is created from this. You can’t have more gas this time than the other as equal parts of everything are being used every time. It’s like saying that if you pour 100ml of water from a jug into a glass, you will only receive 80ml but the next time you will get 110ml. It’s not possible, I do agree that you may get 97ml this time and 99ml the next as water may have been trapped in the jug but still, the results are similar.
Evaluation:
I think that overall, our experiments/investigation was successful except for minor things such as the occasional odd results. On the first graph, these can be identified as when the lines representing 1.25 and 1.5 molar kept on crossing over each other. They were very similar. In theory, all the lines should be apart because the rate of reaction should be increasing every time. Another odd result is that on the second graph, the point which represents 1 molar is no where near the line of best fit. All points should either lie on the line or be pretty close to it. I believe that we got these odd results because our human errors. We may not have collected all the gas produced. Or the gas could have been caught in the collecting tube and this may have resulted in the long time needed for the reaction. I believe that the method provided with us has a few faults that I would like to point out. Firstly, when the magnesium piece is dropped first, then the acid poured, time is taken for the all the acid to drop but as soon as the first drop touches the magnesium it will react. This means that hydrogen gas would have been produced when pouring in the acid and lost through the open top. To change this, I would say in the method that the acid should be poured in to the test tube first then the magnesium piece, as the cork can be replaced without the metal touching the acid and no hydrogen gas would be lost. Secondly, gas can get trapped in the collecting tube as it faces down. When the first amount of gas is produced, it is followed by more which results in the gas pushing forward for more space because it can’t be compressed. When the last amount of gas is produced, nothing is there to push it forward so it just floats around without reaching the measuring cylinder. I don’t really have any improvements for the method but you could try to keep the measuring cylinder closer to the test tube and keep it at an elevated position. This way, more gas reaches it. We should have taken more care when handling the glass equipment as a measuring cylinder had been pushed over the ledge of the worktop and smashed when it had contact with the ground. Overall, the method was good but like everything else, it could be improved. It was generally a fair test but a few things may have altered the results, such as after a few of the first experiments, one of the windows was opened in the room and cold air rushed in. I don’t if this had anything to do with the experiment but it could be something to think over when planning the next investigation. I feel that the measurements were easy to take measurements as we didn’t miss a single reading. We could have repeated the experiment once more to be a little more accurate, the more results there are, the better it is after all. All the graphs showed a pattern to do with the concentration levels of the acids, the trends got higher for rate of reaction, the time decreased for stronger acids and less time was taken to. We kept the few odd results we got as it gave us something to talk about and think about in the future. I strongly believe that the results that we got, supported our conclusion as no matter whose results you saw, all showed the same trend and this proves that the results were reliable. Next time, I would use more concentrations of acids, so that we can be even more accurate and sure about the results. Further investigations you could think about could be changing the temperature of the experiment and investigate if it alters your experiments at all. You could also change the surface area of the metal such as having a block, or reacting it in a powder form. Catalysts could be added to the reaction to see if they show a major difference.