Equipment list:
- Five test tubes
- Test tube rack
- Measuring cylinder
- Hydrochloric acid
- Magnesium (Later cut to length stated in method)
- Digital stopwatch
- Bunsen Burner
- Tripod
- Gauze
- Safety mat
- 250ml Glass beaker
- Tap water
- Safety goggles
- Thermometer
- Pipette
Fair Test:
To make my test fair, I will be using a 100ml measuring cylinder to measure the water and hydrochloric acid accurately, make sure the magnesium strips are all cut to the same length (3cm), use a new test tube after each experiment, be precise with the digital stopwatch, and follow my method even if the experiment is not going to plan. I will start the stopwatch the exactly when the Mg touches my acid and stop the watch when the fizzing (reaction) stops. I will also repeat each of my five tests twice making a total of three experiments to get the best (most accurate) results.
Variables:
- The temperature of water
- Time taken to insert ribbon into test tube
- Time taken to start and stop the stopwatch
- Room Temperature
- Presence of a catalyst
- Cleanliness of apparatus
- Surface area
- Light
Prediction:
I predict that the hotter the water and hydrochloric acid get, the faster the magnesium will dissolve/increase in rate of reaction. This is due the “Kinetic Theory” which states, in my case, that the hotter the hydrochloric acid gets the faster and more vigorously the hydrochloric acid’s molecules will vibrate and rub against each other, causing the molecules to collide and break the magnesium down.
Method:
Set up the needed apparatus, listed above, and measure out 15ml of hydrochloric acid into five different test tubes using a pipette for further accuracy. I will heat the tap water over a Bunsen burner to the required temperature for each test tube. The temperature will be measured with a thermometer which I will suspend in the water making sure that it does not touch any part of the glass beaker. When at the required temperature, I will place the test tube with 15ml of hydrochloric acid, and 3cm of magnesium into the glass beaker and start the digital stopwatch. The stopwatch will continue until the magnesium has completely dissolved and the results will then be recorded. During this experiment safety precautions need to be taken. I will ensure that my safety goggles are worn at all times, and I’ll also make sure that I have sufficient room to perform the experiment safely. Equipment will be thoroughly checked before I begin which will prevent any kind of accident. I will use full advantage of my test tube rack rather than holding and carrying test tubes in my hand. In addition to this I will make sure there are no dangers concerning me or my classmates whilst performing my experiment.
Diagram of Experiment:
Evaluation:
It is clear, after studying my table of results, that the results themselves were drastically varied. This could be down to a number of reasons; the strip of magnesium may have been floating on the bubbles as appose to the acid, this would slow the rate of reaction down. To reduce the number of bubbles that were emitted, I could possibly have chosen a weaker acid. Another thing that affects the rate of reaction is surface area. For example, if I wanted to solve the problem of the magnesium in the bubbles, I could wrap the magnesium around my thermometer and then place it at the bottom of the test tube. However this will decrease the surface area of the magnesium strip and prevent the acid getting to the whole strip therefore slowing the rate of reaction down and making the test unfair. These two examples would be worth thinking about if I was to perform the experiment again.
Part of my prediction shown above (“I predict that the hotter the water and hydrochloric acid get, the faster the magnesium will dissolve/increase in rate of reaction.”) was neither correct nor incorrect because the results were varied. If I was to re-perform my experiment I would definitely think about changing my variable which is temperature and maybe change it to the concentration of the acid because with concentration you will get a more solid set of results instead of varied ones because when increasing the concentration you are introducing more particles in to the reaction which will increase the rate of reaction and ensure more collisions. And therefore a weaker concentration will lessen the rate of reaction. This, like I said, will produce a nicer pattern of results.
As shown in my equipment list above, I used a pipette for greater accuracy, a digital stopwatch instead of a normal wall clock, and I also repeated my experiment three times. These were all key factors to making my results as accurate as possible.
As with any experiment there are always improvisations that can be made. In mine there were a number of things that I would change if I had the chance to perform my experiment again; because all of my work was carried out in lessons, I will limited to the amount of time I could spend measuring accurately – something I hadn’t picked up on prior to the investigation. I think my results would have benefited a great deal if I had had longer to measure in both length and weight my magnesium more accurately because, even the slightest change in length or weight will change the rate of reaction and effect the final result. Other things could also have been improved. For instance, making sure all measuring equipment and test tubes were thoroughly cleaned and dried before I started a new test. This is important because even a miniscule drop of water in the test tube will dilute the acid and slow the rate of
reaction / amount of atomic collisions down – thus reducing the chance of a fair result.
Conclusion:
All in all, I would say that my experiment went reasonably well without any accidents or damages. The practical side of things were very enjoyable and I have learnt a great deal from it. As shown in my evaluation, there were a few unfortunate aspects which where unavoidable – the limitation in time, for instance, consequently resulting in rushed or inaccurate measurements. These problems would definitely be rectified if I had the chance the try this experiment again. Overall, I think things went quite smoothly and I am pleased with the outcome.
