TRIAL RUN-PROCEDURE
- Measure out 2cm of Mg.
-
Measure out 25cm3 of HCl acid in a measuring cylinder.
-
Pour acid into flask and heat to desired temperature. In this run 60°C.
- Add Mg to acid
- At the same time start the stop clock and secure bung into flask.
- Record volume of gas collected in measuring cylinder after 30 seconds.
Results of trial run
In our trial run we used 25cm3 of HCl and our top temperature was 60°C. We used 2 cm of Mg. We found that at 60°C the Mg dissolved very quickly and although we have recorded the volume of gas collected the reaction had finished before 30 seconds.
We decided that we are going to reduce the time to record the volume of gas to 2 seconds, use more Mg and less HCl so that the reaction lasts longer and is still going past 20 seconds. We are going to use 8 cm of Mg and 15 cm3 of HCl so that the reaction lasts at least 20 seconds. The top temperature is lowered to 50°C as 60°C was too fast. We are going to record the volume of gas collected after 20 seconds, as if we let it go on for longer then all of the results would be the same as we will be using the same amount of chemicals but we are looking for the speed of reaction rather than the overall amount of gas produced in the whole reaction.
To make the experiment a fair test:
The variables we will keep the same will be the amount of Mg and the volume of HCl.
We will also use the same concentration of HCl as if the concentration was stronger then there would be more particles of acid to collide with the Mg. The reaction would be faster. This also comes back to the collision theory.
We will also use the same equipment so that each experiment doesn’t vary other than the variables.
We will keep the Mg the same length as if the surface area is larger or smaller, the reaction would be faster or slower as there would be more or less outside Mg particles for the HCl to collide with. We are also using Mg ribbon instead of powder because powdered Mg has a very large surface area so the reaction would be too quick to record an effect which is due to the collision theory.
We will keep the HCl the same concentration because if the concentration differs then there could be a higher or lower number of particles in the volume of HCl we use which could change the results. There would be more collisions happening the more concentrated the acid becomes and this would change the rate.
We will use the hydrochloric acid every time as changing to other acids can vary in strength.
We are planning to repeat the experiment 3 times so that we can get an average and we avoid the chance of an odd result.
In the below diagram when the acid is heated to the correct temperature the flask will be taken off from the heat as the gauze would still be hot and would continue to heat the acid.
The equipment will be set up as follows:
When the Mg is added to the HCl they will produce hydrogen in the reaction. The hydrogen will travel down the delivery tube and will bubble up into the measuring cylinder, therefore we will be able to measure the volume of hydrogen given off. The water in the trough is to prevent the gas escaping out the bottom of the measuring cylinder. We will use a Bunsen to heat the HCl.
To make the experiment safe we will wear safety glasses in case the HCl gets splashed. We will make sure the flask is on a flat surface so it doesn’t fall over. We will also use a diluted HCl so it is not really dangerous if it is spilled. We will limit the highest temperature to 50oC for safety as well.
From this work I hope to find out about the collision theory. This is that as the HCl gets hotter, the particles will move faster so will collide with the Mg more frequently and with greater force. So, the hotter the HCl, the more hydrogen should be produced in 20 seconds. Also, the hotter the particles are, the harder they will collide as they have more energy and so be more likely to react as more bonds will be broken in harder collisions.
Here is an example of the collision theory in every day terms-
Prediction
I predict that as the temperature increases the reaction will go faster and at more force so there will be more gas collected after the 20 seconds due to the collision theory.
OBTAINING EVIDENCE
These results agree with my prediction and also prove the collision theory. This is that the hotter the particles the more frequent collisions between the particles and at more force.
Evaluation
Overall our method was good but the problem was it was a very timely method so we were not able to carry out as many experiments as we had planned. The reason for the experiment taking a long time is that it was very hard getting the temperature of the acid exactly correct, firstly we heated the acid to the correct temperature but then as the flask was still hot the temperature soared above the desired temperature as took a long time to get back down to the right number. Therefore we were only able to get one set of results. If I did the experiment again then I would probably have done the mass loss experiment as people who did that got good results and lots of them! If I did the same gas collection theory again then I would probably put the flask into a trough of water and heated up the water as it would have been a more gradual increase and the bottom of the flask would not have been in direct contact with the bunsen burner so the acid would not keep on increasing in temperature after it was taken out of the water.
Our results are accurate enough and do prove the collision theory well. They are mostly quite even between results but there were a few hurdles on the way-we had to put in 8 cm of Mg in the end as originally we planned to use 4 cm but there was just not enough gas being produced in 20 seconds to give us much difference between the temperatures. There was only one result that didn’t fit in and that was the result for 35°C which broke the pattern of about 3 cm3 between results but it also was a good result as it linked up the next result which was 40°C to the rest as it was in the middle between 30°C and 40°C. I think there was quite a large jump as there reached a point when the collisions broke a sort of barrier at which the particles collided more frequently and with much more force than before as it needed just a bit more energy. This would also make sense as it is the middle result from all the temperatures which would explain a breaking point.
From our graph I can predict that as the temperature increases the amount of hydrogen collected will be higher as the particles would be moving faster so collisions would be more frequent and at more force. Therefore the reaction would be more vigorous so there would be more gas collected. Also as the temperature decreases the amount of hydrogen collected would be less as the particles would be slower and so the collisions would be less frequent and with less force.
There are other experiments that could be carried out to extent the work we have just done. Firstly we could investigate the rate of reaction between Mg and HCl but this time the variable could be the concentration of the acid. This would be a good test to see if the amount of particles in the acid changed the rate of reaction which would also prove the collision(More collisions as particles are denser).To test this theory we would use the same equipment and plan but just change the concentration of the acid instead of the temperature of the HCl. We could also test to see if Mg powder reacted quicker with the HCl as the surface area would be larger so there would be more frequent collisions. This also comes back to the collision theory and would be a good test to prove it. Using this method you could change any of the variables(concentration of the acid, temperature of the acid etc) and compare it with the results using Mg ribbon. The other test we could do is the mass loss experiment. This would prove that the reaction lost weight during the reaction and like the last alternative experiment any of the variables could be changed. This also refers back to the collision theory that a reaction loses weight as if goes on which would be useful to test the different rates of reactions.
Science Coursework
Alex Dixon
