In order to make my experiment fair I am going to control all the variables, except the one I am investigating, concentration. No catalyst will be added, all the reactions will be done at room temperature, the surface area of the magnesium and the volume of the hydrochloric acid will be keep the same for all reactions. The final volumes of each reaction will be kept the same for all reactions.
Preliminary Work
- 50 cm of hydrochloric acid was placed in a 100cm conical flask
- A 4.0 cm strip of magnesium was added.
- The first time the time taken for the magnesium to dissolve was recorded.
- The second time the volume of hydrogen every 5 seconds was recorded.
- The whole experiment was repeated with a stronger acid.
Results:
- From the results of the preliminary work the following has been decided:
- 50cm of hydrochloric acid will be used, as this worked well and seems like a fair even amount.
- We will continue to use 4.0 cm of magnesium, as this works well in the amount of acid that we are using.
- The volume of hydrogen will be measured every 5 seconds up to 60 seconds, as it gives a nice time of a minute and will allow me to do all of my experiments in the time allowed.
- The following concentrations of hydrochloric acid will be used to give a wide range of concentrations:
- 0.5 mol/dm 1 mol/dm 1.5 mol/dm 2 mol/dm 2.5 mol/dm 5 mol/dm
- Each concentration will be will be used twice for accuracy.
Apparatus
- 100cm of 0.5 mol/dm hydrochloric acid
- 100cm of 1 mol/dm hydrochloric acid
- 100cm of 1.5 mol/dm hydrochloric acid
- 100cm of 2 mol/dm hydrochloric acid
- 100cm of 2.5 mol/dm hydrochloric acid
- 100cm of 5 mol/dm hydrochloric acid
- 12 4.0cm strips of magnesium
-
100cm conical flask
- 50 cm measuring cylinder
- Retort stand
- Boss and clamp
- Gas syringe holding 100cm of gas
- Digital Stop clock
Diagram
Plan
- The apparatus will be set up as in the diagram
- 50 cm of 0.5 mol/dm hydrochloric acid will be measured in a 50cm measuring cylinder.
- The acid will be placed on the 100cm conical flask.
- A 4.0cm strip of magnesium will be added to the solution, immediately the bung connected to the gas syringe will be placed in the top of the conical flask.
- The stop clock will be started.
- The conical flask will be swirled 5 times (the same amount for each reaction.)
- The volume of hydrogen will be recorded every 5 seconds.
- The experiment will be repeated with the same concentration of acid.
- All of the above will be repeated for these concentrations of hydrochloric acid 0.5 mol/dm 1 mol/dm 1.5 mol/dm 2 mol/dm 2.5 mol/dm 5 mol/dm
- The results will be recorded, anomalies will be found and where necessary results will be repeated.
Method
- The experiment was carried out exactly as the plan says.
Results
The first table shows the results for our first attempt at the experiment. It shows the time increasing every 5 seconds with the amount of hydrogen (cm ) released from the conical flask for the different concentrations at the different times.
1st attempt
Concentration of HCl (mol/dm )
The second table shows the results for our second attempt at the experiment. It shows the time increasing every 5 seconds with the amount of hydrogen (cm ) released from the conical flask for the different concentrations at the different times.
2nd attempt
Concentration of HCl (mol/dm )
As you can see from both my result tables and graph. I have no anomalous results. Therefore I do not need to repeat any of my results. Below is a table of my average results:
Concentration of HCl (mol/dm )
Using my graph of averages I have been able to work out the rate of reaction for each concentration. I measure all of the rates from 2.5 seconds on the x axis, as the reaction was still taking place rapidly at 2.5 seconds for all the different concentrations.
For 0.5mol of HCl:
Rate of reaction= Change in concentration
Change in time
Rate of reaction = 0.75
2.5
= 0.3cm /sec
Below is a table showing the rate of reaction against concentration.
Conclusion
My results and graph shows that the higher the concentration is the quicker the rate of reaction. As the concentration is increased so is the rate of reaction. For example when the 2mol/dm was used the rate of reaction was 3.1cm/sec, whereas when the 2.5mol/dm was used the rate of reaction was 3.9 cm/sec. The 2.5 mol/dm is the higher concentration of the two and the reaction happens quickest.
My results show what they do because as the concentration is increased so is the number of collisions of particles per second. The chloride ions collide with the magnesium ions to form Mg + Cl which forms a magnesium chloride solution. The hydrogen ions collide with each other to form hydrogen molecules
My results support my hypothesis as I predict that the higher the concentration is the quicker the rate of reaction, and my results proved this correct. In my hypothesis I predicted that the concentration of hydrochloric acid would be directly proportional to the rate of reaction, as the concentration doubled so would the rate. I was correct my results are directly proportional. I know this as the line of best fit is straight. This can also be proved by my line of best fit, as along it when you double the concentration the rate of reaction also doubles. For example, when the 0.5 mol/dm was used the rate of reaction was 0.8cm /sec, 0.5 doubled is 1, when the 1mol/dm was used the rate of reaction was 1.6 cm /sec, 0.8 doubled is 1.6. Therefore, my results are directly proportional. I will check this again to make sure using 1.5 mol/dm and 3.0mol/dm . (1.5 doubled is 3.0) At 1.5mol/dm the rate of reaction is 2.4 cm /sec, and at 3.0mol/dm the rate of reaction is 4.8cm /sec. 2.4 doubled is 4.8, therefore my results are directly proportional, so I have proved that if there are twice as many particles in the same volume then there are twice as many collisions and the rate of reaction is doubles.
Evaluation
My results are very reliable, as I had no anomalies and all of my repeats are very close, with the largest difference between any two results being 5cm. Many of my results were exactly the same the second time round. For example the 5mol/dm concentration did not alter at all.
My results were fairly accurate, as the hydrochloric acid were measured to 0.2cm and the magnesium strips cut to 4.0mm. The digital clock that we used also measured to 0.1 of a second. We had no anomalous results, which shows that the procedure that we used was good, as well as our results being accurate.
We had no anomalies, as our results were close together. However had we had any anomalies they would have occurred because part of our experiment was done on one day and part on another. It would have been ideal if we could have completed the results at the same time, as their would be no chance of concentrations being made up slightly differently, however, this was not practical. Experimental error could have occurred because it takes reaction time for the person watching the stop clock to tell the person reading of the gas syringe the time, before the reading is read. This is bound to put the experiment out by a couple of seconds. Another reason for experimental error could be a slight delayed reaction when putting the bung of the gas syringe into the conical flask. We also swirled the hydrochloric acid when it had the magnesium in it, in order to provide initiation energy for the reaction and to increase the chance of collisions between the magnesium and chloride ions. Some concentrations could have accidentally been swirled more than others, meaning the hydrochloric acid had more initiation energy.
By procedure was quite suitable, and I f eel that the amount of results that we had was adequate, although in an ideal world more results would have been taken for accuracy and an average taken.
My results were sufficient and prove my conclusion as they followed the basic trend that they should. I used a wide range of concentrations of hydrochloric acid, from 0.5 mol/dm to 2.5mol/dm at 0.5 intervals. I also used a 5mol/dm. I produced reliable results, as they were repeated.
I could improve this experiment by making sure that the magnesium strips that I used were from the same batch, to make sure that there was no magnesium oxide on the outside of the magnesium, by cleaning them with energy paper. I could perform the experiment in the same day to make sure that a different batch of HCl was used. I could use a wider range of concentrations of HCl, maybe a 1.25mol/dm, 1.75mol/dm, 2.25mol/dm and a 2.75mol/dm. I would try a 6mol/dm but the reaction would be to fast for us to record. My suggested values would give me more points on my graph and I could be more certain that it is a straight line.
I could extent this experiment my changing an addition variable. For example, temperature, surface area , a catalyst. Obviously, this would take much longer, but would produce some very interesting useful results.
