Temperature. When the temperature increases, the particles have more energy and they then collide with each other more often, therefore making the experiment unfair.
The equation for this reaction is…
Mg + Hcl → H2 + Mgcl2 ………Hydrogen is given off.
The whole experiment must be as fair as possible. As this is a reaction between two chemicals, I will wash out the apparatus (measuring cylinder and conical flask). This is to make sure that there is no acid or magnesium still left inside. If there were, it could alter the experiment, as there may be more Magnesium or Acid than needed. I will also repeat the entire experiment three times to make sure it is accurate. I will then draw the graph using the averages.
Prediction
I predict that the higher the concentration of acid, the faster the reaction. I.e. it will take a shorter time for a certain amount of hydrogen to be produced. The prediction is supported by the Collision theory, which shows that as there are more acid particles when the concentration is higher, then there will be more chance of them colliding with the Magnesium particles. However, if the concentration is lower, there are less particles, so the likelihood of them colliding with the Magnesium particles is smaller. This means that the higher the concentration, the bigger the reaction.
Apparatus
Method
- Collect Apparatus as shown in diagram.
- Set up apparatus as shown.
- Make sure gas syringe is at zero.
- Measure out acid and water and mix into conical flask.
- Measure out 5cm of Magnesium.
- Put magnesium in solution and quickly connect to gas syringe and start the stopwatch and time for 30 seconds.
- Once 30 seconds has passed, look at the gas measured and write down results.
- Pour end solution into designated bucket and repeat 2 more times with same measured out solution before moving onto next concentrated solution.
- Work out average of each experiment and use that in the graph.
Safety
To keep myself and others around me the following should be followed:
- Not do this experiment near fire, as Hydrogen is flammable.
- People should wear goggles, as Hydrochloric acid is very acidic and would sting and burn if it were to get into your eyes.
- People should wear lab-coats as they protect your clothes from discolouring when Hydrochloric acid is spilt on them.
- Girls with long hair should tie it back as they may knock something over with their hair or their hair may touch acid.
Results
Experiment 1
Experiment 2
Experiment 3
Experiment 4
Experiment 5
Note: Due to human error, the results for experiment 5 are incorrect. Because of this, I repeated experiment 5.
Experiment 5
I have worked out the averages of each experiment with a calculator to one decimal place. Here are the averages of each experiment:
Conclusions
My results agree with my prediction. When there is a higher concentration, there are more acid particles, therefore there is a higher chance of one of them colliding and reacting with a Magnesium particle. This is why the reaction occurs so fast to begin with. Then, as there are less acid particles and more water, there is less chance of these collisions, so the time taken is longer. This can be seen in the graph.
Evaluation
My experiment all went well apart from the last three readings, in the last experiment. I must have measured the acid out incorrectly or perhaps the magnesium was not exactly 5cm because all the readings were different by a large amount. Because of this human error, I repeated the experiment. I noticed that through the course of the experiments, the readings seem to get higher in value.
If I had more time, I would have done the experiments more times each for a fairer test. I would also use more accurate and new equipment, as the equipment I used has been used many times before and may not measure the reaction rate perfectly.
