This is the formula for the reaction:
Mg + 2HCl MgCl2 + H2
magnesium hydrochloric acid magnesium chloride hydrogen
There are several factors that could possibly affect the rate of reaction between magnesium and hydrochloric acid. It depends on the surface area of the magnesium used, the mass of the magnesium, the temperature of the hydrochloric acid and the concentration of the hydrochloric acid.
Particles need to collide with enough velocity so that they react. As the temperature is increased the particles move faster; because they have more energy. This means that they are colliding more frequently and more of the collisions have enough velocity to cause a reaction. Since there are more collisions the chemical reaction takes place faster; therefore increasing the rate of reaction.
I will also be expecting the amount off hydrogen given off (within three minutes) to decrease as I increase the concentration of acid. I also predict that all of the experiments within this investigation will gradually slow down towards the end of the three minutes.
Method
Before I begin the main experiment, I am going to perform a smaller preliminary experiment first. In my preliminary work I am going to measure the speed at which gas is produced at three different concentrations molar acid when reacted with 0.1g magnesium. The concentrations that I am going to use will be 2.0, 1.6 and 1.2 molar acid. I am doing this to check that the volume of gas that I have chosen (100cm³) will be sufficient for the experiment.
I will do a mole calculation to work out a suitable volume.
Moles = mass / R.A.M.
= 0.1 / 24
= 0.0041666
volume = moles * 24 000
= 0.00416 * 24 000 = 100
I am going to measure the amount of hydrogen given off by the reaction by using a burette, which will collect the hydrogen, and give an accurate reading as to how much hydrogen has been given off.
This is a list of the apparatus that I am going to use:
- Conical flask
- Measuring cylinder
- Delivery tube
- Plastic tub
- Water
- Magnesium
- Hydrochloric acid
- Stopwatch
- Safety goggles
Here is a diagram of the apparatus hat I am going to use for the experiment:
As with all science experiments, safety precautions need to be used. It is very important that safety is considered as dealing with chemicals in a chemistry lab can cause harm.
Because of this, I am going to ensure that I, along with the rest of my group, are wearing safety goggles during the whole of the experiment, including when we are getting out the apparatus and putting the apparatus away. I shall also make sure that care is taken when handling glass (for example the measuring cylinder) in order to ensure that the glass is not broken. The chemicals shall be cleared away thoroughly and safely.
As well as safety, I must ensure that the test is made as fairly as possible. In order to do this, I shall be keeping the amount of magnesium constant (at 0.1g). In addition to this, I shall be performing all of the experiments at room temperature, so that there is no bias.
Results
Graph
Conclusion
As I expected, hydrogen was given off as a product of the reaction and as the three minutes passed by, more hydrogen was given off. This is shown by the correlation on the graph, which is positive. My other prediction, that as the concentration of acid increased, the amount of hydrogen given off would increase, was, however, incorrect.
However, not all of the results that I have collected from this experiment are sufficient, as they do not follow the same general trend as the rest of the results. The recordings after three minutes for the 1.2, 1.4, 1.6 and 1.8 concentrations of acid (molar) dipped (in the case of the 1.8 recording, it dropped to below the original recording after one minute). These results should have either stayed the same as the two minutes recording or increased (probably increased). This shows that the experiment was not carried out accurately enough.
Evaluation
I felt that overall the investigation for my group went fairly well, though I was disappointed with some of the results, as they did not follow the general trend. As I mentioned in the conclusion, this may be as a result of the experiment not being carried out accurately enough.
There are several possible reasons why some of the results were anomalous. As the magnesium was added to the hydrochloric acid, there was a moment before the bung could be attached, which possibly allowed some hydrogen to escape. To solve this problem, I would have had to use some sort of apparatus that involved using a pre-fixed bung. This would have stopped any hydrogen escaping.
