The hypothesis of this experiment is that an increase in the concentrations of Magnesium and Hydrochloric acid will increase the rate of reaction which is measured by the amount of hydrogen produced.
Method
Apparatus
Ribbon of Mg 2.0M HCL Stopwatch
25cm³ measuring cylinder 100cm³ flask gas measuring syringe
- Add 40 cm³ of 2.0M HCL to 100cm³flask
- Add 2cm strip of Mg starting the stopwatch immediately
- Attach the gas measuring cylinder to the 100cm³ flask via the stopper
- Measure the gas production at regular specified intervals. (usually around 5s)
The experiment was then repeated, but, the lengths of Mg were increased each subsequent time (2cm, 3cm, 4cm, 5cm and finally 6cm ((see table 1)) after each measurement is taken the HCL must be removed and a fresh amount added to the flask. The data from these experiments was then used to find the initial rate, this data was then used to plot rate against concentration of Mg so as to get the order.
When this data is recorded 4cm of Mg is used with varying concentrations of HCL (at 2M, 1.6M, 1.2M, 0.8M and 0.4M((see table 2)) so as to find the order with respect to the HCL. This was achieved by using 40 cc with the 2M and no water, for the 1.6M 4:1 in favour of the HCL, for the 1.2M it was 24:16, for the 0.8 it is 14:26, and finally 8:42.
Results
Table 1
Table 2
Description of Results
Table 1 shows the levels of Hydrogen produced when differing lengths of Mg ribbon are placed into 2.0M HCL, as the data shows the readings were taken every five seconds.
As hypothesised originally, the table shows a direct correlation between the amounts of Mg placed into the 2.0M HCL and the amount of H2 produced. In the columns for 2cm and 3cm of Mg it can be seen that there is a gradual increase in the amount of Hydrogen produced. Whereas in the columns for 4cm, 5cm and 6cm there is a large increase with the amount of Hydrogen produced even at 5 seconds is double the amount produced with the 2cm and 3cm of Mg.
Table 2 shows the levels of Hydrogen produced when the amount of Mg remains a constant (at 4cm) whilst the concentration of the HCL is diluted as described in the method. The results as shown in table 2 corroborate with the hypothesis also, in that as the level of molarity in the hydrochloric acid decreases so does the amount of hydrogen which is produced. This is shown in table 2 as at 2M the reaction is producing large amount of hydrogen whereas when studying the amounts which are produced from the 1.6, 1.2, 0.8 and 0.4 dilutions you can see massive reductions in the amount of hydrogen produced so much so that when the dilution is at 0.4 there is barely any hydrogen produced at all.
Discussion
The results of the experiments carried out confirm the hypothesis stated in the introduction in that an increase in the concentrations of Magnesium and Hydrochloric acid will increase the rate of reaction which can be measured by the amount of hydrogen produced. This was shown by all of the data gathered in that in table 1 the rates of reactions increased in each case when the amounts of reactants were present, to the point that the results showed that to double the amount of reactant would double the amount of hydrogen produced.
The results shown in table 2 further agree with the hypothesis in that as the concentrations of hydrochloric acid decrease so does the amount of hydrogen which is given off.
The theory that we use to explain how different variables change the rate of reaction is called the collision theory. For a reaction to take place, the particles of the substances that are reacting have to collide. If they collide, with enough energy then they will react. The minimum amount of kinetic energy that two particles need if they are going to react when they collide is called the activation energy.
There are therefore a number of ways of increasing the rate of a reaction, firstly you can increase the number of the particles, or increase the amount of kinetic energy so that more of the collisions lead to reaction (basically increase the temperature to an optimum level). The energy from the reaction will heat up the acid solution. If this effect is too large it could have a marked effect on the rate of reaction. So you need to have a large enough volume of acid solution to make sure that its temperature change is very small.
Also as mentioned previously the size of the particles holds a great significance to the rate at which a reaction can occur, as the smaller the particles the greater their surface area so therefore making it easier for reactions to happen. Another possible method to assist in similar experiments to this would be to use a catalyst, but as this reaction is so strong it wasn’t necessary to get a suitable result.
The experiment carried out is a second order one as for reactions of the 2A → products or A + B → products, the rate of the reaction will be first order with respect to each of the reactants therefore as there are two of them it becomes a second order reaction.
Possible errors that could occur during the experiment were that the reaction itself is exothermic so the rate could increase from this factor alone and as the temperature is difficult to control anomalous readings could be shown from group to group. The size of the magnesium could also cause abnormalities in the results as none-uniform strips of Mg are possible.
One of the most obvious places where error could occur is in the dilutions of the hydrochloric acid in the second part of the experiment as due to the very nature of dilutions it makes it possible for human errors to creep into the results.
To improve on the results I would recommend completing each section of the experiment at least twice and comparing the results of each, or if that wasn’t possible to pool the results of all the groups and take an average of them all. Also it may be prudent to use distilled water for the dilutions, as using water directly from the tap may change the pH to a greater level than is required for the experiment.
Also I believe that the positioning of where the experiment was being carried out would have a direct result on the results found as the intensity of the light is a lot more obviously a lot more intense at the window whereas it is more subdued at the other side of the laboratory.
In conclusion, the results of the experiment clearly concurred with the hypothesis in the introduction in that basically the concentration of the reactants in the experiment has a direct influence on the products given off.
REFERENCES
R. Reed, D. Holmes, J. Weyers & A. Jones,
Practical skills in Biomolecular Sciences……
Addison Wesley Longman Limited 1998
B. Rockett, R Sutton,
Chemistry for Biologists at Advanced Level
John Murray Publishers Limited 2001
www.saskschools.ca
