What Factors affect the Rate of Reaction between Hydrochloric Acid and Magnesium Ribbon?

What Factors affect the rate of reaction in an experiment involving Hydrochloric Acid and Magnesium Ribbon? Design and carry out an experiment to investigate this.

As the brief suggests this investigation is aimed at finding out about rates of reaction. Before I can go any further there are some things that I already know about rates of reaction that must be included for me to make any predictions and plan what to test in my experiments.

There are four things that affect the rate of reaction between two substances ( usually a liquid and a solid). These four things are: Concentration [of Acid]

and a Catalyst.

I will now explain how each of the previous factors affect the rate of reaction. I know that when the concentration of acid is high - there is a strong solution - then the rate of reaction increases. This is because in say 5 Molar acid there is more acid particles to react and carry out the reaction than in, say, 0.5 Molar acid.

Next, the surface area of the solid substance has an affect of the rate of reaction. I know that when the substance is larger then the rate of reaction will be greater. Therefore I know that a powdered substance will react faster than a solid.

Now, I will look at the effect of heat. I know that when things are heated, the particles within that substance ‘move around’ faster, therefore if you heat the acid the rate of reaction will increase. Sometimes a 10 degree C temp. rise can double the rate of reaction. This is because as the particles ‘move around’ faster the likelihood that they will collide with the solid is increased and ultimately increases the rate of reaction.

 Finally, if a catalyst is added to a reaction, the reaction is speeded up. A catalyst is another substance which is not used up in the reaction and only speeds up the reaction, it does not cause more of the product to be produced.

In my experiments I intend to vary three things. I would like to vary four, but there is no catalyst for the reaction between Hydrochloric Acid and Magnesium, so I cannot. I will vary the length of the Magnesium Ribbon - to test surface area - , the concentration of Hydrochloric Acid, and the temperature of the whole experiment.

I will now make predictions for my experiments. The three variables are Acid Concentration, Surface area and Temperature.

To begin I will predict the outcome when I increase the length of the Magnesium Ribbon. I predict, using my previous knowledge, that when I increase the length from 5cm to 10cm, for example, the time taken to produce enough gas to fill a test tube will decrease from, say, 20 seconds to 10 seconds. Simply, I mean that when the surface area (or length) increases then time taken to fill a test tube decreases. It is my prediction that they are inversely proportional.

Now, turning to the effect of heat, I predict that when the temperature of the acid decreases, the time taken to fill a test tube with gas will increase. For example if it takes 30 seconds to fill that test tube at 15 degrees C, then it will take only 15 seconds at 30 degrees C. Again I predict these two variables are inversely proportional.

Finally, it is my prediction that the concentration of the Hydrochloric Acid is also similar to my previous predictions. I predict that the relationship between concentration and time is similar to that of inverse proportionality but it will not be identical. If I increase the concentration of acid from 2 Molar to 4 Molar then I predict the time will go from 20 seconds to 5 seconds.

I have not included a prediction for the effect of a catalyst as I am unable to test this variable because for the reaction between Hydrochloric Acid and Magnesium, there is no catalyst, as I said previously.

1. Set up apparatus as show on previous page.
2. Fill conical flask with 20ml of 0.5M Hydrochloric Acid.
3. Prepare stopwatch and fill collecting (test) tube with water, ensuring all air is expelled.
4. Add 3cm of Magnesium Ribbon to the flask, place bung in flask, and start stopwatch, QUICKLY!
1. As soon as gas begins to escape from the collecting (test) tube, stop the stopwatch.
1. Record Time.
1. Repeat steps 3 to 6 three times and find an average time.
1. Repeat steps 2 to 7 again for 1M and 2M acid.

9. Repeat steps 2 to 6 again, replacing the 3cm of Magnesium, with 1cm.
10. Repeat reading.
11. Repeat Steps 9 and 10 using 2cm and 3cm of Acid.
12. Again repeat all readings using 1M and 2M Acid.

1. Set up apparatus as shown above.
2. Boil a kettle and fill the water bath with the boiling water.
3. Fill Boiling tube with 20ml of 0.5M Hydrochloric Acid. Fill collecting (test) tube with water ensuring all air is expelled.
4. Wait until the water has cooled to 70 degrees C and then add 3cm of Magnesium Ribbon.
5. Quickly place bung on the boiling tube, and start stopwatch.
6. When the collecting (test) tube is filled with gas stop stopwatch and record results.
7. Repeat steps 3 to 6.
8. Repeat steps 1 to 7 at 60 and 40 degrees C.
9. Repeat steps 1 to 8 using 1M and 2M Hydrochloric Acid.

To ensure that at all time my tests are fair, there are certain measures I must take. In this section I will state and explain these measures.

Firstly, I will always wash out and replace the acid in the conical flask after every test to ensure there is no residue left and my results are as accurate as possible. Also I will repeat all of my results. However, being limited in time I have taken into account that in some cases it is only possible to test twice instead of three times. By testing three times I ensure a balanced spread of results and a set that I can take an average from.

I will keep the length of magnesium ribbon constant in all cases apart from experiment two. Equally I will take the same amount of readings for each different concentration of acid to ensure fair and accurate results.

When measuring the length of magnesium I will double check to make sure I always have the same length of magnesium.

I will now present the results from these previous tests in the form of tables and graphs. I will briefly explain what the results show and then conclude my experiment.

The graphs that follow overleaf are derived from these three tables. All times used for these graphs are averages. I have done this so I can take into account the fact that I may have some freak results and by using the averages I ensure that my results are as fair as possible. Due to the limits of my variables, I can only produce three substantial graphs that can aid me in proving my predictions.

I will now use the information in the previous section to try to prove my predictions, right or wrong. Firstly I must summarise my predictions to remind us of what they were.

I predicted that:

1. Surface area is inversely proportional to the rate of reaction.
1. Temperature is inversely proportional to the rate of reaction.
1. Finally, Concentration of acid is inversely proportional to the rate of reaction.

I want to look now at the effects of surface area, or the length of the Magnesium Ribbon in this case. If we look at Ex2 and the results table for experiment 2, we can see that my prediction seems to be correct, the lines on the graph do appear to follow the pattern of inverse proportionality. However, these results do not conclusively prove that prediction to be true. Although the graphs for 1M and 2M, have a very good likeness to inverse proportionality, the graph for 0.5M does not. This can be seen more clearly on Ex2.1-3, below.

As we can clearly see now, the increasing length of the Magnesium Ribbon causes the time taken to fill a test tube decreases, but they are not inversely proportional. In a perfect world, we could expect the results to be inversely proportional. There are many things that could have affected these results to make them corrupt. For instance I could have tested more times to find a more accurate average, or I could have taken a wider sample using 4, 5 , 6cm, and so on. However lack of time and resources meant this was not possible. Also, on Ex2 and the table we can see that I have estimated the figures for 1cm of ribbon this was because the magnesium was used up before a whole sample had been collected. This makes my results in this section highly unfair and quite unreliable. Having said this I still cannot prove my prediction to be true, but equally it is not untrue, my limits mean that I cannot provide a definite answer. I can merely suggest that there are some aspects of inverse proportionality in these results and without further tests I cannot state categorically that the factors are inversely proportional.

Turning now to the effect of heat. I predicted that heat was inversely proportional to the rate of reaction. If we look at the table for experiment 3 and Ex3 this will help us find if this is true. we can see from the table that without exception when temperature increases, the time taken to fill a test tube decreases. Again however, I cannot say that their relationship is one of inverse proportionality because as the graph (Ex3) shows, only the line for 0.5M actually does show characteristics of inverse proportionality. Having said this, the graph does suggest that overall the relationship is similar to inverse proportionality, but like before I cannot prove conclusively that their relationship is inversely proportional.

Finally, to find out if my prediction about the concentration of acid is true or not, we must look at all three graphs and tables as I varied this every time. Looking at Ex1 we can see that the graph does show trends associated with inverse proportionality, but my further investigations have proved to me that it is not. Similarly, in Ex2 we see that when we increase the concentration of acid, the time dramatically decreases, the same can be said about Ex3. In all cases the trends are not those of inverse proportionality but are very similar to this. As I have said, in a perfect world the results would be inversely proportional, but due to inaccuracies in my testing they are not.

To overcome some of these inaccuracies I could have taken more samples to find more accurate averages, used a wider range of acids, from 0.5M to 10M, I could have varied the temperature more, by packing the experiment in ice or heating to boiling point. Had I done some of these things I could have ensured my results were more accurate, but lack of time and resources prevented this.

I will briefly state again my predictions and state what I have found out about them.

The same can be said about this prediction. My results were of such a manner that I cannot say that the relationship between concentration of acid and time was inversely proportional. This said, I did not actually say that they were going to be exactly inversely proportional, but instead only similar to this. In this respect my original conclusion was correct.