I chose to investigate how the concentration of hydrochloric acid will effect the reaction, when it is reacted with magnesium ribbon. I decided to investigate concentration because it will be more accurate than over variables available. For example it is easier to change the concentration of the acid accurately, than to try and change the surface area of magnesium because the density and purity of the magnesium might come into play. Changing the concentration will hopefully give me accurate and reliable results from which I can draw up a decent conclusion about the effect that the changing concentration has on the reaction with magnesium ribbon.
Prediction
I predict that a higher concentration reacted with the magnesium will react more quickly and violently than a lower concentration of acid reacted with the magnesium. I think that the concentration will be directly proportional to the rate of reaction. This means that when the amount of concentration increases then so does the speed of the reaction. This was show in my preliminary experiments and also the collision theory state so.
The collision theory deals with the collisions of two molecules. When they collide they cause what we see to be the reaction. We will see the collision between magnesium atoms and hydrochloric acid molecules colliding to forming bonds.
In my investigation I am dealing with concentration. The collision theory states that the higher the concentration of an acid, then the higher the amount of Hcl molecules available in the solution to react with other molecules. Therefore in my experiment the higher the concentration of the hydrochloric acid, the larger the amount of Hcl molecules present to collide and react with the magnesium atoms in the solution.
Method:
Apparatus
For this experiment I will need:
∙ 200ml beaker
∙ Measuring cylinders
∙ Timer
∙ Thermometer
∙ 1 molar hydrochloric acid
∙ Magnesium ribbon
I will use the following concentrations of hydrochloric acid in my experiment: 0.2M, 0.4M, 0.6M, 0.8M and 1M. To create these different concentrations I diluted the 1 molar acid using water.
Table showing the amounts used to make the concentration of acid.
I will be testing all of the concentrations in a series of experiments all the same apart from the variable of the concentration. I will take 25 ml of each solution and one at a time react each one with 5cm of magnesium ribbon.
I will put 25ml of solution into a beaker and will the place the 5cm of magnesium ribbon gently put it into the dilute acid and start the timer.
Once all the magnesium has disappeared I will stop the timer and record. I will then wash out all the equipment I used. Then I will dry the apparatus and start the experiment again with a different concentration. I will repeat my experiments each twice in order to get accurate and similar results
In order to make my investigation fair I must make sure that all apparatus is clean and dried before use. This will eradicate any previous traces of the acid or magnesium. I must also make sure that I set off the timer at exactly the same time as I place the magnesium in to the acid. I also intend to use the same equipment throughout, including the same copper cradle. My concentrations must also be accurate in order to get fair and accurate results, other wise instead of testing 0.8M I ay be testing 0.78M. This will affect my pattern of results and create inconsistency.
Problems
I expected some problems to occur during the experiments, however there was really only one upset. This was the fact that when I tested the 0.2M it was very slow and took a long time. So long that I did not have time to finish the experiment. It took over 50 minutes and was inconclusive. Therefore I decided to test more concentrations of hydrochloric acid to make up for my loss. However I could not test 0.9M, as this would upset any trend in my concentrations, therefore I decided to test extra four concentrations: 0.3M, 0.5M, 0.7M and 0.9M. I now had a collection of eight concentrations. A problem with making these concentrations was that I had to use 50ml of solution to prepare them. Therefore I decided to just half the concentrations I made up to give me 25ml. Below is a table showing the dilutions of extra the concentrations:
I tested these concentrations exactly as I did the others and recorded my results.
I was pleased with this modification as it allowed me to test a wider range of results to give me a clearer picture and more accurate readings.
Results
First set of results
Second set of results:
With my two readings I decided to take the average of them both and then from that I could analyse my results. I added the two times together form each and divided them by two. I also will do this for the temperature change. I will then work out the rate. This will help me discover how the rate of reaction has changed and how it relates to the concentration. To work out the rate I will use the formula 1/time. This will give me rates for each result.
Below is a table of the average results, taken from the two tables above:
Looking at my results it is obvious that the rate increases along with the concentration. As one value increases so does the other. This is exactly what I said in my prediction.
With the results I can now draw a graph showing the rate against concentration.
From my graph I noticed that the line did not pass through all of the points. This is probably because of the inaccuracies in my investigation. For example the concentrations may not have been exactly right, or the timer may have been stopped and started too late or early. My results from the graph are fairly in line and lie on a curve. I am pleased with the shape of my graph, as the results all seem to lie basically inline with each other. As they are on a curve this shows that the rate is proportional to the concentration yet not directly proportional, as my results seem to show. The graph is a curve however the first four pints seem to suggest a steep straight line, which would mean that the rate would be directly proportional to the concentration. However, past the fourth point the graph begins to curve out quickly and fairly smoothly. This could either be from faulty readings or from something else affecting the rate. I think that the fact that this experiment is an exothermic experiment, the heat given off may have altered the results. Looking at the results it began to get a lot hotter past 0.4M, which is where the graph begins to curve. I think that because the particles in the acid are being heated up by the exothermic reaction, they are vibrating a lot more and therefore they will have a greater chance to collide and react with the magnesium atoms. The Hcl molecules and the magnesium atoms are colliding anyway due to the fact that the higher the concentration then the more molecules available to collide with the magnesium atoms. However when the concentration greatens the temperature also seems to become a lot hotter. This shows that the temperature is proportional to the concentration. So, when the Hcl molecules get hotter they will vibrate more, and there are more Hcl molecules in the solution anyway because it is a higher molarity, therefore the likelihood of them colliding with the magnesium atoms is a lot greater.
The same is true for the lower molarities, though in reverse. The lower the concentration then the lower the amount of Hcl molecules there are to react with the magnesium atoms. Therefore, it will take a lot longer for the molecules to find the atoms and eventually react with them.
I think that if I had decided to test a lot higher molarites for example: 1.2(M), 1.4(M), 1.6(M), 1.8(M), and 2(M) then the reactions would have been a lot quicker and more violent. More heat would have been given off and more Hcl molecules would have been available in the concentration. The higher the concentration the higher the amount of molecules there would have been and the hotter they would have got. This would mean they would have collided quicker and more fiercely and the rate of reaction would have increased very quickly. If I had done the opposite end tested smaller molarities for example :0.1(M) the experiment would have taken a very long time, this is because there are not as many molecules available to react in the Hcl and it would have taken a lot longer for the magnesium atoms to find and collide with the Hcl molecules.
Evaluation
From this investigation I think that I have achieved my aim of finding the affect
that surface area of the magnesium ribbon had on the rate of reaction between the hydrochloric acid and magnesium. I think that I obtained enough results to give me a detailed graph and conclusion. I was pleased with my results and were very accurate given the conditions of a classroom.
I am pleased with how my graph formed, from it I can tell that the surface area is proportional to the rate of reaction, as was predicted. There are no major anomolos results which shows that my experiment was carried out with some accuracy.
If I could repeat the experiment I would try to make it more accurate, If possible I would use more accurate and precise equipment. I would have used a ruler with smaller divisions to measure the size of the magnesium ribbon. I would also like to use some kind of machine or incubator to keep the experiment at a constant temperature.
