The rate of reaction can also be defined, by using the collision theory. A collision theory explains how chemical reactions take place and why rates of reaction alter. For a reaction to occur the reactant, particles must collide.
I am going to investigate how the concentration of hydrochloric acid alters the rate of reaction. As I increase the amount of water, I reduce the concentration of the hydrochloric acid. The chemical reaction is shown in the equation, above. This equation shows that a displacement reaction has taken place.
I predict that if I decrease the concentration of hydrochloric acid, the rate of reaction will also decrease. I believe this because; if I decrease the hydrochloric acid in the same 'fixed volume' then the acid particles are less crowded. This means that there is a lesser chance of acid particles colliding with magnesium particles. There are fewer collisions in a certain time and so the rate of reaction decreases.
Below is a list of apparatus and chemicals that I am going to use. The list includes equipment to carry out precise measurements for the different chemicals that I will be using. The list below shows that I will need:
Hydrochloric acid
Tap water
Magnesium strip (3cm)
Safety goggles
2 measuring cylinders (50mls)
Ruler
Scissors
Stop watch
1 beaker (100mls)
Method
Using a ruler and scissors cut out 7 pieces of magnesium ribbon exactly 3cm in length.
With one measuring cylinder measure out the amount of hydrochloric acid needed and pour it into the beaker.
With the other measuring cylinder measure out the amount of water you need and add to the hydrochloric acid in the beaker.
The hydrochloric acid and the water the water together should be exactly 50mls in volume.
Drop one piece of magnesium ribbon 3cm in length into the solution in the beaker and start the stop watch immediately don’t forget to wear safety goggles.
When all the magnesium has dissolved, stop the stop watch and record the time.
Wash all the measuring cylinders and beakers before you do another test.
To make sure that the test is fair I will have to make sure that other factors don’t change like:
The length of the magnesium strip will be kept at 3cm. It is important to make sure that each strip of magnesium is the same length and width, as the greater surface area will cause a faster reaction as there are more particles to collide with.
The temperature of the acid and the water will be kept at room temperature. Making sure the reactions happen at the same temperature is important because if the temperature changes the rate of reaction will change. At higher temperatures the particles would move faster causing the particles to collide with each other more often and with more energy.
The total volume of hydrochloric acid and water will be fixed at 50mls. I need to make sure that the same volume for the different concentrations, otherwise I will not know the change in concentration accurately.
In conclusion, from my results gathered from my table and graph, my initial prediction was correct, the higher the concentration of the hydrochloric acid, the faster the reaction. I tried to make the experiment as fair as possible but I could change a couple of things that could have improved my results, like using a burette for greater accuracy when measuring volumes have solution to two decimal places, also to have achieved even greater results I should have repeated the experiment at least three times and then taken the average because then I could ignore any odd results I did get. The curve on my graph means that it is indirectly proportional because if it was a straight line it would have been directly proportional which means the rate of reaction would have doubled every time but mine didn’t and I was surprised to find that, unlike what I thought it would be, the rate of reaction did not double, triple etc, even if the concentration of acid in moles doubled e.g. 2.0m took 19.64 seconds whilst 1.0m (half the amount) took 72.29 seconds.
As I stated above, I believe my experiment was done fairly but changes could have been made. I could have recorded more of the rates of reaction so that my results were more accurate. I believe there was a set pattern all through my results showing that as the concentration of acid is increased, the rate of reaction also increased. However, I believe that, even bearing these small problems in mind, the experiment was done thoroughly and successfully. Other methods which I could have conducted, which would have helped me support my conclusion, included: Measuring the temperature of the reactions as it happens. Measurements could be taken, for example, every 30 seconds. These results will then be plotted on to a line graph, with each different mole having different coloured line; this will give a clear indication to each concentration. These results will tell us how fast the reaction is happening and how each one differs from the next. Also the time of the reaction would be recorded in line with each temperature taken, e.g. 30sec = 10c, 60sec = 12c, and so on.
Alex Welham 11T
