A change in concentration is a change in the number of particles in a volume. If we increase the volume the particles will collide more because they are crowded.
Factors:
The factors that could affect the rate of reaction are as follows:
Concentration of Acid
This could affect the rate of reaction because the higher that concentration of the acid the more particles there are so there is more collision per second.
Temperature:
If the starting temperature of the acid is different each time then the speed at which the atoms will collide will increase or decrease depending on what the temperature is. This means they atoms will gain more energy and will collide more frequently per second.
Surface Area of Magnesium:
If the magnesium has more surface area then more sides are exposed to the acid this means that the time taken for it to dissolves will speed up.
Type of Acid:
If we changed the acid then the rate of reaction would also change because different acids have different concentrations.
The main factor I have chosen is the concentration of the acid. I have chose this because several different concentrations can me made up for my experiment by the lab technicians.
Diagram:
Method:
Firstly I set all my apparatus up correctly in order to proceed with the experiment. An equation for the reaction:
Magnesium + hydrochloric acid > magnesium chloride + hydrogen
I am going to be using 3 concentrations of hydrochloric acid these are 2 molar, 1 molar and 0.5 molar. I measured the amount of acid in a measuring cylinder then we poured 25cm3 of hydrochloric acid each time to make it a fair test and single piece of magnesium ribbon each time. We placed the saturated test tube full of water in the bowl and measured how much gas was given off every 10 seconds. When we did the experiment we made sure that the stopwatch was started exactly the same time as the magnesium was added to the acid. The reaction ended when the magnesium was dissolved completely. We all wore safety goggles and aprons to protect ourselves from harmful acid. We made sure that we weren’t distracted during the experiment so we could get accurate results.
Results:
The result for the amount of gas produced when magnesium ribbon is dissolved is shown in the tables and graphs below. From my results I can see that the more concentrated hydrochloric acid dissolves the magnesium ribbon quicker than if it was less concentrated. Therefore it supports my prediction and as a result my prediction was correct.
Conclusion:
All together I tested 3 different concentrations. I conclude that if the concentration of the acid is doubled then the amount of gas produced is at least over half if it is not doubled. This is because the ions collide more often in a more concentrated solution. When magnesium was added to the acid it fizzed and hydrogen gas was given off. The solution turned sliver as the magnesium dissolved this is because of magnesium’s physical properties. In the process it is the hydrochloric atoms that need the activation energy because they are the ones that are moving and causing the reaction. They react with the magnesium to form a product called magnesium chloride.
Evaluation:
My method of carrying out the experiment was fairly accurate. This is because I washed out the beakers so they were clean for other concentrations. I measured the same amount of hydrochloric acid each time. I made sure I stopped the stopwatch at the right time. On the other hand it would have been better if I used I new beaker each time so then there wouldn’t be any water left at the bottom of the beaker.
If I was to do the experiment again I would make sure that all the pieces of magnesium ribbon I used were the same size and that I sandpapered the magnesium to make sure it had a clean surface. I would also make sure that the concentration of the acid was exactly what it was supposed to be. I would like to make the magnesium the variable next time and see what would happen if I used different sizes of magnesium ribbon. However I also did an experiment with sodium thiosulphate and I found out that the time taken for the cross to disappear depends on how concentrated the hydrochloric acid is. I say that the acid to water ratio is bigger this means that there is more acid to water and because of this there are more hydrochloric molecules. The colour of the solution also changed in the sodium thiosulphate experiment as they started to react, it turned into a greenish yellowy colour.
Bibliography:
I get hold of most of my information that I needed from my exercise book and from my teacher. I also got hold of some of my information from science textbooks.
