The Rate of Reaction between Hydrochloric Acid and Magnesium when the Concentration of Acid is changed.

The reaction between hydrochloric acid and magnesium will produce hydrogen gas, and the magnesium will dissolve.

Chemical reactions involve reactants, which when mixed, can produce a chemical reaction. The chemical reaction will take place when the magnesium is dropped into the hydrochloric acid. The products, which will be formed in the reaction, are magnesium chloride and hydrogen (gas).

The formula for this is

Mg (s)+ 2HCL (aq) ------- MgCL2 (aq) + H2

Magnesium + Hydrochloric Acid ----- Magnesium Chloride + Hydrogen

The magnesium will react with the Hydrochloric acid, as it is higher in the reactivity series than hydrogen. Anything lower in the series than hydrogen will not react with hydrochloric acid, gold for example would not have a reaction with the acid.

There are certain factors that will make the rate of the reaction change.

For example:

Temperature of the Acid
Mass of Magnesium
Concentration of Acid

The collision theory is why these factors will change the rate. The collision theory states that for a chemical reaction to take place, the reacting particles must collide with eachother, with enough energy to break, or form new bonds between other particles – a successful collision.

If you increase the temperature that the reaction takes place, (heating up the reactants) it will speed up the reaction. For most reactions a 1o degrees increase will double the speed of the reaction. The particles collide more frequently and have more energy.

If you increase the concentration of the reactants the solution will have more particles of the reactants moving around in it, meaning it is more likely they will collide and cause a reaction.

I have decided to change the concentration of the acid, to see how it affects the rate. I will keep the temperature ...

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If you increase the concentration of the reactants the solution will have more particles of the reactants moving around in it, meaning it is more likely they will collide and cause a reaction.

I have decided to change the concentration of the acid, to see how it affects the rate. I will keep the temperature the same, (although it may change as the reaction takes place) and the mass of magnesium. To change the concentration, I will use water and add more each time, keeping the amount of acid the same.

I will place the magnesium into a glass beaker with the hydrochloric acid and water and time it until the magnesium dissolves.

If I did not keep the amount of magnesium the same, then it would not be a fair test, as the bigger the surface area, the more the acid has to collide with so there will be a bigger reaction or smaller each time.

If I were to change the type of acid I am using, then there would be a different reaction each time, for example, Sulphuric and Nitric acid would produce different reactions to hydrochloric acid.

I predict that the higher the concentration if acid then the higher the rate of the reaction will be. I think there will be more collisions per second if the acid is more concentrated.

Method:

I will drop a decided amount of magnesium into a solution of hydrochloric acid mixed with different amounts of water each time. I will record with a stopwatch, how long it takes each time for the magnesium to dissolve. I will repeat the test twice.

To keep my experiment a fair test I will do the following things:

Keep the volume of acid the same each time.
Change the water by five milliliters ONLY each time.
Keep the length of the magnesium the same each time.

To keep the experiment safe I shall:

Wear safety goggles.
Be careful to not spill the acid.
Be careful with the glass I use, as it is easily broken.

I think that the one factor I will find hard to keep the same is the temperature of the experiment. This is because the temperature rises when a reaction takes place. Unfortunately there is not really a way to keep the temperature down.

Preliminary Tests:

During these tests, I discovered that if you use more water than acid in the experiment, with a large piece of magnesium, it will take a very long time, as the acid is not concentrated enough. So, I have decided to use a shorter piece of magnesium, and start with 30 cm 3 of acid. This will be a good measurement. Each time, I will add 5ml of water, up to 50 ml, so there will be 10 results overall.

Diagram:

Results Table:

GRAPH:

On the next page.

Conclusion:

My graph and results show me, that the more concentrated a solution, the more likely a reaction will take place and at a faster rate. As I increased the water and the acid got more diluted, the magnesium did not give off as much hydrogen gas, and it also took longer to dissolve into the water.

I cannot seem to find a relationship between my results and I feel disappointed, as I think I should have. The results on the graph seem quite anomalous, as they are not in line. I would have expected that as the concentration is doubled, the rate should half, but it has not worked.

I think this has something to do with the way the experiment was set up. I think I should have used a different method of finding out the time, like collecting the hydrogen gas for example, which would have been more accurate. I think that next time I would definately try to make it a fairer test and think of all the ways it could be achieved and carry them out, as the way I did it was quite careless.

I think I should have carried the test out more times, to get some more results, to make sure what I was doing was correct. I do not really think my results make sense, which is something I should look into and try to discover what changes, if any, I could do to make it work better and to receive a better set of results.

Bibliography: I obtained most of my information from my textbook and my teacher.

Petrina Fitzgerald 10JF