The rate of reaction between magnesium and sulphuric acid.

Amin Bedri

Science Coursework

Rates of Reaction

Investigation: The rate of reaction between magnesium and sulphuric acid.

My Planning

The task that was set to me was to investigate how much gas is produced when magnesium and sulphuric acid react. I am positive that I will find a connection between the concentration of the acid and the amount of gas produced. I am going to record five sets of results, which will be recorded until the reaction becomes dormant. The results will then be interpreted into a graph. This will help show my conclusion by using a scatter graph by plotting the results and drawing a line of best fit.

The reaction between sulphuric acid and the magnesium ribbon, the sulphuric acid will dissolve the magnesium and produce hydrogen gas. All chemical reactions include reactants which when mixed may produce a chemical reaction which will make products. In my experiment the reactants are sulphuric acid and magnesium ribbon. The chemical reaction takes place when the magnesium ribbon is dropped into the sulphuric acid.

The rate of reaction between the magnesium and the sulphuric acid may increase or decrease depending on certain factors. The factors that may determine this are: temperature of the sulphuric acid, mass of the magnesium ribbon used, concentration of the sulphuric acid, surface area of the magnesium ribbon used. Due to the Collision Theory all of these factors will change the rate of reaction.

Scientific Knowledge

"When a chemical reaction occurs, the particles which combine need to meet up with each other (collide) so that they can swap or share electrons. If you want to speed up a reaction, you need to get these particles to hit each other more frequently."

"If the solution is made more concentrated it means there are more particles of reactant knocking about between the water molecules, which make collisions between the important particles more likely." (GCSE Double Science Revision Guide)

How to keep it a Fair Test

In order to keep my experiment a fair test I will have to make sure that I keep the following factors the same: volume of acid used (cubic centimetres), surface area of the magnesium, length of magnesium. I will also have to make sure that the burette is correctly connected and that the cork is placed quickly and tightly enough so that no hydrogen gas escapes. To make sure that all my results are as accurate as possible I will do each experiment two times and then take an average to prevent ...

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How to keep it a Fair Test

My Safety

The safety of this experiment is very important. There are several things that I will need to consider when conducting my experiment. To make it safe for other students around me and myself I need to:

Wear safety goggles as I am using sulphuric acid that can accidentally fall on me and irritate the skin.

Take good care when returning all used glassware and equipment at the end of the experiment.

Make sure I am pre cautious to my eyes and the skin besides all the other people is always vital and necessary.

Care in using glassware since it is sharp when broken and can cut skin. When finished with the acid I will practice safe disposal of reagents and laboratory chemicals.

What I will measure

The following measurements may be used to find the reaction rate for this experiment.

How much calcium carbonate disappears per unit of time

The amount of acid used per unit of time

The amount of hydrogen produced per unit of time.

I am going to collect and measure the amount of hydrogen given off during the reaction at different temperatures. I have chosen this method as it gives the least error and is easy to collect accurately. The amount of water lost in the burette will be used to calculate how much hydrogen has been produced. I will record amount of water left in the burette every 30 seconds.

Variables

In order to carry out a fair test the only variable I will change is the concentration of acid. I will ensure that the following variables are kept constant:

Surface area of the magnesium strip.

Amount of water used in the burette (50 cm3)

The amount of acid and water used to react with the magnesium strip must always add up to 20 cm3

Plan

The experiment will be done using the equipment shown above. The acid will be measured in a measuring cylinder and then put into a conical flask. The water (if necessary) will be measured in the same way and added to the same conical flask as the acid. The burette will hold 50ml of water. I am going to record how the amount of water left the deduct that from 50. I am doing this because this will find out how much hydrogen has been produced. When I have set the burette up in a clamp (see diagram), I will cut a piece of magnesium ribbon to 5cm long. To make sure that all the gas given off is collected, I will ask some-one else to start the stop-watch as soon as the magnesium ribbon is in and the bung to the cork on the top. I will then time for 3 minutes and take a reading of the gas every 30 seconds. I will use six concentrations for this experiment and they will be:

20ml acid : 0ml water
18ml acid : 2ml water
17ml acid : 3ml water
15ml acid : 5ml water
13ml acid : 7ml water
10ml acid : 10ml water

Prediction

I predict that the higher the concentration of the acid, the faster the rate of reaction will be. Also there will be more hydrogen produced with more acid. The amount of hydrogen will decrease in proportion with the amount of acid taken away. I predict this because I know that the higher the concentration of the acid, the greater the numbers of acid molecules present in that volume. This means that there are more acid molecules colliding with the particles on the surface of the reactant (magnesium) which will increase the rate of reaction and the amount of hydrogen.

My Results

20ml of Acid

18ml of Acid: 2ml of Water

17ml of Acid: 3ml Water

15ml of Acid: 5ml of Water

13ml of Acid: 7ml of Water

10ml of Acid: 10ml of Water

Analysing evidence and drawing conclusions

First three graphs were drawn (one for each time the whole experiment was carried out). I can conclude that if you decrease the concentration of the acid by half the amount of hydrogen produced will also decrease by half, this is because the ions are closer together in a concentrated solution. Or if I doubled the concentration the amount of hydrogen produced will also double. The closer together they are, the more often the ions collide. The more often they collide, the higher the chance of a reaction between the magnesium and the sulphuric acid. Also there are more particles in the solution that would increase the possibility that they would collide with the magnesium so the reaction rate would increase. The graph indicates that if you double the concentration the rate of reaction doubles, this proves my prediction correct. If there is an increase in the number of particles in the solution it is more likely that they will collide more often. In the reaction, when the magnesium hit the acid, it fizzed and produced many bubbles it was silver in colour. The activation energy of a particle gets higher with heat, the particles which have to have the activation energy are those particles which are moving. In this case it is the sulphuric acid particles that have to have the activation energy because they are the ones that are moving and bombarding the magnesium particles to produce magnesium chloride. The graphs indicate that the in proportion to the amount of sulphuric acid used, with the reaction with magnesium, it affects the quantity of hydrogen produced. The more acid the more hydrogen.

All the other points are extremely close to the line verifying that my results are precise.

Evaluation

The anomalous results are when 17ml acid and 3ml of water were used. After 30 seconds it dropped from 41.5 to 27.5 but this seems very out of the ordinary to drop so dramatically. This may be due to the fact that I may have not connected the tubes properly or I may not have recorded the results accurately. But over all the experiment I felt went well. The results are reliable and are sufficient to draw my conclusions. But next time to improve my results I would conduct two sets of experiments and make an average out of the two experiments.