Alloyed forms of magnesium have considerable tensile strength. The metal is used when lightness is an essential factor: alloyed with aluminium or copper, it is used extensively in making castings for airplane parts; in artificial limbs, vacuum cleaners, and optical instruments; and in such products as skis, wheelbarrows, lawn mowers, and outdoor furniture. The unalloyed metal is used in photographic flash powders, incendiary bombs, and signal flares; as a deoxidiser in the casting of metals; and as a getter, a substance that achieves final evacuation in vacuum tubes.
The estimated world production of magnesium in 1989 was 350,000 metric tons. The estimated United States production in the same year was 148,000 metric tons.
When magnesium is heated it reacts with the oxygen that is in the air around it, the magnesium changes from an element to a compound and new ionic bonds are formed between magnesium and oxygen atoms. The new compound is called magnesium oxide and is a white powder; the mass of the magnesium oxide is greater than that of the magnesium. We want to investigate this reaction; the purpose of our investigation is to find out the relationship between the mass of magnesium heated and the mass of oxygen, which has reacted with it. The reaction we will see is between magnesium and oxygen in order to produce magnesium oxide we then want to find a formula for this reaction.
Collision Theory
The faster the reaction, more particles move. The following things affect the rates of reaction:
- Effects of temperature
- Effects of concentration
- Effects of surface area
- Effects of a catalyst
- Effects of stirring
Safe Test
Before I carry out this experiment I must make sure it is safe.The main points of safety are:
- Wear safety goggles at ALL times.
- Wear an apron.
- Wear gloves.
- Put bags and chairs/stools out of the way or under a desk.
- Clear desks of all items which are not required for the experiment.
- Have a designated person to handle the chemicals.
- Always walk carefully around the classroom.
- Be careful whilst handling glass.
- If you have a problem, ASK THE TEACHER.
Fair Test
I must make sure that this experiment is fair because I want to get all of my results as accurate as possible.
The thing that I will be keeping the same is:-
- The length of the magnesium strips (4cm)
The thing I will vary is:-
- The concentration of the hydrochloric acid
Apparatus
Variables
Independent > Concentration of Hydrochloric acid
Controlled > Temperature, surface area of the magnesium and the time
Dependant > Rate of reaction
Prediction
I predict that the higher the concentration of hydrochloric acid the quicker the rate of reaction.
This is because the more concentrated a solution is, the more particles it has. The reaction speeds up due to there being more particles; this is because of the “Collision Theory”. The more particles there are the more frequently the particles collide, thus speeding up the reaction.
As the solution is diluted the number of particles decrease. These particles then collide less frequently causing the reaction to slow down.
Preliminary Work
So I could eliminate any mistakes I encountered I did some preliminary work. I carried out an experiment to find out how concentration affects the rate of reaction of magnesium and hydrochloric acid. Hopefully due to this I can alter anything that seems wrong.
Carrying out the experiment I am going to experiment with different concentrations of hydrochloric acid to get more of a pattern in the results.
The formula for my experiment is:
Mg(s) + 2HCl2(aq) → MgCl2(aq) + H2(g)
The word equation is:
Magnesium + Hydrochloric Acid → Magnesium Chloride + Hydrogen
There is nothing I want to change for my proper experiment. The only thing I need to make sure I do to make it a fair test is to remember to keep an eye on the stopwatch. I need to use the same stopwatch so as I know for certain that the time is the same rate. This will make sure it is a fair test. An accurate stopwatch should be used that records tenths and hundredths of seconds, this will ensure better and more accurate data.
Method
Choose which concentration to start with: 25ml Hydrochloric Acid - 0ml Water
- Measure 25ml of Hydrochloric acid into a measuring cylinder
- Pour this into a test tube
- Cut 4cm of Magnesium ribbon
- Drop Magnesium into acid whilst simultaneously starting the stopwatch
- Watch the experiment closely, when the Magnesium disappears stop the watch
- Record results in a table, repeat this three times so you can compare the results, reducing the risk of any anomalies.
From carrying out preliminary work I discovered that when carrying out the experiment with other concentrations I’ll make sure to mix the acid and water together when it is in the test tube, I’ll make sure to do this for all of them to make it a fair test, also shake before the magnesium is added.
Diagram of experiment
Because my experiment is only testing the time magnesium takes to disappear I am not required to measure the volume of the end product of the reaction, hydrogen, this means the end point of the experiment is when the magnesium disappears
Results
Experiment 1:-
Experiment 2:-
Experiment 3:-
Concentration of acid = Volume of acid *2 = x moles
Total volume of solution
1) Concentration of acid = 25 *2 = 2 moles
25
2) Concentration of acid = 20 *2 = 1.6 moles
25
3) Concentration of acid = 15 *2 = 1.2 moles
25
4) Concentration of acid = 10 *2 = 0.8 moles
25
5) Concentration of acid = 5 *2 = 0.6 moles
25
Analysis
As I repeated each experiment three times I had a fair collection of results and with them the times varied quite a bit. Predominantly in most cases the time increases like it should as the concentration as the of the solution decreases, I know this because of the Collision Theory. The higher the concentration the more particles there are to collide more frequently thus speeding up the reaction time.
But, as an example, in the experiments for the highest concentration (25ml acid, 0ml water) the first time I got was 49.58s, then the third time I carried out the experiment I got 115.36 which is over a minute’s difference. This shows that something is wrong, but on the other hand in the second experiment I got 59.10s which is nearly half way between both results. But it’s closer to the first result which means I must have done something wrong on the third attempt. Looking at the other results from other tests I can see there is no greater difference than the first experiment and I presume the problem is something simple like not washing out a test tube. The test tube may have had a bit of water in it and it could have given an unfair advantage.
To make the results look more simple I produced an average set of results, with these averages I was able to plot it on a graph, if my other results turned out perfectly they would make a smooth curve where I put my line of best fit. Looking at my graph it looks fine apart from a slight hitch at 1.6 moles, this result could be anomalous. But it could be the experiment with 1.6 moles and the one with 2moles. I think this because the way the curve goes it looks as though from 1.2 moles it should go down lower and then slightly higher than it already is at 2 moles. However when I look at the averages in my table it seems just right, it could be that my graph isn’t right.
From this I can draw a conclusion that my average for 2 moles was too quick, it looks like my time for the second experiment for 2 moles dragged the average up. It could be that I put too much acid in and not looked closely enough at the measuring cylinder.
From my results table and graph I can conclude that my prediction was correct. As the concentration increases the speed of the reaction also increases. This is due to the “Collision Theory”, there are more particles in solutions that are more concentrated. This then means there are more particles for the magnesium to collide with. The reaction the magnesium had with 2 moles was a much quicker reaction than 0.4 moles because it’s colliding with more particles because the concentration of the acid is greater.
Evaluation
Looking at my results table I believe that my results aren’t as reliable and accurate as they could be. This is because if my results were better the times where I have repeated them would be closer together. If I had three times that were closer together it would show me they were more reliable. This is because they would be proving the result is quite accurate. The more times you repeat an experiment the more evidence you have got to prove your prediction.
However I think most of my results are reliable, I think this because looking at my graph the results produce a nice curve apart from the kink at 1.6 moles which is my one big anomaly. I believe that mistake crept in with one of my group either not looking at the stopwatch for that set of results properly or someone didn’t read the measuring cylinder properly.
If I were to do this experiment again there are a few improvements I would make:-
- Make the magnesium strips shorter so the reactions wouldn’t take so long, because there wouldn’t be as much magnesium the acid needs to react with. This could mean more time to get more results to get more evidence to back up your opinions.
- By doing this it would also mean that my times might be more accurate because the timekeeper wouldn’t get distracted, and would concentrate on the experiment seeing exactly when the magnesium disappears.
- I would also use a more accurate measuring cylinder. Although the one I used was quite accurate, I may get even better results if I were to use amore accurate cylinder, as I did say it could’ve been a possibility why I got an anomaly was because that someone didn’t read off the measuring cylinder properly. I could use a pipette, as these are a lot more accurate as they measure smaller quantities.
To extend my investigation I could investigate other factors that affect the rate at which the magnesium reacts with acid I could investigate:-
This would also be linked to the “Collision Theory”. Giving more heat/energy to particles makes them move around more quickly, thus the particles collide more frequently.
This is also linked to the “Collision Theory”, the more surface area there is the more particles there are to collide. Thus they collide more frequently to speed up the reaction.
