I will adjust the concentration and still keep the volume the same (50ml) by adding water to the solution.
This goes as follows:
I will collect my equipment and set it up as shown in the diagram. I will then measure out the sulphuric acid and water according to the concentration I am testing, and them pour them into a beaker.
I will measure a 2cm piece of magnesium and put it into the solution. Immediately after I have put the magnesium into the solution I will place the gas syringe into the funnel of the beaker. This will show the amount of hydrogen given off so I can see if there is any relationship between the concentration and the amount hydrogen given off. I predict that the higher the concentration the more gas will be given off.
I will time the reaction until it stops bubbling and I will test all the different concentrations and repeat each test three times.
To ensure that my testing is fair I will only alter the independent variable, which is the concentration of sulphuric acid. I will also record the time the reaction lasts. This is called the dependent variable as it depends on the concentrations I test.
It is important to keep all the control variables the same in order to keep my investigation as reliable as possible.
This will include:
- Measuring precisely the volume of sulphuric acid, water and the length of the magnesium, which will be 2cm.
- Using the same beaker for the reaction to happen in.
- Using all the magnesium off the same roll.
- Washing the beaker between each test to stop concentrations being imprecise.
- Making sure the sulphuric acid is the same temperature in all the tests (room temperature). I will use a thermometer to make sure. High temperatures of sulphuric acid would increase the rate of reaction.
Equipment
Beaker (with measurements written on it)
Gas syringe
Sulphuric acid
Water
Thermometer
Magnesium
Ruler
Stopwatch
Safety Precautions
- Wear goggles and an apron and tie up long hair
- Make sure nothing obstructs the ends of the gas syringe
- Move stools under desks
- If there is a acid spillage mop it up straight away
- Try to refrain from getting acid on hands if however this does happen wash it off with water straight away
To measure precisely I intend to check the length of the magnesium with a ruler. I also intend to use a stopwatch to time each test. Data will be recorded on a table which I will have prepared before I start the investigation. I will record the time and the amount of hydrogen collected in the gas syringe.
I will average my results and then I will be able to determine to what extent the concentration will affect the rate of reaction.
Results Tables
Experiment 1
Experiment 2
Experiment 3
The rate of reaction is calculated by:
Total volume of Hydrogen (Cm³)
=
Total time for reaction to finish (Seconds)
Results
In this experiment I have collected enough results to support my predictions. I have repeated the experiment three times, and I have calculated the average rate of reaction for each experiment. I also have an overall rate of reaction for each of the experiments, as I have taken an average reading, by adding results from experiment 1, 2 and 3 and dividing the total by 3.
My results appear to be as I predicted if I look at the average rate of reaction. I can see from all three tables that the average rate of reaction is higher, when there is a higher ratio of sulphuric acid to water.
Using experiment 1 as an example it is evident from my table of results that 19cm³ of hydrogen is given off in just 31 seconds at a concentration of 50 cm³ of sulphuric acid. When compared with 10 cm³ of sulphuric acid this gives a greater volume of hydrogen, which is 25cm³ but it takes 660 seconds or 11 minutes to obtain this amount of gas.
In experiment 3 my results are exactly as I predicted, showing a steady decline in the rate of reaction as the volume of sulphuric acid is decreased and the volume of water is increased.
Experiment 2 follows this general trend however I would of expected 40cm³ of sulphuric acid to give a higher average rate of reaction than 30cm³ of sulphuric acid. However the difference between the two is fairly insignificant as it is only 0.01 cm³ of hydrogen per second.
In experiment 1 I think that my result for 40cm³ of sulphuric acid is anomalous because it is half the volume of hydrogen per second when compared to 30cm³ of sulphuric acid. I would have expected these two results to be the other way round.
From my knowledge of particles and the collision theory there are not so many acid particles or H+ ions in more of a dilute concentration of acid. Therefore there is much less chance of acid particles colliding with a magnesium atom. Conversely concentrated solutions of sulphuric acid contain many more particles so there is more chance of collisions occurring. The more successful collisions there are the more quickly the reaction.
My averages for the average rate of reaction in all three experiments are broadly inline with my predictions apart from 30cm³ and 40 cm³ of sulphuric acid. Again the difference between the two is not very significant at 0.03 cm³ of hydrogen per second.
My graph clearly shows an anomalous result at a concentration of 40cm³. I would have expected it to follow the trend and produce about 0.5 to 0.6 cm³ of hydrogen. However my graph also shows that my predictions were correct for the rest of the results that I have collected. The higher the concentration of sulphuric acid the higher the amount of hydrogen being produced each second.
I think that measuring the volume of hydrogen produced every 30 seconds or every 1 minute could have developed my investigation further. This would of allowed me to establish the point when the reaction between the magnesium and sulphuric acid was slowing down and ultimately stopping. I would of also been able to produce a line graph to show this information clearly. From my results I am unable to see the variations in the hydrogen production over time. I am only able to establish the volume of gas which is produced on average every second.
I would expect that the rate of reaction is quickest in the first few minutes when all the collisions between sulphuric acid and magnesium take place. This is because at the start of the reaction there are plenty of magnesium and sulphuric acid particles, which would soon get used up. After time there are fewer magnesium atoms and the sulphuric acid is less concentration so the reaction slows down.
During my experimental observations I noticed that my 2cm strip of magnesium always completely reacted with all concentrations of sulphuric acid. I would be interested to find out if I added more magnesium whether I could produce more hydrogen. I think that the lack of magnesium could have limited the reaction. Rather than all the acid being used up I would try two x two centimetre strips of magnesium ribbon if I was to do this investigation again.
I think that my reaction would have been quicker if I had removed the oxide layer from the surface of the magnesium ribbon before carrying out my experiment. Magnesium is a very reactive metal high up in the reactivity series. It will react with oxygen when exposed to the air.
To develop my investigation further I would consider investigating the effects of other variables on the rate of reaction. These would be as follows:
- I would try magnesium powder as appose to magnesium ribbon to establish the effects of surface area on the rate of reaction. I would anticipate that a larger surface area would make more magnesium atoms available and therefore increase the rate of reaction.
- The effects of temperature could also be explored by heating one concentration of sulphuric acid to a range of different temperatures. I would expect that many more collisions between magnesium atoms and sulphuric acid particles would take place at high temperatures. This is because the particles move faster and have more energy so collide more frequently.
- Finally I would add a catalyst, which is usually a transition metal. This will make the rate of reaction quicker but it wont chemically change itself. When a catalyst is added a collision between magnesium atoms and sulphuric acid particles need less energy to be successful.
Overall I think that my investigation provided evidence to show the average rate of reaction between magnesium and sulphuric acid. My results broadly support my predictions but I think that I need more evidence of the rates of reaction at t9imed intervals for each experiment. This would then enable me to see how long it would take for the maximum volume of hydrogen to be produced before the reaction declines.