I have decided to change the variable of concentration as I thought this was the easiest of the four variables to do. Using a catalyst would not have been appropriate because I do not think the results would have been so effective. I would have found temperature hard to do as there are not enough water baths available in school and I did not want to use a Bunsen Burner as it would have be hard to get the acid to an exact temperature. Finally I would have found surface area hard to do as it would have been difficult to cut the exact size pieces of Magnesium.
Prediction
My prediction for this experiment is that when we increase the concentration of the Sulphuric Acid, the rate of reaction will increase. This is due to more acid particles being in a specific places, so this leaves more chance of more successful collisions between the two sets of particles.
I think that if there is 50cm3 of acid and no water that will react quicker than when there is 20cm3 acid and 30cm3 water.
Fair Test
To keep the experiment a fair test we must keep a lot of things the same. Below is a list of things that we will be doing to keep the experiment a fair test.
- Use the same length of magnesium measured by centre metres.
- Keep the temperature of the acid the same for all experiments.
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The total of Acid and Water will always be at a total of 50cm3.
- We will not stir the mixture
- We will always use the same acid at the same strength (molar)
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The room temperature should be the same. (Our room temperature was 19oC).
- We wont be using a catalyst for any of the reactions.
- One thing that we will be changing is the concentration of the Acid and Water used in the mixture, as this is the variable that we have chosen.
Preliminary Work
These are the results that we got for our preliminary work.
These results are for 1 molar Sulphuric Acid
These results are for 2 Molar Acid
The results of our preliminary work above were to try and find out what length of Magnesium strips to use would be most appropriate and also to find out what molar acid to use (1 or 2 molar). We found out that using 3cm length Magnesium strips are best because they are not too quick during reaction and that you cant measure them in time, and aren’t too slow and that they take too long to record in 1 lessons time. We also found out that 2 molar acid is better to use than 1 molar acid. The 2 molar is better because the 1 molar acid will take to long to react with the Magnesium.
Apparatus
The list below is all the apparatus we used:
2 Molar Sulphuric Acid (H2SO4)
A Stopwatch
100cm3 Beaker
10 strips of 3cm Magnesium
50cm3 measuring cylinder
Water
Safety Glasses
Method
- First of all we need to collect all the apparatus from the apparatus list and put on the safety glasses.
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Measure out the desired amount of acid and water required for the certain concentration that you are doing into the 50cm3 measuring cylinder. For example I will talk about 50cm3 and no water.
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Now pour the acid into a 100cm3 beaker. Next put the 3cm Magnesium strip in to the acid and as soon as the reaction starts, start the stopwatch.
- When the Magnesium stops reacting, stop the stopwatch and take the reading to the nearest second and record on to results table.
- Now repeat the experiment with all the different concentrations. The concentrations are below.
- Now repeat the experiment all over again in the same manner to make sure that the results were accurate and no mistakes were made.
Accuracy
We have decided to use a 50cm3 measuring cylinder to measure the water and acid because it is best to use the lowest possible measuring cylinder. If we used a 100cm3 cylinder then it might not be as accurate. We always measure to the nearest second because our human reactions are not quick enough to be exact with the stopwatch and the result may not be very accurate, so measuring to the nearest second is more accurate. To measure the length of the Magnesium we used a ruler and cut the magnesium with scissors as we thought this was the most accurate way. We made sure that the measuring cylinder was on a flat surface and that we look eye level on. If you are not on eye level with the certain point, then you will not get an accurate measurement because of the parallax of the top of the liquid. When there is a liquid in a tube the upper surface is curved so we always measure the lowest measurement of the liquid.
Sometimes when we do experiments we can make mistakes, and you may end up with some anomalous results, so we repeat the whole experiment again, once we have done it the first time.
Results
Here are our results from the 1st and 2nd experiments.
1st Experiment
2nd Experiment
I have also drawn out a scatter graph to show the results.
This is a table to show the results averaged out between the two experiments.
Conclusion
In my experiment I found out that when you increase the concentration, the rate of reaction is higher. We can prove this from our results because 50cm3 acid and no water reacts quicker than when there is only 10cm3 acid and 40cm3 water. When the concentration is higher, there are more particles in one space. This means that there are going to be more successful collisions. The faster that the particles collide, there is more chance that the collisions will be more successful. This means that the reaction will finish a lot quicker than an experiment with a lower concentration.
Evaluation
I think our experiment was very well done and our results were very accurate. We were sure that our results were accurate as we repeated the experiment twice and we got roughly the same results twice. Between the two sets of results there was only about 2-3 seconds difference between them. We also had no anomalous results, which shows our results were accurate and this is also shown on the scatter graph.
One slight problem we had was when one of the members working in our group spilt some acid on the table and on his book.
Overall I think the experiment was very successful and if we were to do the experiment again then we could maybe collect some of the gas produces to make sure if it is hydrogen by collecting some of the gas and doing the pop test. Also we could have done the experiment for a 3rd time just to make certain that our results are successful and accurate.
As I predicted, the higher the concentration the quicker the reaction rate.