The more reactive the metal, the stronger the bonds it will make to the sulphate anions, and the more energy will be released when the metal forms those bonds. Thus energy given out by the reaction is proportional to the bond strength.
In a reaction such as Copper Sulphate and Zinc, the Zinc is more reactive than the Copper. As a result, it acts a bit like a bully, demanding that the Copper give it the Sulphate ions. Energy is needed to break the bonds between the Copper ions and the Sulphate ions. When the Zinc bonds to the Sulphate ions, energy is given out. The more Zinc that is there, the more ‘demanding' it is because every Zinc ion wants to bond with a Sulphate ion and so they are competing with each other as well as with the Copper.
Safety
Before we can even begin, utmost precautions must be taken when it comes to safety. We will ensure that all things that aren’t absolutely necessary are cleared of the bench and placed underneath it, so as to ensure that no one can trip over them. Shirts will be tucked in to prevent any mishaps, and we will be wearing safety goggles, to prevent anything from getting in our eyes. Throughout the entire investigation we will be standing up, to make sure that if there is any major problem on the bench, we will be in a position to do something about it. We will also have to take precautions when it comes to a metal like magnesium. Since it can react with water on skin, we must make sure that it does not come into contact with any part of our body.
Fair Test
To make sure that my experiment is a fair test I have to take certain things in account.
The controlled variables:
One of the most important variables that I have to control is how much of each metal I need to use. We must use the same amount of metal each time. However, this does not mean that I must use the same number of grams of each metal, I must use the same number of moles of each metal. We have 0.2 molar Copper Sulphate Solution.
We are lucky that all the metals we have been given to investigate will form 2+ ions in solution. We are also lucky that the SO4 anions have a charge of 2-. This means that when we form equations they will all have molar reacting ratios of 1:1.
X(s)+ Cu2+(aq)SO42-(aq) X2+(aq)SO42-(aq) + Cu(s)
Where ‘X’ is one of the three metals.
And if X does not react with Copper Sulphate Solution, then we will have:
X(s)+ Cu2+(aq)SO42-(aq) à X(s)+ Cu2+(aq)SO42-(aq)
Either way the reacting ratios will still be 1:1.
So 1 mole of X will react with 1 mole of Copper Sulphate solution. To make sure the test is fair, we must use the same number of moles of each metal we test.
But, there is a problem we have to deal with first. It will be impossible to put in exactly the right amount of metal to react with the Copper Sulphate solution. If we add too much metal than some of that metal will not react with the Copper Sulphate. So we must add Copper Sulphate solution in excess, so all the metal reacts. To make sure that the Copper Sulphate is in excess I will work out how much of each metal will react with 20cm3 of Copper Sulphate solution.
We can find the number of moles of metal needed to react with 20cm3 of solution by doing the following:
Finding how many moles of Copper Sulphate there are in 20cm3 of 0.2 molar solution.
MAGNESIUM ZINC IRON
0.02 x 24 = 0.48g 0.02 x 65 = 1.3g 0.02 x 56 = 1.12g
To make sure that all the copper gets displaced I will use 10% excess. Therefore I will use the following amounts of metals:
MAGNESIUM = 0.53g ZINC = 1.43g IRON = 1.23g
There are other factors we must take into consideration when we do our investigation. For instance, temperature. The temperature of the room in which we do the investigation must remain constant. This does not appear to be much of a problem as the temperature of the lab is controlled by the air conditioner. So we can be assured that temperature of the room will not be an issue. Another issue is the temperature of the copper sulphate solution. This too, will not be an issue, because the Copper Sulphate Solution is left out in the lab, and so will have the same temperature as the room, whose temperature is controlled by the air conditioner.
Another precaution we will have to take is with the container we do the reactions in. We will ensure that before we repeat each test, we will wash out the container.
One other precaution I must take is to make sure that all the heat is kept in the container. There is no point in doing the test if what I want to measure (heat or temperature rise) just dissipates. As a precaution against this I have decided to use expanded polystyrene cups with lids. This is because expanded polystyrene cups are very good insulators and are excellent at keeping heat in. Also I have decided to shake the cup so the metal is effectively mixed with the copper sulphate. This will make my readings fairer.
The independent variable:
The variable we must change is that of which metal we will test. We have three metals; iron, magnesium and zinc.
The dependent variable:
The dependant variable will be temperature. We will measure the rise in temperature.
Equipment
- Polystyrene cup and lid
-
Copper Sulphate Solution (9 x 20cm3)
- Measuring Cylinder
- Metal in powder form
Magnesium = 0.53g x 3
Zinc = 1.43g x 3
Iron = 1.23g x 3
- Spatula
- Plastic Weighing Boats
- Top Pan balance
Method
- I will measure 20ml of 1M Copper Sulphate Solution and then transfer it to the polystyrene cups.
- I will then insert the thermometer through the lid and cover the cup with the lid.
- I will measure the temperature and take it down as my starting temperature.
- I will then weigh out 1.23g of Iron (powder form).
- Now I will add the iron filings carefully to the Copper Sulphate Solution and promptly cover the cup with the lid and insert the thermometer.
- When the temperature becomes stable I will write that temperature down as my finishing temperature.
- I will repeat this two more times for Iron so I can get a fair average.
- I will repeat this with Magnesium and Zinc. I will use 0.53g of Magnesium and repeat the experiment three times. I will use 1.43g of Zinc and repeat the experiment three times.
This is what my tables for recording results will look like:
Results
While I was doing my experiment I noticed that the changes that occur when the metals are placed in Copper Sulphate is not just temperature, I say this as I saw colour change and Copper atoms deposited. But as we are not investigating these I did not record any results for them.
The following will show the results I got when I constructed my experiment:
Analysis
Look below to see a bar chart on the temperature change:
Iron’s temperature change was 4.3 degrees Celsius on average.
Zinc’s temperature change was 41.7 degrees Celsius on average.
Magnesium’s temperature change was 61.6 degrees Celsius on average.
Please look on the next page to see a line graph on the temperature change.
My bar chart and line graph clearly show that Magnesium has the biggest temperature change when compared to the other two metals (Zinc and Iron). To be exact Magnesium’s temperature change was 61.6 degrees Celsius on average, Zinc’s temperature change was 41.7 degrees Celsius on average and finally Iron’s temperature change was 4.3 degrees Celsius on average. From this I can state that temperature change is linked with metal reactivity. When I say this I mean that the higher the metal in the reactivity series the higher the temperature change when immersed in Copper Sulphate (a salt solution). This means that my aim can be fulfilled as I have investigated displacement reactions to find out the order of reactivity of some metals. The order of reactivity series I have found as a result of investigating displacement reactions is as follows:
Magnesium
Zinc
Iron
My prediction stated that my reactivity series would look like the one above (Magnesium, Zinc and then Iron) and that I believe that the most energy will be released by Magnesium. My results support my original prediction as due to my results I did produce the reactivity series I stated I would get in my prediction.
In my prediction I also stated that Magnesium will have the most vigorous reaction and the temperature change for this metal will be the most. Zinc will have a vigorous reaction with the solution but it will not be as vigorous as the reaction Magnesium will have. Iron will have the least vigorous reaction, as it is closest to Copper in the reactivity series (when compared with Zinc and Magnesium). Therefore the displacement reaction will occur between Iron and the Copper Sulphate solution but it will not be as significant as the displacement reaction Zinc and Magnesium will have with the Copper Sulphate solution. From what I observed these predictions are correct. My results also supported my original prediction as the most energy was released by Magnesium. I can say this as I used the formula Q = CM T to find out the energy that was released by each metal. I got the following results:
Energy exchanged between reactants and surroundings = Specific heat x mass x temp
capacity of the of the change
solution solution
Q/J C/J g-1k-1 m/g T/K
Q = 4.18J cm-3 k-1 x Volume cm3 x temp change/K
MAGNESIUM
Q = 4.18J cm-3 k-1 x 20 cm3 x 61.6 = 5149.76
ZINC = 1.43g
Q = 4.18J cm-3 k-1 x 20 cm3 x 41.7 = 3486.12
IRON = 1.23g
Q = 4.18J cm-3 k-1 x 20 cm3 x 4.3 = 359.48
As you can see from the last page Magnesium has the highest energy exchanged between reactants and the surroundings when compared to both Zinc and Iron. Therefore I can state that my prediction was correct as the most energy was released by Magnesium when compared with Zinc and Iron.
Look below to see a bar chart showing the energy exchanged between the three metals reactants and surroundings:
On the next page you will see a line graph showing the energy exchanged between the three metals reactants and surroundings.
Evaluation
In my experiment I encountered no problems. Even though I checked my results by repeating my results three times I still think that I should have repeated the experiments at least six times to get a better average. I obtained similar results when I repeated them, this in my opinion confirms that my results are reliable. If I were to repeat the whole experiment, in the light of my experience, I would try to improve it by maybe measuring the volumes of liquids more accurately by using a pipette, burette or syringe instead of a measuring cylinder and by using other metals e.g. Aluminium and Lead. I hope that if I received the chance to improve my experiment I would be able to provide additional evidence for the conclusion. Another way of finding what I found could have been done by measuring the Copper deposited, therefore if I were to do the experiment again I will measure the temperature change and the amount of Copper deposited and I would hope that this would give me a more firm conclusion. I also think that my results were reliable, as I got no anomalous results. I think my procedure was suitable as I did receive reliable results. My evidence was also sufficient enough to support a firm conclusion, my conclusion was that the higher the metal in the reactivity series the higher the temperature change will be when the metal is immersed into a salt solution such as Copper Sulphate.