- They must be safe to use in this particular environment
- Inexpensive
- Accessible to the school
From these guidelines I have come up with 8 metals:
- Lead
- Iron
- Zinc
- Silver
- Tin
- Aluminium
- Magnesium
- Platinum
Prediction
As I vary the metals,I expect the voltage to change. And I believe the greater the reactivity of the varying metal, the greater the voltage produced will be.
Preliminary results
Using copper as the standard metal in a simple cell:
Fair test
To make this investigation a fair test I will try to keep all the possible variables constant at all times. I will always use the same amount of electrolyte in the same size beaker keeping the concentration the same. The gap between the metals in the beaker will always be the same, as the metals will be pushed to opposite ends of the beaker keeping the same distance. The temperature is something I cannot control but will stay at room temperature and not receive any additional cooling or heating.
However, Icannot control the amount of surface area exposed to the electrolyte, as I must work with the materials provided by school. I also will not be able to keep the purity of the metals the same as we have limited materials to work with, but I will try to remove oxides from the surface of the metal at the beginning of each experiment with some emery paper. For each metal I will take three results and from these I will find an average.This will reduce the margin of error
Table of results for a simple cell using copper as the standard metal
This is a table to show the results of another group
These results are not exactly the same as mine but I did not expect them to be. But they still are similar which shows that we are both on the right track.
Explanation for my results
As you can see the order of metals is similar in voltage and reactivity series, but there are some errors than can be explained: aluminium does not produce its potential voltage because as soon as it comes into contact with air an oxide layer is formed which will affect the voltage produced. The voltage is lowered due to the fact that the surface area is covered in a tarnish, which does not conduct electricity as well as pure platinum. Iron is also out of place as the metal we used was an alloy called steel. This is two metals combined which lowers the voltage produced. Apart from these two errors, which can be explained, my results are fairly accurate which shows that reactivity and voltage produced are linked in some way. Now I believe that it is not the reactivity that creates the voltage but the difference in reactivity between the two metals.
Negative results
These are caused because copper, the standard metal, is more reactive than silver or platinum and the flow of electrons is in the opposite direction causes the reading on the multimeter to be negative.
Order of reactivity series
High reactivity
- Magnesium
- Aluminium
- Zinc
- Iron
- Tin
- Lead
- Silver
- Platinum
Low reactivity
Order of my results measured in volts
High voltage
- magnesium
- Zinc
- Aluminium
- Lead
- Iron
- Tin
- Platinum
- Silver
Low voltage
Evaluation
My experiment produced sufficient evidence for a firm conclusion as I tested 8 metals taking 24 readings. These readings also had a strong pattern which correlated with my predicted results (the reactivity series)
Improving the experiment
The results could be more accurate with more sensitive equipment. Better conditions for the metals to be kept in could be improve results therefore improving the investigation e.g. no oxygen (that may create tarnishes) because this affects the electrical contact between the electrolyte and metal resulting in unreliable results. Taking more results from a bigger variety of metals would strengthen the conclusion. There would need to be a more controlled environment for this experiment to take place as temperature was rising and falling all the time and the metals were not always held in their rightful places.
Irregular results
There were two outstanding/irregular metals, which did not fit in with my prediction about the reactivity series: the first one being iron which produced a lower voltage than expected. This can be explained, as the metal we used was not in fact iron but an alloy of iron and copper. With copper being low in the reactivity series this would have brought the reactivity of steel down to lower than iron. This was not the only problem, which may have affected my results. In addition, there was an oxide layer formed on the surface, which I believe to be iron oxide, commonly known as rust. This would affect the electrical contact between the electrolyte and the pure metal. The metal in question is platinum, which was out of place as it instantly forms tarnish when in contact with oxygen in the air and water, affecting the electric contact and not conducting as well as it should do.
Extending the experiment
I could extend this experiment further with more results such as cu and cu being tested in the same simple cell, or more rare reactive metals. Metals used could also be of higher purity. But the best improvement could be at the other end of the reactivity series. I could use a different electrolyte and see how that affected my results (changing any of the suggested variables in my plan would extend my experiment).
Accuracy of results
Some results will always be more accurate then others as magnesium having an average result of 1.36 is more accurate then silver having an average result of –0.02 this because the result is inaccurate by 0.1 it will have more effect on silver than platinum.
A new prediction
There are two results that have changed my initial prediction significantly, these being the two negative results silver and platinum because these produced a negative voltage. I now believe that it is the difference in reactivity that produces the voltage. Thus, when a highly reactive metal is placed in a simple cell with a low reactive metal, it produces the biggest voltage. Therefore the bigger the difference in reactivity, the bigger the voltage produced will be.
