The length of wire, amount of ammonium chloride, voltmeter settings and the surface area of metal in sodium chloride solution did not be changed in the practice. I also tried to keep the METAL A and B the same distance apart.
Prediction
Electricity can be produced when two strips of different metal is dipped into a solution
a spontaneous reaction will takes place. The more reactive metal will lose electrons and the less reactive metal will gain the electrons in order to become neutral. Chemical reactions that proceed by transfer of electrons from one species to another by called oxidation - reduction (REDOX) reactions. The substance that is losing electrons is said to be oxidized and the substance gaining electrons is reduced. The reaction between metal A(more reactive) and metal B(less reactive) may be written as:
A → Ax+ + 2 e
Bx+ + 2 e → B
This reaction will force the electrons to move around the circuit producing a current and voltage; the best electron donor will produce highest voltage with the least reactive metal. Therefore it can be predicted that the further away the two metals in the reactivity series the more voltage they will produce, hence the order of reactivity can be worked out using the voltage produced when a metal is used with another constant type of metal (e.g. Zinc with copper and Lead with copper).
The out come of my result should match the real reactivity series in the order below:
Safety:
- Goggles must be worn to prevent chemicals get into eyes.
- Lead is poisonous, wash hands thoroughly after the experiment.
- Try to avoid in contact with ammonium chloride solution.
Result Table
Analysis:
From the results table it generally showed that less reactive metals (metals below Zinc) are positive and more reactive metals are negative. The highest voltage produced is by the metals Magnesium and Copper, this meant that out of the two metals one of them is the most reactive and the other most unreactive.
The graph showed that the different voltages produced by a metal with copper. The amount of voltage produced can be used to identify the reactivity of metals, the higher voltage the metals produced the further away from copper in the reactivity series, therefore it is possible to decide how reactive the metal is, since copper is the least reactive. In the order of the reactivity in metals, the graph produced a result very similar to the theoretical one.
From my experiment my result produced a reactivity list in the following order (from most reactive to least reactive):
Magnesium
Zinc
Aluminium
Lead
Nickel
Tin
Copper
Evaluation
Theoretically the second most reactive metal should be aluminium, however from my result it shown that aluminium produces the least amount of voltage amongst the negative metals. Is this an ‘error’ of my experiment?
From other experiment results collected, the same ‘error’ is found. After some research, I have identified that the aluminium we used is already reacted with the oxygen in the air and formed a thin layer of aluminium oxide; this ‘coat’ prevents the pure aluminium in contact with ammonium chloride thus the result did not match with the theoretical prediction.
The positions for ‘Lead’, ‘Nickel’ and ‘Tin’ in the reactivity series is very hard to define, because they have such close voltage values in the experiment that a digital voltmeter will be required instead of an analogue one to work out the exact value of reactivity. Also other manmade errors (e.g. two metals being tested at a variable contact area with the solution) may be taken into account.
Overall, my experiment was successful. By checking the reference book it proved that, generally metals above zinc is negative and below zinc is positive. The most reactive and least reactive metal will also produce the most voltage in an electrochemical cell. Therefore metals can be put into an order by measuring which metals can produce the higher voltage by comparing whether if it is a good electron donor.
In order to improve the accuracy of the experiment and produce a firmer conclusion next time, I would use a digital voltmeter and a fixed position for the metals in the solution. Also I would change the amount of ammonium chloride solution to find out whether it affects my result.
Reference:
http://www.micrecol.de/elecE6.html
Encarta Encyclopaedia
Shelnet- electrochemistry
