- A strip of zinc was dipped into the solution and left for 5 minutes. Upon removing the zinc strip a note of the temperature of the solution was taken and the surface of the zinc strip examined, recording any changes that were observed.
- 1g of zinc powder was carefully weighed on balanced scales and transferred to the copper (II) sulphate solution previously used and stirred while a note of the maximum temperature gained was recorded.
- The Mixture was then passed through a filter funnel and paper into a chronicle flask and a comparison of the appearance of the filtrate was made with the colour of the original Copper (II) sulphate solution, this was done against a white background in order to make a fair comparison. The results of the comparison were recorded.
- Using Zinc (II) sulphate solution in place of the Copper (II) sulphate solution and a copper strip instead of the zinc strip the experiment was repeated between steps 1 and 2 and the results recorded as before.
- Magnesium and Aluminium powders were individually placed into beakers of Zinc (II) sulphate solution stirred and the maximum temperature was recorded.
Experimental Observations.
Conclusions.
In order for a deposit to form on the zinc strip and a rise in temperature a reaction must have taken place and this can be shown as;
Zn (s) + CuSo4 (aq) → Cu (s) + ZnSo4 (aq)
Zn (s) + Cu2+ (aq) → Cu (s) + Zn2+ (aq)
Therefore Zn (s) → Zn2+ + 2e- which is an oxidation and Cu2+ (aq) + 2e- → Cu (s) which is a reduction. This reaction accounts also for the temperature rise seen in the experiment with the zinc powder, and once the comparison of the filtrates was noted the results led us to believe that the copper had been reduced which was why there was a slight colour change from the original solution. We could therefore say that the copper (II) ion was responsible for the blue colour in the Copper (II) sulphate solution. The extra temperature rise that was seen between the zinc strip and the zinc powder evidence that the reaction worked better.
The reverse reaction did not take place between the copper strip and the zinc (II) sulphate solution.
The very small temperature change recorded when the magnesium was added to the zinc (II) sulphate solution shows that a Redox reaction has taken place, but not as vigoroursly as the zinc in copper (II) sulphate solution, and this reaction can be show as;
Mg (s) → Mg2+ + 2e- Oxidation and Zn2+ (aq) + 2e- → Zn (s) Reduction
Al (s) → Al2+ + 2e- Oxidation and Zn2+ (aq) + 2e- → Zn (s) Reduction
Questions.
Repeating the experiment ensuring that all the steps of the method are taken with care, accuracy and using thermal insulated test tubes instead of beakers, giving a greater concentration of the solution, would have yielded greater temperature changes in a shorter time, which would ensure as accurate a result as possible.
