An Investigation Into The Effect Of An Electric Current On Copper Sulphate Solution

Chemistry Coursework 2002

Alice Boagey 10JS – Mr Martin

Aim

In this experiment my aim is to enforce and develop ideas about the investigation into the effect of an electrical current through copper sulphate solution.

Safety

Electricity is dangerous
Aware of coppers sharp edges
Long hair tied back
Use of acids in experiment

Diagram

1) Weigh the cathode

2) Set up apparatus below

3) After a minute, remove the copper and shake off the excess copper sulphate solution. Wipe the copper with acetone and waft in the air to remove as much of the solution as possible.

4) Weigh the cathode again and record results. Repeat this procedure for the other currents.

The anode does not need to be changed

Prediction

I predict that as you increase the voltage the mass of the cathode will increase. However much the cathode increases in mass the anode will increase in mass proportionately. I also think that the change in mass will be directly proportional to the charge giving a straight line that passes through the origin.

Justification Of Prediction

I think the increase of voltage will result in the increased mass of the cathode. This is because the higher the voltage, the more electrons are ‘pulled’ off the anode therefore more can be deposited onto the cathode resulting in a higher mass. Theoretically as you double the voltage the mass should double giving us a graph, which goes through the origin. Using the equation Cu² - 2eˉ → Cu (s) we know that 1 mole of copper ions requires 2 moles of electrons to produce 1 mole of copper metal. We can also use the equation to predict how much copper should be deposited. The formula is:

½ x I x T

95600

Next I will show a results table of predicted results, based on the formulas I have given. This will be useful when I have my actual results as I can compare these to what the ideal results should be, and then evaluate whether I have valid results.

Theoretical Results Table

Time / s Current / I Charge / c ...

This is a preview of the whole essay

½ x I x T

95600

Theoretical Results Table

Time / s Current / I Charge / c Av. Mass Deposited / g ½ x (IxT / 96500x64)

60 0.5 30 0.007 0.010

60 0.6 36 0.013 0.012

60 0.7 42 0.021 0.014

60 0.8 48 0.027 0.016

60 0.9 54 0.024 0.018

60 1.0 60 0.032 0.020

Actual Results Table

Time / s Current / I Charge / c Av. Mass Deposited / g ½ x (IxT / 96500x64)

60 0.5

60 0.6

60 0.7

60 0.8

60 0.9

60 1.0

Analysis

By using the equation, ‘Cu² - 2eˉ → Cu (s)’ and the formula Q = I x T / 95600 we can work out how much copper should have been deposited. Once we have found out the charge (Q) we divide it by 2. This is because you have 2 moles of electrons to 1 mole of copper. This is proven by the equation ‘ moles = mass / R.A.M (relative atomic mass).’ The ratio of this being 2:1 as the moles of electrons equals out to be half of the moles in the outcome of copper deposited, proved by the formula, ‘ moles of electrons = Q / 95600.’ We find these formulas from the first formula I gave: ‘Cu² - 2eˉ → Cu (s)’.

The graph shows a relationship between charge and the mass deposited. As the charge increases, more electrons are removed from the anode. This enables more copper ions to move across to the cathode and therefore be deposited, increasing the mass. The graph shows that in our experiment the mass increased far higher from 42 coulombs and onwards than expected. Also I had predicted the mass to be directly proportional to the increase of charge, but this did not happen. We can find our mistakes by looking through the procedure. I think that when we were drying the cathode, we accidentally left some of the copper sulphate present, which added to the mass when weighed.

Evaluation

Our experiment gave us 10 results, which were averaged down to 5 points to plot on the graph and evaluate from. The results we collected were not as we had expected and in places fell quite a way from the line. I have circled the points I feel to be anomalous, and I will now explain how I perceive we found them. I think that my odd results were due to human error. It is the last two results I believe to be odd, which may explain something. I think it was the last two results that were wrong as it was towards the end of the experiment that we had less time, and therefore weren’t as careful drying the copper as we could have been. To make the results more reliable I would have liked to weigh the anode each time, and compare it to the weight of the cathode to make sure if the loss was equal to the gain. I think that bigger cathodes would gain accuracy, and also making sure that the cathode and anode stayed the same distance away from each other throughout the experiment. If I could explore this experiment more thoroughly I would investigate a greater range of currents and voltages. Also different concentrations of copper sulphate solution.