PREDICTION:-
I predict that as the distance between the electrodes increases, the amount of current flowing will decrease. I think this because the further that the electrodes are apart the greater the resistance will be between them, making it more difficult for the current to pass. This theory is justified by looking at the formula; current = voltage ÷ resistance. The physics rule, ‘the longer the length of wire, the greater the resistance’, can be applied to the path of the current when passing through the electrolyte. As the distance between the two electrodes increases, the resistance also increases making it more difficult for the current to get around the circuit.
I predict that as the depth of the electrode in the dilute acid increases, so will the current flowing. I think this because there will be a greater surface area submerged in the dilute acid, on which ion neutralisation can occur. Ion neutralisation occurs on the surface of the electrode.
Negative ions (anions) are attracted to the anode (positive electrode). Here, theygive up the extra electrons to form neutral atoms. In the example of sodium chloride, the chloride ions give up electrons and bubbles off:
2Cl- → Cl2 + 2e-
Positive ions (cations) are attracted to the cathode (negative electrode). Here the ions accept electrons and become neutral atoms. Again, using sodium chloride as an example, the hydrogen atoms accept the electrons and so bubbles off:
2H+ + 2e- → H2
Therefore, more current will flow as the surface area of the electrode submerged in the dilute acid increases as there will be a larger area on which the charged atoms (ions) can be neutralised.
I also predict that as the current flow increases, so will the amount of oxygen and hydrogen omitted from the experiment. Faraday’s First Law of Electrolysis states that: ‘The amount of substance liberated in electrolysis is proportional to the current flow.’ Therefore, as the distance between the electrodes increases, the amount of oxygen and hydrogen given off will decrease because the current flow will go down. As the depth of the electrode in the dilute acid increases, so will the amount of hydrogen and oxygen liberated because the current will be going up.
RESULTS:-
- Investigating the affect of varying the distance between electrodes:
- Investigating the affect of varying the depth of the electrode in dilute acid:
ANALYSIS OF RESULTS:-
Distance Between Electrodes
From looking at the graph produced from these results, I can conclude that as the distance between the electrodes increase, the current flow decreases. I think that this is because of an increase in resistance as the electrodes are moved further apart. These results support my prediction because as the distance between the electrodes increases, the flow of current decreases. This is because the further apart that the electrodes are moved, the more resistance is formed making it more difficult for current to flow. This can be proved by using the formula: current = voltage ÷ resistance. The voltage was kept constant throughout the experiment at 4V, therefore as the resistance increased every time that the electrodes were moved further apart, the current would get smaller.
Depth of Electrodes
From looking at the graph produced from these results, I can conclude that as the depth of the electrode submerged in the dilute acid increased, so did the current flow. I think that this happened that there was a greater surface on which ion neutralisation could occur. When the electrodes were only submerged for 10mm, there was not a lot of space on which ion neutralisation could occur and therefore completing the current flow. However, when the electrodes were submerged 60mm, the current flow increased considerably as there was a large surface area on which ion neutralisation can occur.
At the cathode hydrogen gas bubbles off. This is because the hydrogen ions accept four electrons from the cathode and the neutral hydrogen atoms that are produced bubble off:
4H+ + 4e- → 2H2
At the anode, oxygen and water are formed. This is because the hydroxide ions (OH-) give up their electrons more readily than the sulphate ions (SO42-). The oxygen bubble off and the sulphate ions remain in the solution:
4OH- → 2H20 + 02 + 4e-
The overall result is that the water is broken up, rather than the acid:
water → hydrogen + oxygen
2H2O (l) → 2H2 (g) + O2 (g)
EVALUATION:-
I think that my experiment was very good because I carried out each experiment twice and the results produced were very similar. Also, both sets of results produced graphs with a very smooth curve.
There was a very small margin of error when investigating the distance between electrodes as the distance was preset. However, I had to make sure when reading the ammeter that the electrodes were upright. The fact that the distances were preset meant that when the experiment was repeated the second time, I was able to use exactly the same distancing to ensure accurate results.
I found it difficult to submerge the electrodes to the exact depth but I think that by doing each experiment twice and taking the average I have reduced the margin of error from this. When investigation the depth of the electrode I found one slightly anomalous result on my second attempt at a depth of 50mm. I think that this could be because I did not submerge the electrode far enough into the dilute acid because the result gave a smaller current than expected and did not fit in with the curve produced by the rest of the results. However, by averaging the results and ignoring this point when drawing the line of best fit, I think that an accurate graph was produced to represent the data.
I think that my results are very conclusive and support my prediction well. I feel that my conclusion is reliable because my graph produced a smooth curve and the repeat results for each experiment were similar. The results that I received followed my prediction. There is no doubt from my results that as the distance between the electrodes increases, the current flow decreases. Also, as the depth of the electrode submerged in the dilute acid increases, so does the current flow.
In order to improve the accuracy of my experiments there are various things that I could do. When carrying out the electrode depth experiment, I would use a clamp when submerging the electrodes to ensure that the electrodes were held still in the dilute acid. This would ensure that the electrodes were held at the exact correct depth when reading the ammeter. It would also ensure that the electrodes were held the exact same distance apart as from the first experiment, one can see that this is another factor that affects current flow. I also think that by extending the ranges for both of the experiments, i.e. extending distance between electrodes to 100mm the extending the submerged depth of the electrodes to 100mm, this would ensure that a wide enough range was covered to be sure about the shape of the graph as I would get a lot more readings. This could also be used to determine whether or not the graphs will eventually level off.
Zilia D’Mello Page Chemistry Coursework