Paper will be cut in the following lengths to be tested:
5cm, 10cm, 15cm, 20cm, 25cm, 30cm.
It will be a fair test as I am using a constant voltage, keeping the paper horizontal so the solution is spread evenly, and also cleaning the bull-dog clips with glass paper before each set of results. As well as this, both the width and the thickness of the paper will remain constant.
I am taking readings from 4 voltage sets so as to get an average and make the results fair.
Prediction
During the experiment, electrolysis will be taking place. Electrolysis is the passage of electricity through an
electrolyte in liquid form. An electrolyte is a compound which, in solution or in molten state, conducts electric current and is simultaneously decomposed by it – electrolytes can be acids, bases or salts and can be dissolved in a polar solvent such as water. During the electrolysis of the brine water, the current is not carried by electrons, as in metals, but by ions. The saline solution (sodium chloride dissolved in the polar solvent water) will be ionised into electrically charged ions, and when an electric current is passed through them by means of conducting electrodes (in this case bull-dog clips), they give up their electric charges and become uncharged atoms. These atoms or groups are either liberated or deposited on the electrode, or react chemically with the electrode (making rust on the bull-dog clips).
Due to electrolysis, during the experiment the sodium ions will be attracted to the cathode as they are positively charged and the cathode is negative (opposite charges attract each other). The chloride ions will be attracted to the anode as they are negatively charged and the anode is positive. When the sodium ions come into contact with at the cathode they gain electrons which make the outer shell of the atom eight and they stabilise. When the chloride ions converge at the anode their extra atom is taken away which makes their outer shell also stabilise. This means that the two substances in sodium chloride will be split.
Due to my previous work using copper wire to measure resistance, I found that the longer the wire, the proportionally larger the resistance is.
For this experiment - I think that as the length increases, the resistance will also increase proportionately.
Experiment
Here are the results I collected:
The graph shows that length is directly proportional to resistance, which is what I had previously predicted. This means that as length increases, resistance also increases at the same rate.
Extension
I am going to extend the experiment by determining how paper width and concentration of brine solution effect resitance.
Width:
The experiment will be the same, except that the length will remain a constant, while the width will become the variable. I am using 1,2,3,4 and 5cm width measurements to test this.
Due to my previous work using copper wire to measure resistance, I found that the thicker the wire, the proportionally smaller the resistance is.
For this experiment - I predict that as the width increases the resistance will decrease inversely.
Here are the results I collected:
The graph shows that width decreases inversely to resistance, which is what I had previously predicted. This means that as width increases, resistance decreases at a faster rate.
Concentration:
The experiment will be the same, except that the width will remain a constant, while the concentration of the brine solution will become the variable. I am going to use 0.05, 0.1, 0.2, 0.3, 0.4, 0.5M solutions to test it.
Due to my previous work using copper wire to measure resistance, I found that the denser the wire, the proportionally smaller the resistance is.
For this experiment - I predict that as the concentration increases the resistance will decrease inversely.
Here are the results I collected:
The graph shows that resistance decreases inversely to concentration, which is what I had previously predicted. This means that as concentration increases, resistance decreases at a faster rate.
Conclusion
From the graphs I have plotted, I can see that:-
• Length is directly proportional to resistance
• 1/width is directly proportional to resistance
• 1/concentration is directly proportional to resistance
From this information, I can see each one is directly proportional as it is a straight-line graph, for example – as one value increases, so does the other by the same relative amount.
Length increases the number of ‘jumps’ the ions make, therefore making the resistance rise.
As the width increases, so ‘the the path is wider’ resistance is less as more current is able to flow through the paper at the same time – it produces a curve. 1/width compared to resistance gives a straight line.
If the concentration is higher then more current is able to flow due to the little amount of space between each atom. 1/concentration compared to resistance gives a straight line.
These agree with my predictions, although I did not predict 1/width and 1/concentration.
From these results, I can safely assume that:
Width X Thickness = Area ➔ Resistance is directly proportional to 1/area.
Using a constant to simplify and using a combination of rules I can say that:-
Resistance = Constant X Length ➔ R = C L
Area A
I after researching what I could about electricity, I found that this equation was similar to that of resistivity. Resistivity is measured in ohm meters and is a constant value for a given material; the resistance of a unit length of the material per unit cross-sectional area. I can re-arrange the above equation so I can calculate resistivity:
R A = p l ➔ R A = P ➔ P = R A
L L
Evaluation
Most of my points were on or very close to the line of best fit, and so my results were reliable and demonstrate the connection between the variables we were testing. We could have used lower voltages using more sensitive equipment – to minimise the electrolysis taking place and could have collected more results although this would not have been worthwhile due to the minor accuracy advantage.
We did our experiments over a period of days so a temperature change could have occurred, but the effect of this is negligible. The stock solution used for the brine may not have been the same and may have differed (also to a negligible effect) slightly due to evaporation.
For extension work, I would try and find an equation that would allow me to acquire readings without the practical experiment.
