· voltage
· the area of the two electrodes
· the concentration of a salt solution
· the distance between the anode and the cathode
I chose to change the concentration of salt in a salt solution as the input variable. This means that the outcome variable that would change would be the current flowing through the circuit and hence, the resistance of the salt solution when a new concentration is introduced. I will range the amount of salt in the solution from 1M to 0.8M to 0.6M etc until it reaches 0.2M. 100ml of solution will be used. Each reading will be taken 5 times so an average can be found and accurate results are taken. Also, in order to keep it a fair test, the input voltage, the area of the electrodes and the distance between the two electrodes will remain the same throughout the entire experiment. Other variables that may have some affect will be kept the same too if possible such as temperature etc. using a voltmeter and an ammeter to find the current and the voltage I will use the following formula to work out the resistance of the salt solution at each different concentration:
Ohm’s law states that R = V
I
Method
A beaker was filled with 100ml of a range of different concentrations of salt solutions. Two electrodes were attached to the minus and positive terminals of a low voltage power unit. An ammeter was wired in series and a voltmeter in parallel to measure the current and the voltage of the circuit could be measured, this could then lead to the resistance being calculated. The power setting on the low voltage unit was not changed throughout the whole experiment or it would not have been a fair test. The equipment was set up as in the diagram below.
The current and the voltage were recorded in a table, and the results are shown below.
Analysis
From the graph I can see that my prediction was correct. As the concentration increased the resistance decreased. The results make a smooth curve, but there is one result that may be anonymous. It was the 0.6M result. It is circled in green on the graph. From the graph I can conclude that a solution with a low salt concentration has a high resistance, whereas a solution with a high salt concentration has a low resistance.
Evaluation
I believe that the experiment was fairly accurate. Care was taken to ensure that the correct amount of solution was added into the beaker, and that the electrodes were in the same positions in the electrolyte so that an equal was in contact with the electrolyte. There was 1 anonymous result, which was different to the others. It is circled in green on the graph. I repeated each reading 5 times, to ensure that a reliable result was recorded. This could have been increased to produce an even more reliable result. The results on the graph show a smooth curve.
