Investigating the factors that affect the conductance of a solution

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Investigating the factors that affect the conductance of different solutions

Introduction

Just as metallic conductors have a resistance when a current is passed through them so do ionic solutions. However, when dealing with solution it is more convenient to look at its conductance, G, rather than its resistance and is simply the reciprocal of the resistance, R. The unit of measurement is siemens,Ω-1 G=1/R. We can also work the conductance from knowing the current and the voltage G=I/V.

The ability of a solution to conduce electricity is due to the dissociation of the compounds presence into its constituent ions. Theses ions play the same role, in solutions, as electrons do in metallic conductors, they transport the electric charge from one electrode to the other.

Aim

To investigate how certain factors affect the conductance of a solution.

The factors I have considered investigating, that may have an affect on the conductances of a solution are:

  • different concentrations of the solution (0.5M, 1M, 1.5M, 2M, 2.5M & 3M)
  • the temperature of the solution (ranging between 20°C to 90°C)
  • different solutions (Sodium Chloride& Sulphuric Acid)
  • different electrodes (Carbon & Copper)

Summary

In this investigation I analysed certain factors that I thought might affect the conductance of a solution i.e. concentration, temperature, different solutions, different electrodes. Before carrying out my actual experiment I carried out a trial to see whether they’re any areas for improvement. After inputting the improvements I carried the actual experiment. Once the results were obtained I used graphical techniques to present the data.

My results for all the factors showed a definite trend, which were easy to provide simple superficial explanations for. However underneath lay a much more complex relationship between the individual factors and conductance, which were far more intricate then I had imagined at the on set of the investigation

At the end of the investigation I felt that this was a very worthwhile and extremely interesting topic. Before conducting this investigation I knew very little about this field of physics but after doing the research and carrying out the experiments I have learned a much greater insight to the workings of conductance.

Method

Different concentrations

To begin with it was essential that all concentrations of solutions used in the experiment were uncontaminated since this would immediately make the results of the experiment invalid. First collect the required apparatus and set it up as shown in diagram 1. Then measure 50ml of 0.5M sodium chloride solutions in a beaker using a measuring cylinder. Then place the graphite electrodes into the solution and connect it up to the circuit using crocodile clips. After that switch the power pack on and take the readings from the ammeter and the voltmeter. Repeat the process three times in order to take an average reading. Then carry out the experiment for the different concentrations i.e. 1M, 1.5M, 2M, 2.5M & 3M. Once you finish the experiment with carbon electrodes, and then repeat the experiments again but this time alter the electrode and use copper electrode instead of carbon electrode.

 Now do the experiment again but this time with sulphuric acid. Making sure all the process is repeated.

Modifications to experimental method following trial.

In my trial I used a d.c current. This altered my experiment results because I found that using a d.c. Current caused chlorine gas to be given off, identifiable from the smell. This happened because the electrodes were producing their own voltage, so electrolysis was taking place. This also meant the concentration of the solution would have changed. These could have caused a large inaccuracy in my results.

Improvement- Instead of using d.c use a.c current. By using an a.c current electrolysis is avoided because the ions are constantly flowing in alternating directions so do not get time to form at either electrode.

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Before carrying out the actual experiment I improved my method by altering the problems found during the trial.

Temperature     

Again make sure that all concentrations of solutions used in the experiment are uncontaminated since this would immediately make the results of the experiment invalid. Then set up the apparatus as shown on diagram 2. Then measure 50 ml of sodium chloride into the beaker. Place the digital thermometer into the solution then Heat the solution using the Bunsen burner. Remove the heat and place the electrodes into the solution. Afterwards switch the power pack ...

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