Investigate the effect of the amount of sodium chloride, i.e. concentration gradient, in the aqueous solution on the electric current during electrolysis.

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When an electric current passes through sodium chloride solution, chemical reactions take place at both cathode and anode. If one passes through sodium chloride solution, there will be passage of ions moving through this solution. This results in positively charged sodium ions, which have been dissolved into the solution, moving towards the cathode and deposited there. At the same time, negatively charged chloride ions will be moving towards the anode and discharged at the anode. This is called electrolysis.

Aim of experiment

My aim is to investigate the effect of the amount of sodium chloride, i.e. concentration gradient, in the aqueous solution on the electric current during electrolysis.

Key Factors/ variables that affect the results of the experiment

The experiment carried out aimed to monitor the current during electrolysis when the amount of sodium chloride was changed. To ensure a fair test, only one of the listed key variables is allowed to change at a time with the rest of the variables are kept constant.”

This will give me an accurate set of results, which, I hope, enables me to make a decent conclusion. If we do not control the factors apart from the concentration we are testing, you can turn around and say that it was the other factors that had caused the difference and that it had nothing to do with the concentration. By keeping the factors controlled and equal, you can prove it is the concentration.

The following factors/variables must be controlled or monitored during the experiment:

  1. Temperature
  2. Quantity of solution
  3. Voltage
  4. Size of electrodes
  5. Distance between electrodes
  6. Surface on the electrodes
  7. Distilled water

I plan to finish the experiment in one day, so the temperature won’t change drastically and use a stop-clock to maintain the time duration for applying voltage to 10s. By using a volumetric flask and pipette, I can measure and control the quantity of solution for each test batch more accurately. To make it fair, I will keep the voltage the same at 5V all throughout the experiment. I will use a variable voltage power pack to control the voltage at a certain setting during the experiment. I will use fresh new electrodes from the same pack and use the same electrode holder to fix the electrodes so the electrodes’ distance and size won’t change significantly. Finally, tap water contains magnesium and other impurities, therefore I will use distilled water throughout the experiment.

Apparatus and Materials

  1. Electrode holder
  2. scale
  3. crocodile clip
  4. graphite rods
  5. volumetric flask
  6. pipettes 50ml/ holder
  7. beakers
  8. 4 wires
  9. filter
  10. voltmeter
  11. variable voltage power pack
  12. access to distilled water
  13. access to NaCl
  14. electric supply
  15. marker pens
  16. spatula


First, I checked in the textbook and found that the maximum amount of salt can dissolve in 1000ml water is 360g at room temperature.

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Also, from my preliminary work, I found that the current and voltage for solution with10g NaCl is:

And the current and voltage for solution with 30g NaCl is:

Therefore, I decided to use batches of solution with 5g, 10g, 15g, 20g and 30g NaCl.

I have to clear the desk first, so I can have more room to do the experiment. I will also check if the apparatus I am going to use are clean, to prevent contamination. I will dissolve the 5 different measures of NaCl into 100ml of water ...

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