Investigate the factors that effect the current flowing during the electrolysis of an aqueous solution of sodium chloride.

EQUIPMENT

  In this experiment, I will use:

• an electrode holder
•  a power pack
•  an ammeter
•  two carbon electrodes
• a glass rod
• a set of electronic scales
• a 500-CL beaker
• two crocodile clips
• a thermometer
• two splints

DIAGRAM

METHOD

• I will set up my equipment as the diagram shows.

• I will pour 500-cl of distilled water into a 500-cl beaker.
• I will weigh 5 grams of sodium chloride on a set of scales.
• I will then dissolve the 5 grams of sodium chloride into the beaker containing water. I will do this by stirring the solution with a glass rod.
• I will balance the electrode holder by using two splints, on the rim of the beaker
• I will measure each electrode with a ruler to make sure that each is dipping into the solution by 10 cm.
• I will set the power pack at 7 volts.
• I will then note the current showing on the ammeter.

• I will then add another 5 grams to the solution and repeat the experiment.
• I will continue to add 5 grams to the solution until I have dissolved 25 grams in my beaker.

• I will then repeat the experiment three times.

• Throughouut this experiment I will use the thermometer to make sure that the temperature of my solution stays constant.

SAFETY

To ensure a safe test, throughout, the experiment I will wear safety goggles and a overall. As I am aware that chlorine gas, which is toxic and an acid is being produced as a result of this experiment. I have not planned to use vast quantities of sodium chloride in this experiment, as that would result in more chlorine gas being produced.

PRELIMINARIES

To make sure that the equipment I used would ensure accurate and reliable results; I carried out a series of preliminary results. In these preliminary tests I varied the length of electrode in the water and the mass of the sodium chlorine I used. These tests also helped determine what variables and controls I was going to use. I chose to use the electrodes 10-cm in the water, as this meant I could have higher results. This is because the more electrodes there is in the water, the larger the surface area is for the ions in the solution to be electrolysed. I decided to vary the mass of salt, as I thought this would be easier to vary and therefore have the most accurate readings.

RESULTS OF PRELIMINARY TESTS

Depth of electrodes         Amount of NaCl added        ammeter reading

In Sol. (Cm)                            (grams)                                  ( amps)

1.3                                5                                0.11

5.5                                5                                0.38

10                                5                                0.47

1.5                                10                                0.14

5                                10                                0.38

10                                10                                0.60

1.5                                15                                0.26

4.5                                15                                0.45

     9.5                                15                                0.81

OBTAINING

                   

Amount of NaCl added            1                       2                                3        average

       (grams)    

           5                                     0.48                 0.46                        0.43          0.46

           

           10                        0.63                 0.58                        0.61             0.61

           

           15                        0.90                 0.94                        0.79             0.85

           

           20                        0.97                 0.83                        0.93             0.91

           

           25                        1.21                 1.21                             1.20             1.21

ANALYSIS

• describe the features of your processed results the graphs, for example
  - is your graph a straight line, or a curve?
  - are there any striking patterns in your results?
• describe how the trends or patterns that you can see support (or not) the ideas and predictions you set out in your plan
• account for any results that you got which don't fit the pattern or which seem to be "wrong"

This part of the account of your investigation should tie together the ideas in the parts that have come before. You'll need to think carefully about what you set out to do, how you did it and the results you got. How do these all fit together? Your report on the investigation should lead the reader through all these things, and your conclusions should leave them in no doubt what YOU think your results mean.

Evaluating

If the previous sections of your report on your investigation have been leading up to "who did it", the evaluation can be likened to someone asking the question "how sure are you that you're right?"!

When a salt is dissolved in water, its ions become mobile. 

Hence, the solution can be electrolysed. However, the products from the salt solution will be different to the molten solution because of the presence of the water, which itself produces ions.

During electrolysis, these ions compete with the metal and non-metal ions from the dissolved salts, to receive or give up electrons.

So who wins?

At the cathode:

The more reactive a metal is the more it prefers being ions.

Therefore, if a reactive metal such as zinc or magnesium is present it will remain as the ions. The H+ ions will accept the electrons and hydrogen gas will be given off at the cathode.

If a less reactive metal, such as copper or silver is present it would rather accept the electrons than H+. 

Hence, the metal forms at the cathode.

At the anode:

If halide ions are present, Cl-, Br-, I-, they will give up there electrons to become molecules of Cl2, Br2 and I2 respectively.

If no halogen is present, OH- will give up electrons more readily than other non-metal ions, and oxygen forms.

 

If we take the reaction between magnesium and hydrochloric acid, in order for them to react together:

1. They must collide with each other

2. The collision must be with sufficient energy.

ANALYSIS