How Varying the Concentration of an Electrolyte Effects the Electrolysis Current

Chemistry coursework

“how varying the concentration of an electrolyte affects the electrolysis current”

Aim

To test how varying the concentration of an electrolyte affects the eloctrolysis current using carbon electrodes with my chosen electrolyte, hydrochloric acid.

Apparatus

2 carbon electrodes, beakers, an ammeter, a battery pack, wires, crocodile clips, electrode holder, hydrochloric acid, distilled water

Diagram

Plan

I will set up the experiment as in the diagram and I will start by using the lowest mole 0.5 conc. I will measure 25mls of 0.5 m HCL using a burette for accuracy. I will put this in a beaker and weigh my two carbon electrodes. My chosen voltage is 6 v as this is a fairly low voltage that will give better results. I will run the current through the circuit for a few seconds only. This is because 1: -the electrodes wear down if they are in the process of electrolysis for too long. We do not want this to happen because we are using the same electrodes all the way through and if they wear down they would have a smaller surface area and therefore a smaller effect. I will do the same for 1,2,3,4+5molar HCL. I will measure the current with an ammeter and record the readings on a graph and table.

Prediction

I predict that the graph will curve up quickly at the beginning but will level out at the end this therefore means that I predict the current will go up sharply at the beginning (a big current) and the current will increase with the molarity. I also predict that the higher concentrated the electrolyte, the more current will flow. This is because there are more particles in the same space. This is why it is important to get the measurements right for each experiment and is the reason for using a burette.

Fair test

You must only ...

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Prediction

Fair test

You must only have one variant and everything else must be the same; the temperature, volume of electrolyte, and the same voltage for the battery. The electrodes will be carefully washed so as not to contaminate the electrolyte. They will then be put in propanone so the water is washed off, then the propanone evaporates. As propanone evaporates very quickly, this will speed up the process and the experiment without causing contamination.

Scientific knowledge

When chemicals conduct electricity, a chemical reaction is taking place we call this type of reaction an electrolysis reaction. Any substance that contains ions will conduct electricity during electrolysis. A metal or hydrogen forms at the cathode and a non-metal (except hydrogen) forms at the positive anode. The cathode attracts positive ions (anions) and the anode negative ions (Cations) therefore the metals and hydrogen, which go to the cathode, are cations. Only substances containing free electrons can conduct electricity, no solid substances can, they must be molten or dissolved in water. During electrolysis, the electrons from the battery go to the negative cathode. At this point they meet the positive ions in the electrolyte (generally metal ions). The ions then turn into a neutral element. These ions are attracted to the positive anode

Variants

As I said before there can only be one variant for it to be a fair test and the variant chosen is the concentration of an electrolyte as is stated in the coursework title.

Range of results

My chosen electrolyte was hydrochloric acid therefore I needed to find a suitable range of values for my experiment I chose to use 0.5 molar 1,2,3,4,and 5molar concentrate hydrochloric acid.

Preliminary work

I did some preliminary work to gain background information on how long to leave the circuit connected for to get a good reading and I practised measuring exactly and working with the different molar hydrochloric acid.

Results

Conclusion and evaluation

This experiment proved my prediction that the current would increase as the molarity increased, because as I said before there are more particles in the same space as before. When a 1 molar solution is measured as 5cm3 it may have 1 million particles whereas a 5 molar solution may have 5 million particles. The graph was a curved graph and also levelled out in gradient as well. The results were worked out into an average. This worked well because the results were very similar in the 5 readings I took for each one, except for the 5th one. This was an anomalous result and is indicated so on the graph with a circle.

Altogether I think that this experiment was done well and was an easy experiment to do. It had the variant already stated in the title so no thinking had to be done there. It was very easy to set-up and electrolysis had been done in great detail more than once gaining valuable knowledge for the project. Gaining the evidence was very easy using the ammeter. There was one anomalous result on the 5th test, however the graph proved that accurate results were taken by the smooth line (except for the last one). The experiment could have been improved by using ready processed hydrochloric acid as I had to make some of the molars by measuring and diluting with water. This may account for any misfits on the graph though it is unlikely. My prediction was a sound and correct prediction

Further work

To carry the work further I could use a wider variety of molarities and different electrodes also I could change the variant instead of changing the molarity I could change the current for example, and measure the resistance.