Potassium Alum and Electrolysis

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Eliman134
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Potassium Alum and Electrolysis

Post by Eliman134 »

For a science fair project I dissolved copper into water through electrolysis with alum as my electrolyte. I am not sure what all happened. The copper dissolved, and the solution turned blue as expected, but I'm not sure what happened to the Alum. I need help figuring out what the byproducts of the experiment are. I have researched a lot without finding hardly anything pertaining to Alum being used as an electrolyte.
norman40
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Re: Potassium Alum and Electrolysis

Post by norman40 »

Hi Eliman134,

Could you post a description of your experiment and electrolysis set-up? I’m assuming that one electrode was copper. What was the other electrode? Perhaps one of the contributors to the forum can help with some more information about your project.

I hope this helps. Please post again if you have more questions.

A. Norman
Eliman134
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Joined: Wed Feb 03, 2016 2:34 pm
Occupation: Student

Re: Potassium Alum and Electrolysis

Post by Eliman134 »

I put 200 ml of water into a beaker. Both electrodes were copper together weighed 25 g. I mixed the water with 20 grams of alum. I hooked the electrodes to a power supply at 12 Voltz. I let it run for 2 min shy of an hour. The solution turned dark blue. The Anode was coated with black stuff, and there was a gel like stuff that floated at the top. After the experiment was over the beaker was very warm to the touch. After it cooled the gel stuff disappeared. I weighed the copper wires together afterward and they weighed 23g so about 2g dissolved into the water.
norman40
Former Expert
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Re: Potassium Alum and Electrolysis

Post by norman40 »

Hi Eliman134,

A well-known electrolysis experiment involves placing copper electrodes in a solution of copper sulfate. When the electrodes are connected to a battery, copper metal from the positive electrode is oxidized to the Cu +2 ion. Copper ions in the solution are reduced to copper metal at the negative electrode. As a result of this oxidation/reduction reaction, the positive electrode loses weight while the negative electrode gains weight. The weight loss at the positive electrode should equal the gain at the negative electrode. The concentration of copper ions in the electrolyte solution remains constant.

In your experiment you started with copper electrodes immersed in a solution of potassium aluminum sulfate (alum). When you connected your electrodes to a power supply, copper metal from the positive electrode was oxidized to the Cu +2 ion. This was confirmed by the blue color of the electrolyte solution.

What happened at the negative electrode is complicated by the fact that you have ions present that might compete with the reduction of Cu +2 to copper metal. After turning on the power, your electrolyte solution contained the cations Cu +2, K +, Al +3, and H +. The question is which of these is most likely to be reduced to the element at the negative electrode?

The following sites cover various factors that affect electrolysis reactions and products. Post again if you have questions after reviewing this information.

https://www.youtube.com/watch?v=R__dBvuTCp0

http://www.bbc.co.uk/schools/gcsebitesi ... rev4.shtml

http://www.slideshare.net/Janadi/factor ... ectrolysis

A. Norman
Kartik007
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Re: Potassium Alum and Electrolysis

Post by Kartik007 »

Did you observe any bubbling on negative electrode
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