MadSci Network: Chemistry

Re: what happens in the electrolysis of copper sulphate, potassium iodide ...?

Date: Tue Jun 20 23:59:17 2000
Posted By: Gabriel Harris, Grad student, Food Science and Technology, The Ohio State University
Area of science: Chemistry
ID: 956097872.Ch


First of all, let me explain the basics of electrolysis.  As you know, it 
is a method of splitting molecules.  Basically, this is done by passing 
electric current through a container filled with salty water.  In order to 
pass current through the water and split molecules in the process, there 
must be positive and negatively charged pieces of metal (called poles) at 
opposite ends of the container.  The electric current, made up of 
negatively charged electrons, flows from the negative pole to the positive 
pole.  The negative pole is called the cathode, while the positively 
charged pole is called the anode.  The water must be salty because salt is 
needed to "carry" the electrons through the water from the cathode to the 
anode.  In your experiment the salts used were potassium iodide and 
potassium dichromate.

When current is applied and a metal containing compound such as copper 
sulphate is added to the water, the metal will disocciate from the rest of 
the molecule.  You will then have positively charged copper atoms in 
solution.  Positively charged molecules are called cations.  Because 
opposite charges attract one another, the positively charged copper 
cations will be attracted to the negatively charged cathode, not the 
anode, in your system.  

Gas is given off in this system because water itself dissociates when the 
current is applied.  The result is that hydrogen and oxygen gas are given 
off when electrolysis is occurring.

Thank you for your question.  I hope this helped.


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