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Reaction of Cu with HCl and H2O

August 24, 2009

when I was doing the electrolysis of HCl with copper electrodes (not sure of purity) with 2.5 ml of HCl (not sure of concentration) 5ml of water, I found that there was gas coming out of -ve electrode and there was deposition of copper on the same terminal

can I please know what reaction is taking place?

can I know what is Cu reacting with....

James Earl C.
student - Bangalore, Karnataka, India

August 25, 2009

Hi, James. Don't get lazy with capitalization when studying chemistry! We have corrected your posting because chemistry is completely impossible to follow if you start confusing CL with Cl.

Positive ions are attracted to the negative electrode (cathode). These would include both hydrogen (the source of the gassing) and Cu (the source of the copper color). The copper of the positive electrode (anode) oxidizes into solution. If electrons are taken from Cu metal at the anode, it becomes Cu++ ions. If electrons are added to Cu++ ions, they become Cu metal. If electrons are added to H+ ions, they become hydrogen gas. Good luck.


Ted Mooney,
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

August 31, 2009

It can get into some deep electrochemistry, but at a given voltage for the solution, copper plates out. At another voltage, H+ ions are converted int H2 gas. So, you frequently have both and that contributes to the efficiency of the plating bath. It can be 99+% at one voltage and 90% at another voltage.

James Watts
- Navarre, Florida

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