Subject: Electrolysis of Water - Nonproduction of oxygen

My son is performing a science fair experiment using the classic 
electrolysis of water with a 6 volt battery producing hydrogen at one 
electrode and oxygen at the other.  He is capturing the two gases in 
an inverted test tube.  We have encountered a major problem.  
Hydrogen is readily being produced at one electrode, however no 
oxygen is being produced at the other.  We are using two copper wires 
for the electrode which is placed in a beaker of tap water with a 
tablespoon of salt as the electrolyte.  Can someone offer an 
explanation as to why there are no bubbles or the appearance of 
oxygen at the one electrode.

Re: Electrolysis of Water - Nonproduction of oxygen