Posted by Larry Robinson on 8/11/08

I have seen this little experiment done in classrooms. But
it is based on bad science, and it could be dangerous.

The basic experiment involves dropping a 9-volt battery into
a glass of salt water, and watching the "hydrogen and
oxygen" bubble off as the electricity electrolyzes the water.

The truth is that those gases are hydrogen and chlorine. The
salt changes the chemical reaction. The experiment teaches
this reaction:

2 H2O + energy -> 2 H2 + O2

But adding salt changes the reaction to:

2 H2O + 2 NaCl + energy -> H2 + cl2 + 2 NaOH

Both the chlorine gas and the sodium hydroxide (lye) left in
the glass are poisons. If the reaction is allowed to
continue long enough, the concentrations could approach
harmful values.

An electrolyte that enters the reaction produces different
compounds:

salt: hydrogen, chlorine, and lye
baking soda: hydrogen, carbon dioxide, and lye
k-salt (KCl): hydrogen, chlorine, and potash

Some people having seen this little demonstration have built
large tanks at home to make hydrogen with. It's a wonder
that they haven't been poisoned.

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