Re: during electrophoresis, why are there twice as many bubbles on one pole?

Dear Mike,

You are very observant! You probably noticed that there were twice as many bubbles on the black pole (the cathode, close to the wells) than on the red pole (the anode, close to the end of the gel). These bubbles are hydrogen (cathode) and oxygen (anode) gas resulting from the electrolysis of water:

As you can see, twice as many molecules of hydrogen than oxygen are produced per molecule of water. At room temperature, these gases behave nearly ideally (i.e. PV=nRT), so the volume of gas is directly proportional to its amount. In other words, the hydrogen gas produced has twice the volume, and therefore gives twice as many bubbles!

Now, you may also be wondering why hydrogen is created at the cathode and not at the anode. Well, by definition, the cathode is negatively charged, so that electrons are flowing out of the black pole. Water can accept these electrons as follows:

Note that hydrogen gas is produced, not oxygen. At the positively charged anode, electrons are pulled from the hydroxide (OH^-) produced above according to the following half-reaction:

Thus, oxygen gas is produced. If you add these two reactions together, the electrons and hydroxide cancel to give the overall reaction up top.

Thanks for the good question, and I hope you remain curious about chemistry!

Your MAD Scientist,
Raymond Cheong

References
Home electrolysis experiment