# Why is twice as much hydrogen produced than chlorine in the electrolysis of brine?

I have seen a great many number of diagrams which show the electrolysis of brine in a diaphragm cell, but show twice the volume of hydrogen produced. For example:

On the other hand, other diagrams show that the same volume of hydrogen and chlorine is produced. For example:

So who's right and why?

• These are just qualitative schemes; they don't specify volumes at all. At least, I don't see any indication of it whatsoever. – Ivan Neretin Aug 1 '16 at 13:31
• No they did not pay attention to the volumes (otherwise they would have shown them equal, as the equation requires). You are inferring meaning which is simply not there. – Ivan Neretin Aug 1 '16 at 14:16
• @IvanNeretin I appreciate your response. Are you suggesting that there is evidence of systematic error in the creation of these diagrams relating to the electrolysis of brine? – Turbo Aug 1 '16 at 14:17
• I would not even call that an error. They never said their volumes are 2:1 or whatever; you inferred that from some random details which (I think) simply aren't supposed to mean anything. – Ivan Neretin Aug 1 '16 at 14:24
• @IvanNeretin I think I've worked it out - see my answer below – Turbo Aug 1 '16 at 14:32

I'm not sure how the first diagram shows a $$2:1$$ volume ratio. But I am sure about the balanced chemical equations:
\begin{align} \ce{2 Cl^- &→ Cl2 + 2 e-} \\ \ce{2 H2O + 2 e- &→ H2 + 2 OH-} \\ \hline \ce{2 H2O + 2 Cl- &→ H2 + Cl2 + 2 OH-} \end{align}