# When using the Hofmann Voltameter, which of the two gases collected are positively or negatively charged?

May 31, 2018

Slightly confusing question if the solution you are using is just slightly acidic water (as it often is.)

#### Explanation:

The reason why the question confuses is me is that the two gases collected (hydrogen and oxygen) are both neutral (uncharged) diatomic gases. I think you meant to ask how do you know which gas collect at the anode (positive side) and which at the cathode (negative side), yes?

If that is the case it is the oxygen that collects at the anode, losing two electrons per atom ($2 {O}^{2 -} \rightarrow 4 {e}^{-} + {O}_{2}$) and the converse at the cathode ($2 {H}^{+} + 2 {e}^{-} \rightarrow {H}_{2}$)

Any help?

Forgot to say, you collect twice the volume of ${H}_{2}$ as you are electrolysing water, whose formula is ${H}_{2} O$.