During the electrolysis of water we have gotten $\pu{10 dm3}$ of hydrogen. Temperature was $\pu{0 °C}$ and pressure was $\pu{101325 Pa}$.
What charge has passed trough the electrolysis article/joint?

I don't know how to find the charge while knowing pressure, temperature and volume. How do I proceed with this question?

  • $\begingroup$ I have found a formula for charge that goes "Q=CxV" and I do have volume, but how do I find C (capacity), I don't remember doing that in school, but I might be mistaken. $\endgroup$
    – Kat
    Apr 13, 2021 at 13:46

1 Answer 1


$PV = nRT$ and $\ce{2H+ + 2e- -> H2}$ are your best friends.

Step 1: Find the number of moles of hydrogen gas released

Use the formula: $PV = nRT$, where $P =$ Pressure exerted by the gas, $V =$ Volume of gas, $n = $ number of moles of gas, $R = $ universal gas constant, $T = $ temperature of gas.

Using this formula with $P$ in atm and $V$ in liters we get:

$$n =\frac{PV}{RT} = \pu{0.0044 mol}$$

Step 2: Find the number of farads of charge used

We know that $$\ce{2H+ + 2e- -> H2}$$

This means that for every mole of hydrogen released, $\pu{2 moles}$ of electrons are used. A farad is the charge on $\pu{1 mol}$ of electrons and so number of farads of would be two times the number of moles of electrons. So charge would be $\pu{0.0088 F}$.

Step 3: One farad = 96500 coulombs

Therefore, $\pu{0.0088 F = 850.32 C}$ and that should be the answer.


Not the answer you're looking for? Browse other questions tagged or ask your own question.