# Energy required for obtaining required mass of aluminium from alumina via electrolysis

How do I know how much energy I need to obtain 20 g alumunium from alumina with 5 V?

I calculated the quantity of electricity is 2.22 F.

Any help appreciated!

Required energy $$E$$ can be found as a product between voltage $$U,$$ current $$I$$ and time $$t$$:

$$E = UIt\label{eqn:1}\tag{1}$$

Unknown multiplier $$It$$ can be found using united Faraday law:

$$m = \frac{MIt}{zF}\quad\implies\quad It = \frac{mzF}{M}\label{eqn:2}\tag{2}$$

where $$m$$ is the mass of the substance liberated at the electrode; $$M$$ is the molar mass; $$z$$ is the number of electrons transferred per ion; $$F$$ is Faraday constant. Considering aluminium is produced via Hall–Héroult process or similar, at the cathode the following reaction takes place:

$$\ce{Al^3+ + 3 e− → Al}$$

and $$z = 3.$$ Plugging \eqref{eqn:2} into \eqref{eqn:1} allows to finally find the energy:

\begin{align} E &= \frac{mzUF}{M}\\ &= \frac{\pu{20 g} × 3 × \pu{5 V} × \pu{96485.33 C mol-1}}{\pu{26.98 g mol-1}}\\ &= \pu{1.07 MJ}\tag{3} \end{align}

• With much respect, can you assist me to understand chemistry? Can i have your email or whatever platform, so i can ask simple chemistry question to you? Basically, i dont have privilege to ask many questions in this forum. @andselisk – Lifeforbetter Oct 29 '19 at 6:03
• @Lifeforbetter I prefer not to share my personal information and I don't do private teaching. If you have a question, the better way would be to ask community and post a new question. Also, please note this is not really a forum, but a Q&A site with somewhat restricted back-and-forth communication capabilities. In the meantime, I'd suggest to look at Resources for learning Chemistry, or enroll in free chemistry courses online. – andselisk Oct 29 '19 at 6:25