Question

Define Reference electrode.
How many faradays of electricity are required to produce $13$ gram of aluminium from aluminium chloride solution? (Given: Molar mass of $Al = 27.0{\text{ gram mo}}{{\text{l}}^{ - 1}}$ )

Answer 1

An electrode which has a well-known and stable electrode potential is called a reference electrode. Reference electrodes can be used as a half cell in electrochemical cells. The Calomel electrode is an example of a reference electrode. It has mercury and mercury-chloride molecules in it. Reference electrodes can be used as third electrodes in three electrode electrochemical cell systems. The potential of this electrode is arbitrarily taken as zero or is known exactly. Standard hydrogen electrode, glass electrode and silver-silver chloride electrodes are examples of reference electrodes.

Complete answer:
Faraday is the unit of electricity and it is used in the study of electrochemical reactions. It is equal to the amount of electric charge that liberates one gram equivalent of an ion from an electrolytic solution.
The number of moles of aluminium produced $= \dfrac{{{\text{mass of Al}}}}{{{\text{molar mass of Al}}}} = \dfrac{{13}}{{27}} = 0.48{\text{ moles}}$
$AlC{l_3} \to A{l^{ + 3}} + 3C{l^ - }$
$A{l^{ + 3}} + 3{e^ - } \to Al$
One mole of aluminium requires three moles of electrons.
$0.48$ mole of aluminium requires $3 \times 0.48 = 1.44$ moles of electrons.
One faraday of electricity corresponds to one mole of electrons.
So, $1.44$ moles of electrons corresponds to $1.44$ faradays of electricity.
Therefore, $1.44$ faradays of electricity are required to produce $13$ gram of aluminium from aluminium chloride solution.

Note:
One faraday of electric charge corresponds to the charge on one mole of electrons i.e. $6.022 \times {10^{23}}$ electrons. The elementary which can be represented in moles can be molecules, atoms, ions and even other particles like electrons. A mole is defined as $6.022 \times {10^{23}}$ of a chemical unit like atoms, molecules, ions, etc.