Question

Draw a labelled diagram of standard hydrogen electrode.

Answer 1

Hint: In standard hydrogen electrode, pure and dry hydrogen gas (pressure 1 atm) is passed over a platinized platinum plate dipped in 1M hydrogen ion solution at 298K. A standard hydrogen electrode is used as a reference electrode.

Complete step by step answer:
Construction of standard hydrogen electrode is as follows:
-platinum plate is coated with platinum black to increase surface area of platinum plate.
-platinized platinum plate is dipped in 1 M hydrogen ion solution, catalytic properties.
-Platinized platinum plate has a high surface area and it absorbs hydrogen gas.
-pure and dry hydrogen at 1 atm is continuously passed into the 1 M solution of hydrogen ions.

-Reaction takes place on platinum electrode, platinum is used due to its relatively inert nature,
-standard reduction and oxidation potential of hydrogen is zero.
-standard electrode potential of standard hydrogen electrode is zero so it is used as reference electrode. It is also known as a primary reference electrode.
So it can act as anode and cathode depending upon other elements.
When standard hydrogen electrode acts as anode:
${{H}_{2(g,1atm)}}\to 2{{H}^{+}}_{(1M)}+2{{e}^{-}}$

When standard hydrogen electrode acts as cathode:
\[2{{H}^{+}}_{(1M)}+2{{e}^{-}}\to {{H}_{2(g,1atm}})\]

Difficulties in standard hydrogen electrode:
-it is difficult to obtain pure and dry hydrogen gas.
-it is difficult to maintain concentration of hydrogen ions as 1M.
-it is difficult to maintain hydrogen gas at 1 atm.

Note: As standard hydrogen electrode has standard cell potential as zero. It is known as a primary reference electrode. Salt bridge is used to connect standard hydrogen electrodes to other half cells whose electrode potential is unknown. In standard hydrogen electrodes, pure and dry hydrogen gas (pressure 1 atm) is passed over a platinized platinum plate dipped in 1M hydrogen ion solution at 298K.