What do you understand by normal hydrogen electrode ? Give its structure and working.

Explanation

The common standard reference electrode is the standard is the standard hydrogen electrode (SHE) shown in fig. it is also called normal hydrogen electrode (NHE). A normal hydrogen electrode consists of a platinum wire sealed in a glass-tube and carrying a platinum foil at one end. the platinum foil is coated with finely divided platinum, aclled platinum black. it is dipped into an aqueous solution containing one molar concentration of hydrogen ions `(H^(+))`. hydrogen gas at 1 atmospheric pressure is constantly bubbled through the solution. the temperature of the solution is maintained at 298K.

One of the following reactions occurs at the surface of the platinum electrode depending upon the electrode withwhich it is connected.
`H_(2)(g) to 2H^(+)(aq)+2e^(-)`
or `2H^(+)(aq)+2e^(-) to H_(2)(g)`
The finely divided platinum black coated over platinum odsorbs `H_(2)` helps to establish equilibrium between `H_(2) and H^(+)` ions. the reduction potential of hydrogen electrode is taken to be zero under standard conditions.
When hydrogen electrode in a cell acts as anode i.e., when oxidation takes place at hydrogen electrode the following reaction takes place.
`H_(2)(g) to 2H^(+)+2e^(-)`
WHen it acts as cathode (i.e., reduction takes place) the following reaction takes place.
`2H^(+)(aq)+2e^(-) to H_(2)(g)`
The standard hydrogen electrode is represented as:
`Pt,H_(2)(g)(1" atm")//H^(+)(ar)(1M)`