Name: Gibbs Free Energy, EMF and Equilibrium Constant
Uploaded: 2019-07-19
Duration: 6 min 15 s
Description: There are various thermodynamic parameters that are to be considered while studying the working of an electrochemical cell. Let's learn about them here!

Question

Give the construction of standard hydrogen electrode? Give its significance.

Accepted Answer

The electrode in which hydrogen gas is in contact with $H^{+}$ ions of $1 M$ concentration, at $298 K$ temperature and one bar pressure is known as standard hydrogen electrode. It is constructed as follows:

(i) $1 M$ $HCl$ is taken in a glass vessel and maintained at $298 K$ .

(ii) A small platinum foil is coated with Pt-black is connected to the Pt-wire sealed in a gas tube.

(iii) This Pt- electrode is fitted in a glass jacket having an inlet for hydrogen gas. This assembly is immersed in $1 M$ $HCl$ .

(iv) Hydrogen gas is bubbled into the electrode through the inlet. The pressure of hydrogen gas is maintained at one bar. Hydrogen gas gets absorbed on platinum black. Thus, hydrogen is in contact with $H^{+}$ ions of $HCl$ solution at the electrode surface. The assembly so obtained is standard hydrogen electrode. The various reactions take place in this half cell depends upon whether it acts as anode or cathode.

If the electrode acts as anode then: $H_{2} (g) \to 2 H^{+} (aq) + 2 e^{-}$

If the electrode acts as cathode then: $2 H^{+} (aq) + 2 e^{-} \to H_{2}$

The above two reactions can be written as $H_{2} (g) ⇌ 2 H^{+} (aq) + 2 e^{-}$ . The electrode potential of standard hydrogen electrode is taken as zero.

Significance of standard hydrogen electrode: It is used as a primary reference electrode to determine the relative values of electrode potentials of other electrodes as there is no other method to find out the absolute value of single electrode potential.

Give the construction of standard hydrogen electrode? Give its significance.

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