Advertisements
Advertisements
Question
Explain the following:
When a dilute aqueous solution of sodium chloride is electrolysed between platinum electrodes, hydrogen gas is evolved at the cathode but metallic sodium is not deposited. Why?
Advertisements
Solution
\[\ce{NaCl -> Na+ + Cl-}\]
\[\ce{H2O <=> H+ + OH-}\] or
\[\ce{H2O + H2O <=> H3O+ + OH-}\]
H+ (H3O+) and Na+ move to the cathode. Hydrogen is evolved at the cathode because, despite the high concentration of Na+, H+ acquires electrons more readily than Na+ and is also lower than Na+ in the electrochemical series.
\[\ce{H+ + e- -> H}\]
\[\ce{H + H -> H2}\]
RELATED QUESTIONS
Select the ion in the following case, that would get selectively discharged from the aqueous mixture of the ions listed below:
\[\ce{SO^2-_4, NO^-_3 {and} OH-}\]
Select the ion in the following case, that would get selectively discharged from the aqueous mixture of the ions listed below:
Pb2+, Ag+ and Cu2+
Name two substances in the following case:
Contain only ions.
Explain the following:
On electrolysis of dilute copper (II) sulphate solution, copper is deposited at the cathode but no hydrogen gas evolves there. Explain why?
Arrange the following according to the instruction given in bracket:
Cu2+, Na+, Zn2+, Ag+ (The order of Preferential discharge at the cathode)
