Which of the following will give H2(g) at cathode and O2(g) at anode on electrolysis using platinum electrodes ?
A
Concentrated aqueous solution of NaCl
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B
Molten NaCl
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C
Dilute aqueous solution of NaCl
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D
Solid NaCl
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Solution
The correct option is C Dilute aqueous solution of NaCl When a dilute aqueous solution of NaCl is electrolysed, hydrogen and oxygen gases are released at cathode and anode respectively. This is because of the high reduction potential of Na+ as compared to H+ and high oxidation potential of Cl− as compared to OH−.
NaCl(Aqueoussolution)⟶Na++Cl−
H2OpresentinaqueoussolutionofNacl⟶H++OH− At anode: 2Cl−→Cl2+2e−;Eooxi=+1.36V 4OH−→O2+2H2O+4e−;E0oxi=+1.23V At cathode: Na++e−→Na;Eored=−2.71V 2H++2e−→H2;Eored=−0.83V