On electrolysis of dilute sulphuric acid using platinum electrodes, the product obtained at the anode will be:
A ) Hydrogen
B ) Oxygen
C ) Hydrogen sulphide
D ) Sulphur dioxide
Hint: During electrolysis, an electric current flows through an electrolyte solution, initiating a chemical reaction. Identify the various ions present in the solution. Next, determine which ions are drawn toward the anode. Then, by using electrode potential values, identify which ion is preferentially discharged.
Complete step by step answer:
In an aqueous solution, dilute sulfuric acid dissociates to produce hydrogen ions and sulfate ions. Additionally, the self-ionization of water generates hydrogen ions and hydroxide ions. Therefore, the dilute sulfuric acid solution in water contains hydrogen ions, hydroxide ions, and sulfate ions.
H2SO4(aq)→2H+(aq)+SO2−4(aq)
H2O(l)→H+(aq)+OH−(aq)
The anode is the positively charged electrode. It draws in hydroxide ions and sulfate ions. At the anode, hydroxide ions are discharged (instead of sulfate ions) to produce oxygen gas.
4OH−(aq)→2H2O(l)+O2(g)+4e−
The electrode potential for the above reaction is 0.0 V.
The electrode potential for the discharge of sulphate ions is 1.23 V
SO2−4(aq)+4H+(aq)→2H2O(l)+SO2(g)+4e−
When hydroxide ions are released, oxygen gas is produced at the anode. However, if sulfate ions are discharged instead, sulfur dioxide gas is released. Since the electrode potential value for hydroxide ion discharge is lower than that for sulfate ions, hydroxide ions will preferentially be discharged at the anode. As a result, oxygen gas will be produced rather than sulfur dioxide gas at the anode.
In the electrolysis of dilute sulfuric acid in aqueous solution with platinum electrodes, oxygen gas is released at the anode.
Thus, option B) oxygen is the correct answer.
Note: The cathode is the negatively charged electrode. It attracts hydrogen ions. At the cathode, hydrogen ions are discharged, resulting in the formation of hydrogen gas.
2H+(aq)+2e−→H2(g)
When hydroxide ions are released, oxygen gas is produced at the anode. However, if sulfate ions are discharged instead, sulfur dioxide gas is generated. Because the electrode potential for discharging hydroxide ions is lower than that for sulfate ions, hydroxide ions will preferentially discharge at the anode. Consequently, oxygen gas will be released rather than sulfur dioxide gas at the anode.