Question

Predict the products of electrolysis in an aqueous solution of ${\mathrm{AgNO}}_3$ with Platinum electrodes.

Answer 1

Electrolysis:

• Electrolysis is a process by which electrical energy is used to produce a chemical change.
• The electrolysis cell consists of two metallic rods known as electrodes that are connected to a battery and dipped into molten electrolyte or electrolyte solution.
• The electrode connected to the positive side of the battery is called the anode.
• The electrode connected to the negative side of the battery is called the cathode.
• The electrically charged cations and anions in the electrolyte move towards the respective electrodes.
• That is, positively charged cations move toward the cathode and negatively charged anions move towards the anode.
• When the anions reach the anode, they are discharged through electron removal(oxidation), liberating neutral atoms or molecules at the electrode.
• Cations are neutralized through electron addition(reduction) when they reach the cathode.

Electrolysis in a dilute solution of ${\mathrm{AgNO}}_3$ with platinum electrodes:

• In an aqueous solution, dilute Silver nitrate dissociates to form Silver cation (${\mathrm{Ag}}^{+}$) and the Nitrate anion (${\mathrm{NO}}_3^{-}$) and the autoionization of water gives protons and Hydroxide ions.

$\underset{\mathrm{Silver}\mathrm{nitrate}}{{\mathrm{AgNO}}_3\left(\mathrm{aq}\right)}\to \underset{\mathrm{Silver}\mathrm{ions}}{{\mathrm{Ag}}^{+}\left(\mathrm{aq}\right)}+\underset{\mathrm{Nitrate}\mathrm{ions}}{{\mathrm{NO}}_3^{-}\left(\mathrm{aq}\right)}$

$\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}\to \underset{\mathrm{Protons}}{{\mathrm{H}}^{+}\left(\mathrm{aq}\right)}+\underset{\mathrm{Hydroxide}\mathrm{ions}}{{\mathrm{OH}}^{-}\left(\mathrm{aq}\right)}$

• Thus, the dilute aqueous Silver nitrate solution contains protons, Hydroxide ions, Silver ions and Nitrate ions.
• Anode(positive electrode) attracts Hydroxide ions and Nitrate ions.
• Hydroxide ions having lower discharge potential will be discharged in preference to Nitrate ions.
• Thus, the Hydroxide ions will decompose to give Oxygen gas at the e anode.
  $\underset{\mathrm{Hydroxide}\mathrm{ions}}{4{\mathrm{OH}}^{-}\left(\mathrm{aq}\right)}\to \underset{\mathrm{Water}}{2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}+\underset{\mathrm{Oxygen}}{{\mathrm{O}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{electrons}}{4{\mathrm{e}}^{-}}$
• However, the cathode is a negative electrode and it attracts protons and Silver ions.
• Silver ions donate one electron to form $\mathrm{Ag}$ metal and get deposited on the cathode.

$\underset{\mathrm{Silver}\mathrm{ions}}{4{\mathrm{Ag}}^{+}\left(\mathrm{aq}\right)}+\underset{\mathrm{Electron}}{4{\mathrm{e}}^{-}}\to \underset{\mathrm{Silver}}{4\mathrm{Ag}\left(\mathrm{s}\right)}$

• The net cell reaction is $\underset{\mathrm{Silver}\mathrm{nirate}}{4{\mathrm{AgNO}}_3\left(\mathrm{aq}\right)}+\underset{\mathrm{Water}}{2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}\to \underset{\mathrm{Silver}}{4\mathrm{Ag}\left(\mathrm{s}\right)}+\underset{\mathrm{Oxygen}}{{\mathrm{O}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Nitric}\mathrm{acid}}{4{\mathrm{HNO}}_3\left(\mathrm{aq}\right)}$

Therefore, in the electrolysis of dilute aqueous Silver nitrate, using Platinum electrodes, Oxygen gas is liberated at the anode, and silver metal is deposited at the cathode.