Question

Predict the products of electrolysis in an aqueous solution of ${\mathrm{AgNO}}_3$ with Silver 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 present 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.
• When cations reach the cathode, they are neutralized through electron addition(reduction).

Electrolysis in a dilute solution of ${\mathrm{AgNO}}_3$ with silver 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.

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

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

• Thus, the dilute aqueous Silver nitrate solution contains protons, Hydroxide ions, Silver ions, and Nitrate ions.
• However, the cathode is a negative electrode and it attracts protons and Silver ions.
• In the electrolysis of ${\mathrm{AgNO}}_3$, silver electrodes are not inert.
• Due to the polarity of the electrodes, Silver metal and Hydrogen gas will form at the cathode, and this is because Silver ions and Hydrogen ions are positive and are attracted to the negative cathode.
• Silver ions have a lower discharge potential than hydrogen ions.
• Thus, the silver ions will be deposited in preference to hydrogen ions.
• Silver ions donate one electron to form $\mathrm{Ag}$ metal and get deposited on the cathode.

$\underset{\mathrm{Silver}\mathrm{ions}}{{\mathrm{Ag}}^{+}}+\underset{\mathrm{Electron}}{{\mathrm{e}}^{-}}\to \underset{\mathrm{Silver}}{\mathrm{Ag}}$

• Anode(positive electrode) attracts Hydroxide ions and Nitrate ions.
• As the electrodes are attackable silver at the anode, they will dissolve to form ${\mathrm{Ag}}^{+}$ ions.
  $\underset{\mathrm{Silver}}{\mathrm{Ag}}\to \underset{\mathrm{Silver}\mathrm{ions}}{{\mathrm{Ag}}^{+}}+\underset{\mathrm{Electron}}{{\mathrm{e}}^{-}}$

Therefore, in the electrolysis of dilute aqueous Silver nitrate, using silver electrodes, $\mathrm{Ag}$ will deposit at the cathode and dissolve at the anode to form ${\mathrm{Ag}}^{+}$ ions.