When a copper rod is dipped in aqueous silver nitrate solution, the colour of the solution changes to blue. This is because

When a copper rod is immersed in an aqueous silver nitrate solution, a spontaneous redox displacement reaction occurs. Copper (Cu) is more reactive than silver (Ag) and has a lower reduction potential (0.34 V) compared to silver (0.80 V). Consequently, silver ions (Ag+) are more easily reduced than copper ions. In this reaction, silver ions gain electrons to form solid silver metal, which deposits on the rod, while copper atoms lose electrons (oxidation) to form copper(II) ions (Cu2+). The accumulation of these Cu2+ ions in the solution is responsible for the characteristic blue color change. The nitrate ions (NO3-) act as spectator ions and do not participate in the redox process. Therefore, the reaction proceeds because Ag+ is more readily reduced than Cu2+.