Question

Although \[Au\] is soluble in aqua regia but \[Ag\] is not. Explain.

Answer 1

Hint : We know that gold cannot be dissolved in any single acid. This is because of the fact that the gold lies at the bottom of the metal reactivity series. So the gold is a very less reactive metal. Also we know that a metal less reactive than the other is not able to replace the other one from its compound.

Complete Step By Step Answer:
We know that most powerful acids like hydrochloric acid and nitric acid alone are not able to dissolve gold. This is because gold being one of the least reactive metals is not able to replace the hydrogen from the given acids as it is also less reactive than the hydrogen.
We know that most powerful acids like hydrochloric acid and nitric acid alone are not able to dissolve gold. This is because gold being one of the least reactive metals is not able to replace the hydrogen from the given acids as it is also less reactive than the hydrogen. Also we know that a metal less reactive than the other is not able to replace the other one from its compound.
Aqua regia dissolves gold, though neither constituent acid will do so alone, because, in combination, each acid performs a different task. Nitric acid is a powerful oxidizer, which will actually dissolve a virtually undetectable amount of gold, forming gold ions \[\left( A{{u}^{3+}} \right).\]The hydrochloric acid provides a ready supply of chloride ions \[\left( C{{l}^{-}} \right),\]which react with the gold ions to produce tetrachloroaurate \[\left( III \right)\]anions, also in solution. The reaction with hydrochloric acid is an equilibrium reaction that favors formation of chloroaurate anions \[\left( AuCl_{4}^{-} \right)\].
\[Au+3HN{{O}_{3}}+4HCl\rightleftharpoons {{[AuC{{l}_{4}}]}^{-}}+3[N{{O}_{2}}]+{{[{{H}_{3}}O]}^{+}}+2{{H}_{2}}O\]
Silver actually forms a silver chloride layer that protects the metal from further attack. Silver can only be attacked by Aqua regia when the silver chloride layer is ruptured.

Note :
Remember that thus, although the strong acids are not able to dissolve gold alone due to its least reactive nature, the aqua regia which is a mixture of hydrochloric and nitric acid is able to dissolve it. This is because both the acids in aqua regia perform different functions.