why AlCl3 dissolves on addition of concentrated HCl?
Aluminum metal reacts with hydrochloric acid when added to form aluminum chloride. The reaction starts slowly due to the initial formation of aluminum oxide resulting from the air's oxygen. The protective layer formed prevents reaction, but after the hydrochloric acid has worn it out, it commences. It leads to an aqueous solution of aluminum chloride, where the addition of concentrated hydrochloric acid seems to dissolve due to chloride ions. It results in a more aqueous solution of aluminum chloride hence the dissolving nature.