copper does not react with dilute hydrochloric acid even on heating but reacts with sulphuric acid . why?
Generally the reaction of a metal with an acid is written as
Metal + acid ------> Metal salt + hydrogen gas
Now this reaction is not true for all the metals. Only those metals which are more reactive than hydrogen will liberate hydrogen from the acid and form the corresponding metal salt. These metals are placed above hydrogen in the reactivity series. As copper is less reactive than hydrogen, therefore it will not liberate hydrogen gas from the acids like HCl, HNO3, H2SO4 etc.
But sulphuric acid is a strong oxidising agent, therefore it will oxidise copper metal to Cu2+ ion. However, no hydrogen gas will be formed, only copper metal will be oxidised here. On the other hand, HCl is not that strong oxidising agent, in fact its use as an oxidising agent is not too well known. Hence it does not react with copper metal at all.