علل تترسب المجموعه الثانيه علي هيئة كبريتيدات في الوسط الحامضي بينما تترسب المجموعه الرابعه علي هيئة كبريتيدات في الوسط القاعدي مع المعادلات

Cations of the second group are deposited as sulfides in an acidic medium by dissolving the salt in water and adding diluted hydrochloric acid to make the solution acidic. Hydrogen sulfide gas is then passed through the solution to detect cations like copper (Cu (II). The basic experiment involves adding the group reagent (HCL + H2O) to the salt solution, resulting in a black precipitate of copper sulfide (CuS) which dissolves in hot nitric acid. This process is used because sulfides of this group do not dissolve in water. The reaction can be summarized as CuSO4 + H2S >>> H2SO4 + CuS.