A student is provided with two unlabelled solid salts, Salt P and Salt Q. Refer to the diagnostic test observations in the diagram:
Salt P dissolves in water to form a pale green solution.
Addition of aqueous sodium hydroxide produces a dirty green precipitate that is insoluble in excess and slowly turns brown at the liquid surface on standing. Identify the cation present in Salt P.
Write an ionic equation, including state symbols, for the formation of the dirty green precipitate.
To an acidified sample of solution P, aqueous silver nitrate is added, producing a bright yellow precipitate.
Identify the anion present in Salt P.
Give the full chemical formula and name of Salt P.
Solid Salt Q is dissolved in water and heated with aqueous sodium hydroxide and aluminium foil. A pungent, alkaline gas G is evolved that turns damp red litmus paper blue.
Identify gas G and state the anion confirmed by this test.
Describe the chemical role of aluminium foil in this test.
A clean nichrome wire dipped in concentrated hydrochloric acid and solid Salt Q produces a persistent lilac flame in a non-luminous Bunsen flame.
Identify the metal cation in Salt Q.
Give the chemical formula of Salt Q.
Explain why dilute nitric acid (), rather than dilute hydrochloric acid (HCl) or dilute sulfuric acid (), must always be used to acidify solutions prior to adding aqueous silver nitrate or barium nitrate.