Hydrogen iodide is unstable, decomposes in light, fumes in moist air and can cause severe burns to skin and eyes. When hydrogen iodide is heated, it breaks down as shown in the equation:
2HI(g) → H2(g) + I2(g)
Hydrogen iodide is also very soluble in water and it dissociates fully in water to produce ions.
(a) Give the chemical formulae of the ions present when hydrogen iodide dissolves in water.
(b) In the laboratory preparation of lead(II) iodide, aqueous solution of hydrogen iodide can be used as one of the starting materials. However, it is not a good choice as a starting material because it is a very corrosive solution.
(i) Give an alternative starting material in the laboratory preparation of lead(II) iodide.
(ii) Outline the main steps in the method of preparing a pure and dry sample of lead(II) iodide in the laboratory, starting from the reagent given in (b)(i).
(a) H+, I–, OH–
(b) (i) KI/ NaI/ NH4I , or any other soluble iodide 
(ii) Add KI/NaI/ NH4I into Pb(NO3)2
Filter the mixture to obtain the precipitate (PbI2)
Wash residue with deionised water and dry between filter paper.
REJECT: Filtrate the mixture