(a) Aqueous solutions of copper(II) sulfate contain the [Cu(OH₂)₆]²⁺ ion. The pH of a 0.10moldm⁻³ aqueous CuSO₄ solution is 4.17. Explain the reason why the solution is acidic, and determine K_a for the [Cu(OH₂)₆]²⁺ ion.

(b) When NH₃ is added to aqueous CuSO₄, the complex [Cu(OH₂)₂(NH₃)₄]²⁺ is ultimately formed. Initially, however, addition of NH₃ results in the formation of a precipitate of Cu(OH)₂ (K_sp = 2.20 × 10⁻²⁰). What is the origin of [OH]^– ions in this solution, and why does Cu(OH)₂ form? [Other data: for NH₃, Kb = 1.8 × 10⁻⁵]