TEST OF PRACTICAL KNOWLEDGE QUESTION State what you would see on; (i) bubbling SO\(_2\) into acidified KMnO\(_4\) solution (ii) mixing zinc dust with CuSO\(...

Answer Details

(a) Observations

• (i) SO₂ bubbled into acidified KMnO₄: the purple (pink) solution is decolourised, becoming colourless. SO₂ reduces the tetraoxomanganate(VII).
• (ii) Zinc dust with CuSO₄ solution: the blue colour of the solution gradually fades until it becomes colourless, and a reddish-brown (pink) deposit of copper is formed.
• (iii) Concentrated HNO₃ added to freshly prepared FeSO₄ solution: the solution changes colour from green to brown as Fe²⁺ is oxidised to Fe³⁺.

(b) Substances added to dilute H₂SO₄

• (i) To give H₂(g): magnesium and zinc (iron is also acceptable).
• (ii) To give ZnSO₄(aq): zinc oxide (ZnO) and zinc trioxocarbonate(IV) (ZnCO₃); zinc metal is also acceptable.

(c) Separation set-ups I to IV

• (i) Techniques: I - Filtration; II - Chromatography; III - Use of a separating funnel (solvent extraction); IV - Evaporation.
• (ii) Concentrating a dilute salt solution for crystallisation: set-up IV (evaporation).
• (iii) Obtaining clear water from muddy water: set-up I (filtration).
• (iv) Separating a polar solvent from a non-polar solvent: set-up III (the separating funnel).
• (v) Modifying set-up IV to separate NaCl and NH₄Cl: cover the evaporating dish with an inverted funnel and heat. The NH₄Cl sublimes and re-solidifies on the cool funnel, leaving NaCl in the dish.