A chemist combines three aqueous solutions in a single beaker at 25 °C: • 0.050 M…
CHEMISTRY · Multi-part · A Level · Chemistry · Oxidation, reduction and redox reactions · Oxidation, reduction and redox reactions
Problem
A chemist combines three aqueous solutions in a single beaker at 25 °C:
• 0.050 M KMnO₄(aq) (deep purple)
• 0.10 M KI(aq) (colorless)
• 0.10 M Ba(NO₃)₂(aq) (colorless)
An excess of dilute H₂SO₄(aq) is also present to maintain acidic conditions. After stirring, the chemist observes that the solution becomes colorless and a fine white solid appears. A particulate-level sketch of the final mixture shows the following:
• Clusters of alternating large light-gray spheres (Ba²⁺) and tetrahedral groups of four small yellow spheres (SO₄²⁻) that have settled to the bottom.
• Numerous pale pink spheres labeled Mn²⁺ and pairs of green spheres bonded together, each pair sharing a single negative charge overall (I₂), dispersed in the liquid phase.
• Free K⁺ and NO₃⁻ ions remain in solution.
Answer the questions below.
(a) Identify the species that is reduced and the species that is oxidized, citing changes in oxidation number as evidence.
(b) Write the balanced net ionic equation for the redox process occurring under the acidic conditions described.
(c) Write the balanced net ionic equation for the precipitation process that forms the white solid.
(d) Combine the reactions from parts (b) and (c) into a single overall ionic equation consistent with the particulate description.
(e) Explain how principles of charge balance and solubility account for the stoichiometric ratios of particles observed in the final sketch.