Redox

Given the balanced equation representing a reaction:

2KClO₃(s) 2KCl(s) + 3O₂(g)

The oxidation state of chlorine in this reaction changes from

• –1 to +1

• –1 to +5

• + l to –1

• +5 to –1

What is the oxidation number of chromium in the chromate ion, CrO₄^2– ?

• +6

• +2

• +3

• +8

In which compound does carbon have an oxidation state of –4?

• CO

• CO₂

• CCl₄

• CH₄

In which compound is the oxidation number of oxygen treated as –1?

• CO

• CO₂

• H₂O

• H₂O₂

In an oxidation-reduction reaction, the number of electrons lost is

• equal to the number of electrons gained

• equal to the number of protons gained

• less than the number of electrons gained

• less than the number of protons gained

Which half-reaction correctly represents reduction?

• Mn⁴⁺ → Mn³⁺ + e^–

• Mn⁴⁺ → Mn⁷⁺ + 3e^–

• Mn⁴⁺ + e^– → Mn³⁺

• Mn⁴⁺ + 3e^– → Mn⁷⁺

In the reaction

MnO₂ + 4 HCl → MnCl₂ + 2 H₂O + Cl₂,

which species is reduced?

• Mn⁴⁺

• O^2–

• H⁺

• Cl^–

Which statement describes where the oxidation and reduction half-reactions occur in an operating electrochemical cell?

• Oxidation and reduction both occur at the anode.

• Oxidation and reduction both occur at the cathode.

• Oxidation occurs at the anode, and reduction occurs at the cathode.

• Oxidation occurs at the cathode, and reduction occurs at the anode.

Base your answer on the diagram below which represents a chemical cell at 298 K and 1 atmosphere.

Which species represents the cathode?

• Zn

• Zn²⁺

• Cu

• Cu²⁺

Which half-reaction can occur at the anode in a voltaic cell?

• Ni²⁺ + 2e^- → Ni

• Sn + 2e^- →Sn²⁺

• Zn → Zn²⁺ + 2e^-

• Fe³⁺ → Fe²⁺ + e^-