9.1 Oxidation and Reduction

Which of the following is the correct definition of oxidation?

A. Gain of electrons

B. Loss of electrons

C. Gain of protons

D. Loss of protons

In the reaction: 2Fe^3+ + 3S^2- -> Fe2S3, which species is reduced?

A. Fe^3+

B. S^2-

C. Fe2S3

D. None of the above

For balancing the following half-reaction in a basic solution: MnO4^- -> MnO2, which of the following steps is correct?

A. Add 2 electrons to the right side

B. Add 4 hydroxide ions to the left side

C. Add 2 water molecules to the right side

D. Add 2 electrons to the left side

Which of the following rules is NOT correct for assigning oxidation states?

A. The oxidation state of an atom in its elemental form is zero.

B. The oxidation state of hydrogen in most compounds is +1.

C. The oxidation state of oxygen in peroxides is -1.

D. The oxidation state of fluorine in all compounds is +1.

In the reaction: 2Al + 3Br2 -> 2AlBr3, what is the change in oxidation state of bromine?

A. From 0 to -1

B. From 0 to +1

C. From -1 to 0

D. From +1 to 0

a) What is meant by the term "oxidation state"? List two rules for assigning oxidation states to elements in a compound. [3]

b) In the reaction: 2H2 + O2 -> 2H2O, which element undergoes oxidation and which undergoes reduction? [2]

a) What is the half-reaction method used for in the context of redox reactions? [2]

b) Balance the following redox reaction in an acidic solution using the half-reaction method: MnO4^- + C2O4^2- -> Mn^2+ + CO2 [4]

a) How does balancing redox reactions in acidic solutions differ from balancing them in basic solutions? [3]

b) Balance the following redox reaction for a basic solution: ClO^- + Cr^3+ -> Cl^- + CrO4^2- [3]

a) Define the term "oxidation" in terms of electron transfer. [1]

b) For the reaction: 2Fe^3+ + 3S^2- -> Fe2S3, identify the species being oxidised and the species being reduced. [2]

c) What is the change in the oxidation state of iron in the above reaction? [2]

a) What is the significance of the half-reaction method in balancing redox reactions? [2]

b) Given the half-reaction: NO3^- -> NO + H2O, balance it in acidic conditions. [3]

c) How would you modify the balanced half-reaction if the conditions were basic instead of acidic? [2]