Chemistry: Electron Transfer in Redox Reactions (LEO Says GER) Practice
Identify oxidation, reduction, electron flow, and redox agents
Chemistry: Electron Transfer in Redox Reactions (LEO Says GER) Practice
Identify oxidation, reduction, electron flow, and redox agents
Chemistry - Grade 9-12
- 1
In the half-reaction Zn -> Zn2+ + 2e-, is zinc oxidized or reduced? Explain using LEO says GER.
Look for whether electrons are on the reactant side or product side.
Zinc is oxidized because it loses 2 electrons. LEO says loss of electrons is oxidation. - 2
In the half-reaction Cu2+ + 2e- -> Cu, is copper ion oxidized or reduced? Explain using LEO says GER.
Copper ion is reduced because it gains 2 electrons. GER says gain of electrons is reduction. - 3
For the reaction Zn + Cu2+ -> Zn2+ + Cu, identify the substance oxidized and the substance reduced.
Compare the charges of each element before and after the reaction.
Zinc is oxidized because Zn loses electrons to become Zn2+. Copper ion is reduced because Cu2+ gains electrons to become Cu. - 4
Write the oxidation half-reaction for magnesium changing into magnesium ions in the reaction Mg + Cl2 -> MgCl2.
The oxidation half-reaction is Mg -> Mg2+ + 2e-. Magnesium loses 2 electrons, so it is oxidized. - 5
Write the reduction half-reaction for chlorine gas changing into chloride ions in the reaction Mg + Cl2 -> MgCl2.
One Cl2 molecule contains two chlorine atoms, so the product should contain two chloride ions.
The reduction half-reaction is Cl2 + 2e- -> 2Cl-. Chlorine gains 2 electrons total, so it is reduced. - 6
In the reaction 2Na + Cl2 -> 2NaCl, which reactant is the reducing agent? Explain your answer.
Sodium is the reducing agent because it loses electrons and causes chlorine to be reduced. The reducing agent is the substance that is oxidized. - 7
In the reaction 2Na + Cl2 -> 2NaCl, which reactant is the oxidizing agent? Explain your answer.
The oxidizing agent takes electrons from another substance.
Chlorine is the oxidizing agent because it gains electrons and causes sodium to be oxidized. The oxidizing agent is the substance that is reduced. - 8
Assign oxidation numbers to iron and oxygen in Fe2O3. Then state whether iron is more oxidized in Fe2O3 than in elemental Fe.
In Fe2O3, oxygen has an oxidation number of -2 and iron has an oxidation number of +3. Iron is more oxidized in Fe2O3 than in elemental Fe because elemental Fe has an oxidation number of 0. - 9
For the reaction Fe + CuSO4 -> FeSO4 + Cu, identify what is oxidized, what is reduced, the oxidizing agent, and the reducing agent.
Sulfate stays the same, so focus on Fe and Cu.
Iron is oxidized because Fe changes from 0 to +2 in FeSO4. Copper ion is reduced because Cu2+ in CuSO4 changes to Cu with an oxidation number of 0. CuSO4 is the oxidizing agent, and Fe is the reducing agent. - 10
A student says, "If a substance is oxidized, it must gain oxygen, not lose electrons." Correct the statement using LEO says GER.
The statement is incomplete. Oxidation can involve gaining oxygen, but in redox chemistry oxidation is defined as losing electrons. LEO says loss of electrons is oxidation. - 11
Balance the electron transfer between these two half-reactions: Al -> Al3+ + 3e- and Ag+ + e- -> Ag. How many silver ions are reduced for each aluminum atom oxidized?
The number of electrons lost must equal the number of electrons gained.
Three silver ions are reduced for each aluminum atom oxidized. Aluminum loses 3 electrons, and each Ag+ gains 1 electron, so 3 Ag+ ions are needed to take the 3 electrons. - 12
Use LEO says GER to explain the electron transfer in this reaction: 2Al + 3Cu2+ -> 2Al3+ + 3Cu.
Count total electrons lost by aluminum and total electrons gained by copper.
Aluminum is oxidized because each Al atom loses 3 electrons to form Al3+. Copper ion is reduced because each Cu2+ gains 2 electrons to form Cu. In the balanced reaction, 2 aluminum atoms lose 6 electrons total, and 3 copper ions gain 6 electrons total.