Self Assess 1.1:
1. What is the meaning of a redox reaction?
2. Table 1.5 shows the equations for several redox reactions.
For each of the above redox reaction:
(a) write the half equations for oxidation and reduction.
(b) identify the oxidised substance, reduced substance, oxidising agent and reducing agent.
Explain your answer in terms of the transfer of electrons.
Answer:
1. A chemical reaction where oxidation and reduction process occur simultaneously.
2.
Reaction I
(a)
Oxidation half equation: Cu → Cu2+ + 2e−
Reduction half equation: Ag+ + e− → Ag
(b)
– Copper is oxidised because copper, Cu atoms lose electrons to form Cu2+ ions, while Ag+ ions are reduced because Ag+ gains electrons to form silver, Ag atoms.
– Ag+ ions are oxidising agents because Ag+ ions are the electron acceptors, while copper is a reducing agent because copper is the electron donor.
Reaction II
(a)
Oxidation half equation: Pb → Pb2+ + 2e−
Reduction half equation: O2 + 4e− → 2O2−
(b)
– Lead is oxidised because lead, Pb atoms lose electrons to form Pb2+ ions, while oxygen is reduced because oxygen, O2 molecules gain electrons to form oxide, O2− ions.
– Oxygen is an oxidising agent because oxygen is the electron acceptor, while lead is a reducing agent because lead is the electron donor.
Reaction III
(a)
Oxidation half equation : Al → Al3+ + 3e−
Reduction half equation : Cl2 + 2e− → 2Cl−
(b)
– Aluminium is oxidised because aluminium, Al atoms lose electrons to form Al3+ ions, while chlorine is reduced because chlorine, Cl2 molecules gain electrons to form chloride, Cl− ion.
– Chlorine is an oxidising agent because chlorine is the electron acceptor, while aluminium is a reducing agent because aluminium is the electron donor.
Reaction IV
(a)
Oxidation half equation: 2I− → I2 + 2e−
Reduction half equation: Br2 + 2e− → 2Br−
(b)
– I− ions are oxidised because I− ions lose electrons to form iodine, I2 molecules while bromine is reduced because bromine, Br2 molecules gain electrons to form bromide, Br− ions.
– Bromine water is an oxidising agent because bromine is the electron acceptor, while iodide ions are reducing agents because I− ions are the electron donors.
1. What is the meaning of a redox reaction?
2. Table 1.5 shows the equations for several redox reactions.
For each of the above redox reaction:
(a) write the half equations for oxidation and reduction.
(b) identify the oxidised substance, reduced substance, oxidising agent and reducing agent.
Explain your answer in terms of the transfer of electrons.
Answer:
1. A chemical reaction where oxidation and reduction process occur simultaneously.
2.
Reaction I
(a)
Oxidation half equation: Cu → Cu2+ + 2e−
Reduction half equation: Ag+ + e− → Ag
(b)
– Copper is oxidised because copper, Cu atoms lose electrons to form Cu2+ ions, while Ag+ ions are reduced because Ag+ gains electrons to form silver, Ag atoms.
– Ag+ ions are oxidising agents because Ag+ ions are the electron acceptors, while copper is a reducing agent because copper is the electron donor.
Reaction II
(a)
Oxidation half equation: Pb → Pb2+ + 2e−
Reduction half equation: O2 + 4e− → 2O2−
(b)
– Lead is oxidised because lead, Pb atoms lose electrons to form Pb2+ ions, while oxygen is reduced because oxygen, O2 molecules gain electrons to form oxide, O2− ions.
– Oxygen is an oxidising agent because oxygen is the electron acceptor, while lead is a reducing agent because lead is the electron donor.
Reaction III
(a)
Oxidation half equation : Al → Al3+ + 3e−
Reduction half equation : Cl2 + 2e− → 2Cl−
(b)
– Aluminium is oxidised because aluminium, Al atoms lose electrons to form Al3+ ions, while chlorine is reduced because chlorine, Cl2 molecules gain electrons to form chloride, Cl− ion.
– Chlorine is an oxidising agent because chlorine is the electron acceptor, while aluminium is a reducing agent because aluminium is the electron donor.
Reaction IV
(a)
Oxidation half equation: 2I− → I2 + 2e−
Reduction half equation: Br2 + 2e− → 2Br−
(b)
– I− ions are oxidised because I− ions lose electrons to form iodine, I2 molecules while bromine is reduced because bromine, Br2 molecules gain electrons to form bromide, Br− ions.
– Bromine water is an oxidising agent because bromine is the electron acceptor, while iodide ions are reducing agents because I− ions are the electron donors.