REDOX RXNS
Name ______Class ______Date ______
1. What happens to the manganese in the following reaction?
2MnO4–(aq) + 5H2O2(aq) + 6H+(aq) → 2Mn2+(aq) + 8H2O(l) + 5O2(g)
A. It is oxidized and its oxidation number increases.
B. It is oxidized and its oxidation number decreases.
C. It is reduced and its oxidation number increases.
D. It is reduced and its oxidation number decreases.
2. Nitrogen monoxide may be removed from industrial emissions via a reaction with ammonia as shown by the equation below.
4NH3(g) + 6NO(g) → 5N2(g) + 6H2O(l)
(i) Deduce the oxidation number of the nitrogen in the reactants and product.
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(ii) Deduce the oxidation and reduction half-equations and identify the oxidizing agent for the reaction.
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3. What happens to iodine when iodate ions, IO3–, are converted to iodine molecules, I2?
A. It undergoes reduction and its oxidation number changes from –1 to 0
B. It undergoes oxidation and its oxidation number changes from –1 to 0
C. It undergoes reduction and its oxidation number changes from +5 to 0
D. It undergoes oxidation and its oxidation number changes from +5 to 0
4. Consider the following reactions of three unknown metals X, Y and Z.
2XNO3(aq) + Y(s) → 2X(s) + Y(NO3)2(aq)
Y(NO3)2(aq) + Z(s) → No reaction
2XNO3(aq) + Z(s) → 2X(s) + Z(NO3)2(aq)
What is the order of increasing reactivity of the metals (least reactive first)?
A. X < Y < Z
B. X < Z < Y
C. Z < Y < X
D. Y < Z < X
5. Deduce the oxidation number of chromium in Cr2O72–.
6. Which definition of oxidation is correct?
A. Loss of electrons and a decrease in oxidation number
B. Loss of electrons and an increase in oxidation number
C. Gain of electrons and a decrease in oxidation number
D. Gain of electrons and an increase in oxidation number
7. Consider the following three redox reactions.
Cd(s) + Ni2+(aq) → Cd2+(aq) + Ni(s)
Ni(s) + 2Ag+(aq) → Ni2+(aq) + 2Ag(s)
Zn(s) + Cd2+(aq) → Zn2+(aq) + Cd(s)
(i) Deduce the order of reactivity of the four metals, cadmium, nickel, silver and zinc and list in order of decreasing reactivity.
(ii) Identify the best oxidizing agent and the best reducing agent.
8. Consider the following reaction.
2FeSO4(aq) + H2O2(aq) + H2SO4(aq) → Fe2(SO4)3(aq) + 2H2O(l)
Which species is the oxidizing agent and which is the reducing agent?
Oxidizing agent / Reducing agentA. / H2O2(aq) / H2SO4(aq)
B. / H2O2(aq) / FeSO4(aq)
C. / FeSO4(aq) / H2O2(aq)
D. / H2SO4(aq) / H2O2(aq)
9. In which species does sulfur have an oxidation number of 0?
A. SO3
B. S8
C. Na2SO4
D. H2S
10. What is the reducing agent in the reaction below?
2MnO4–(aq) + Br–(aq) + H2O(l) → 2MnO2(s) + BrO3–(aq) + 2OH–(aq)
A. Br–
B. BrO3–
C. MnO4–
D. MnO2
11. The word redox comes from a combination of the terms reduction and oxidation.
Redox reactions affect our daily lives.
The overall reaction that takes place in a voltaic cell is shown below.
Pb(s) + PbO2(s) + 2H2SO4(aq) → 2PbSO4(s) + 2H2O(l)
(i) Determine the oxidation number of lead in Pb, PbO2 and PbSO4.
In order to determine the position of three metals in a reactivity series, the metals were placed in different solutions of metal ions. The table below summarizes whether or not a reaction occurred.
Ag+(aq) / Cu2+(aq) / Pb2+(aq)Ag(s) / No reaction / No reaction
Cu(s) / Reaction / No reaction
Pb(s) / Reaction / Reaction
State the equations for the three reactions that take place. Use this information to place the metals Ag, Cu and Pb in a reactivity series, with the strongest reducing agent first, and explain your reasoning.
12. Fertilizers may cause health problems for babies because nitrates can change into nitrites in water used for drinking.
(i) Define oxidation in terms of oxidation numbers.
(ii) Deduce the oxidation states of nitrogen in the nitrate, NO3–, and nitrite, NO2–, ions.
13. The following equations indicate reactions that occur spontaneously.
Fe(s) + NiCl2(aq) → FeCl2(aq) + Ni(s)
Zn(s) + FeCl2(aq) → ZnCl2(aq) + Fe(s)
Ni(s) + PbCl2(aq) → NiCl2(aq) + Pb(s)
Which is the increasing order of the reactivity of the metals?
A. Fe < Ni < Zn < Pb
B. Pb < Ni < Fe < Zn
C. Ni < Zn < Pb < Fe
D. Zn < Fe < Ni < Pb
14. (a) Define oxidation in terms of electron transfer.
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(b) Chlorine can be made by reacting concentrated hydrochloric acid with potassium manganate(VII), KMnO4.
2KMnO4(aq) + 16HCl(aq) → 2MnCl2(aq) + 2KCl(aq) + 5Cl2(aq) + 8H2O(aq)
(i) State the oxidation number of manganese in KMnO4 and in MnCl2.
KMnO4 ......
MnCl2 ......
(ii) Deduce which species has been oxidized in this reaction and state the change in oxidation number that it has undergone.
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15. Which are redox reactions?
I. 2FeCl2 + Cl2 → 2FeCl3
II. Mg + 2HNO3 → Mg(NO3)2 + H2
III. H2O + SO3 → H2SO4
A. I and II only B. I and III only
C. II and III only D. I, II and III