A reaction takes place when a rechargeable battery is used:

Pb(s) + PbO₂(s) + 4H⁺(aq) + 2SO₄²⁻(aq) → 2PbSO₄(s) + 2H₂O(l)

Which statements are correct?

I.     H⁺ is reduced
II.     The oxidation state of Pb metal changes from 0 to +2
III.     PbO₂ is the oxidising agent

A.     I and II only

B.     I and III only

C.     II and III only

D.     I, II and III

C

D

Which element is reduced in the following decomposition?

(NH₄)₂Cr₂O₇(s) → N₂(g) + Cr₂O₃(s) + 4H₂O(g)

A.     N

B.     H

C.     Cr

D.     O

C

Which change represents oxidation?

A.     HClO₄ to HClO₃

B.     N₂ to NH₃

C.     N₂O to NO

D.     SO₄²⁻ to SO₃²⁻

C

What is the correct order of reaction types in the following sequence?

A

What is the name of \({\text{Mn}}{{\text{O}}_{\text{2}}}\)?

A.     Manganese(II) oxide

B.     Magnesium(II) oxide

C.     Manganese(IV) oxide

D.     Magnesium(IV) oxide

C

The following equations indicate reactions that occur spontaneously.

\[\begin{array}{*{20}{l}} {{\text{Fe(s)}} + {\text{NiC}}{{\text{l}}_2}{\text{(aq)}} \to {\text{FeC}}{{\text{l}}_2}{\text{(aq)}} + {\text{Ni(s)}}} \\ {{\text{Zn(s)}} + {\text{FeC}}{{\text{l}}_2}{\text{(aq)}} \to {\text{ZnC}}{{\text{l}}_2}{\text{(aq)}} + {\text{Fe(s)}}} \\ {{\text{Ni(s)}} + {\text{PbC}}{{\text{l}}_2}{\text{(aq)}} \to {\text{NiC}}{{\text{l}}_2}{\text{(aq)}} + {\text{Pb(s)}}} \end{array}\]

Which is the increasing order of the reactivity of the metals?

A.     \({\text{Fe}} < {\text{Ni}} < {\text{Zn}} < {\text{Pb}}\)

B.     \({\text{Pb}} < {\text{Ni}} < {\text{Fe}} < {\text{Zn}}\)

C.     \({\text{Ni}} < {\text{Zn}} < {\text{Pb}} < {\text{Fe}}\)

D.     \({\text{Zn}} < {\text{Fe}} < {\text{Ni}} < {\text{Pb}}\)

B

Consider the following half-equations:

I₂ (s) + 2e^– \( \rightleftharpoons \) 2I^– (aq)                 E^θ = +0.54 V
(brown)          (colourless)

MnO₄^– (aq) + 8H⁺ (aq) + 5e^– \( \rightleftharpoons \) Mn²⁺ (aq) + 4H₂O (l)                 E^θ = +1.51 V
(purple)                                      (colourless)                                                         

Which statement is correct for the reaction between KMnO₄ (aq) and KI (aq) in acidic conditions?

A. MnO₄^– reduces I^– to I₂.

B. I^– reduces MnO₄^– to Mn²⁺.

C. The colour changes from brown to purple.

D. MnO₄^– is oxidized to Mn²⁺.

B

Which is a redox reaction?

A.     \({{\text{[Cu(}}{{\text{H}}_{\text{2}}}{\text{O}}{{\text{)}}_{\text{4}}}{\text{]}}^{2 + }}{\text{(aq)}} + {\text{4C}}{{\text{l}}^ - }{\text{(aq)}} \to {{\text{[CuC}}{{\text{l}}_{\text{4}}}{\text{]}}^{2 - }}{\text{(aq)}} + {\text{4}}{{\text{H}}_{\text{2}}}{\text{O(l)}}\)

B.     \({\text{A}}{{\text{g}}^ + }{\text{(aq)}} + {\text{C}}{{\text{l}}^ - }{\text{(aq)}} \to {\text{AgCl(s)}}\)

C.     \({\text{Zn(s)}} + {\text{2HCl(aq)}} \to {\text{ZnC}}{{\text{l}}_{\text{2}}}{\text{(aq)}} + {{\text{H}}_{\text{2}}}{\text{(g)}}\)

D.     \({\text{2}}{{\text{K}}_{\text{2}}}{\text{Cr}}{{\text{O}}_{\text{4}}}{\text{(aq)}} + {\text{2HCl(aq)}} \to {{\text{K}}_{\text{2}}}{\text{C}}{{\text{r}}_{\text{2}}}{{\text{O}}_{\text{7}}}{\text{(aq)}} + {{\text{H}}_{\text{2}}}{\text{O(l)}} + {\text{2KCl(aq)}}\)

C

D

Consider the following reaction.

\[{\text{MnO}}_4^ - ({\text{aq)}} + 8{{\text{H}}^ + }({\text{aq)}} + 5{\text{F}}{{\text{e}}^{2 + }}({\text{aq)}} \to {\text{M}}{{\text{n}}^{2 + }}{\text{(aq)}} + 5{\text{F}}{{\text{e}}^{3 + }}({\text{aq)}} + 4{{\text{H}}_{\text{2}}}{\text{O(l)}}\]

Which statement is correct?

A.    \({\text{MnO}}_4^ - \) is the oxidizing agent and it loses electrons.

B.     \({\text{MnO}}_4^ - \) is the reducing agent and it loses electrons.

C.     \({\text{MnO}}_4^ - \) is the oxidizing agent and it gains electrons.

D.     \({\text{MnO}}_4^ - \) is the reducing agent and it gains electrons.

C

Which species are the oxidizing and reducing agents in the following reaction?

\[{\text{SO}}_3^{2 - }{\text{(aq)}} + {\text{Pb}}{{\text{O}}_2}{\text{(s)}} + {{\text{H}}_2}{\text{O(l)}} \to {\text{SO}}_4^{2 - }{\text{(aq)}} + {\text{Pb(OH}}{{\text{)}}_2}{\text{(s)}}\]

D

Which compounds can be reduced?

I.     C₂H₄
II.     CH₃COOH
III.     CH₃CHO

A.     I and II only

B.     I and III only

C.     II and III only

D.     I, II and III

D

Which species are produced at each electrode during the electrolysis of molten lead(II) bromide, \({\text{PbB}}{{\text{r}}_{\text{2}}}{\text{(l)}}\)?

D

Candidates needed to notice that it is the “species produced” that is required. Many gave B, the ions attracted to the electrodes or A, the wrong ions attracted to the electrodes.

Which are correct statements about a voltaic cell?

I.     A spontaneous redox reaction occurs which converts chemical energy to electrical energy.

II.     Oxidation occurs at the negative electrode (anode).

III.     Electricity is conducted by the movement of electrons through the salt bridge.

A.     I and II only

B.     I and III only

C.     II and III only

D.     I, II and III

A

Consider the following reaction.

\[{\text{2Cr(OH}}{{\text{)}}_3}{\text{(s)}} + {\text{6Cl}}{{\text{O}}^ - }{\text{(aq)}} \to {\text{2CrO}}_4^{2 - }{\text{(aq)}} + {\text{3C}}{{\text{l}}_2}{\text{(g)}} + {\text{2O}}{{\text{H}}^ - }{\text{(aq)}} + {\text{2}}{{\text{H}}_2}{\text{O(l)}}\]

Which statement is correct?

A.     \({\text{Cr(OH}}{{\text{)}}_{\text{3}}}\) is the oxidizing agent and the oxidation number of chromium changes from +3 to +6.

B.     \({\text{Cr(OH}}{{\text{)}}_{\text{3}}}\) is the reducing agent and undergoes reduction.

C.     \({\text{Cl}}{{\text{O}}^ - }\) is the oxidizing agent and the oxidation number of chlorine changes from +1 to 0.

D.     \({\text{Cl}}{{\text{O}}^ - }\) is the reducing agent and the oxidation number of chlorine changes from –1 to 0.

C

Which represents a redox reaction?

A.     \({\text{NaH(s)}} + {{\text{H}}_{\text{2}}}{\text{O(l)}} \to {\text{NaOH(aq)}} + {{\text{H}}_{\text{2}}}{\text{(g)}}\)

B.     \({\text{CaC}}{{\text{O}}_{\text{3}}}{\text{(s)}} \to {\text{CaO(s)}} + {\text{C}}{{\text{O}}_{\text{2}}}{\text{(g)}}\)

C.     \({\text{CuC}}{{\text{l}}_{\text{2}}}{\text{(aq)}} + {{\text{K}}_{\text{2}}}{\text{S(aq)}} \to {\text{CuS(s)}} + {\text{2KCl(aq)}}\)

D.     \({\text{HCl(aq)}} + {\text{N}}{{\text{H}}_{\text{3}}}{\text{(aq)}} \to {\text{NH}}_4^ + {\text{C}}{{\text{l}}^ - }{\text{(aq)}}\)

A

In the electrolytic cell shown, at which electrode will chlorine form, and what is the process taking place there?

D

Which compound contains nitrogen with an oxidation number of +3?

A.     NH₄Cl

B.     HNO₃

C.     N₂O₄

D.     KNO₂

D