Question 1(multiple choice worth 4 points) (04.05 lc) what is the oxidation number of manganese in mno41−? +3 +4 +7 +8 question 2(multiple choice worth 4 points) (04.05 lc) which of the following reactions could be used to power a battery because of the transfer of electrons? pb22+ + 2br− → pbbr cacl2 + 2naoh → ca(oh)2 + 2nacl koh + hcl → kcl + h2o zn + cu2+ → zn2+ + cu question 3(multiple choice worth 4 points) (04.05 mc) read the following chemical equation: 2al + 3br2 → 2albr3 which statement best identifies and describes the oxidizing agent in the reaction? al is the oxidizing agent because its oxidation number increases. al is the oxidizing agent because its oxidation number decreases. br2 is the oxidizing agent because its oxidation number increases. br2 is the oxidizing agent because its oxidation number decreases. question 4(multiple choice worth 4 points) (04.05 mc) in which of the following reactions is chlorine (cl) oxidized? br2 + 2cl− → cl2 + 2br− cl2 + 2e− → 2cl− 2clo3− + 12h+ → cl2 + 6h2o 2na + cl2 → 2nacl question 5(multiple choice worth 4 points) (04.05 mc) the diagram shows the setup of an experiment. a few observations of the experiment are listed in the table below the diagram. a beaker filled three-fourths with a liquid labeled colorless silver nitrate solution is shown. a small strip is shown inside the beaker. the strip is labeled copper strip. the title of the image is experimental setup. experimental observations observation description 1 solution turned blue 2 gray particles were deposited on the edge of the strip which of the following is the correct explanation for one of the given observations? observation 2 is a result of nitrate ions moving into the solution. observation 1 is a result of copper ions moving into the solution. observation 1 is a result of silver atoms losing one electron. observation 2 is a result of silver ions losing one electron.

1) Answer is: the oxidation number of manganese in MnO₄⁻ is +7.

Permanganate anion has negative charge 1-.

Oxygen (O) in permanganate anion has oxidation number -2.

x + 4 · (-2) = -1.

x - 8 = -1.

x = +7; oxidation nzmber of manganese.

Oxidation number shows the degree of oxidation of an atom in a chemical compound.

2) Answer is: Zn + Cu2+ → Zn2+ + Cu.

In this chemical reaction, there is transfer of electrons from zinc (Zn) to copper (Cu). Zinc change oxidation number from 0 to +2 (lost electrons) and copper change oxidation number from +2 to 0 (gain electrons).

Oxidation half reaction: Zn⁰ → Zn²⁺ + 2e⁻.

Reduction half reaction: Cu²⁺ + 2e⁻ → Cu⁰.

In other chemical reactions, there is no change of oxidation number of elements.

3) Answer is: Br2 is the oxidizing agent because its oxidation number decreases.

Balanced chemical reaction: 2Al + 3Br₂ → 2AlBr₃.

In this chemical reaction, aluminium change oxidation number from 0 to +3 (lose electrons) and bromine change oxidation number from 0 to -1 (gain electrons, reduced).

Oxidizing agent is a substance that has the ability to oxidize other substances, to cause them to lose electrons.

In oxido-reduction reaction, at least one element lose and one element gain electrons.

4) Answer is: Br2 + 2Cl− → Cl2 + 2Br⁻.

Oxidation is increase of oxidation number.

In this balanced chemical reaction, chlorine change oxidation number from -1 (Cl⁻) to oxidation number 0 (Cl₂).

Oxidation half reaction: 2Cl⁻ → Cl₂⁰ + 2e⁻.

Reduction half reaction: Br₂ + 2e⁻ → 2Br⁻.

In other chemical reactions, chlorine is reduced.

5) Answer is: Observation 1 is a result of copper ions moving into the solution.

The reactivity series is a series of metals from highest to lowest reactivity. Metal higher in the reactivity series will displace another.

Copper (Cu) is higher in activity series than silver (Ag), so copper lose electron and silver gain electrons.

Copper is oxidized (increase of oxidation number) and silver is reduced.

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