redox

Question 1

oxidation

Answer 1

loss of electrons; gain of oxygen

Question 2

reduction

Answer 2

gain of electrons; loss of oxygen

Question 3

metals in redox reactions

Answer 3

undergo oxidation; reducing agents

Question 4

non-metals in redox reactions

Answer 4

undergo reduction; oxidizing agents

Question 5

oxidation numbers of halogens

Answer 5

• 1 unless bonded to a more electronegative element

e. g. ClF (Cl = +1)

Question 6

oxidation numbers of oxygen

Answer 6

• 2 unless bonded to a more electronegative element
  e. g. OF₂ (O = +2)
• 2 unless in a peroxide
  e. g. H₂O₂ (O = -1)

Question 7

oxidation numbers of hydrogen

Answer 7

+1 unless in a metal hydride

e.g. NaH (H = -1)

Question 8

↑/↓ oxidation number

Answer 8

↑ : oxidation

↓ : reduction

Question 9

balancing redox equations

Answer 9

write skeletal half-equations

balance atoms (not hydrogen or oxygen)

balance oxygen with H₂O

balance hydrogen with H⁺

balance charge with e⁻

multiply half-equations (e⁻ gain = e⁻ loss)

cancel identical species

Question 10

galvanic cell

Answer 10

spontaneous redox reaction

chemical energy → electrical energy

Question 11

anode/cathode in a galvanic cell

Answer 11

anode : where oxidation occurs; negative electrode; strongest reducing agent

cathode : where reduction occurs; positive terminal; strongest oxidizing agent

Question 12

purpose of a salt bridge in a galvanic cell

Answer 12

enables the flow of e⁻ by completing the circuit

balances charges of the two half-cells

anions → anode

cations → cathode

Question 13

acidic fuel cell

Answer 13

2H⁺ + 2e⁻ ← H₂

O₂ + 4H⁺ + 4e⁻ → 2H₂O

2H₂ + O₂ → 2H₂O

(H₃PO₄)

Question 14

basic fuel cell

Answer 14

2H₂O + 2e⁻ ← H₂ + 2OH⁻

O₂ + 2H₂O + 4e⁻ → 4OH⁻

2H₂ + O₂ → 2H₂O

(KOH)

Question 15

standard electrode potential (V)

Answer 15

Eᵒ = Ereduction − Eoxidation

Question 16

electrolytic cell

Answer 16

non-spontaneous redox reaction

electrical energy → chemical energy

Question 17

anode/cathode in an electrolytic cell

Answer 17

anode : where oxidation occurs; positive electrode; strongest reducing agent

cathode : where reduction occurs; negative terminal; strongest oxidizing agent

Question 18

electrolysis of molten, aqueous dilute & aqueous concentrated NaCl

inert electrodes (e.g. graphite or platinum)

Answer 18

molten : 2Na (liquid) + Cl₂ (gas)

dilute : 2H₂ (gas) + O₂ (gas)

concentrated : H₂ (gas) + Cl₂ (gas)

Question 19

electrolysis of aqueous CuSO₄

reactive electrodes (copper)

Answer 19

Cu (solid) + O₂ (gas)

Question 20

electroplating

Answer 20

metal electrode is the positive anode

object is connected to the negative cathode

metal ions oxidize at the anode & travel to the cathode where they reduce to form a coating

Question 21

electrorefining

Answer 21

impure copper is connected to the positive anode

pure copper is connected to the negative cathode

copper ions oxidize at the anode & travel to the cathode where they reduce to form pure copper