REDOX

Question 1

Oxidation Number

Answer 1

• Oxidation number of element = 0
• Oxidation number of ion = same as charge
• Oxidation number of H+ = 1
• Oxidation number of H+ in metal Hydrides = -1
• Oxidation number of oxygen in compounds = -2
• Oxidation number of oxygen in peroxides = -1
• Oxidation number of oxygen in F2O = 2

-

Question 2

Salt Bridge

Answer 2

• Completes the reaction
• Usually a concentrated electrolyte solution
• Should not react w/ the contents of the beakers
• Allows for flow of +ive and -ive ions to maintain electrolyte neutrality
• kno3

Question 3

Primary Standards for REDOX

Answer 3

• Oxalic Acid H2C2O4.2H2O
• ammonium iron(II) sulphate.
• [(NH4)2Fe(SO4)2.2H2O¬)

Question 4

electrochemical cell

Answer 4

• spontaneous redox reaction occurs and chemical energy is converted to electrical energy.
• conducting wire = external circuit
• flows neg to pos
• anode to cathode

Question 5

• Primary cells

Answer 5

• the spontaneous redox reaction cannot be reversed.

Question 6

• Secondary cells

Answer 6

• can be recharged by passing a current through them to convert products back to reactants

Question 7

dry cell (or Leclanché cell)

Answer 7

• anode = zinc container
• cathode = graphite rod surrounded by powdered Mn02
• electrolyte is a moist paste of NH4Cl and ZnCl2
• Has a limited shelf life due to NH4Cl corrodes Zn
• Can’t be recharged due to Zn removed from anode
• A primary cell

Question 8

Secondary Cell = Lead Acid Accumulator

Answer 8

• Anode = Pb
• Cathode = Lead grid w/ Lead (IV) Oxide
• electrolyte is sulfuric acid.

Question 9

Rusting

Answer 9

• Rusting of iron occurs in the presence of oxygen and water.
• Factors such as impurities in the iron and the presence of electrolytes dissolved in the water enhance the rate of the rusting process.
• Rust occurs faster if exposed to atmosphere + bodies of water
• Rust forms on cathode where OH- is produced

Question 10

Preventing Corrosion

Answer 10

• Surface Coating
• > protecting surface of iron
• > coating w/ a less reactive metal is counter intuitive
• > therefore iron becomes anode and produces more corrosion
• > coat w/ a metal more reactive than iron
• Galvanising the surface w/ a more reactive metal
• > iron becomes cathode, other anode
• Connecting the iron / steel with conducting wire to a piece of more reactive metal
• > reactive metal = sacrificial anode
• > easily replaced
• Making iron the cathode
• > Consists of DC power source
• > Apply voltage so it is negatively charged * scrap metal

Question 11

Redox Process

Answer 11

• Anode produces electrons that travel to cathode through external circuit
• the ions in solution pick up these electrons and the ions in solution become reduced

Question 12

Standard reduction potential limitations

Answer 12

• Only in AQ soln
• Only at standard temp
• Only at standard pressure
• In 1mol concentration only
• No indication of reaction rate

Question 13

Common Oxidants

Answer 13

O2, 
Cl2, 
MnO4-, 
Cr2O72-, 
ClO-, 
H+, 
concentrated H2SO4 and HNO3.

Question 14

Common reductants

Answer 14

Zn,
H2,
Fe2+
C2O4 2-

Question 15

oxidant

Answer 15

• undergoes reduction
  e. g Cu2+ + 2e -> Cu(s)

cu2+ = oxidant

Question 16

reductant

Answer 16

• undergoes oxidation

Question 17

reduction

Answer 17

• gain electrons

Question 18

oxidation

Answer 18

• loses electrons

Question 19

Standard reduction potential

Answer 19

E.cell = E.oxidant - E.reductant

• dont flip just bracket K