Redox

Question 1

What is an oxidation state?

Answer 1

Oxidation state is a measure of the degree of oxidation of an element in a compound

Question 2

What is oxidation number?

Answer 2

Oxidation number is the charge each atom in a molecule would have if its valence electrons were assigned to the more electronegative atom in a bond

Question 3

What does a increase in oxidation state imply?

Answer 3

Oxidation

Question 4

What does a decrease in oxidation state imply?

Answer 4

Reduction

Question 5

What is the oxidation state of group 1 metals?

Answer 5

Always +1

Question 6

What is the oxidation state of group 2 metals?

Answer 6

always +2

Question 7

What is the oxidation state of oxygen?

Answer 7

Usually -2 except peroxides and F₂O

Question 8

What is the oxidation state of hydrogen?

Answer 8

Usually +1, except metal hydride (-1)

Question 9

What is the oxidation state of fluorine?

Answer 9

Always -1

Question 10

What is the oxidation state of chlorine?

Answer 10

usually -1 except compounds with O or F

Question 11

What is the oxidation number of a free element?

Answer 11

Zero. e.g [Al]

Question 12

What is the oxidation number of an ion of an element?

Answer 12

equal to its charge e.g [Al³⁺]

Question 13

What is the oxidation number for atoms in a complex ion?

Answer 13

The sum of oxidation numbers of the atoms is equal to the charge [AlCl₄]⁻

Question 14

What are the oxidation numbers of K₂Cr₂O₇?

Answer 14

K = +1, Cr = x, O = -2
2(+1)+2(x)+7(-2) = 0
2+2x-14=0
2x-12=0
x=6 (6x2=12)
K = +1, Cr = +6, O= -2

Question 15

What is oxidised and reduced:
5H⁺+ Cr₂O₇²⁻+ 3HNO → 2Cr³⁺ + 4H₂O +3NO₃⁻

Answer 15

Cr₂ → 2Cr³⁺ reduction because 6+ →3+
N → 3N oxidation because 3+ → 5+

Question 16

What is electrolysis?

Answer 16

requires energy

Question 17

What is galvanic cell?

Answer 17

produces energy

Question 18

What is cell potential?

Answer 18

measure of the difference in potential between the cathode and the anode

Question 19

what is the definition of current?

Answer 19

it is a measure of the rate of flow of electrical charge

Question 20

What is the definition of power?

Answer 20

it is a measure of the rate of energy flow

Question 21

What is the E° cell equation?

Answer 21

E°cell = E° RHE - E° LHE

Question 22

What is LHE?

Answer 22

Left hand electrode, it is where oxidation occurs, anode, reducing agent/reductant

Question 23

What is RHE?

Answer 23

Right hand electrode, it is where reduction occurs, cathode, oxidating agent/oxidant

Question 24

How would we rewrite to make this reaction spontaneous?
Cu(s) Ι Cu²⁺(aq) ‖ Sn²⁺(aq) I Sn(s)
E° Cell = -0.48 V

Answer 24

Sn(s)ISn²⁺(aq) ‖ Cu²⁺(aq)ΙCu(s)
E° Cell = 0.48 V

Question 25

What is faraday constant?

Answer 25

represented as F in equation, 96485 C mol⁻1

Question 26

What is the equation for ΔG?

Answer 26

ΔG = -nFE°cell

Question 27

what does -n mean for ΔG = -nFE°cell?

Answer 27

number of mols of electrons being transferred

Question 28

What is the -n of Cr(s) I Cr³⁺ (aq) ‖ Cu²⁺ (aq) I Cu(s)

Answer 28

2Cr(s) → 2Cr³⁺ (aq) + 6e- 6e- + 3Cu²⁺ (aq) → 3Cu(s) -n = 6 electrons being transferred

Question 29

what do we add to equation under basic conditions?

Answer 29

For every H⁺ we add an OH⁻, we add OH⁻ to both sides of the equation

Question 30

Under basic conditions what happens if theres H⁺ and OH⁻ on the same side of an equation?

Answer 30

They combine to form water

Question 31

Whats the last step of balancing redox equation under basic conditions?

Answer 31

Cancel waters if possible

Question 32

What are the simplified steps of balancing redox equations?

Answer 32

1. Split into half reactions 2.Balance elements besides O and H 3. balance O with H₂O 4. Balance H with H⁺ 5. Balance charges with e- 6. match numbers of electrons 7. combine half reactions. For basic conditions → 8. Add hydroxides to both sides 9. combine H⁺ and OH⁻ to make H₂O 10. Cancel waters if possible

Question 33

When there is multiple species (aq) in at the cathode, which is closest to salt bridge?

Answer 33

IUPAC, oxidant species (reactant) will be closest to salt bridge

Question 34

How would we write the IUPAC cell notation for: 2MnO4-(aq) + 5Cu(s) + 16H+(aq) → 2Mn2+(aq) + 5Cu2+(aq) + 8H2O

Answer 34

Cu(s) | Cu2+(aq) || MnO4-(aq), Mn2+(aq), H+ (aq) | Pt(s) Pt(s) is used when theres no solid. H+ is included because its required for the reaction.

Question 35

How do we determine whats oxidised and reduced from E° Cell potential?

Answer 35

species with the more positive reduction potential will be reduced, species with the more negative reduction potential will be oxidised