Redox

Question 1

in a peroxide ?

Answer 1

O = -1

Question 2

redox =

Answer 2

reduction reaction + oxidation reaction

Question 3

oxidation number?

Answer 3

no. of electrons, lost gained or shared when an element reacts

Question 4

half reactions overall give

Answer 4

ionic equation

Question 5

oxidising agent?

Answer 5

are reduced, CAUSING OXIDATION

Question 6

Reducing agent?

Answer 6

are oxidised, CAUSE REDUCTION

Question 7

Can’t do half equations when

Answer 7

molecules involved bc no e- transfer

Question 8

when reactions are in aq solution?

Answer 8

• H20, H+ present so use these to balance

Question 9

to get overall eq?

Answer 9

• e- number must be same in each equation

* cancel anything that comes up on both sides

Question 10

if O bonded to F?

Answer 10

no longer -2

Question 11

if H is in a hydride?

Answer 11

no longer +1

Question 12

No. of change in ox =

Answer 12

no of change in reduction

Question 13

balance using Ox numbers?

Answer 13

• balance spectator ions last

* if 2 of the species (little no.) , x2 the number of change

Question 14

A half cell

Answer 14

element in 2 diff oxidation states

Question 15

electrode potential symbol

Answer 15

Eθ

Question 16

Why is an inert electrode needed when there is an ECC w ions in diff ox states?

Answer 16

e.g. Pt or C bc no solids so can’t just dip crocodile clips into solution

Question 17

how are SEP measured?

Answer 17

by connecting half cells to a SHE and measuring the PD

Question 18

Half cells can be combined to form?

Answer 18

an electrochemical cell

Question 19

salt bridge?

Answer 19

• connects the 2 solutions allowing ions to be trans between 2 half cell, completing the circuit
• doesn’t react w solutions in half cells
• KNO3 (aq) usually, has to have a conducting solution

Question 20

the more + value is the

Answer 20

reduction

Question 21

conc of solutions in half cells?

Answer 21

1moldm-3

Question 22

SEP is

Answer 22

the tendency to gain e-

Question 23

SEP definition?

Answer 23

voltage of a half cell compared to SHE measured at 298K, 100kPa, 1 moldm-3

Question 24

eq to calc Eθcell?

Answer 24

Eθ positive -( Eθ negative)

or Eθ reduced - Eθ oxidised

Question 25

Eθ NOT

Answer 25

measured by mole, don't multiply up

Question 26

when changing a conc look at

Answer 26

both equations!!

Question 27

Positive Eθ =

Answer 27

feasible

Question 28

⭐ can only change [] of

Answer 28

(aq) ions not solid

Question 29

how to work out the best reducing agent?

Answer 29

* smallest E theta value | * least likely to be reduced

Question 30

oxidising/ reducing agent?

Answer 30

• write the right species e.g. for reducing agent write the thing that is ABOUT TO BE oxidised

Question 31

types of electrochemical cells?

Answer 31

* used as cells and batteries * non-rechargeable cells * rechargeable cells * fuel cells

Question 32

lead-acid battery: negative electrode?

Answer 32

Pb

Question 33

lead-acid battery: positive electrode?

Answer 33

PbO2

Question 34

lead-acid battery: electrolyte?

Answer 34

Sulfuric acid

Question 35

one disadvantage of use lead acid battery in cars?

Answer 35

* Pb is heavy * acid may leak out and corrode vehicle * may be no charge left in battery - may go flt

Question 36

what is a fuel cell?

Answer 36

an electrochemical device that combines hydrogen or a hydrogen rich fuel and O2 to produce electricity with water and heat as its by product

Question 37

Fuel cells: fuel

Answer 37

* a log as fuel is supplied, fuel cell will continue to generate power - doesn't need to be disposed of or recharged * Since the conversion of fuel to energy takes place via an ECC process not combustion, the process is clean (no CO2 produced), quiet and high efficient

Question 38

fuel cell overall equation

Answer 38

half equations for ox and red add together to give the same overall eq as combustion

Question 39

what is reduced in a fuel cell?

Answer 39

oxygen, at cathode to water

Question 40

what is oxidised in a fuel cell?

Answer 40

fuel , to CO2 at anode

Question 41

the fuel always

Answer 41

gets converted into CO2, but not if fuel is H2

Question 42

rechargeable and non-rechargable ECC are called

Answer 42

storage cells

Question 43

+ of rechargeable cell?

Answer 43

can be used many times

Question 44

+ of non- rechargeable cell?

Answer 44

cheaper

Question 45

+ of fuel cell?

Answer 45

efficent, clean and quiet

Question 46

fuels for fuel cell?

Answer 46

* alcohol * alkanes * alkenes * hydrogen

Question 47

problem w hydrogen fuel cell?

Answer 47

* H2 = explosive | * not universally available