topic 14: redox 2

Question 1

standard electrode potential

Answer 1

potential difference of an electrode measured compared to the SHE

Question 2

standard conditions for standard electrode potential

Answer 2

• 298 K
• 1 atm
• 1 mole of ion

Question 3

describe how the cell is usually set up

Answer 3

• high resistance voltmeter
• 2x metal electrodes in 1M of its ion solution
• salt bridge connecting the two

Question 4

why must the voltmeter be high resistance

Answer 4

• stop current flowing in circuit
• to measure max possible potential difference

Question 5

how to make. salt bridhe

Answer 5

filter paper soaked in potassium nitrate

Question 6

why use a salt bridge

Answer 6

• teh free moving ions conduct charge
• must be UNREACTIVE WITH THE ELECTRODES AND SOLUTIONS
• not a wire as wouldnt allow the flow of ions

Question 7

more positive electrode

Answer 7

is reduced

Question 8

cell diagram

Answer 8

x | most oxidised form || most oxidised form| Y
- solid vertical line = change of state
- double line = salt bridge

Question 9

what to use if theres no solid metal electrode?

Answer 9

• PLATINUM ELECTRODE
• unreactive
• conducts electricity

Question 10

what to use in cell diagram is no change of state?

Answer 10

comma, then platinum
eg Fe3+,Fe2+ |Pt

Question 11

describe SHE

Answer 11

LHS
- 1M hcl
- platinum electrode
- H2 gas at 1 atm
KNO3(AQ) SALT BRIDGE
RHS
- metal electrode
- metal ion solution

Question 12

SHE potential

Answer 12

0 volts

Question 13

hydrogen electrode eqm

Answer 13

H2(g) -> 2H+ (aq) + 2e-

Question 14

how to represent the SHE in a cell diagram

Answer 14

Pt | H2(g)|H+ (aq)

Question 15

if u want fe2+ fe3+ how do u do it

Answer 15

• platinum electrode
• 1M fe2+ and 1M fe 3+ mixed together

Question 16

calculating EMF

Answer 16

Erhs - Elhs
AS IT IS

Question 17

E cell is directly proportional to …

Answer 17

• delta s total
• lnK

Question 18

if current is allowed to flow waht happens to E cell?

Answer 18

• react occurs
• e cell falls to 0 as reaction proceeds and [reactants] drop

Question 19

why might a reaction not happen despite e cell postiive

Answer 19

• high activation energy
• non standard conditions

Question 20

what can be used in fuel cells

Answer 20

• anything with hydrogen
• uses the energy of the reaction to create a voltage

Question 21

hydrogen oxygen fuel cell

Answer 21

• EQUATION
  2H2 + O2 = 2H2O
• KOH electrode
• h2 in , o2 from air
• CONSTANT VOLTAGE as cells are continuously fed with fresh O2 and H2

Question 22

advantage of fuel cells

Answer 22

• less pollution
• fewer co2 emissions
• more efficient

Question 23

limitations of fuel cell

Answer 23

• expensive equipment
• storing and transporting hydrogen unsafe
• hydrogen needs to be done by electrolysis of water, but requires electricity

Question 24

what else could u use in fuel cells?

Answer 24

methanol , ethanol

Question 25

advantage of ethanol fuel cell

Answer 25

- ethanol can be made in a reneweable and carbon neutral way - less explosive

Question 26

why is a manganate titration self indication

Answer 26

MnO4 - = purple Mn 2+ = colourless ((pink)

Question 27

considerations of which acid for Manganate titration?

Answer 27

ONLY EVER DILUTE SULFURIC 1. if not enough acid (or too weak) -> only reduced down to MnO2. brown, masks colur change 2. cant be HCl: Cl- would be oxidised by MnO4- to Cl2 as the e cell is v positive. PROBLEM: poisonous Cl2, titre diff 3. cant be nitric acid, as would oxidise the Fe2+

Question 28

for the manganate ethanedioate reaction what must u do at first?

Answer 28

- heat reaction - mn2+ catalyst - reaction too slow at first due to repulsion

Question 29

ethanedioate alwasy goes to

Answer 29

co2

Question 30

consideration with IRON ETHANEDIOATE and manganate

Answer 30

the fe2+ also reacts with mno4 - - add together the overall eqn for fe2+ mno4- and the overall eqn of c2o4 2- mno4 -

Question 31

in cell diagrams, if applicable what do u do with oh- , h+, h2o

Answer 31

INCLUDE THEM

Question 32

IN CELL DIAGRAMS HOW DO.U INCLUDE RATIOS

Answer 32

as they are in teh half equations

Question 33

suitable anion for a solution

Answer 33

so4 2- cl-

Question 34

suitable cation for a solution

Answer 34

k+

Question 35

if you have eg Cr2(so4)3 then what conc does the solution need to be?

Answer 35

0.5 mol dm -3 MUST BE 1 M OF YOUR ION

Question 36

PURPOSE OF SALT BRIDGE

Answer 36

flow of ions

Question 37

when saying an ox or reducing agent specify

Answer 37

ACIDIFIED

Question 38

n in faradays equation

Answer 38

the number of electrons in each half

Question 39

thiosulfate ion

Answer 39

S2O3 2-

Question 40

3 properties transioin metals

Answer 40

- variable oxidation states - complexes - coloured

Question 41

name the aqua complex

Answer 41

hexa aqua metal (oxidation state)

Question 42

what happens if u add starch indicator too early in the iodine thisoulfate

Answer 42

- forms an insoluble complex - ititre too low

Question 43

when considering less eror in a titration

Answer 43

- less conc of reactant so greater volume - larger mass of solid - use a 3dp balance

Question 44

State one important feature of a fuel cell that is different from a conventional storage cell

Answer 44

- fuels react to give ELECTRICAL energy

Question 45

overall equation hydrogen oxygen fuel cell

Answer 45

2H2 + O2 = 2H2O

Question 46

to find delta h nuetralisation it is for

Answer 46

ONE mole of WATER FORMED !!!!

Question 47

hwo will temperature change be different if you double all the values

Answer 47

- the same - double the energy spread over double the volume

Question 48

is it an issue if u read from top of meniscus

Answer 48

NO burette measures by difference

Question 49

electron configuration exceptions

Answer 49

copper chromium

Question 50

Br2 at room temp

Answer 50

liquid not gas