electrochemistry

Question 1

redox reaction

Answer 1

a reaction involving the transfer of electrons

Question 2

oxidation

Answer 2

loss of electrons

Question 3

reduction

Answer 3

gain of electrons

Question 4

oxidising agent

Answer 4

substance that accepts electrons
(is reduced)

Question 5

reducing agent

Answer 5

substance that donates electrons
(it is oxidised)

Question 6

spontaneous redox reaction

Answer 6

self sustaining
stronger reactants preferentially

Question 7

non-spontaneous redox reaction

Answer 7

does not happen on its own
2 relatively weak agents
requires potential

Question 8

galvanic cell

Answer 8

electrochemical cell that converts the chemical energy of a spontaneous redox reaction into electrical energy
has capacity to deliver current until rxn reaches eqm or has run to completion - voltage of cell = 0

Question 9

cathode

Answer 9

electrode where reduction takes place
(RED CAT)
plating

Question 10

anode

Answer 10

electrode where oxidation takes place

Question 11

anode

Answer 11

electrode where oxidation takes place

Question 12

function of salt bridge

Answer 12

completes circuit (allows ions to flow)
maintains electrical neutrality in half cells

Question 13

cell notation

Answer 13

anode metal | anode soln || cathode soln||cathode metal

or RA reactant| RA product || OA reactant | OA product

Question 14

electrolyte

Answer 14

substance that can conduct electricity due to the presence of free (mobile) ions when molten or dissolved in solution (in salt bridge)
KNO3 (aq ) - strong,very soluble - no precipitate
also KCl, AgNO3, NaCl
slower slay bridge will slow down rxn- lower current

Question 15

choosing electrodes

Answer 15

inert - Pt
conductive non metal - graphite

Question 16

Standard electrode potential

Answer 16

indication of pos of eqm
more negative - eqm lies left
more positive- eqm lies right

Question 17

standard conditions

Answer 17

temp of 25 degrees celsius (room temp)
concentration of ion soln- 1 mol.dm-3
gas pressure of 1 atm

Question 18

calculating emf

Answer 18

Ecell = Ecathode - Eanode
OR
Ecell= Eoxidising agent - Ereducing agent

pos,big gap- spontaneous rxn
neg,small gap- non-spontaneous

Question 19

standard hydrogen electrode

Answer 19

reference electrode
connected as anode (may not spontaneously act as anode)
written as anode in cell notation
ie Pt| H2 | H+
neg emf will indicate that rxn does not occur spontaneously in direction given in cell notation

Question 20

SHE connected as and reacted as anode

Answer 20

Voltmeter +
notation shows spontaneous rxn
H2 (g) is stronger reducing agent
spontaneous e- flow

Question 21

SHE connected as and reacted as anode

Answer 21

Voltmeter +
notation shows spontaneous rxn
H2 (g) is stronger reducing agent
spontaneous e- flow
E - pos

Question 22

SHE connected as anode BUT reacting as cathode

Answer 22

voltmeter -
notation non spontaneous
hydrogen ions bring reduced
E neg
non spontaneous e- flow
rxns must be written spontaneously

Question 23

emf

Answer 23

indicates how close system is to reaching eqm
max- far
low- close
zero- at eqm

Question 24

LCP and emf

Answer 24

increase [reactants] or decrease [products] - fwd favoured - emf increased
decrease [reactants] or increase [products] - rvs favoured - emf decreased
increase in temp favours endothermic rxn (rvs rxn) - decreased emf
decrease in temp favours exothermic rxn (fwd rxn) - increased emf
as anode metal is oxidised , anode ions increase - LCP- favour rxn to use - rate of reduction favoured - eqm shifts right -E more positive
as cathode ions reduced , ion concentration decreases - LCP -favour production - rate of oxidation favoured - eqm shift left
E more neg

Question 25

if factors change in way that oxidation at cathode and reduction at anode favoured

Answer 25

emf decreases

Question 26

if factors change in way that oxidation at anode and reduction at cathode favoured

Answer 26

emf increase

Question 27

internal resistance

Answer 27

opposition to the flow of charge through electrodes and electrolytes in a cell

Question 28

increased surface area of electrodes …

Answer 28

increases rate of rxn by lowering internal resistance and increasing max current that cell can deliver (does not affect emf of cell )

Question 29

wider shorter or more conductive salt bridge

Answer 29

lowers internal resistance and increased max current cell can deliver (does not affect emf of cell )

Question 30

rate changes

Answer 30

no effect on pos of eqm - no impact on emf

Question 31

faradays constant

Answer 31

q =nF mole ratio applies to e- if no of moles of e- is determined - faradays constant can be used to determine quantity of charge can link to q=It once moles of e- have been converted to charge

Question 32

electrolytic cells

Answer 32

electrochemical cell that uses electrical every four cause a non spontaneous redox reaction to occur ,thus, electrical every is converted into chemical energy. consists of 2 inert electrodes dipped into electrolyte , DC supply, e- flow from neg terminal of battery to electrode, pos and neg ions carry CURRENT through electrolyte, e- glow from second electrode back to battery

Question 33

electrolysis

Answer 33

when electricity flows through molten state or through soln containing ions and ions undergo chemical rxn

Question 34

types of substances that undergo electrolysis

Answer 34

ionic salts in soln molten ionic salts aqueous solns

Question 35

identifying cathode in electrolytic cell

Answer 35

electrode connected to negative terminal becomes negatively charged pos. charged ions will be attracted to neg. charged electrode where ions gain electrons (due to repulsion from cell) - thus being reduced therefore CATHODE typically plating

Question 36

identifying anode in electrolytic cell

Answer 36

electrode connected to pos. terminal of cell - positive electrode negative ions attracted - ions will lose e- due to attraction - thus oxidised ANODE typically bubbles

Question 37

Cu colour

Answer 37

blue

Question 38

MnO4- colour

Answer 38

purple

Question 39

Cr207, colour

Answer 39

orange

Question 40

Cr3+ colour

Answer 40

green

Question 41

Cl2 colour

Answer 41

pale green

Question 42

Br2 colour

Answer 42

orange / brown

Question 43

I2 colour

Answer 43

purple

Question 44

I2 colour

Answer 44

purple

Question 45

S colour

Answer 45

yellow

Question 46

identify predominant reactions at electrodes in electrolysis of aqueous soln

Answer 46

the specific half cell reactions that will occur during electrolysis are those with the smallest difference in their standard electrode potentials - the ones with the closest E values will take place bcus they require less energy to drive the non spontaneous rxn

Question 47

role of concentration in predicting predominant anode half rxn during electrolysis

Answer 47

dilute soln- inherent reactivity will determine which half reaction occurs at anode as it would oxidise innately faster concentrated soln- increased concentration of ions - favour rxn to use them- increasing rate - adjusting that electrode potential

Question 48

under which circumstances will anode be oxidised in preference to ions in soln

Answer 48

relative strengths of reducing agents determine which reaction predominates

Question 49

brine

Answer 49

concentrated sodium chloride soln

Question 50

best conductor

Answer 50

largest current

Question 51

non electrolyte

Answer 51

no current - no products

Question 52

elements that don’t plate

Answer 52

weaker oxidising agents than water ( above water on left- Mn2+ upwards )

Question 53

metals above Cu in electro refining of copper

Answer 53

stronger reducing agents than cu will be oxidised and form ions in soln weaker oxidising agents than Cu ions will remain in soln

Question 54

metals below Cu in electro refining of copper

Answer 54

weaker reducing agents - won’t be oxidised- remain as unreacted metal falls off anode as it is eroded- collect in pile- anode sludge

Question 55

membrane cell requirements

Answer 55

for electrolysis of brine - supply of electricity - inert electrodes - purified, concentrated brine - only water supplied to cathode side - positive ion permeable membrane separate anode and cathode compartments- only allow movement of Na+ cations