U2- Electrochemistry

Question 1

displacement

Answer 1

an element displaces another element from a compound

Question 2

addition

Answer 2

one molecule attaches to another across a double bond

Question 3

decomposition

Answer 3

a substance breaks down into one or more smaller particles

Question 4

condensation

Answer 4

produces a small molecule byproduct, usually water

Question 5

oxidation

Answer 5

loss of electrons
increases in oxidation number
gain O2/ loss of H

Question 6

reduction

Answer 6

gain of electrons
decreases in oxidation number
loss of O2/ gain of H

Question 7

what type of reaction is a redox reaction

Answer 7

displacement

Question 8

oxidant/ oxidising agent

Answer 8

reactant that cause another substance to be oxidised (what is reduced)

Question 9

reductant/ reducing agent

Answer 9

reactant that causes another substance to be reduced (what is oxidised)

Question 10

oxidation number

Answer 10

measure of electron density around an atom, compared to its elemental form (sign b4 no.)

Question 11

Ox rule: 1

Answer 11

sum of oxidation numbers = total charge

Question 12

Ox rule 2 and 3

Answer 12

2: F= -1
3: G1= +1, G2= +2

Question 13

Ox rule 4

Answer 13

H bonded to non metals = +1
H bonded to metal = -1

Question 14

Ox rule 5

Answer 14

Oxygen = -2 unless in peroxides the O= -1

Question 15

Ox rule 6

Answer 15

If 2 or more different G7 elements present, more electronegative one is -1

Question 16

KOHES

Answer 16

Key element
balance oxygens
balance hydrogens
balance charges by adding electrons
STATES
(separate into 2 half equations)

Question 17

why do oxidation and reduction occur simultaneously during any redox

Answer 17

bc any loss of e by one substance must be accompanied by a gain in e by something else

Question 18

conjugate oxidant/reductant

Answer 18

substance produced when a reductant loses/ oxidant gains e, containing the element that has increased/decreased in oxidation number

Question 19

standard redox conditions

Answer 19

all solutions = 1M
all gases @ 1atm
all solids = pure
electrode= made of reductant if it is solid and conductive otherwise inert electrode eg graphite or platinum

Question 20

salt bridge

Answer 20

structure containing free-moving unreactive ions that provides a connection bw two half cells. (often filter paper soaked w KNO3)

Question 21

electrochemical series

Answer 21

higher on left= oxidants at cathode that are preferentially reduced
lower on right= reductants at anode that are preferentially oxidised

Question 22

predicting spontaneous reaction: electrochemical series

Answer 22

if oxidant is higher in the series than reductant, reaction will occur
\
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Question 23

anode

Answer 23

site of oxidation
galvanic cell= negative (bc a loser)
electrolytic cell = positive (bc PANIC)

Question 24

cathode

Answer 24

site of reduction
galvanic cell= positive
electrolytic cell = negative (bc PANIC)

Question 25

galvanic cells vs direct contact

Answer 25

direct contact: nag released in the form of heat
galvanic cell: nag released in the form of electrical energy

Question 26

cell potential

Answer 26

difference bw standard electrode potential value of the cathode and that of the anode
= E (cat or oxidant) - E (anode or reductant)
(NEVER MULTIPLY BY MOLES)

Question 27

electrical potentual

Answer 27

pressure with which electrons are forced around the circuit

Question 28

standard cell notation

Answer 28

anode I conj oxidant II oxidant I cathode
or (if inert electrodes)
anode I reductant, conj oxidant II oxidant, conj reductant I cathode

Question 29

galvanic vs electrolytic

Answer 29

G. E
produce e. Consume e
ions spontaneously react ions don’t spontaneously react
convert chem nrg -> e nrg convert e nrg -> chem nrg
anode = neg; cathode = pos anode = pos; cathode = neg

Question 30

conjugate redox pair

Answer 30

two substances (one oxidant and one reductant) that share an atom (or atoms) that have gained or lost electrons

Question 31

applications of electrolysis

Answer 31

electrolysis of water
production of reactive metals
production of the substances
electroplating
electrorefining

Question 32

electrolysis of water

Answer 32

diaphragm/ separator may be required bc products are able to spontaneously react

Question 33

extraction of AL

Answer 33

treat bauxite (Al2O3) with NaOH to remove impurities
Dissolve Al2O3 in molten cryolite (Na3AlF6)- cryolite has a lower mp vs alumina which reduces operating costs
electrolyse using graphite electrodes

side reaction: C(s) +O2 (g) –> CO2 (g)

Question 34

why are graphite electrodes used and why do they have to be replaced regularly

Answer 34

inert + cheap + high MP
react w oxygen produced in side reaction to form CO2 gas

Question 35

why does Al sink to the bottom during extraction

Answer 35

denser than cryolite

Question 36

corrosion + rusting

Answer 36

corrosion= disintegration of a metal as a result of a redox chemical reaction
rusting= specific eg involving iron

Question 37

role of water droplet in rusting

Answer 37

enables ion transfer between the anodic site and cathodic site

Question 38

prevention of the corrosion of iron

Answer 38

barrier: remove O2 or water from system eg paint
chemical: coat iron with more reactive metal that preferentially oxidises vs iron

Question 39

commercial batteries

Answer 39

galvanic, storage cells the favour spontaneous redox reactions producing e current.
reactant chemicals are not replenished and eventually run out

Question 40

electroplating

Answer 40

metal substance to be electroplated @ cathode

Question 41

electrorefining

Answer 41

purifying metals
eg impure copper anode + pure copper cathode
anodic sludge formed