electrochemistry II

Question 1

define electrolyte

Answer 1

a solution that conducts electricity due to ions being able to flow past each other. may be a molten ionic compound or a dissolved ionic compound

Question 2

define electrolytic cell

Answer 2

a cell that uses an electric current to force a chemical reaction to occur that would otherwise not happen

Question 3

what is an electrolytic cell composed of?

Answer 3

two electrodes in an electrolyte that is commonly an aqueous solution or molten ionic compound

Question 4

why is there only one beaker in electrolytic cells?

Answer 4

because we can remove one beaker as the ions will not spontaneously react - so they don’t need to kept apart BUT products may spontaneously so must add separator to keep them apart

Question 5

do electrolytic cells produce or consume electricity?

Answer 5

consume/require electricity

Question 6

do electrolytic cells have spontaneous or non-spon. reactions?

Answer 6

non-spontaneous reactions

Question 7

_____ energy is converted to ____ energy in electrolytic cells

Answer 7

electrical energy -> chemical energy

Question 8

____ energy is converted to _____ energy in galvanic cells

Answer 8

chemical energy -> electrical energy

Question 9

in electrolytic cells, anode is ____ and cathode is _____

Answer 9

anode = positive and cathode = negative
PANIC

Question 10

where does oxidation and reduction occur in electrolytic cells?

Answer 10

oxidation at anode and reduction at cathode
AN OIL RIG CAT still applies, polarities just switched

Question 11

differences b/w galvanic and electrolytic cell

Answer 11

galvanic cells contain a salt bridge w/as electrolytic cells do not
galvanic cells must separate reactants w/as don’t need to in electrolytic bc NON SPONTANEOUS
galvanic cells = no power source w/as electrolytic cells do

Question 12

electron flow in electrolytic cells?

Answer 12

still from anode to cathode
anode (pos) electrons are pulled away for oxidation to occur and travel to cathode (neg) where electrons are pulled in for reduction to occur

Question 13

steps to identify electrolysis in a compound

Answer 13

1. identify all species present (aqueous sol = contains water)
2. circle species on electrochem series
3. find strongest oxidant at cathode
4. find strongest reductant at anode
5. write equations
6. answer q

Question 14

applications of electrolysis

Answer 14

-electrolysis of water -> produce oxygen and hydrogen gas
-production of reactive metals
-production of other substances
-electroplating
-electrorefining

Question 15

define electroplating

Answer 15

using electrolysis to cover a metal item with another metal in order to improve appearance or reduce corrosion

Question 16

define electrorefining

Answer 16

the use of electrolysis and an impure anode to plate a pure metal into the cathode

Question 17

define corrosion

Answer 17

the disintegration of a metal as a result of a redox chemical reaction

Question 18

define rusting

Answer 18

a specific example of corrosion involving iron

Question 19

electroplating process

Answer 19

the metal substance to be electroplated would be present in the electrolytic cell as the cathode
metal whose ions are a stronger oxidant that water = plated onto cathode to improve appearance and reduce corrosion
impure anode containing metal used for plating = source of ions/replenish

Question 20

method of extracting aluminium

Answer 20

1. treat aluminium oxide (bauxite) w. NaOH to remove impurities
2. dissolve Al2O3 in molten cryolite, bc it has lower melting point of 1009 vs 2072 that reduces operating costs
3. electrolyse using graphite electrodes

Question 21

why are graphite electrodes good?

Answer 21

cheap
inert
high mp

Question 22

why does graphite anode need to be replaced regularly

Answer 22

carbon in anode reacts w oxygen produced in oxidation reaction. to form carbon dioxide and burns away

Question 23

why does Al sink to bottom of electrolyte

Answer 23

bc more dense than cryolite so extracted from side

Question 24

electrorefining copper

Answer 24

-impure copper anode (blister copper) used to replenish Cu2+ ion in solution, loses mass
-pure copper cathode gains mass
=electrolyte = a solution of the metal ion eg. CuSO4

Question 25

what happens to impurities in the blister copper?

Answer 25

eg. lead and nickel, stronger reductants that copper, are preferentially oxidised into Pb2+ and Ni2+ whenever atoms=exposed on surface of anode
eg. silver and gold, weaker reductants than copper, will not be oxidised and fall to bottom of cell -> anodic sludge

Question 26

what does rusting involve

Answer 26

-the oxidation of iron atoms and reduction of oxygen atoms in presence of water = electrolyte = enables ion transfer bc anodic and cathodic sites, to form hydrated iron III oxide = rust
-electron transfer occurs in metal = iron = external circuit

Question 27

define sacrificial anode

Answer 27

a more reactive metal in contact w iron, that oxidises preferentially instead of the iron

Question 28

define storage cell

Answer 28

a galvanic cell in which the reactant chemicals are not replenished and will eventually run out

Question 29

two methods of preventing corrosion of Fe

Answer 29

1. barrier = eg. painting iron or using oil to remove oxygen or water
2. chemical = more reactive metal eg. zinc, al or chromium is used to coat the iron, so oxidises in preference to iron and produces regenerative oxide layer on surface

Question 30

commercial batteries

Answer 30

-galvanic cells that favour the spontaneous redox reactions
-increasing rate of spontaneous fwd reaction while minimising rate of rev