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electrolysis Flashcards

reactive metals -> contaminate products in electrolysis (54 cards)

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1
Q

electrodes made of

A

electrolysis
graphite/Pt (non-react)
others (reactive)

simple cell
made of 2 diff materials

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2
Q

electrolyte must be…

A
  1. must be conductor of electricity
  2. must be ionic compound (aq/molten)

  1. in electrolyte, dissociate, form mobile ion when in (aq)
  2. break down of electrolyte, chemical reaction occurs

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3
Q

batteries funct in electrolysis setup

A

batteries (Power supply)
- electron pump, mode electrons anode -> cathode
- create positive charge, anode, negative charge, cathode

AS LONG AS THERE IS BATTERY IT IS SIMPLE CELL

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4
Q

components of simple cell

A

voltmeter/ammeter/lightbulb/resistor
- wires
- electrodes
- electrolyte

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5
Q

why cannot do electrolysis on solid ionic compound

A

cannot conduct electricity, solid form

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6
Q

When NaCl (l) means…

A
  • molten
  • pure

binary

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7
Q

When NaCl (aq) means…

A
  • aqueous
  • impure
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8
Q

neg/pos charge ions in electrolyte move to cathode/anode?

A

both simple cell, electrolysis
cations -> negatively charged cathode, connected, negative terminal power source
anions -> positively charged anode

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9
Q

what is discharge

A

lose charge

i.e. cation
Na+ (l) + e- -> Na (l)

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10
Q

molten
metal element
forms on surface of water

A

globules of silvery metal forms

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11
Q

h2o (l) electrolysis

A
  1. no reaction
  2. h2o(l) does not have ions
  3. in electrolyte, dissociate, form +, - ions

H+, Oh- ions only present, ionic compound (aq)

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12
Q

In very conc. soln (aq)
will number of Cl- > Oh-

A

no
- Cl- ions will nvr outnumber Oh-
- Oh- is solvent
- in conc. soln, no of Cl- ions is more than usual

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13
Q

which anions are not affected by conc. (anode)?

what happens instead?

A
  1. So4 2-, No3 -
  2. even when conc. ___ sulfate/nitrate Oh- will be selectively discharged

anyth w/ ions can be discharged i.e. acid/alkali

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14
Q

Oh- discharged half eqn

A

4OH- (aq) -> 2H2o (l) + O2 (g) + 4e-

keep in mind
OH- ions is in water when other ions present.

water (l) (pure water) // water with no ions dont have Oh-

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15
Q

for visible observation for electrolysis…

A
  1. any solid formed
  2. color change of soln.
  3. efferverscence + gas released

DO NOT write water level rise/drop

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16
Q

industrial use, electrolysis
besides extraction, metals

A
  1. electrolytic purification
  2. electroplating
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17
Q

desc electroplating process, anode, cathode, electrolyte

A
  • coat metal with a layer of another metal
  • anode: pure plating metal
  • cathode: plated obj (must b conductor of electricity w/ few exceptions i.e. diamond)
  • electrolyte: (aq) soln. (nitrate), salt of plating metal

anode metal, if non-reactive (Not Pt, graphite), tends to diminishes in size

cathode metal tends to thicker in size

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18
Q

electrolytic purification

A
  • purify metals, Cuso4
  • anode (impure metal, dissolve, electrolyte)
  • cathode (pure metal, increase in mass)
  • impurities like silver, fall, bottom container, anode slime
  • aq salt., purified metal
    e.g. electrolysis aq CuSo4, copper electrodes
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19
Q

in electrolysis, which is anode, cathode?

A

https://docs.google.com/document/d/1Ep_FO9CxYSFbxmf3Zqg9mgm9NNyt2enpfMDr49gufrU/edit?tab=t.0 page 14

cathode mostly goes by react. series but always use logical reasoning abt what the set up is for

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20
Q

Simple cell

  1. when is more electricity generated?
  2. when is no electricity generated?
A
  1. difference between reactivity of both electrodes is greater
  2. two same metals in simple cell, same reactivity, no difference in reactivity, hence no voltage generated

voltmeter will also read

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21
Q

simple cell

which metals dont use

A

ones higher up in reactivity series
Potassium, Sodium

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22
Q

what are fuel cells

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A

chemical cell in which reactants are continuously supplied, produce electricity directly

i.e. hydrogen-oxygen fuel cell

23
Q

fuel cell vs simple cell

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A

fuel cell: electrodes are same material

24
Q

fuel cell vs dry cell

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A

fuel cell
reactants are continuously pumped in, external reservior

dry cell
contained within

dry cells are not a type of fuel cell
both fuel and dry cells are type of simple cell

25
hydrogen fuel cell anode and cathode half eqns
**anode - oxidation is lose**: 2h2 (g) -> 4H+ (aq) + 4e- **cathode - reduction is gain**: o2 (g) + 4H+ (aq) + 4e- -> 2h2o (l) **overall**: 2h2 + o2 -> h2o (l)
26
how does fuel cell work
1. electrons drawn from anode -> cathode through internal circuit, produce direct current 2. electrolyte special design, ions can pass thru it, electrons cannot 3. anode catalyst usually very fine platinum powder 4. cathode catalyst usually nickel ## Footnote **basically** potential difference (aka difference in reactivity)... - force molecules lose/gain electrons - this is sped up by catalyst - drawn from more reactive -> less reactive
27
electroplating usages
1. metals more resistant, corrosion i.e. chromium, nickel plating 2. improve appearance, metals i.e. coat cutlery, jewelry w/ silver
28
why electrolyte cannot be metal
electrolysis involve, mobile ions, conduct electricity, allow chem reaction occur metals only, mobile electrons, no mobile ions ## Footnote **!** Ions need mobile, cations able move cathode anions able move anode ion migration
29
when desc lose charge, electrolysis
selectively discharge **ION**
30
what used as inert electrode? Reasoning
Pt/Graphite (Carbon) 1. **Unreactive** -> must write! 2. good conductor, electricity 3. for Pt: not easily corroded, gases 4. oxygen oxidise a carbon electrode need replace
31
electrolysis
2. reaction occurs, electrolyte which is molten/aq electrolytic conductor 3. electron flow driven, battery ## Footnote reaction involves 1. breaking down, electrolyte 2. movement, ions simple cell **driven by chem reaction**
32
how are ions discharged
cations recieve electrons -> cathode (reduction) anions give up electrons -> anode (oxidation) ## Footnote cations move towards cathode and vice versa
33
anions ease of discharge, reasoning
1. go down grp 17, easier discharged, less reactive 2. **OH- ions easiest, discharge**, most readily oxidise ## Footnote SHOE Anode is oxidation, where need to lose electron go down grp 17, size of nucleus increase, more valence e- easier lose valence e-
34
cations ease of discharge reasoning
oxidation, gain electron, discharge less reactive element gain electron easier ## Footnote rest just use react series format
35
simple cell char.
1. electricity generated, **spontaneous** movement, electrons, wires 2. aka electric cell 3. electrolyte, 2 diff metals, electrodes, connect external circuit 4. voltage, how far apart, 2 metals, react series
36
simple cell fuel cell and dry cell anode, cathode neg/pos?
anode negative terminal cathode positive terminal ## Footnote **electron flow in these cells are** more reactive electrode (anode) -> less reactive electrode (cathode) anode is more reactive as its the one which supplies the electrons (ions lose electrons to anode)
37
electrolysis stuff remaining, hence universal indicator...
(Ion) and (Ion) remains in solution, hence Universal Indicator green -> () ## Footnote always look for which ions are discharged first :) **remember: H+ , OH- ions make up H2o (l) so if you want to say solution increases in conc., must say both h+ oh- are selectively discharged**
38
why metal anode have priority for discharge
metal anode loses electrons more readily than (nonmetal) ions, selectively discharged ## Footnote all anode ions are nonmetal **!! metal only gets selective discharge priority in anode, not cathode. Cathode, as usual, always follows lowest reactivity**
39
solubility of __ gas affect ratio of gases collected for electrolysis
some __ gas produced, dissolve in soln., smaller than expected vol of __ gas collected ratio will be greater than expected
40
difference between expected ratio greater when electrolysis starts, aft run for some time, unnoticeable why?
1. start of electrolysis, conc. dissolved gas in soln. low, 2. electrolysis run some time, soln, saturated w/ dissolved gas, 3. gas produced less likely dissolve, soln. ## Footnote dissolved gas i.e. dissolved o2
41
why impure h2o got H+ and Oh- ions
H2O(l) ⇌ H+(aq) + OH–(aq)
42
electrolytic purification - why electrolyte colour intensity does not change
anode discharge, replenish (metal) ions
43
electrolytic purification - if copper anode replace with graphite/platinum anode, can still discharge pure copper?
yes Cu2+ (aq) ions in copper salt soln. of electrolyte can still discharge in cathode
44
how non conductive items get electroplated
coat w/ layer, graphite, before immerse in electrolyte
45
simple cell metal anode (reactive)
undergo oxidation, diminishes in size form cations, enter electrolyte ## Footnote does not matter which electrolyte is in simple cell as long as (aq/l) ionic compound
46
simple cell no battery what powers it?
electrical energy produced through chemical reactions
47
simple cell use what electrodes?
reactive metals
48
simple cells e.g.
lithium-ion batteries
49
ratio h2:o2 consumed in hydrogen fuel cell
H2 : O2 2 : 1
50
making hydrogen fuel cell one consideration
**hydrogen fuel dont come in direct contact, o2** - ensure h2 is not spontaneously oxidised **excess hydrogen pumped back, anode chamber** - reduce waste
51
in a circuit, moles of electron is...
always the same (molar ratio can be different) ## Footnote i.e. Ag(s) -> Ag+ (aq) + e- 4oh- (aq) -> o2 (g) + 2h2o (l) + 4e- If e- is 0.005mol, **whole circuit electron moles are 0.005mol** therefore, 4e- = 0.005mol e- = 0.005/4 = 0.00125 so mole of o2, for example, is 0.00125
52
can use "UV" in olvl
no. spell fully ultraviolet
53
simple cell electron flow driven by
difference, electronic potential, materials ## Footnote basically difference in reactivity of metals
54
why conc. of electrolyte nvr change
rate of formation of () ion from oxidation of anode same as rate of selective discharge of () ion, cathode
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