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Chem 30 > Redox/Electrochemistry > Flashcards

Redox/Electrochemistry Flashcards

1
Q

Cations:

A
  • Positive charge
  • Atoms lose electrons to become a cation
  • Goal to have full outer shell
  • Usually Metals because they have fewer valance electrons to lose
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2
Q

Anions:

A
  • Negative charge
  • Atoms gain electrons to become an anion ( become more negative)
  • Non metals tend to gain electrons because their valance shells are almost full
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3
Q

How are cation and anion charges written

A

Cation: number +
Anion: number -
number representative of # electrons

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4
Q

Examples of electrochemical processes

A
  • Metabolism of food
  • Corrosion of metals
  • Manufactured products like batteries, electroplating, phjotographs
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5
Q

What are electrochemical (redox) reactions

A

An electron transfer between species in a chemical reaction

> made up of 2 half reactions
Redox Rxn = reduction 1/2 + oxidation 1/2

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6
Q

Electrons cant be ___ so:

A

created or destroyed
#electrons lost = # electrons gained

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7
Q

Reduction:

A
  • happens with the use of a reducing agent
  • RA undergoes oxidation to promote reduction
  • Leo says Ger : Ger - gain electrons reduction
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8
Q

Oxidation:

A
  • happens with the use of a oxidizing agent
  • OA promotes oxidation by undergoing a reduction
  • Leo says Ger : Leo - Lose electrons oxidation
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9
Q

RA and OA are determined by

A

finding net ionic equation
OA - gets reduced
RA - gets oxidized

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10
Q

Hjow can you find whole net ionic equation

A

Find half reaction of oxidation and reduction then put them together buf have electrons cancel out

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11
Q

Balancing redox reactions in acidic environments entails that

A

H+ ions present in acidic solutions and OH- in basic

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12
Q

Mostcredox reactions take place

means what must be considered

A

in aqueous solutions that are often basic ir acidic in nature

so when balancing equations environment must be considered

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13
Q

Steps to finding redox rxns in acidic environments

A

1- Write out the reactants and products unbalanced

2- Balance all atoms except H and O

3- To balance O add H2O(l)

4- To balance H, add H+ (aq)

5- Balance charges by adding electrons on side it needs

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14
Q

When given entire reactions that occurs in a acidic condition andctrying to determine RA and OA steps

A

1- Separate rxn into two half rxns

2- Balance hjalf reactions

3- Balance electrons by multiplying

4- add two half reactions together and cancel electrons

Then determine RA and OA

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15
Q

A spontaneous redox reaction occurs when

A

OA is higher than RA
OA

         RA
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16
Q

A reaction is non spontaneous when

A

it does not take place since the RA is higher than OA
ex:
RA

OA

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17
Q

5 steps to predict a redox rxn

A

1- List all entities present in the mixture and list OA and RA
> break up strong acids n soluble compounds, add water if sol is aq and H+ if acidic , dont break apart molecular or weak acids or s,l,g

2/3- Choose SOA and SRA and write ualf rxn from data book

4- Balance electrons

5- Add half rxns together to get balanced redox reaction and predict spontaneity

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18
Q

Hjjow to build Redox Tables

A

1- Label OAs and RAs

2- For each determine strongest OA

3- List all OAs from strongest to weakest and fill in half rxns then products backwards r SRA

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19
Q

What are oxidation numbers

A

a method of book keeping electrons
- a positive or negative number corresponding to thje oxidation state assigned to atom in covalent bond
* charge before number +1 or -1

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20
Q

Rules for assigning ONs

A
  • elements by themselves are zeros
  • simple ions ON same as charge of ion
  • Oxygen in compound is -2
  • Oxygen -1 only in peroxides(two oxygen)
  • Hydrogen in compound +1 except when bonded to merals its -1
    -all else found thru algebra
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21
Q

Whats the point of ONS

A
  • helps identify oxidation: ON more positive and reduction: ON more negative
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22
Q

Steps to balancing ONs

A

1- Assign known ONs and determine what was oxidized n reduced

2- Using ONs determine electrons transferred to reactants

3- Determine electrons transferred per entity ex C2

4- Determine simplest coefficient ti balance e

5- Balance the rest considering the products

6- Add H2O or H+ if needed to balance O and H

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23
Q

What is disproportion

A

When a single species is both oxidized and reduced

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24
Q

Whats a titrant

A

solution in burette progressively added to measure vil of another solution (sample) in Erlenmeyer flask

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25
What goes in the erlenmeyer flask
sample or analyte
26
a doubnle replacementreaction can njever be
a redox reactionnbc no charge balanced alr
27
In a redox titration the colour change comes from
a change in oxidation state/number of oxidizing agent
28
the colour chanbge at enbdpoint occurs because
the titranbt is no longer reacting with the sample & is staying in the flask
29
how dyk whars a titranbt in lab question
titrant is whatever it says solution is titrated with comes after
30
key words to know if adding H+ or H2O
H+ if it says acidic H2O if aq
31
whats electrochemistry
study of processes involved in converting chemical energy into electrical energy and vice versa
32
Two types of electrochemical cells what they are and their cell potential, OA RA relationship
Voltaic cells: spontaneous, produces energy- electricity - measured in volts, positive cell potential , OA higher than RA Electrolytic cells: Non spontaneous, needs input of energy to make cell rxn happen, cell potential negative and RA higher than OA
33
Voltaic cells: -Electrode and inert electrodes -Annode -Cathode -Electrolyte -External Circuit
Electrodes are solid conductors that carry electrons from annode/cathode Inert Electrodes not part of reaction dont write in, juust let electrones pass through (ex. C or Pt) Anode: electrode oxidation take place (an ox) Cathode: electrode reduction takes place (ref cat) Electrolyte: conductive solutions External circuit: a wire. circuit for electrons to move from annode to cathode (leo to ger) si anode ti cathode
34
which way do electrons travel always in both voltaic and electrolytic cells
anode to cathode , RA to OA or leo to ger
35
What a salth hridge n its role in a voltaic cell
contains an ionic electrolyte (conductive solution) ex KCL or KNO3 , want it to not react withh ions that pass through it - NO SRA OR SOA
36
A voltaic cell will have
Spontaneous rxn release energy cell potential +ive two separate half cells (reduction separated from oxidation rxn) 2 half fells connected by porous boundary (salt bridge) ion flows thru 2 electrolytic solutions 2 electrodes (anode and cathode) almost always metals solid voltmeter measuring energy released
37
In a voltaic cell Oxidation happens @ __ Reduction happens @__ electrons flow from ___ to ___ electrons do not flow through __, that only allows for flow of ____
anode cathode anode to cathode salt bridge/ porous boundary that only lets ions through
38
Whats molten
No water just reaction w the elements etc
39
What happens to ion flow in voltaic cell for cathode and anode
Annode- loses electrons so solid leaves anode electrode and increases conbcetration of solution Cathode- gains electrons so ions flow into solid electrode and increase weight of it but concetrationj of solution decreases
40
What are inert electrons anbhd when is it present common examples
When OA or RA is njot solid but gas or sum so use inert electrons to let electronbs pass through bnbut not in the redox rxns ex. Carbon or platinum, or sum not on data shjeet
41
If a injbert electrons presenjt what is the cathode
the solution
42
When writing voltaic cell in cell notation hjjow written and line meaning
Electrode anode| electrolyte anode 1/2 rxn|| electrolyte cathode | electrode cathode Written cathode or anode even if inert || is salt bridge
43
Cell potenjbtial formula
Enet = E cathode - E anode
44
Votaic cells and Electrolytic cell potenjtials are
Voltaic - positive Electrolytic- negative
45
When changing refrenjce cell how calculate
calculate how to get from ref cell hydrogen to there anjd apply that to all other potenjbtial minus
46
change in ref cell can occur
only for 1/2 rxns as full one always has same voltage
47
What is Corrosion rxn type
process by which metals r oxidized (leo) to form ore ( compound withh a metal in it) Spontaneous rxn bc we live in environment with lots of O2 oxidizing environment
48
Hjow do u tell whats easy to hne corroted and whats hard
Compare ti OA O2 + H2O + 4e > If the RA is higher on top of it its hard to oxidize, doesn’t rust easily and usually more exps > If RA below it, its easy to oxidize and rusts but cheaper
49
What are the exceptions to corroding that react diff
Al is helow O2 but makes Al2O3 so sticks clise to Al anjbd prevenjts further corrosion Hjowever Fe forms Fe2O3 which flakes and oxidizes in continuous cycle
50
Corrosion Prevention 2
1- Isolation by coating in wax , oil or another metal 2- Use another metal rither strong RA so it reacts easily instead of the metal protected or weak RA so not many OAs react w it anbhd it protects
51
Electrolytic cells are
non spontaneous so energy required to make rxn happen cell potential negative and represents amnt of energy needed to make rxn happen need outside power source battery electrons flow anode to cathode only one electrolytic solution
52
cell notation electrolytic cells
C| CuSO4 | C c is electrode but usually inert unless on table include water as species to find soa n sra unless molten and separate middle electrolyte for cathode n anode
53
Execption to electrolyticccells
Cl - always the SRA over water even if reverse on chart
54
In a electrolytic cell what is the cathode if reg one inert
The SOA of electrolyte when separated from middle
55
Whats electroplating
taking a solid metal (anode) and coating the cathode occurs at cathode cations reduced to solid state requires bbattery energy
56
what’s electro refining whatscwhat
Making a pure metal impure metal is anode Like copper pure copper is cathode Impure copper oxidized loses mass = impurities that fall to bottom abbd pure copper gains mass from electrons of impure onjbne
57
The downs cell profuce n how
produces pure sodium metal from molten NaCl liquid in furnace No water so Nja soa n cl sra makes pure Na store at bottom
58
Faradays law formula n imp when using faradays constant
Q= It when using constant make relative to mol of electrons in half rxns
59
electroplating always involves the
reduction of cations
60
Corrosion prevention using another metal : if metal is SRA called weaker RA
Stronger RA it will react in hate as - called sacrificed anode or catholic protectiobn Use weaker RA so it will not react w air
61
62
What metals r easy to oxidize
group 1&2 metals r strong ra so easy to oxidize as many oas above them including h20 n o2 which r naturally found
63
corrosion of Al and Fe
Al not bad bc it forms Al2O3 which sticks to. al solid preventing further corrosion Fe forms Fe2O3 which flakes off exposing Fe solid that’s continuously oxidized
64
What’s corrosion
metals oxidized Leo to form ore spiny oxidation bc we live in oxidzinbg environment w lots O2
65

Chem 30 (3 decks)

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