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Georges chem > Redox and electrode potential chp 23 > Flashcards

Redox and electrode potential chp 23 Flashcards

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1
Q

what is oxidation in terms of oxidation number

A

increase in oxidation number

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2
Q

what is reduction in terms of oxidation number

A

decrease in oxidation number

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3
Q

what will always be present in a redox reaction

A
  • oxidising agent
  • reducing agent
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4
Q

what is the role of oxidising agents in redox reactions

A
  • oxidising agent takes electrons from species being oxidised (oxidising agent contains species that is reduced)
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5
Q

what is the procedure for carrying out manganate (VIII) titrations

A
  • add potassium manganate, KMnO4, of known conc to burette
  • add ? solution to conical flask.
  • Add excess dilute H2SO4 to conical flask, H+ allows reduction of MnO4-
  • End point is when slight pink colour is seen in conical flask (indicates excess MnO4-)
  • repeat titration till concordant results

do not need indicator

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6
Q

what is the role of a reducing agent in redox reactions

A
  • reducing agent adds electrons to species being reduced (reducing agent contains the species that is oxidised)
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7
Q

what is a tip to make it easier to write the overall redox equation for a reaction

A
  • balance the electrons
    ^times the half equations so that the number of electrons is equal
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8
Q

what can manganate (VIII) titrations be used to analyse

A
  • reducing agents that reduce MnO4^-to Mn^2+
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9
Q

what can iodine/thiosulfate titrations be used to determine

A
  • the ClO- content is household bleach
  • the Cu ^2+ content in copper (II) compounds
  • the Cu content in copper alloys

concentrations

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10
Q

what colour changes can be seen when carrying out iodine/thiosulfate titrations

A
  • when yellow/brown colour fades add starch solutions, turns blue/black
  • blue/black fades as end point nears
  • at end point blue/black disappears and goes clear
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11
Q

what is a voltaic cell

A

a type of electrochemical cell called a voltaic cell

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12
Q

what does a half cell contain

A
  • contains the chemical species present in a redox half-equation
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13
Q

what is a half-cell

A

consists of a metal rod dipped into solution of its aqueous metal ions

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14
Q

how can a voltaic cell me made from half cells

A

by connecting 2 half cells, allowing electrons to flow

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15
Q

what does the flow of electrons between half cells depend upon

A
  • the tendency of an electrode to release electrons (whether it is an oxidising or reducing agent)
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16
Q

what electrode is used if there is no metal to transport the electrons

A
  • platinum
17
Q

how do you know which metal electrode has a greater tendency too gain or lose electrons

A
  • in a cell with 2 metal/metal ion electrodes the more reactive metal will release electrons more readily and will be oxidised
18
Q

how can you tell which electrode is oxidised and reduced

A
  • the electrode with more reactive metal loses electrons and is oxidised
  • electrode with less reactive metal, gains electrons, is reduced
19
Q

what is the standard electrode potential a measure of
whats the symbol for standard electrode potential

A
  • the tendency to be reduced and gain electrons
  • E^standard conditions
20
Q

what is the standard electrode

A
  • a half-cell containing hydrogen gas (pumped into HCl)
  • an inert platinum electrode is used to allow electrons into and out of half-cell
21
Q

How can the standard half-cell be used to find out the standard electrode potential of other half cells

A

the standard electrode potential is the electromotive force of the half-cell connected to a standard hydrogen half-cell, under standard conditions

22
Q

what is the standard electrode potential of a hydrogen electrode

remember the units

A
  • 0 v
23
Q
  • what must be placed between the 2 half cells to allow for a flow of ions
  • what does it contain
A
  • a salt bridge
  • contains concentrated solution of an electrolyte that does not react with either solution
24
Q

what does a negative standard electrode potential value mean

A
  • the greater the tendency to lose electrons and undergo oxidation
  • the less the tendency to gain electrons and undergo reduction
25
Q

what does a positive standard electrode potential mean

A
  • the greater the tendency to gain electrons and undergo reduction
  • the less the tendency to lose electrons and undergo oxidation
26
Q

what standard electrode potential values do metals and non-metals tend to have

A
  • the more neg the value the greater the reactivity of a metal in losing electrons
  • the more positive the value, the greater the reactivity of a non-metal in gaining electrons
27
Q

what the equation to find out the overall electrode potential value of a reaction

A
  • Ecell = E(right) - E(left)
28
Q

what are some rules that can be used to write overall reactions from half equations

A
  • the redox system with the more positive E value will react from left to right and gain electrons
  • the redox system with the more negative E value will react from right to left and lose electrons
29
Q

How can you predict the feasibility of redox reactions

A
  • most negative system has the greatest tendency to lose electrons
  • most positive system has the greatest tendency to gain electrons
  • if this happens in reverse the reaction is not feasible
30
Q

What are the limitations of using E values for prediciting redox reactions

A
  • does not tell you any thing about the rate of reaction
  • reactions can have large activation energy
  • if concentrations and conditions not standard, value will differ from standard value
31
Q

what are primary cells

A
  • non-rechargeable
  • only used once
  • chemical energy converted to electrical energy
  • reaction not reversible
32
Q

what are examples of primary cells

A
  • carbon-zinc dry cells
  • alkaline dry cells
33
Q

what are secondary cells

A
  • rechargeable
  • chemical energy converted to electrical energy (is a reversible reaction)
34
Q

what are some examples of secondary cells

A
  • lead-acid batteries
  • lithium-ions cells
35
Q

what are fuel cells

A
  • uses energy from reaction of a fuel with oxygen to create voltage
  • fuel and oxygen flow into fuel cell and products flow out, electrolyte remains in cell
  • can operate continuously as far as fuel and oxygen are supplied
36
Q

what are hydrogen fuel cells

A
  • can have either alkali or acid electrolyte
  • reactants are hydrogen and oxygen
  • products are water

Georges chem (29 decks)

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