Redox and Electrode Potentials Flashcards

1
Q

What are the steps to construct redox equations

A

Write half equations
Balance hydrogens
Balance electrons

Form full equation - electrons cancel out

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2
Q

What are the two common redox titrations you need to know

A

Potassium manganate (VII) (KMnO4(aq)) under acidic conditions

Sodium thiosulfate (Na2S2O3(aq)) for determination of iodine (I2(aq))

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3
Q

What are the examples of manganate(VII) titrations

A

Iron(II) ions (Fe2+)

Ethanedioic acid (COOH)2

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4
Q

In iodine/ thiosulfate titrations what is oxidised and what is reduced
What are the 2 half and overall equations

A

Thiosulfate are oxidised
Iodine is reduced

Oxidation: 2S2O3^2-(aq) -> S4O6^2- + 2e-

Reduction: I2(aq) + 2e- -> 2I-(aq) + S4O6^2-

Overall: 2S2O3^2- + I2(aq) -> 2I-(aq) + S4O6^2-(aq)

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5
Q

What is a voltaic cell

A

A type of electrochemical cell that converts chemical energy into electrical energy

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6
Q

What are half-cells

A

Half cells contain chemical species present in a redox half-equation

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7
Q

How can you make a voltaic cell

A

By connecting together two different half cells which allows electrons to flow

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8
Q

What are the two types of half cells

A

Metal/ metal ion

Ion/ ion

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9
Q

How do you know which electrode has a greater tendency to gain or lose electrons

A

In a cell with two metal/metal ion half cells connected, the more reactive metal releases electrons more readily and is oxidised

Operating cell

  • electrode with more reactive metal loses electrons - is oxidised Operating cell- negative electrode
  • the electrode with the less rreactive metal gains electrons and is reduced - positive electrode
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10
Q

Define standard electrode potential

A

The tendency to be reduced and gain electrons
With standard conditions -
- solutions have a concentration of exactly 1 moldm-3
- temperature is 298K
- pressure is 100kPa (1bar)

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11
Q

How do you measure standard electrode potential

A

Half-cell connected to a standard hydrogen electrode
- the two electrodes are connected by a wire to allow a controlled flow of electrons

  • the two solutions are connected with a salt-bridge which allows ions to flow. The salt bridge typically contains a concentrated electrolyte solution that does not react with either solution
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12
Q

If an electrode potential is more negative:

A
  • the greater the tendency to lose electrons and undergo oxidation
  • the less the tendency to gain electrons and undergo reduction
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13
Q

The more positive the electrode potential:

A
  • the greater the tendency to gain electrons and undergo reduction
  • the less the tendency to lose electrons and undergo oxidation
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14
Q

How do you calculate standard cell potential from standard electrode potentials

A

Cell potential = positive electrode potential - negative electrode potential

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15
Q

How do you construct overall equations from half equations

A

The redox system with more positive electrode potential will react from left to right - gain electrons

System with more negative will react from right to left - lose electrons

Reduction half equation is same way around
Oxidation half equation is reversed

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