DM 3 - Redox Flashcards

1
Q

What is a half-cell?

A

A half-cell contains the chemical species present in a redox half equation

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2
Q

What is a metal/metal ion half-cell?

A
  • A half-cell where a metal rod is dipped in a solution containing an ion of the same metal
  • An equilibrium will be set up at the boundary where the metal is in contact with its ions
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3
Q

What is an ion/ion half-cell?

A
  • An ion/ion half-cell contains a solution of ions of the same element but of different oxidation states
  • The electron is usually graphite or platinum
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4
Q

What is a standard electrode potential?

A

The EMF/voltmeter reading when a half-cell of interest is connected to a hydrogen half-cell via a salt bridge, with all solutions having a concentration of 1 moldm-3, under standard conditions (101 or 100 kPa and 298K)

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5
Q

What is a hydrogen half-cell?

A
  • A half-cell containing hydrogen gas and a solution containing hydrogen ions
  • An inert platinum electrode is used to allow electrons into and out of the half-cell
  • 2H+(aq) + 3e- <=> H2(g)
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6
Q

How do you use standard electrode potentials to calculate the standard cell potential, E0cell?

A

E0cell = E0(positive electrode) - E0(negative electrode)

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7
Q

What is an electrochemical cell?

A
  • Two different half-cells are connected by a salt bridge, with their electrodes connected to a voltmeter (measures EMF/cell potential)
  • This allows the flow of electrons
  • It generates electrical energy from chemical redox reactions
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8
Q

What is a salt bridge?

A
  • A salt bridge allows the transfer of ions
  • It is typically a concentrated solution of an electrolyte i.e. KNO3(aq) that doesn’t react with either half cell solution
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9
Q

Why may a graphite or platinum electrode be used?

A

They are very unreactive i.e. will not react with the half-cell solutions and will not affect the voltmeter readings. Usually used in ion/ion half-cells

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10
Q

How do you predict which half-cell is being oxidised and which one is being reduced?

A
  • The more negative the E0 value, the greater the tendency for the system to be oxidised
  • The more positive the E0 value, the greater the tendency for the system to be reduced
  • Hence the half-cell with the more positive E0 is oxidised and the half-cell with the more negative E0 is reduced
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11
Q

How do you predict the feasibility of a redox reaction?

A
  • The reaction is feasible if the oxidising agent has a lower standard cell potential than the reducing agent
  • The greater the difference in E0 value, the more likely the reaction to occur
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12
Q

Why may a reaction not occur?

A
  • Non-standard conditions (298 K, 101 kPa, 1 moldm-3 solutions)
  • Ambient energy of the system is lower than the activation energy
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13
Q

What is rusting?

A
  • Rust in an iron oxide, (usually red) formed from the redox reaction of iron and oxygen in the presence of water/moisture
  • Iron is oxidised, oxygen (dissolved in water) is reduced. The products of this redox reaction then react to form a hydrated iron oxide
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14
Q

How do you prevent rusting?

A
  • To protect iron from rust, the surface needs to be separated from air and water, i.e. by keeping the metal in oil
  • Coatings can be applied to iron
  • Alloys (e.g. stainless steel) can be made to prevent rusting
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