Chapter 23 - Redox And Electrode Potentials Flashcards

1
Q

Define redox

A

A reaction in which both reduction and oxidation take place.

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2
Q

Define oxidation

A

The loss of electrons or an increase in oxidation number.

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3
Q

Define reduction

A

The gain of electrons or a decrease in oxidation number.

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4
Q

What is the Manganate half reaction?

A

MnO(4)- + 8H+ + 5e- -> Mn2+ + 4H(2)O

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5
Q

What is the iodine sodium thiosulphate reaction?

A

2S(2)O(3)2- + I(2) -> S(4)O(6)2- + 2I-

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6
Q

Why is there no clear colour change at the end point of a Vanadium and Potassium Manganate titration?

A

KMnO(4) is purple/pink

V2+ is violet

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7
Q

What property does the voltmeter have in a cell?

A

High resistance

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8
Q

Which way does the current flow in the cell?

A

Negative electrode to the positive electrode

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9
Q

How do the ions flow between cells?

A

Salt bridge

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10
Q

What is the salt bridge generally made of?

A

Potassium nitrate

Ammonium nitrate

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11
Q

What is the electrode made of in a standard hydrogen cell?

A

Platinum

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12
Q

What is in the half cell of Fe3+ and Fe2+?

A

Inert Pt electrode

Equimolar Fe2+ and Fe3+ (1 mol dm^-3)

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13
Q

When two half cells are connected, which is oxidised and which is reduced?

A

More reactive metal is oxidised

Less reactive metal is reduced

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14
Q

Define standard electrode potential (E°)

A

The emf of a half cell compared with a standard hydrogen half cell, measured at 298K with solution concentrations of 1 mol/dm^3 and a gas pressure of 101kPa.

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15
Q

What is the electrode potential of a hydrogen half cell?

A

0.00V

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16
Q

What is the electrode potential of the cell?

A

Electrode potential(E°) of the more positive terminal minus the electrode potential(E°) of the more negative terminal

17
Q

How do we know if a cell is feasible?

A

If the electrode potential of the cell is positive, the reaction is feasible.

18
Q

Which electrode goes on the right when asked about a labelled diagram?

A
  • The half-cell with the more +ve E° (electrode potential)

- The metal ions that are more easily reduced

19
Q

Which electrode goes on the left when asked about a labelled diagram?

A
  • The half-cell with the more -ve E°

- The metal ions that are more easily oxidised

20
Q

What does the more positive value for E° mean for the position of the equilibrium?

A
  • Equilibrium lies further to the RIGHT than the other half-cell
  • So the metal ions are more easily REDUCED than the other half-cell.
  • So the metal is an OXIDISING agent
21
Q

What does the more negative value for E° mean for the position of the equilibrium?

A
  • Equilibrium lies further to the LEFT than the other half-cell
  • So the metal ions are more easily OXIDISED than the other half-cell.
  • So the metal is an REDUCING agent
22
Q

Does it go Bigger or smaller, Metal ion –> Metal Solid
E.G. The copper
2Cr + 3Cu2+ –> 2Cr3+ + 3Cu

A

-gets Bigger, metal ion to metal solid
-Less concentrated
-Copper is REDUCED
2Cr + 3Cu2+ –> 2Cr3+ + 3Cu

23
Q

Does it go Bigger or smaller, Metal solid –> Metal ion?
E.G. the chromium
2Cr + 3Cu2+ –> 2Cr3+ + 3Cu

A

-gets Smaller, metal solid to metal ion,
-More Concentrated
-Chromium is OXIDISED
2Cr + 3Cu2+ –> 2Cr3+ + 3Cu

24
Q

State 2 reasons why the actual cell potential may be different from the value calculated?

A
  • Non- standard conditions

- High Ea, so very slow rate of reaction

25
Q

What’s in a Metal/Metal ion half cell?

E.g. Cu2+ | Cu half cell

A
  • Metal rod (Cu)

- dipped into aq solution of metal ion (Cu2+)

26
Q

What’s in a Ion/ ion half-cell?

E.g. Fe3+ | Fe2+

A
  • Contains ions of the same element in different oxidation states ( Equimolar of Fe3+ & Fe2+ (1 moldm-3
  • Pt electrode
27
Q

Why does Fe2+ | Fe half cell sometimes form the metal ion Fe3+?

A
  • Fe2+ oxidises in air to form Fe3+ which has a partially filled d-subshell so gives greater stability.
  • So Fe3+ is a more likely product
28
Q

What’s in a Standard Hydrogen half cell?

H2 | H+

A
  • inert Pt electrode
  • Glass tube with holes in to allow bubbles of H2(g) to escape
  • H2(g) coming in through the top at 298K,1 atm
  • Acid solution at bottom containing 1.0 moldm-3 of H+(aq)
29
Q

What is the overall cell eqn and both half eqns for the zinc-copper cell?
Zn2+ +2e- –> Zn , -0.76 V
Cu2+ + 2e- –> Cu , +0.34 V

A

Red: Cu2+ + 2e- –> Cu (MP)
Oxi: Zn –> Zn2+ + 2e- (MN)
Ovll: Zn + Cu2+ –> Zn2+ + Cu

30
Q

State the key difference between a primary cell and a secondary cell.

A
  • A primary cell is only used one and is non-rechargeable

- A secondary cell is rechargeable

31
Q

State the key characteristics of a fuel cell.

A
  • A fuel cell uses the energy from the reaction of a fuel with oxygen to create a voltage.
  • A fuel cell can be run continuously provided that the fuel and oxygen are continually being supplied to the cell.