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Chemistry A-Level > Redox II > Flashcards

Redox II Flashcards

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1
Q

Standard electrode potential Conditions

A
  • 298°K
  • 100 kPa for gasses
  • 1.00 mol dm^-3 concentration for ions
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2
Q

SHE (Standard Hydrogen Electrode) Structure

A
  • Porous platinum foil immersed in 1 moldm^–3 HCl,
  • This is enclosed in a tube containing hydrogen gas at standard pressure (100kPa).
  • Platinum wire
  • State temperature is 298 ° K
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3
Q

Why is using standard conditions important?

A
  • The position of equilibrium can change if we alter these conditions
  • In order to make a fair comparison with other metals we make the conditions the same
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4
Q

Why is Platinum foil covered in Porous Platinum used? for the SHE.

A
  • Hydrogen gas can adsorb onto the platinum surface

- This allows for a Hydrogen ion solution to quickly be established

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5
Q

What are the components in a complete cell?

A
  • High resistance voltmeter

- Salt Bridge (e.g. KNO3)

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6
Q

Why is a salt bridge needed?

A
  • To complete the electrical circut
  • Allows the movement of ions
  • BALANCE THE CHARGES
  • Make sure the correct salt is used for the salt bridge
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7
Q

How do you set up a metal half cell?

A
  • Solid Metal dipped in a solution of 1moldm^-3 of its salt
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8
Q

Anode

A

+ve electrode site of oxidisation

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9
Q

Cathode

A

-Negative electrode site of reduction

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10
Q

Electromotive force (emf)

A
  • the potential difference of a cell is measured when there is no current flowing.
  • The difference between the voltages of 2 different half cells
  • E(RHS) - E(LHS)
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11
Q

What is the significance of the +ve & -ve values of the standard electrode potential of cells?

A
  • Tells us if it forms the positive electrode or the negative electrode
  • Tells us how reactive certain elements are based on how readily they release electrons
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12
Q

What is meant by the term standard electrode potential?

A
  • The emf of a cell formed with the half cell your measuring (e.g 1/2Br(aq)/Br-(aq)
  • And the cell is in standard conditions (1moldm^-3, 298°K, 100kPa)
  • Compared to SHE
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13
Q

Electrochemical cell

A
  • Combination of two half cells to produce electricity (voltage)
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14
Q

Standard Hydrogen Electrode Cell Diagram (Half Cell) (ROOR)

A
  • Pt(s) | 1/2 H2(g) | H+ (aq) | |
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15
Q

How do you determine the order of a cell diagram?

A
  • -ve electrode on left
  • ROOR (Reduced | Oxidised | | Oxidised | Reduced)
  • If the other half cell is a SHE then the SHE is always on the left (Pt(s) | 1/2 H2(g) | H+ (aq) | |)
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16
Q

Why is Porous platinum foil necessary in some half cells?

A
  • If a system does not include a metal that can act as an electrode, then a platinum electrode must be used and included in the cell diagram
  • Both aqueous ions
  • One state is gaseous (e.g. Hydrogen)
17
Q

What is the relationship between E cell (standard cell potential) and ln(k) and TOTAL Entropy Change(∆S Total)?

A
  • Direclty propertional
18
Q

What is the equation relating ln(k) (Equilibrium constant) and the E cell?

A

ln(k) = (nFE Cell)/(RT)

19
Q

How can changing conditions affect the E cell?

A
  • The position of equilibirum can be shifted affecting the voltage produced
20
Q

How can disproportionation reactions relate to standard electrode potentials?

A
  • 2Cu+ -> Cu + Cu2+
  • Cu+(aq) + e− -> Cu(s) Eo = +0.52 V
  • Cu2+(aq) + e− -> Cu+(aq) Eo = +0.15 V
  • So Eo cell = 0.52 − 0.15 = +0.37 V
  • The E cell is determined by each of the reduction and oxidization reactions
21
Q

What are storage cells? (secondary / rechargeable cells)

A
  • Cell that can be recharged by passing a current through it in the opposite direction to the current generated by the cell
22
Q

What is a fuel cell?

A

A fuel cell uses the energy from the reaction of a fuel with oxygen to create a voltage

23
Q

What fuels can be used in fuel cells?

A
  • Hydrogen
  • Methanol
  • Ethanol
  • Other fuels
24
Q

Reaction at the Electrodes of a Hydrogen Fuel cell in Acidic conditions

A

-ve: H2(g) -> 2H+(aq) + 2e-

+ve: 1/2O2(g) + 2H+(aq) +2e- -> H2O(l)

25
Q

Reaction at the Electrodes of a Hydrogen Fuel cell in Alkaline conditions

A

-ve: H2(g) + 2OH-(aq) -> 2H2O(l) + 2e-

+ve: 1/2O2(g) + 2H+(aq) + 2e- -> H2O(l)

26
Q

Advantages of Hydrogen fuel cells

A

+ Alternative to fossil fuels
+ CO2 not produced
+ More Efficient
+ Lighter engines

27
Q

Disadvantages of Hydrogen Fuel Cells

A
  • Expensive
  • Preassurised Hydrogen gas is a hazard
  • Finding a suitable material for the Hydrogen to adsorb too
  • Infrastructre not currently present to store large quantities of hydrogen
28
Q

Why is starch added only when nearly all the iodine has reacted?

A
  • High concentrations of iodine react with the starch to form an insoluble blue complex

Chemistry A-Level (14 decks)

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