Redox And Electrode Potential Flashcards

1
Q

Reducing agents

A

Donates electrons and decreases oxidation number of another species.

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2
Q

Oxidising agent

A

Accepts electrons and increase oxidation number of another species.

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3
Q

Standard electrode potential (E•)

A

E.m.f of a half-cell compared with a standard hydrogen half cell
- 1 mol dm-3
- 298K
- 100kpA
- Platinum electrode

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4
Q

Salt bridge

A

Allows ions to move

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5
Q

Wire

A

Allows electrons to flow

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6
Q

What is the process taking place at the positive and negative electrodes?

A

Electrons flow away from the least positive electrochemical cell and flows to the most positive.

  • Least positive loses electrons, most positive gains
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7
Q

What does a more negative electrode potential tell us ?

A
  • Greater tendency to lose electrons and undergo oxidation
  • Less tendency to gain electrons and undergo reduction
  • Equilibrium shifts to the left
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8
Q

Cell potential equation

A

(most positive)-(least positive)

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9
Q

What value do all feasible electrode potential reactions have?

A

+ V

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10
Q

When will a reaction occur

A

If the oxidising agent has a more positive value than the redox system of the reducing agent

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11
Q

Steps of comparing feasibility in equations

A
  1. identify which is being oxidised
  2. Reverse oxidised equation
  3. Combine 2 equations to obtain feasible reaction
  4. Compare equation to one stated in question
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12
Q

Limitations of predicting feasibility (concentration)

A

Non standard conditions alter value for E, half equations are at equilibria so changes in concentration will shift the position which affects electron transfer

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13
Q

Limitations of predicting feasibility (rate of reaction)

A

Reaction rate may be very slow due to a high activation energy and electrode potential give no indication of rate of reaction.

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14
Q

Limitations of predicting feasibility: Aqueous solutions

A

Standard electrode potentials apply to aqueous equilibria but some reactions that may take place are not aqueous.

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15
Q

Three types of electrochemical cells

A
  • Non rechargeable cells (1• non-reservable)
  • Rechargeable cells (2• reversible)
  • Fuel cells
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16
Q

What are fuel cells

A

Electricity is generated by a continuous external supply of fuel and oxygen (acid/alkali)

17
Q

What products are made in fuel cell reaction?

A

Water

18
Q

Advantages of fuel cells

A
  • don’t need to recharge
  • less environmental impact as water is only product
  • no combustion: less energy dissipates as heat = more efficient
19
Q

Disadvantages of fuel cells

A
  • High flammable: has safety and economic issues with transportation
  • Involves electrolysis- an energy intensive process (involves burning of fossil fuels)
20
Q

Why don’t you need an indicator in some redox titration

A

They are self indicating, permanent colour change= endpoint

21
Q

What is a good oxidising agent to find the conc of reducing agent such as Fe2+, (COOH)2

A

KMnO4

22
Q

What is the colour change in KMnO4 and Fe2+

A

Purple to colourless to permanent pink

23
Q

Why do we add excess acid to the unknown concentration?

A

To allow the oxidising agent to fully reduce

24
Q

Why does the solution containing Fe3+ and Mn2+ remain pink?

A

The reaction has reached an endpoint as all the Fe2+ had reacted with MnO4- so anymore MnO4- is in excess

25
Q

Why do we take reading from the top of the miniscus in KMnO4 titration?

A

KMnO4 is very dark so it hard to see

26
Q

Why is starch added to iodine-sodium thiosulfate reaction?

A

For a sharper colour change, continues titration until colourless to blue black which indicated all I2 had reacted

27
Q

Iodine-sodium thiosulfate titration colour change

A

Colourless to pale yellow

28
Q

Which solution do you put in the burette?

A

The one with the known concentration

29
Q

Steps to finding out the concentration of oxidising agent?

A

1- Use mean titre to find moles of Na2S2O3 in equation 2
2- Find the moles of Iodine in equation 2 to find the moles of Iodine in equation 1
3- Use the moles of Iodine in equation 1 to find the moles of IO3-