Electrode Potentials Flashcards

1
Q

Where is equilibrium if there is a large voltage

A

To the right

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2
Q

Where is equilibrium if there is a small voltage

A

To the left

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3
Q

What does the voltmeter do

A

Prevents electrons flowing

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4
Q

What does the salt bridge do

A

Completes the circuit and allows flow of ions

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5
Q

Why is platinum a suitable electrode

A

Unreactive and conducts electricity

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6
Q

Standard hydrogen electrode

A

Used to compare single electrodes and voltage is 0
H2 gas pumped in at 100kpa
Solution of h+ conc is 1moldm-3
Must be a platinum electrode
Temp must be 298k

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7
Q

What is the voltage of standard hydrogen electrodes

A

0v

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8
Q

Electrode potential value oxidation

A

Most negative value more likely to show oxidation

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9
Q

Electrode potential value reduction

A

Most positive value more likely to show reduction

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10
Q

Conventional cell representation.

A

Zn|zn2+||cu2+|cu|pt
One line = phase boundary if same state use comma
Two lines = salt bridge
At other on end if platinum electrode
Reduction on right and oxidation on left

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11
Q

EMF

A

EMF = reduction - oxidation

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12
Q

What happens if condition are changes

A

Equilibrium will shift

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13
Q

Condition changing examples for mg2+
Decrease

A

Equilibrium opposes the decrease in concentration of mg2+ and shifts to the left hand side
So electrode potential value becomes more negative as there is an increase in electrons
So emf becomes more positive

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14
Q

Single use battery

A

Reaction is irreversible

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15
Q

Rechargeable batteries li(coO2)

A

Negative electrode
Li->li+ +e-
Positive electrode
CoO2 + li+ + e- -> Li(CoO2)

Overall equation
CoO2 + li -> Li(CoO2)

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16
Q

Equation when recharging

A

Flip everything

17
Q

Fuel cell

A

Uses the energy from the reaction of a fuel with oxygen to create a voltage.

18
Q

Advantages of fuel cell over fossil fuels

A

Greater efficiency than burning h2 in a combustion engine
Less polluting as water is only product

19
Q

Disadvantages of using fuel cell over fossil fuels

A

H2 is difficult to store
Fossil fuels are combusted to produce the hydrogen which release co2

20
Q

Advantages of fuel cells to other types of cell

A

Voltage is constant as fuel and oxygen is supplied constantly so concentrations of reactions remain constant

21
Q

Hydrogen oxygen fuel cell in alkaline solution

A

At anode
H2 + 2oh- <-> 2h2o + 2e- Oxidation. -0.83
At cathode
1/2o2 + h2o + 2e- <-> 2oh- Reduction. +0-40

Overall equation
H2 + 1/2o2 -> h2o. 1.23

22
Q

Hydrogen oxygen fuel cell in acidic solution

A

Anode
H2 <-> 2h+ + 2e- 0.0
At cathode
1/2 o2 + 2h+ +2e- <-> h2o 1.23

Overall equation
H2 + 1/2o2 -> h20. 1.23

23
Q

Ratio of cr2o72- to fe2+

A

1:6