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Chem > Elecrotrodes > Flashcards

Elecrotrodes Flashcards

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1
Q

What is oxidation

A

Loss of electrons / increase in oxidation number

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2
Q

What is reduction

A

Gain of electrons/ reduction in oxidation number

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3
Q

Rules for assigning oxidation numbers:
Any element on its own

A

0

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4
Q

Rules for assigning oxidation numbers:
A simple ion

A

The charge on the ion

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5
Q

Rules for assigning oxidation numbers: a group 1,2 or 3 element in a compound

A

Charge is equal to group number, always positive

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6
Q

Rules for assigning oxidation numbers:
Oxygen in a compound

A

Usually -2

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7
Q

Rules for assigning oxidation numbers:
Group 7 element in a compound

A

Usually -1

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8
Q

Rules for assigning oxidation numbers:
Hydrogen bonded to non-metal

A

+1

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9
Q

Rules for assigning oxidation numbers: a compound

A

The sum of oxidation numbers of all atoms and ions in a compound is zero

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10
Q

Rules for assigning oxidation numbers:
Complex ion

A

The sun of oxidation numbers of all atoms and ions in a ion is equal to the charge

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11
Q

What is a half cell/ electode

A

A strip of metal dipped into a solution of its own ions

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12
Q

DirectionFlow of electrons in batteries

A

Flow from more reactive metal to less reactive metal

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13
Q

How are two electrodes connected to mearsure the voltage between them

A

2 metal rods are connected with wires and a high resistance voltmeter, 2 beakers of electrolyte ( positive ions dissolved into the solution with a metal strip in that collects the electrons giving it a negative charge ) are connected with a salt bridge to complete the circuit

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14
Q

What’s a salt bridge and why is this substance suitable

A

Glass tube or porous material soaked in KNO3 solutions.
It is unreactive with the electrodes and the ions are free to move

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15
Q

What is the role of the voltmeter in connected half cells

A

Prevents electrons from flowing enabling voltage to be mearsures, Without it electrons will flow from left (most reactive metal) to right (least reactive metal)

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16
Q

Which side does reduction take place on in a cell

A

Positive right reduced

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17
Q

What electrode to use when there is no solid metal in reaction

A

Platinum electrode as a metal rod needed from another unreactive metal which aslo conducts electricity
For example if metal ions of 2 differnet charges in solution Fe2+ and Fe3+ which void be made from dissolving Fe2(SO4)3

18
Q

Essential conditions of standard hydrogen half cell

A

H2 gas pumped in at 100kPa
Electrolyte contains H+ ions of conc 1moldm-3
Platinum electrode
298K

19
Q

Voltage on standard hydrogen half cell

A

0V

20
Q

Purpose of standard hydrogen electrode

A

If another electrode is connected up to the standard hydrogen electrode and voltage between them is measured then the voltage on the meter must be of the other electrode

21
Q

Conventional cell representation of Zn and Cu metal rods

A

Zn(s)|Zn2+(aq)||Cu2+(aq) | Cu(s)

22
Q

What does the vertical solid line and double solid line represent in conventional cel representation

A

One - Indicates a phase boundary
Two - salt bridge

23
Q

Which species should be written closest to salt bridge

A

Species with highest oxidation state

24
Q

Cell representation of standar hydrogen half cell

A

Pt(s) | H2(g) | H+(aq) ||

25
Q

Identifying the strongest oxidising agent and weakest reducing agent via electrochemical series

A

SOWR - most positive value
WRSO - most negative value

26
Q

Using the electrochemical series to calculate Ecell values

A

More positive - least positive

27
Q

Determining whether reacting feasible using electrochemical series

A

If Ecell value is positive
It mean the cell discharges producing a current

28
Q

Why are conditions important when calculating electrode potentials

A

If conditions are changed then:
- the equailbrai could shift to the right meaning more metal and less metal ions and electrons, as few electrons the electrode potential would come more positive
- try e equillbira could shift to the left so less metal and more ions and electrons , as more electron present the electrode potential would come more negative
CAUSES A KNOKON EFFECT ON ANY E CELL VALUES CALCULATED AND MAY BR FEASIBLE UNDER SIME CONDITIINS BUT NOT ORHERS

29
Q

electrodes in lithium ion battery

A

Positive electrode is made of lithium cobalt oxide and the negative is made of graphite

30
Q

what happens when the battery is discharged in lithium ion battery

A

Layer of Li on the negative carbon electrode dissociates to form Li+ and release electrons
At the positive electrode a lithium ion and electron combine with CoO2 from the electrolyte to form Li+(CoO2)-

31
Q

Overall reaction occurring when the lithium battery is being used

A

CoO2 + Li ~> Li(CoO2)

32
Q

Convention cell representation of lithium battery

A

Li|Li+||Li+,CoO2| Li(CoO2) | Pt

33
Q

how is a lithium battery reversible

A

When the battery has run out because either all the CoO2 or Li has been used up it can be connected to a stronger electrical current which forced the reaction back in the reverse direction to recharge

34
Q

What is a fuel cell

A

generates electrical current from electrochemical reactions , it uses the energy from the reaction of a fuel cell with oxygen to create a voltage

35
Q

What is the modern fuel cell

A

Hyrgogen fuel cells
Using hyrgogen rich fuel like methanol, natural gas and petrol

36
Q

Advantages and disadvantages of fuel cells instead of fossil fuels

A

Pros :
- Greater efficiency than burning hydrogen in a combustion engine
- less polluting as water is the only product
Cons:
- h2 is difficult to store
- fossil fuels are combusted to produce the hydrogen which released CO2

37
Q

Advantages of fuel cell compared to other types of cells

A

Voltage is constant as fuel and Oxygen is supplied constantly so conc of reactants remain constant

38
Q

Draw and label a diagram of standard hyrgogen half cell

A

Google it

39
Q

Draw a labelled diagram of hydrogen fuel cell

A

Google it

40
Q

Half equation and overall equations of hydrogen fuel cell in alkaline solution

A

At the negative electode:
H2(g) + 2OH-(aq). <-> 2H20(l) + 2e- (oxidation)
At positive electode:
1/2 O2(g) + H2O(l) + 2e- <-> 2OH- ( reduction)
Overall : H2 (g) + 1/2 O2 (g) ~> H2O (l)

41
Q

Half equation and overall equation of hydrogen fuel cell in acidic solution

A

Negative electrode :
H2(g) <-> 2 H+(aq) + 2e-
Positive electode:
1/2 O2 (g) + 2 H+ (aq) + 2e- <->H2O(l)
Overall equation:
H2(g) + 1/2O2(g) ~> H2O(l)

Chem (33 decks)

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