Elecrotrodes Flashcards by Leoni Brady

What is oxidation

Loss of electrons / increase in oxidation number

How well did you know this?

Not at all

Perfectly

What is reduction

Gain of electrons/ reduction in oxidation number

How well did you know this?

Not at all

Perfectly

Rules for assigning oxidation numbers:
Any element on its own

How well did you know this?

Not at all

Perfectly

Rules for assigning oxidation numbers:
A simple ion

The charge on the ion

How well did you know this?

Not at all

Perfectly

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

Charge is equal to group number, always positive

How well did you know this?

Not at all

Perfectly

Rules for assigning oxidation numbers:
Oxygen in a compound

Usually -2

How well did you know this?

Not at all

Perfectly

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

Usually -1

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

Rules for assigning oxidation numbers: a compound

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

How well did you know this?

Not at all

Perfectly

Rules for assigning oxidation numbers:
Complex ion

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

How well did you know this?

Not at all

Perfectly

What is a half cell/ electode

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

How well did you know this?

Not at all

Perfectly

DirectionFlow of electrons in batteries

Flow from more reactive metal to less reactive metal

How well did you know this?

Not at all

Perfectly

How are two electrodes connected to mearsure the voltage between them

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

How well did you know this?

Not at all

Perfectly

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

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

How well did you know this?

Not at all

Perfectly

What is the role of the voltmeter in connected half cells

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

How well did you know this?

Not at all

Perfectly

Which side does reduction take place on in a cell

Positive right reduced

How well did you know this?

Not at all

Perfectly

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

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

Essential conditions of standard hydrogen half cell

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

Voltage on standard hydrogen half cell

Purpose of standard hydrogen electrode

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

Conventional cell representation of Zn and Cu metal rods

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

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

One - Indicates a phase boundary
Two - salt bridge

Which species should be written closest to salt bridge

Species with highest oxidation state

Cell representation of standar hydrogen half cell

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

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

SOWR - most positive value WRSO - most negative value

Using the electrochemical series to calculate Ecell values

More positive - least positive

Determining whether reacting feasible using electrochemical series

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

Why are conditions important when calculating electrode potentials

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

electrodes in lithium ion battery

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

what happens when the battery is discharged in lithium ion battery

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)-

Overall reaction occurring when the lithium battery is being used

CoO2 + Li ~> Li(CoO2)

Convention cell representation of lithium battery

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

how is a lithium battery reversible

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

What is a fuel cell

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

What is the modern fuel cell

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

Advantages and disadvantages of fuel cells instead of fossil fuels

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

Advantages of fuel cell compared to other types of cells

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

Draw and label a diagram of standard hyrgogen half cell

Google it

Draw a labelled diagram of hydrogen fuel cell

Google it

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

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)

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

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)