CH3.1 Redox and standard electrode potential Flashcards
what is a redox reaction
A redox reaction is a combination of oxidation and reduction.
what is oxidation in turms of electrons and oxidation number
Oxidation is lose of electrons meaning a more positve oxidation number.
what is reduction in terms of electrons and oxidation number
reduction is gain of electrons resulting in a more negative oxidation number.
why does oxidation and reduction have to hapen at the same time
Because the electrons that are lost in the reduction are the same electrons that are gained in the oxidation.
oxidation agent
Is a substance that takees electrons from another substance and so it is reduced.
reducing agent
Is a substance that gives electrons to another substance and so it is oxidised.
what does the half equation of a reaction represent
wither the oxidation or reduction reaction (one of the redox equations)
What is the point of a half cell
the point of setting up a half cell is so that the reduction and oxidation can occur at two different places seperatly.
salt bridge
The salt bridge is a piece of apparatus that connects the solutiongs in two half-cells so that the circuit can be complete and the current can flow without the solution mixing.
what is a salt bridge made of
gel soaked in a solution of potassium nitrate, or filter paper soaked in potassium nitrate.
what must be at both hald cells
The reactants and the products of that half equation, as well as a metal that allows electrons to flow into or out of the half cell.
what are the three main different types of half cells
metal/ metal ions
a gas in contact with a solutiong of non-metal ions
A soultion containing ions of metal in two different oxidation states using an inert metal electrode
metal/metal ions half cell
This is when the electrode is the metal that is needed for the half eqaution which is submerged in 1 moldm-3 solution of the metal ion.
gas in contact with a solutiong of non-metal ions half-cell
gas is bubbled over the inert electrode which is dipping into a solution of the ions
What is a inert electrode used for
When there is not a metal for the electrons to move across, (non metals are not conductors) The platinum half cell allows the electrons to flow in or out o the half-cell
soution containing ions of the metal in two different oxidation states half cell
uses inert metal platinum electrode. because there are no conductors, typically used for tanisition metals as they have several oxidation states.
which half cell always produces a colour change
solution containg ions of metal with different oxidation state wiht a platinum inert metal electrode.
which half cell sometimes produces a colour change
metal/ metal ions
which half cell never produces a colour change
A gas in contact with a solution of non-metal ions with an inert platinum metal electrode.
when representing a half cell what do the lines represent
chagne in state
standar electrode potential
a measuer of the ability of the half cell to gain or lose electrons.
what is hydrogens standard electrode potential
0
what does a negative standard electrode potential mean
The species is easier to reduce then hydrogen
what does a positive standard electrode electrode potential mean
The substance is easier to oxides
what is another name for the hydrogen half-cell
the standard hydrogen electode
what type of half cell is the standard hydrogen electrode/hydrogen half cell
A gas in contact with a solution of non-metal ions witha n inert metatl electrode
what electrode is used in the hdyrogen half-cell
inert platinum black electrode
exsplain the hydrogen half cell
inert platinum black electrode
H2 gas pupem over electrode, at standard conditions, electrode dipped in solution of 1 moldm-3 H+ ions
how is the standard electrode potential for half-cell measuerd
it is done by joining it to the standard hydrogen electrode.
standard hydrogen electrode drawn eqaution
Pt(s) l H2(g) l H+(aq) ll (the secound electrode that you want to find the standard electrode potential of)
which electrode has the more positive standard electrode potentiala
The positve electrode has a more positive eectrode potentials
which way do the electrons flow
The electrons flow towards the more positive standard electrode potential.
how does reactiveity of the metals and non metals , and electrode potential relate
The more reactive metals have the most negative electrode potential, with the most reactive non-metals having the most positive value for standard electrode potential.
how is the e.m.f. worked out using the standard electrode potential
The e.m.f of an electrochemical cell is worked out by the difference in the standard electrode potential of the two half cells. it is always a postive value.
feasible reaction
A reaction that can occur spontanuosly
finding the feasiblity of two half equations using standard electrode potentital values.
use the anticlockwise rule
write both the half equations in order of increasing standard electrode potentials, with the most negative value first
start from the top right hand conrner and move anticlockwise around the equation. This means that in the feasible reaction the top reaction goes in reverse and the bottom goes in the direction it is written.
EMF standard electrode potential equation
E.M.F. of reaction = standard electrode potential of reductino - standard electrode potential of oxidation
if this value is negative then the reaction is feasible
what are fule cells being developed as
a method of releasing energy very effeciently fom fuels such as hydrgoen methane or methanol.
how does the fuel cell work
The fuel cell system passes the fuel over a platinum metal which acts as both a catalys and electrode. The electrons are removed from the hydrogen at one electrode. The protons (H+) diffuse through a semi permeable membrance to the other electrode where they recive electrons and oxygen molecules to form water molecules.
equations for the fuel cell and voltage produced
H2 –> 2H+ + e-
O2 + 4H+ + 4e- –> 2H2O
2H2 + O2 –> 2H2O
1.23v
benefits of fule cell 3
- convinient way of storing and relasing energy
- energy efficiey is much high than standard fuel system (35-45% compared to 22% of disel)
- emission ffrom fuel cells is less damaging than the carbon dioxide from traditional energies.
drawbacks of fuel cell 3
- The hydrogen fuel must be generated elsewhere and this is likely to use fossil fuel energy sources which will cause their own carbon dioxde emission
- an energy loss compared to liquid fuels
- fule cells operate at lower temperatures so need very efficient catalysts which use expensive metals.
