3.1 and 3.2 Redox and standard electrode potentials

oxidation

loss of electrons

reduction

gain of electrons

oxidising agent

a species that accepts electrons

reducing agent 

a species that donates electrons

where does reduction occur in an electrochemical cell

right hand side

where does oxidation occur in an electrochemical cell

left hand side

purpose of the salt bridge in an electrochemical cell

completes the circuit

two solutions do not mix

what does the high resistance voltmeter measure 

the EMF produced by the cell

3 types of half cell

metal/ metal ion

gas/ non metal ion solution

solution of a metal in two different oxidation states

metal/ metal ion half cell

metal electrode conducts the electrons

solution always concentration of 1 mol/dm3

gas/ non metal ion solution

inert platinum electrode conducts the electrons

gas at 1 atm is bubbled over the electrode that is dipped in a solution of ions

NO COLOUR CHANGE

solution of a metal in two different oxidation states 

usually used for transition metals

platinum electrode used 

colour of Fe2+ solution 

pale green

colour of Fe3+ solution

rusty orange

which electrode is placed on the RHS of a cell diagram

more positive

conditions of the standard hydrogen electrode

hydrogen gas at 1 atm pressure

H+ solution at 1mol - usually HCL

Temperature of 298K

standard electrode potential

the potential difference between the standard hydrogen electrode and any half-cell

where is the hydrogen half cell drawn in a diagram

on the left

for a reaction to go ahead…

its EMF must be positive

the oxidation half-reaction

has the most negative E value

the reduction half reaction

has the most positive E value 

fuel cells

convert chemical energy stored in the fuel into electrical energy

electrodes in fuel cells

platinum - acts as a catalyst

what happens at the cathode in a fuel cell

H+ ions receive electrons and react with oxygen to form water

advantages of fuel cells

Only produce water, so no CO2, which is a greenhouse gas, is produced

Far less energy is wasted as heat, so they are far more efficient

Hydrogen gas is a renewable energy source

disadvantages of fuel cells

Hydrogen gas is highly flammable, and is

therefore difficult to store

The usual production method for hydrogen gas is from fossil fuels, so this leads to an overall energy loss