5.2.3 Redox and electrode potential

what is redox reaction

reaction where both reduction and oxidation happens

what is the oxidation number of Hydrogen

+1 ( unless when bonded to a metal)

what is the oxidation number of Oxygen

-2 ( unless H₂O₂)

what is oxidation

losing e⁻

what is reduction

gaining e⁻

what does OILRIG stand for

what is it when a ion becomes more positive

Oxidation ( losing electrons )

what is it when a ion becomes less positive & negative

reduction ( gains electrons)

when balancing half equations where do e⁻ go when element is reduced

the + e⁻ goes to the REACTANTS side when oxidation number gains e⁻

( Reduced Reactants )

when balancing half equations where do e⁻ go when element/ion is oxidised

the + e⁻ goes to the PRODUCTS when oxidation number loses electrons

method to balancing half equations

Work out the oxidation number /state for element/ion

balance the elements

work out if electrons were lost or gained

add to reactants side ( gained) or product side ( lost)

balance O₂ with H₂O

balance hydrogens with H⁺

method to combine half equations

work out the half equation

balance the e⁻ ( same on each equation) / whatever you do to e⁻ do to equation

cancel out the same species on both equations ( e⁻ / H₂O)

add the reactants then add the products

what are the conditions for metal ion cells

25°C

101 kpa

1 mol dm⁻³

what factors does electrode potential depend on

Temperature

Pressure

concentration

in the metal/metal ion cells what is the function of the salt-bridge 

regulates neutrality 

metal/metal ion cells how do e⁻ and ions carry charge ?

e⁻ → charge carriers through the wire

ions → charge carriers through the solution/ salt bridge

when working out P.D which cell is always oxidised 

the more negative E⁰ is always oxidised

when working out P.D which cell is always reduced

the more positive E⁰ is always reduced

why is the redox system oxidised 

 in a more negative reaction the equilibria moves to the left 

why is the redox system reduced

the more positive reaction = equilibria moves to the right 

In a P.D reversible reaction what direction does the more E⁰ negative go

goes left ( oxidation)

how to work out the E⁰ cell

E⁰ ( Positive) - E⁰ ( Negative)

Standard electrode potential defintion

the difference in potential difference between a standard electrode potential and a standard hydrogen half-cell.

what is the best oxidising agent in half-cell equations 

the half-cell equation with the most positive E⁰/V

Metal/metal ion cell ( Image)

Why may results be different in a E° reaction

Not standard conditions

Rate of reaction too slow

Ea too high

Disadvantages and advantages of electrochemical cells

Disadvantage: Use toxic chemicals /Chemicals are flammable

Advantages: cheap to make