Electrochemistry - Battery cells

Sec 4 Chemistry 2010

Metals of the reactivity series

Arrange the highlighted metals according to their reactivity.

Displacement Reactions More reactive metal (Cu) + Less reactive metal ion (Ag+)

Displacement ReactionsK

Na

Ca

Mg

Al

Zn

Fe

Sn

Pb

Cu

Ag

Au

Cu(s) + Ag+ Cu2+ + Ag(s)

Cu(s) Cu2+

Ag+ Ag(s)

+ 2e-

e- +

Half-reactions

oxidation

reduction

Displacement ReactionsK

Na

Ca

Mg

Al

Zn

Fe

Sn

Pb

Cu

Ag

Au

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

Zn(s) Zn2+

Cu2+ Cu(s)

+ 2e-

2e- +

Half-reactions

oxidation

reduction

Half-reactions

e-

e-

e-

e-e-

Oxidation:Zn Zn2+ + 2e-

Reduction:

Cu2+ + 2e- Cu

Zn

Cu2+

Electrodes

Zn

A half-cell

Cu2+

Doesn't react with Zn, e.g. Zn2+

Doesn't react with Cu2+, e.g. Cu

Electrodes

Half-cells A half-cell contains half of the redox reaction.

The anode is where the oxidation half-reaction takes place. The cathode is where the reduction half-reaction takes

place. What properties must the two electrodes have?

Note: by convention, we draw the anode half-cell on the left hand side.

Is the circuit complete?

Zn

Cu2+?

?

Zn2+

Cue-

e-

oxidation

anode

Zn Zn2+ + 2e-

cathode

reductionCu2+ + 2e- Cu

The salt bridge Allows the flow of ions between the two half-cells.

Consists of an electrolyte: Doesn't react with the chemical reagents in the cell. Example: NaNO3 or KNO3

The salt bridge

Zn

Cu2+?

?

Zn2+

Cue-

e-

saltbridge

anions (A-)

cations (C+)

oxidation

anodecathode

reduction