Making Electricity.• A cell is an apparatus which generates

electricity from a chemical reaction.

• A Battery is when two or more cells are joined together.

• There are in general, two main types of cell i.e. Wet and Dry Cells. In a dry cell the liquid of the wet cell is replaced by a paste.

• We more commonly use dry cells since they don’t leak.

• Some cells can be Recharged. The Lead/acid cell is a rechargeable cell.

Chemical Reactions in cells• To make a cell all we require is two

different metals and an Electrolyte.

Salt or Ion Bridge.(To complete the circuit)

Zn/Zn2+ Cu/Cu2+

Electrons flow from the more active metal to the least active metal

Zn metal is Oxidised and Cu2+ions are Reduced

Other types of Voltaic Cell

As with all three representations of the Voltaic Cell the Electrons flow from the

More Active metal to the Least Active Metal.The Further the metals are

apart in Electrochemical Series, the bigger the reading on the Voltmeter.

In each case:

Zn= Zn2++ 2e (Oxidation) and Cu2++2e=Cu (Reduction)=

No Ion Bridge required here as ions can move freely through the solution.

Br2(aq) SO32-/SO4

2-aq

We can also get a flow of electrons between two non-metals. Here the Sulphite ions are oxidised to Sulphate ions as they Reduce Bromine molecules to bromide ions.ie The electrons flow from the solution that is Oxidised to the one that is Reduced.

Half- Equations:

SO32- +H2O = SO4

2-+2H++2e

Br2 + 2e = 2Br-

In Half-Equations the electrons go on the right-hand side if the species is being Oxidised and on the left if it is Reduced

The Electrochemical SeriesThe Electrochemical Series• Potassium• Sodium• Calcium• Magnesium• Aluminium• Zinc• Iron• Nickel• Tin• Lead• Hydrogen• Copper• Mercury• Silver • Gold• Platinum

A Displacement Reaction will occur if a Metal higher up in the Electrochemical Series is added to an Ionic solution which contains Metal Ions of a Metal lower down in the Electrochemical Series.

Imagine Magnesium is added to a Copper Sulphate Solution • Mg(s) + Cu2+SO2-

4(aq) Mg2+SO2-4(aq) + Cu(s)

Ion-Electron Half –Equations:

Mg(s) Mg2+(aq) + 2e (Oxidation)

Cu2+(aq) + 2e Cu(s) (Reduction)

Cu2+ + Mg Mg2+ + Cu (Redox or Ionic equation)

Copper Sulphate + Mg Brown Copper metal is seen at the bottom of the beaker

Spectator Ion (doesn’t change charge).

The blue colour will eventually disappear as all the Copper Ions are used up

OILRIG

Oxidation is Loss of Electrons

Reduction is Gain of Electrons