TOPIC 10 Making Electricity

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/Zn 2+ Cu/Cu 2+ Electrons flow from the more active metal to the least active metal Zn metal is Oxidised and Cu 2+ ions are Reduced

Other types of Voltaic Cell In the three cells, the electrons flow from the more active metal to the less active metal. The further the metals are apart in Electrochemical Series, the bigger the reading on the voltmeter. In each case: Zn  Zn e (oxidation) and Cu 2+ +2e  Cu (reduction) Ion bridge NOT required here as ions can move freely through the solution.

Br 2 (aq) SO 3 2- /SO 4 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 : SO H 2 O SO H + +2e Br 2 + 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 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.

Mg (s) + Cu 2+ SO 2- 4(aq) Mg 2+ SO 2- 4(aq) + Cu (s) Ion-Electron Half –Equations: Mg(s)Mg 2+ (aq) + 2e (Oxidation) Cu 2+ (aq) + 2e Cu (s) (Reduction) Mg + Cu 2+ Mg 2+ + Cu (Redox or Ionic equation) Mg + Copper SulphateBrown 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 Magnesium is added to a Copper Sulphate Solution

OIL RIG Oxidation is Loss of electrons Reduction is Gain of electrons