Alkenes and Addition

What are alkenes?

• Unsaturated hydrocarbons which have a double bond between two carbon atoms
• Always end in -ene
• Alkenes are a homologous series
• General formula: \(C_nH_{2n}\)
• Alkenes can be produced from alkanes by cracking
• 

Addition Reactions

• Addition reaction: A reaction in which one molecule combines with another to form a larger molecule with no other products
• Hydrogenation: When hydrogen is added to an alkene under pressure with a metal catalyst
• This reaction is the test for an alkene
• Orange bromine water turns colourless in the presence of an alkene
• 

Making alkenes from alkanes

• 
• Remove the tubing from the water before removing the heat from the boiling tube to avoid suck back
• Test the tubes of gas as follows:
• By adding bromine water - it will change from orange to colourless because the gas collected is unsaturated
• By placing an lighted splint in the test-tube - it will ignite
• By adding a few drops of acidified potassium permanganate- if it turns from purple to colourless then alkene is present