OCR A2 Chemistry notes - Alcoholc

Alcohols - Revision Notes

1. General

• Functional group is -OH
• General formula is C_nH_2n+1OH
• The –OH group means that alcohols hydrogen bond with each other. Alcohols have low volatility (high boiling points) for their size because the hydrogen bonds have to be broken
• Alcohols are highly soluble in water because hydrogen bonding occurs between –OH of alcohols and water molecules

2. Classifying Alcohols

• Classified according to the number of carbons attached to C-OH
• Primary alcohols have 1 carbon attached e.g. ethanol
• Secondary alcohols have 2 carbons attached e.g. propan-2-ol
• Tertiary alcohols have 3 carbons attached e.g. 2-methylpropan-2-ol

3. Reactions of Alcohols

• Reagents = the other chemicals needed
• Conditions = required temperature, pressure, catalyst etc

a) Combustion

• Example C₂H₅OH + 3O₂ ® 2CO₂ + 3H₂O
• Balance C’s then H’s then O’s
• Don’t forget the O in the OH when balancing

b) Dehydration to form an alkene

• Example C₂H₅OH ® CH₂=CH₂ + H₂O
• Needs heat and a strong acid catalyst (concentrated sulphuric acid or concentrated phosphoric acid)

c) Reaction with a carboxylic acid to form an ester (esterification)

• Carboxylic acids contain the functional group –COOH, esters have the form RCOOR’
• Example C₂H₅OH + CH₃COOH ® CH₃COOC₂H₅ + H₂O

Ethanoic acid ethyl ethanoate

• Conditions catalyst of concentrated H₂SO₄