CARBOXYLIC ACIDS

1. Carboxylic acids are organic compounds which form an homologous series with the general
    formula of CnH2n+1COOH.

2. Carboxylic acids are compounds which contain a -COOH functional group.


3. Carboxylic acids are weak acid which ionize partially in water to produce lower  concentration of 
    hydrogen ions compare to strong acid. Ethanoic acid turns moist blue litmus paper red.


      CH₃COOH <–> CH₃COO^- + H⁺

   

 

4. Physical properties of carboxylic acid

Name	Molecularformula	Boiling point (°C)
Methanoic acid(Formic acid)	HCOOH	101
Ethanoic acid(Acetic acid)	CH3COOH	118
Propanoic acid	C2H5COOH	141
Butanoic acid	C3H7COH	164

• Solubility in water – generally in carboxylic acid (the less than four carbon atoms) are very soluble in water and ionise partially to form weak .
• Density of carboxylic acid – density of carboxylic acid increases due to the increases in the number of carbon atoms in a molecule.
• Boiling points – all carboxylic acid in general have relatively high boiling points than the corresponding alkanes. This is due to the presence of carboxyl group in carboxylic acid.
• Smell – carboxylic acid (< 10 carbon) are colourless and pungent smell. Carboxylic acid (>10 carbons) are wax-like solids.

Formula	Common Name	Source	IUPAC Name
HCO2H	formic acid	ants (L. formica)	methanoic acid
CH3CO2H	acetic acid	vinegar (L. acetum)	ethanoic acid
CH3CH2CO2H	propionic acid	milk (Gk. protus prion)	propanoic acid
CH3(CH2)2CO2H	butyric acid	butter (L. butyrum)	butanoic acid
CH3(CH2)3CO2H	valeric acid	valerian root	pentanoic acid
CH3(CH2)4CO2H	caproic acid	goats (L. caper)	hexanoic acid
CH3(CH2)5CO2H	enanthic acid	vines (Gk. oenanthe)	heptanoic acid
CH3(CH2)6CO2H	caprylic acid	goats (L. caper)	octanoic acid
CH3(CH2)7CO2H	pelargonic acid	pelargonium (an herb)	nonanoic acid
CH3(CH2)8CO2H	capric acid	goats (L. caper)	decanoic a

5. Preparation of carboxylic acid

Oxidation of an alcohol

• The oxidation of ethanol is used to prepare ethanoic acid.
              C₂H₅OH + 2[O] –> CH₃COOH + H₂O
  Carried out by refluxing* ethanol with an oxidising agent
  [acidified potassium dichromate(VI) solution – orange colour turns to green /
  acidified potassium manganate(VII) solution – purple colour turns to colourless]

6. Chemical properties of carboxylic acid

• Reaction with metals
• Ethanoic acid reacts with reactive metals (copper and metals below it in the reactivity series cannot react with ethanoic acid).
• (K, Na, Mg, Al, Zn, Fe, Sn, Pb, Cu, Hg, Au)
• Reaction with bases acid neutralises alkalis (sodium hydroxide).

• 
  CH₃COOH + NaOH –> CH₃COONa + H₂O
  In this reaction, a salt (sodium ethanoate) and water are formed.

• Reaction with carbonates
  Ethanoic acid reacts with metal carbonates (calcium carbonate, magnesium carbonate, zinc carbonate).
  2CH₃COOH + CaCO₃ –> Ca(CH₃COO)₂ + CO₂ + H₂O
  In this reaction, a salt (calcium ethanoate), carbon dioxide and water are formed.

• Reaction with alcohols (Esterification)
  Ethanoic acid reacts with alcohol (ethanol, propanol, butanol)
  CH₃CO-OH + H-OC₄H₉ –> CH₃COOC₄H₉ + H₂O (Concentrated H2SO4 is a catalyst)
  In this reaction, an ester (colourless sweet-smelling liquid) (butyl ethanoate) and water are formed.

7. Uses of Carboxylic Acid

soap

vinegar

aspirin

coagulant

dye