Alkanoic acids are also known as carboxylic acids. A carboxylic acid can he identified from the carboxyl functional group and the ‘-oic’ name ending.
|HCOOH||C1 : meth||-an-||-COOH|
|CH3COOH||C2 : eth||-an-||-COOH|
|C2H5COOH||C3 : prop||-an-||-COOH|
|C3H7COOH||C4 : but||-an-||-COOH|
|C4H9COOH||C5 : pent||-an-||-COOH|
General formula of carboxylic (alkanoic acids) : CnH2n+1COOH or R-COOH
Examples of Carboxylic (Alkanoic) Acids
Structural Examples of carboxylic acids
Nomenclature (Naming Alkanoic Acids)
Alkanoic acids are named as follows:
- The number of carbon atoms in the longest carbon atom chain is noted
- The corresponding alkane is then named
- Finally, the name of this corresponding alkane is modified by removing the ane and replacing it with alkanoic acid
Preparation of ethanoic acid
The Complete Oxidation of Ethanol to Ethanoic Acid by acidified sodium heptaoxochromate(VI) solution. Ethanol undergoes oxidation first to ethanal and then to ethanoic acid.
The reaction of sodium dichromate(VI) solution with ethanol gives a carboxylic acid, ethanoic acid, a dilute solution of which is sold as vinegar.
Ethanoic acid can also be prepared by
- distilling anhydrous sodium ethanoate, CH3COONa with concentrated H2SO4
- or boiling methyl cyanide CH3CN with an acid
CH3COONa(aq)+ H2SO4(aq) → CH3COOH(g) + NaHSO4 (aq)
CH3CN(aq) + HCl(aq) → CH3COOH(g) + NH4Cl(aq)
- Ethanoic acid is usually a colourless liquid with a characteristics sharp and pungent smell
- It is soluble in water and a dilute solution has the usual sour taste of acid
- It has a boiling point of 1180C
- Pure anhydrous ethanoic acid freezes into ice-like crystals at temperature below 170C
- It turns blue litmus paper red
- Dilute solution has a sour taste
Chemical Properties of Carboxylic (Alkanoic) Acids
- Carboxylic (alkanoic) acids are weak acids, the acid dissociation constant, Ka, is small.
- Soluble carboxylic (alkanoic) acids dissociate slightly in water.
Neutralization: acid + base → salt + water
Carboxylic (alkanoic) acid + base → salt (metal alkanoate) + water
RCOOH + MOH → RCOO–M+ + H2O
e.g. CH3COOH + NaOH → CH3COO–Na+ + H2O
Ethanoic acid + sodium hydroxide → sodium ethanoate + water
Soluble salts of long-chain (fatty) acids are soaps
e.g. C17H35COOH + NaOH → C17H35COO–Na+ + H2O
Stearic acid + sodium hydroxide → sodium stearate + water
Reaction with Carbonates
acid + carbonate → salt + carbon dioxide gas + water
Carboxylic (alkanoic) acid + metal carbonate → metal alkanoate + carbon dioxide + water
e.g. 2CH3COOH + Na2CO3 → 2CH3COO–Na+ + CO2 + H2O
Ethanoic acid + sodium carbonate → sodium ethanoate + carbon dioxide + water
e.g. CH3COOH + NaHCO3 → CH3COO–Na+ + CO2 + H2O
Ethanoic acid + sodium bicarbonate → sodium ethanoate + carbon dioxide + water
Reaction with Active Metals
Acid + metal → salt + hydrogen gas
Carboxylic (alkanoic) acid + metal → metal alkanoate + hydrogen
e.g. 2CH3COOH + 2Na(s) → 2CH3COO–Na+ + H2(g)
Ethanoic acid + sodium → sodium ethanoate + hydrogen
Esters are produced in a condensation reaction between a carboxylic (alkanoic) acid and an alkanol (alcohol).
This is known as an esterification reaction.
carboxylic (alkanoic) acid + alkanol (alcohol) ester + water
e.g. 2CH3COOH + CH3OH CH3COOCH3 + H2O
Ethanoic acid + methanol methyl ethanoate + water
- It can be used as a solvent
- It is used in food industries as vinegar for preserving and flavouring food
- It is used In the manufacture of cellulose ethanoate which is used for making synthetic fibres, such as rayon
- It is used in making compounds like ethyl ethanoate, ethanoic anhydride (used in aspirin), cellulose ethanoate (used for packing), propanone etc
- Ethanoic acid is usually a colourless liquid with a characteristics sharp and ……. smell
- Esters are produced in a condensation reaction between a carboxylic (alkanoic) acid and an alkanol (alcohol) known as …….
- Ethanoic acid reacts with active metal to give off ……….. gas
- Boiling point of Ethanoic acid is …….
It is used in food industries as vinegar for preserving and flavouring food. True/False
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