SS3 First Term Chemistry Lesson Note – Alkanoic Acid

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WEEK 1        

TOPIC: ALKANOIC ACID

1. Sources, nomenclature and structure of alkanoic acid,
2. Physical and chemical properties,
3. Laboratory test and uses

PERIOD 1: SOURCES, NOMENCLATURE AND STRUCTURE OF ALKANOIC ACID

Alkanoic acids have carboxylic group as their functional group i.e –COOH. The general molecular formular is C_nH_2n+1COOH. They occur in fats and oils. They are prepared in the laboratory by the oxidation of primary alkanols with excess acidified potassium tetraoxomanganate (vii).

The name of any alkanoic acid ends with –ioc

1. Methanoic acid or formic acid (from insect bite) HCOOH
2. Ehanoic acid CH₃
3. Propanoic acid. CH₃CH₂COOH
4. Butanoic acid. CH₃CH₂CH₂COOH

PERIOD 2 AND 3: PHYSICAL AND CHEMICAL PROPERTIES OF ALKANOIC ACID

PHYSICAL PROPERTIES

1. Alkanoic acids are very soluble in water each alkanoic acid forms hydrogen bond with water molecule. The solubility of alkanoic acid in water decreases as the carbon atom increases. Therefore, lower members are more soluble in water.
2. They have high boiling and melting points. Their two pairs of hydrogen bond per molecule of alkanoic acid. The boiling and melting points increase as the carbon chain increases.
3. they turn blue litmus paper red.

CHEMICAL PROPERTIES

1. Reaction with active metals

Alkanoic acids react with active metals to liberate hydrogen gas.

2RCOOH + Zn → (RCOO)₂Zn + H₂

2CH₃COOH + Zn → (CH₃COO)₂Zn + H₂

2. Reaction with base.

Alkanoic acids react with bases to form salt and water.

RCOOH + NaOH  → RCOONa + H₂O

e.g CH₃CH₂COOH + NaOH  →  CH₃CH₂COONa + H₂O

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