ALKANOIC ACID AND ALKANOATE
Week: NINE Date:
Period: Duration: 1 HR 20 MIN. Average age of learners: 17YEARS
Subject: CHEMISTRY Class: SS 3
Topic:
ALKANOIC ACID AND ALKANOATE
Sub topic:
Reference materials:
(1) ESSENTIAL CHEMISTRY, TONALD PUBLISHERS, I. O ODESINA
(2) NEW SCHOOL CHEMISTRY, AFRICAN FIRST PUBLISHERS, OSEI YAW ABABIO
(3) INTERNET
Instructional materials: vegetable oil
Entry behavior: The students have been familiar with fats and oils.
Behavioural objective: At the end of the lesson the students should be able to:
1. Write the general formula and the structure of alkanoic acid.
2. State the properties and the reaction of alkanoic acid
3. Write the relationship between alkanoic acid and alkanoates
4. State the chemical properties of fats and oils
5. Mention the uses of fats and oils
CONTENT
ALKANOIC ACID AND ALKANOATE
Alkanoic acids, also known as organic or carboxylic acid. Carboxylic acids are a family
of organic compounds containing carbon, hydrogen and oxygen. The general formula of carboxylic acids is CnH2n+1COOH
(n = 0, 1, 2, 3, 4…). The functional group is the –COOH group. Carboxylic acids
end with –oic acid. They are sometimes called fatty acids because some of them
are found in natural fats and oils.
The most common of these
are the aliphatic monocarboxylic acids which contain one carboxyl group per
molecule.
Dicarboxylic acid have two
carboxyl groups per molecules e.g ethanedioic acid (oxalic acid),
cis-butenedioic acid (maleic acid) and 2,3dibydroxybutanedioic acid (tartaric
acid) while tricarboxylic acids have three carboxyl groups per molecule e.g.
2-hydroxypropane-1,2,3-tricarboxylic acid (citric acid).
Two important aromatic
carboxylic acids are benzoic acid and 2-hydroxybenzoic acid (salicylic acid).
|
Molecular formula |
Structural formula |
IUPAC name |
Common name |
|
CH2O2 |
HCOOH |
Methanoic acid |
Formic acid |
|
C2H4O2 |
CH3COOH |
Ethanoic acid |
Acetic acid |
|
C3H6O2 |
CH3CH2COOH |
Propanoic acid |
Propanoic acid |
|
C4H8O2 |
CH3(CH2)2COOH |
Butanoic acid |
n- Butyric acid |
|
C4H8O2 |
(CH3)2CHCOOH |
2-methyl propanoic acid |
Iso- Butyric acid |
Structure
of carboxylic acids
|
Carboxylic
acid |
Molecular
formula |
Structural
formula |
Ball-and-stick
model |
|
Methanoic acid |
HCOOH |
|
|
|
Ethanoic acid |
CH3COOH |
|
|
Vinegar is a dilute solution of ethanoic acid.
– Ethanoic acid is formed by the oxidation of
ethanol.
• By
using atmospheric oxygen:
• CH3CH2OH
+ O2 CH3COOH
+ H2O
• By
using acidified K2Cr2O7.
• CH3CH2OH
+ 2[O] CH3COOH
+ H2O
• The
orange dichromate (VI) solution changes from orange to green.
• A
vinegar smell is detected.
Properties and
reactions of carboxylic acids
1. Many carboxylic acids have unpleasant smells and tastes. They are responsible for: the taste of vinegar, the smell of sweaty socks, and the taste of rancid butter.
2. Carboxylic acids are weak acids. This means that dilute solutions of carboxylic acids have higher pHs (ie are less acidic) than dilute solutions of strong acids such as hydrochloric acid, nitric acid and sulfuric acid. Weak acids are less reactive than strong acids.
3. The lower members of the alkanoic acids are colourless liquids at room temperature. Their boiling points are much higher than expected when compare with their molecular sizes. This is due to hydrogen bonds that bind the molecules.
4.
It dissociate in aqueous solution to produce
hydrogen ions. - Eg.
CH3COOH <--> CH3COO- + H+
Carboxylic acids show the
normal characteristic reactions of acids.
Reaction with metals
acid + metal → salt + hydrogen
For example:
ethanoic acid + magnesium → magnesium ethanoate + hydrogen
Reaction with alkali
acid + soluble hydroxide → salt + water
For example:
ethanoic acid + sodium hydroxide → sodium ethanoate + water
Reaction with carbonate
acid + metal carbonate → salt + water + carbon dioxide
ALKANOATES [ESTHERS]
When an alkanol reacts with a carboxylic acid, an ester and water are formed. This reaction is called an esterification reaction, and it is a reversible reaction, quite analogous to the neutralization reaction.
Alkanol + Carboxylic acid Ester + water.
The
functional group of an ester is –COO- (it also contains the polar carboxyl
group is a C=O bond and two C-O single bonds attached to the same oxygen atom).
All the bonds which make up the functional group are polar. Esters are named as
alkyl derivatives of carboxylic acids.
Esters are neutral compound with a sweet smell. Esters
are present in fruits.
Uses of esters
– Artificial
flavouring
– Solvents
for organic compounds
– Vegetable
oils
FATS AND OILS
Fats and oils belong to a group of compounds known as lipids. Fats are solids and of animal origin, while oils are liquid mainly from plants at room temperature. They are complex mixture of esters of trihydric alkanol, propane-1,2,3,-triol.
Fatty acid + propane-1,2,3-triol Ester + water
CLASSIFICATION OF FATTY ACIDS
I. Saturated fatty acid: it have no double bonds in their hydrocarbon chain.
II. Unsaturated fatty acid: have one or more double bonds in their hydrocarbon chain.
PHYSICAL PROPERTIES OF FATS OR OILS
I. Fats have higher melting points because they consist of higher proportion of esters of saturated fatty acids.
II. Oils have lower melting points because they consist of higher proportion of esters of unsaturated fatty acids.
III. They are insoluble in water and decompose at temperature above 300oC.
CHEMICAL PROPERTIES OF FATS OR OILS
I. HYDROGENATION OF OILS: This process is known as hardness of oil because it produces solid fats. The process involves passing hydrogen into an unsaturated oil at 200oC and 5 atmospheric pressure in the presence of finely divided nickel catalyst.
The unsaturated part of the oil is saturated and the oil become hardened. The hardened oils are then mixed with salt, vitamin and skimmed milk and various fat to form margarine.
II. FORMATION OF SOAP (SAPONIFICATION): The general process of alkaline hydrolysis of ester by which soap is obtained is called SAPONIFICATION.
Fat or oil + caustic soda soap + glycerol (propan-1,2,3-triol)
Example of saturated and unsaturated fatty acids
|
IUPAC NAME |
OLD NAME |
SOURCES |
MOLECULAR
FORMULA |
|
Hexadecanoic acid |
Palmitic acid |
Palm oil |
CH3(CH2)14COOH |
|
Octadecanoic acid |
Stearic acid |
Animal fat |
CH3(CH2)16COOH |
|
Octadeca-9-enoic acid |
Oleic acid |
Olive or Peanut |
CH3(CH2)7CH=CH(CH2)7COOH |
|
Octadeca-9,12-dienoic acid |
Linoleic acid |
Vegetable oil |
CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH |
USES OF FATS AND
OILS
I. Fats and oils are used as essential ingredients of food.
II. Vegetable oil are used in soap production.
III. Oil are hardened into fats to make margarine.
IV. Linseed oils is a raw materials used in the manufacture of paints and varnishes.
V. They are used in making glycerol and candles.
PRESENTATION
I. The teacher states the general molecular formula and structure of alkanoic acid.
II. The teacher states the physical and chemical properties of alkanoic acid.
III. The teacher establishes the relationship between alkanoic acid and alkanoates
IV. The teacher explains fats and oils
V. The students mention different types of oils
VI. The teacher states the classes and the properties of fats and oils.
EVALUATION
The teacher evaluates the lessons by asking the following questions:-
1. What is the general formula of alkanoic acid.
2. State the properties and the reaction of alkanoic acid
3. Write the relationship between alkanoic acid and alkanoates
4. State the chemical properties of fats and oils
5. Mention the uses of fats and oils
ASSIGNMENT
1. An
alkanoic acid Y has a relative molecular
mass of 74.
(a) State the functional group of Y.
(b) What type of reaction is involved when Y is converted to alkanoate?
(c) Determines the structural formula of Y.
2. A vegetable oil A was treated with activated charcoal and then with a gas B in the present of catalyst order to manufacture margarine
a. Identify B
b. State the function of the activated charcoal.
c. What is catalyst used?
d. If a sample of A is heated with concentrated NaOH solution, list the product that will be obtained.
e. What term is used to described alkaline hydrolysis of fats and oils.
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