ALKANOATES
General molecular formula, nomenclature, preparation, properties and uses.
SOURCES:
The alkanoic acid or carboxylic acids are also called fatty acids because some of them are found in natural fats and oils. They contain the functional group called carboxy group.
NOMENCLATURE:
The IUPAC name of each homologue is obtained by changing the “-e” endind of the corresponding alkane to “-oic” acid e.g. mathanoic, ethanoic etc.
STRUCTURE:
Alkanoic acid has a general molecular fomular of CnH2n + 1COOH where n > 0. or RCOOH. Thus it has the following structure.
PHYSICAL PROPERTIES
1. It is colourless liquid with a sharp and pungent smell.
2. It has sour taste.
3. It is soluble in water.
4. It freezes into ice-like at temperature below 170C therefore called gluciaethanoic acid (anhydrous ethanoic acid).
5. It has boiling point of 1180C
6. It turns blue litmus papers to red.
CHEMICAL PROPERTIES
1. It librates carbon(IV) oxide from either trioxocarbonate (IV) or hydrogen trioxocarbonate (IV) salts. 2CH3COOH + Na2CO3 → 2CH3CONa + H2O + CO2.
2. It librates hydrogen gas when it reacts with highly electropositive metals e.g.
Mg &Ca; 2CH3COOH + Ca → (CH3COO)2Ca + H2.
3. As an acid, it neutralizes boxes or alkalis to form salts known as ethanoate and water only
CH3COOH + NaOH → CH3COONa + H2O.
4. It reacts with alkanols to form ester e.g. CH3COOH + CH3CH2OH → CH3COOCH2CH3 + H2O
5. Reduction:
It can be reduced to ethanol in the presence of lithiumtetrahydridoaluminate III as
reducing agent (LiAlH4)
CH3COOH + 4H → CH3CH2OH + H2O
6. It reacts with chloroform successively to form chloroethanoic acid e.g.
CH3COOH + Cl2 → CH2ClCOOH + HCl
CH2ClCOOH + Cl2 → CHCl2 COOH +HCl
CHCl2 COOH + Cl2 → CCl3COOH + HCl
EVALUATION
1. (a) State four (4) chemical properties of ethanoic acid.
(b) Give two (2) physical properties of ethanoic acid.
2. How would you prepare ethanoic acid in the laboratory.
USES OF ETHANOIC ACID
1. It is used in making compounds like cellulose ethanoate, dyes etc.
2. It is used as organic solvent.
3. It is used in the food industries for preserving and flavoring food.
4. Used for coagulating rubber latex.
EVALUATION
1. Give three (3) classes of alkanoic acid.
2. State four (4) uses of ethanoic acid.
READING ASSIGNMENT
New School Chemistry by O.Y. pages.504-506
ALKANOATES
General molecular formula.
The alkanoates are called esters. They have general molecular formula of RCOOR’.
CHEMICAL PROPERTIES
1. Hydrolysis.
Ethyl ethanoate can be hydrolysed by water to produce ethanoic acid and ethanol.
CH3COOC2H5 + H2O → CH3COOH + C2H5OH.
N.B:If an alkali is used instead of water, it will produce the salt of the acid e.g.
CH3COOC2H5 + NaOH → CH3COONa + C2H5OH
2. REACTION WITH AMMONIA
Ethyl ethanoate reacts with ammonia to produce ethanol and thenamide
CH3COOC2H3 + NH3 → C2H5OH + CH3COOH2
3. REDUCTION
Ethyl ethanoate can be reduced by hydrogen from lithium tetrahydridoalluminute (III) as reducing agent CH3COOC2H5 + 4[H] → 2C2H5OH
USES OF ALKANOATES/ESTERS
– They are used as food flavours.
– Used in perfumes and cosmetics
– Used as solvent for cellulose nitrate .
– Used for quick-drying substances like paints, nail varnishes etc.
EVALUATION
1.Write the general structure of the ester.
2.Write a balanced equation for the reaction between propanol and butanoic acid.
(a) Name the products formed.
(b) What type of reaction is involved.
READING ASSIGNMENT
New School Chemistry by Osei Yaw Ababio page.504-509
WEEKEND ASSIGNMENT
1. The name of (CH3)2 CHCOOH is
A. Propane acid B. 2-methylhutanoic acid C. Dimethyl butanoic acid
D. Propanoic acid
2. Citric acid appears in unripe orange while enthanwie acid appears in
A. Unripe pawpaw B. Carrot C. Vineger D. Rice
3. Esters are employed in the following except.
A. Making perfumes B. Making cement C. Nail varnishes D. Making yeast
4. An alkanoic acid reacts reversibly with an alkanol to produce.
A. a salt B. an ester C. a sugar D. an alkene
5. Ethan-1, 2-dioe acid is
A. a mineral acid B. dicarboxylic acid C. citric acid D. a soap
THEORY
1a. Give the formula of ethanoic acid and indicate its functional group.
- Ethanoic acid reacts with both sodium hydroxide and ethanol, suing equations to comparethe reactions and classify the products.
2a. Ethylethanoate reacts with both water and alkali; using equation to compare the reaction.
b. What happens when ethanoic acid is heated strongly with soda-line.
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