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ALKANOIC ACIDS

Chemistry

Chemistry

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.

O

RC

OH

 

E.g.Ethanoic acid CH3COOH

H

O

H          C       C

 

H            OH

PREPARATION   e.g.Ethanoic acid

Ethanoic acid can be prepared by the complete oxidation of ethanol by acidified sodium heptaoxo dichromate (VI) solution.  The oxidation reaction is a two stages of reaction

  1. Ethanol oxidized to ethanol; CH3CH2OH             O3         CH3CHO

 

  1. Ethanol oxidized to ethanoic acid; CH3CHO        O3          CH3COOH

Or

CH3CH2OH  +    [O]            CH3CHO  +     [O]               CH3COOH

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 17C therefore called gluciaethanoic acid (anhydrous ethanoic acid).
  5. It has boiling point of 118C
  6. It turns blue litmus papers to red.

 

CHEMICAL PROPERTIES

  1. It libratescarbon(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.

  1. As an acid, it neutralizes boxes or alkalis to form salts known as ethanoate and water only

CH3COOH + NaOH              CH3COONa + H2O.

  1. It reacts with alkanols to form ester e.g. CH3COOH + CH3CH2OH CH3COOCH2CH3 + H2O
  2. Reduction:

It can be reduced to ethanol in the presence of lithiumtetrahydridoaluminate III as

reducing agent (LiAlH4)

CH3COOH  + 4H          CH3CH2OH + H2O

  1. It reacts with chlorme 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.

  1. How would you prepare ethanoic acid in the laboratory.

 

CLASSIFICATION OF ALKANOIC ACID

Alkanoic acids are classified based on the number of carbonxylic groups present per molecules.

  1. Monocarboxylic Acids: these have one carboxylic group per molecule e.g.

methanoic acid (HCOOH)

 

 

O

 

H          C

OH

 

Ethanoic acid CH3 COOH

 

H

O

H          C          C

 

H                 OH

  1. Dicarboxylic Acids: these have two carboxyl groups per molecules e.g. ethan -1, 2-dioe acid

(oxalic acid)

COOH               O          O

or                  C     C

COOH             HO                  OH

 

  1. Tricarboxylic acids: these have 3 carboxylic acid per molecule e.g. 2-hydroxy propan 1,2, 3-

tricaboxylic acid.

H

H          C          COOH

HO       C          COOH

H          C          COOH

H

N.B:      Two important aromatic caborxylicacid are

(1)        Benzoic acid

(2)        2-hydroxy benzoic acid

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.

 

ALKANOATES

General molecular formula.

The alkanoates are called esters.  They have general molecular formula of RCOOR’.

It has structural formula of

O

R     C

OR

e.gethylethanoate CH3COOCH2CH3

NOMENCLATURE

Naming of alkanoates are obtained by substituting “e” ending in alkane with “oates” in

alkanoates.

Preparation e.g. ethyl ethanoate .

Ethyl ethanoate is prepared by the esterification between ethanol and glaciusethanoic acid at 150C  in the presence of concentrated tetraoxosulphate (VI) acid

C2H5OH + CH3COOH                 CH3COOC2H5 + H2O

 

PHYSICAL PROPERTIES

  1. Ethyl ethanoate is a colourles volatile liquid with a pleasant smell.
  2. It is slightly soluble in water.

3..It has boiling point of 75C.

 

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

 

  1. REACTION WITH AMMONIA

Ethyl ethanoate reacts with ammonia to produce ethanol and thenamide

CH3COOC2H3 + NH3               C2H5OH + CH3COOH2

 

  1. 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.

 

WEEKEND ASSIGNMENT

  1. The name of (CH3)2 CHCOOH is
  2. Propane acid    B. 2-methylhutanoic acid  C.           Dimethyl butanoic acid
  3. Propanoic acid
  4. Citric acid appears in unripe orange while enthanwie acid appears in
  5. Unripe pawpaw B. Carrot    C.  Vineger     D.  Rice
  6. Esters are employed in the following except.
  7. Making perfumes   B.  Making cement    C. Nail varnishes    D.  Making yeast
  8. An alkanoic acid reacts reversibly with an alkanol to produce.
  9. a salt  B.  an ester     C.  a sugar     D.  an alkene
  10. Ethan-1, 2-dioe acid is
  11. 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.

  1. 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

 

See also

ALKANOLS

AROMATIC HYDROCARBONS

ALKYNES

UNSATURATED HYDROCARBONS

Saturated Hydrocarbons

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