CHE4: ALCOHOLS

Organic compounds which contain a hydroxyl group bounded to a group of hydrogen and carbon only.

General formula Cn H2n + 10H

structural

Laboratory preparation

Ethanol is prepared by fermentation of glucose in the presence of yeast. Yeast contains the enzymes which catalyses the reaction .The reaction is exothermic.

C6 H12 06 (aq)                   Yeast                                C2 H5 0H (aq) + C02 (q) +   Energy.

Glucose

Fermentation

Incomplete breakdown of glucose (sugar) to give Ethanol, carbon dioxide and energy

 Concentration of Ethanol-by fractional distillation

The distillation which comes off between 780 and 820c is collected. It contains about 5% water.

Absolute Ethanol

It is 100% Ethanol

Conc Ethanol is concentrated to absolute ethanol by adding a drying agent like calcium oxide in a stopped flask/corked flask then left to stand for about 24 hours .It is filtered and is re-distilled. 

Properties of Ethanol

It is a colourless liquid with L.b.p (volatile) 700 C

It is miscible with water.

 Chemical Reaction of Ethanol

It can be dehydrated with conc sulphuric acid or aluminium (iii) oxide inn the presence of heat to give ethane.

Problems associated with excess drinking of alcohol.

  • It impairs judgement
  • Alcohol is a drug and it is addictive.
  • Up to 12% of all road accidents are associated to alcohol.
  • Alcoholic have problems in their families and workplaces
  • Excessive alcohol intake can damage organ in the body e.g. liver can cause death.

Effects

I-Hangover

II-Death

III-Headache

IV- Causes dizziness in vomiting

Manufacture of Ethanol

In the manufacture of Ethanol one of the requirements is a source of starch e.g. barley.

Starch is hydrolyzed to glucose which is then fermented to form ethanol. Ethanol is concentrated by fractional distillation.

Uses of Ethanol

-Solvent in perfumes.

-Used in beers as a part of composition

-Major constituent in alcoholic drinks.

-Used in thermometer

-Used as a source of energy e.g. to drive motor engines.

CARBOXYLIC ACIDS (organic acids) or (alkanioc acids)

They contain the carboxyl group, C00H or – C – O – H

O

General formula                                     CnH2n + 2 02    or RC00H where n is the number of carbon atoms and R is hydrogen atom or an alkyl group.

Examples

methanoic acid

acetic acid

oxalic acid

Acid properties

Effect on litmus

Blue litmus paper turns red

They react with carbonates and carbonates hydrogen to give salts, carbondoixide and water e.g.

equation

Acid     + carbonate                         organic salt + carbondoixide   +   water

Observation

Slow evolution a colourless gas that turns lime water milky (it’s slow because) the acid is weak)

Reaction with bases or alkalis

Organic acids react with alkalis to give salts water

eq

Ionic equation

H+ + OH [aq]                             H2O [L]

Note:

All organic acids are weak acids and are only slightly ionized in dilute aqueous solution.

 

 THIS VIDEO EXPLAINS MORE ABOUT ALCOHOL IN CHEMISTRY

 

ASSIGNMENT : ALCOHOLS MARKS : 10  DURATION : 1 week, 3 days

 

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