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Alcohols
and acids
Francine
Taylor-Campbell, Contributor
It
is important to note:
- Alcohols
can be prepared by the hydration
of alkenes.
- Alcohols
have the general formula Cn H2n+1OH.
- Carboxylic
acids are generally weak acids and
have the formula Cn H2n+1COOH
- Alcohols
and carboxylic acids combine to
produce esters which have the general
formula RCOOR' where R is an alkyl
group such as CH3 and C2H5.
REACTIONS
OF ALCOHOLS (USING ETHANOL)
1.
Alcohols burn in air or oxygen to
produce carbon dioxide, heat and energy.
2C2H5OH
(l) + 7O2 (g) =========== 4CO2 (g)
+ 6H2O (g)
2.
Alcohols react with metals such as
Na, Li, Mg and Ca to yield hydrogen
gas and to form salts called alkoxides.
The reaction is similar to the reaction
of metals with water because of the
presence of - OH. (H2O can be written
as H - OH)
2Na
(s) + 2C2H5OH (l) ======= 2C2H5ONa
(aq) + H2 (g)
Sodium
ethoxide
3.
Alcohols can be oxidised to organic
acids using powerful oxidising agents
such as acidified potassium dichromate
(VI) or acidified potassium permanganate
(VII) solution.
C2H5OH
(l) + 2[O] ====== CH3COOH(aq) + H2O
(l)
Ethanoic
acid
The
oxygen is from the oxidising agent.
If potassium permanganate is used,
the reaction mixture changes from
purple to colourless, and if potassium
dichromate is used, the mixture changes
from orange to green as the dichromate
VI ion is reduced to green chromium
III ion. This forms the basis for
the breathalyser test for drunken
drivers.
4.
Alcohols can undergo dehydration reactions
to the corresponding alkene using
concentrated sulphuric acid (170 0C)
or passing the vapour activated alumina
(Al2O3)
C2H5OH
(l) ========== C2H4 (g) + H2O This
reaction effectively removes water
from the alcohol to form the alkene.
5.
Alcohols react with acids to form
esters.
C2H5OH
+ CH3COOH =========== CH3COOC2H5 +
H2O
Ethylethanoate
REACTIONS
OF ORGANIC ACIDS
1.
Organic acids are weak acids (incompletely
dissociated in solution) and can react
with metals to form salts and liberate
hydrogen.
2Na
(s) + 2CH3COOH (aq) ===== 2CH3COONa
(aq) + H2 (g)
Sodium
ethanoate
Only
the hydrogen of the -COOH is replaceable
in these acid type reactions.
2.
Acids react with oxides and hydroxides
of metals.
MgO
(s) + 2CH3COOH (aq) ==== (CH3COO)2Mg
(aq) + H2O
Magnesium
ethanoate
3.
Organic acids react with carbonates
and hydrogencarbonates to form salts
and carbon dioxide.
CH3COOH
(aq) + NaHCO3 (aq) =====CH3COONa (aq)
+ CO2 (g) + H2O
4.
They react with alcohols to produce
esters in a reaction called an esterification
reaction. Ester formation is a type
of condensation reaction in which
a large molecule is formed from the
joining of two reactive groups with
the elimination of a small molecule
such as H2O.
Esters
can be hydrolysed (broken down) using
acid or alkali to yield the acid (or
salt of the acid) and alcohol that
formed the ester.
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Garth
McKenzie (third left), director
of region metro at Jamaica Public
Service Company (JPS), chats
with five students of excellence
during a luncheon hosted by
the JPS at the Terra Nova All
Suite Hotel on Thursday, February
12. From left are Immaculate
Conception High's Kaydi-Ann
Newsome, top physics student;
José Marti High School's
Zori-Ann Rhoden, top student
in agricultural science; Immaculate
Conception's Theresa Wong, top
student in biology and chemistry;
Rashaun Lindo, an excellent
performer in agricultural science
at St Catherine High; and Jhoelle
Beckford the mathemetics-brain
from Immaculate Conception.
- Peta-Gaye Clachar/Staff Photographer
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Francine
Taylor-Campbell is an independent
contributor.
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