Chemistry Reference
In-Depth Information
However, a word of caution is necessary. The new
biotechnologies may not be without dangers. For
example, new pathogens (organisms that cause disease)
might be created accidentally. Also, new pathogens
may be created deliberately for use in warfare. As
you can imagine, there are very strict guidelines
covering these new biotechnologies, especially in the
area of research into genetic engineering.
methanoic acid
O
H
C
O
H
ethanoic acid
H
Question
1
What do you understand by the term 'biotechnology'?
In your answer make reference to the making of bread.
O
H
C
C
O
H
H
●
Carboxylic acids
The carboxylic acids form another homologous
series, this time with the general formula
C
n
H
2
n
+1
COOH. All the carboxylic acids possess
-COOH as their functional group. Table 15.3
shows the fi rst four members of this homologous
series along with their melting and boiling points.
Figure 15.9 shows the actual arrangement of the
atoms in these members of this family.
propanoic acid
H
H
O
H
C
C
C
O
H
H
H
butanoic acid
H
H
H
O
H
C
C
C
C
Table 15.3
Some members of the carboxylic acid series.
OH
H
H
H
Carboxylic
acid
Formula
Melting point/
°C
Boiling point/
°C
Methanoic acid
HCOOH
9
101
Figure 15.9
The molecules look like the 3D models in the photographs.
Ethanoic acid
CH
3
COOH
17
118
Ethanoic acid also undergoes other typical reactions
of acids, in that it reacts with indicators, metals and
carbonates in the usual way.
Ethanoic acid will react with ethanol, in the
presence of a few drops of concentrated sulfuric
acid, to produce ethyl ethanoate - an ester.
Propanoic acid
CH
3
CH
2
COOH
−21
141
Butanoic acid
CH
3
CH
2
CH
2
COOH
−6
164
Methanoic acid is present in stinging nettles and
ant stings. Ethanoic acid, however, is the most well
known as it is the main constituent of vinegar. Like
other acids, ethanoic acid affects indicators and will
react with metals such as magnesium. However,
whereas the mineral acids such as hydrochloric acid
are called strong acids, ethanoic acid is a weak acid
(Chapter 8, p. 120). Even though it is a weak acid, it
will still react with bases to form salts. For example,
the salt sodium ethanoate is formed when ethanoic
acid reacts with dilute sodium hydroxide.
conc
ethanoic
+
ethanol
ethyl
+
water
acid
H
2
SO
4
ethanoate
CH
3
COOH(
l
) + C
2
H
5
OH(
l
)
CH
3
COOC
2
H
5
(
aq
) + H
2
O(
l
)
This reaction is called
esterifi cation
.
Members of the 'ester' family have strong and
pleasant smells. They have the general formula
C
n
H
2
n
+1
COOC
x
H
2
x
+1
. Esters are named after the
acid and alcohol from which they are derived:
•
name - alcohol part fi rst, acid part second,
e.g. propyl ethanoate
•
formula - acid part fi rst, alcohol part second,
e.g. CH
3
COOC
3
H
7
ethanoic
+ sodium →
sodium
+ water
acid hydroxide ethanoate
CH
3
COOH(
aq
) + NaOH(
aq
) → CH
3
COONa(
aq
) + H
2
O(
l
)
