inversion A chemical reaction involving a change from one optically
active conÜguration to the opposite
conÜguration. The Walden inversion
is an example. See nucleophilic substitution.
iodic acid Any of various oxoacids
of iodine, such as iodic(V) acid and
iodic(VII) acid. When used without an
oxidation state speciÜed, the term
usually refers to iodic(V) acid (HIO 3 ).
iodic(V) acid A colourless or very
pale yellow solid, HIO 3 ; r.d. 4.63; decomposes at 110°C. It is soluble in
water but insoluble in pure ethanol
and other organic solvents. The compound is obtained by oxidizing iodine with concentrated nitric acid,
hydrogen peroxide, or ozone. It is a
strong acid and a powerful oxidizing
agent.
iodic(VII) acid (periodic acid) A hygroscopic white solid, H 5 IO 6 , which
decomposes at 140°C and is very
soluble in water, ethanol, and
ethoxyethane. Iodic(VII) acid may be
prepared by electrolytic oxidation of
concentrated solutions of iodic(V)
acid at low temperatures. It is a weak
acid but a strong oxidizing agent.
iodide See halide.
iodine Symbol I. A dark violet
nonmetallic element belonging to
group 17 of the periodic table (see
halogens); a.n. 53; r.a.m. 126.9045;
r.d. 4.94; m.p. 113.5°C; b.p. 184.35°C.
The element is insoluble in water but
soluble in ethanol and other organic
solvents. When heated it gives a violet vapour that sublimes. Iodine is
required as a trace element (see essential element) by living organisms; in animals it is concentrated in
the thyroid gland as a constituent of
thyroid hormones. The element is
present in sea water and was formerly extracted from seaweed. It is
now obtained from oil-well brines
(displacement by chlorine). There is
one stable isotope, iodine–127, and
fourteen radioactive isotopes. It is
used in medicine as a mild antiseptic
(dissolved in ethanol as tincture of iodine), and in the manufacture of iodine compounds. Chemically, it is
less reactive than the other halogens
and the most electropositive (metallic) halogen. In solution it can be
determined by titration using thiosulphate solution:
I 2 + 25 2 O 3
2–
→ 2I
– + S u O 6
2– .
The molecule forms an intense blue
complex with starch, which is consequently used as an indicator. It was
discovered in 1812 by Courtois.
A
• Information from the WebElements site
iodine(V) oxide (iodine pentoxide)
A white solid, I 2 O 5 ; r.d. 4.799; decomposes at 300–350°C. It dissolves in
water to give iodic(V) acid and also
acts as an oxidizing agent.
iodine value A measure of the
amount of unsaturation in a fat or
vegetable oil (i.e. the number of double bonds). It is obtained by Ünding
the percentage of iodine by weight
absorbed by the sample in a given
time under standard conditions.
iodoethane (ethyl iodide) A colourless liquid *haloalkane, C 2 H 5 I; r.d.
1.9; m.p. –108°C; b.p. 72°C. It is made
by reacting ethanol with a mixture of
iodine and red phosphorus.
iodoform See triiodomethane.
iodoform test See haloform reaction.
iodomethane (methyl iodide) A
colourless liquid haloalkane, CH 3 I;
r.d. 2.28; m.p. –66.45°C; b.p. 42.4°C. It
can be made by reacting methanol
with a mixture of iodine and red
phosphorus.
ion An atom or group of atoms that
inversion
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active conÜguration to the opposite
conÜguration. The Walden inversion
is an example. See nucleophilic substitution.
iodic acid Any of various oxoacids
of iodine, such as iodic(V) acid and
iodic(VII) acid. When used without an
oxidation state speciÜed, the term
usually refers to iodic(V) acid (HIO 3 ).
iodic(V) acid A colourless or very
pale yellow solid, HIO 3 ; r.d. 4.63; decomposes at 110°C. It is soluble in
water but insoluble in pure ethanol
and other organic solvents. The compound is obtained by oxidizing iodine with concentrated nitric acid,
hydrogen peroxide, or ozone. It is a
strong acid and a powerful oxidizing
agent.
iodic(VII) acid (periodic acid) A hygroscopic white solid, H 5 IO 6 , which
decomposes at 140°C and is very
soluble in water, ethanol, and
ethoxyethane. Iodic(VII) acid may be
prepared by electrolytic oxidation of
concentrated solutions of iodic(V)
acid at low temperatures. It is a weak
acid but a strong oxidizing agent.
iodide See halide.
iodine Symbol I. A dark violet
nonmetallic element belonging to
group 17 of the periodic table (see
halogens); a.n. 53; r.a.m. 126.9045;
r.d. 4.94; m.p. 113.5°C; b.p. 184.35°C.
The element is insoluble in water but
soluble in ethanol and other organic
solvents. When heated it gives a violet vapour that sublimes. Iodine is
required as a trace element (see essential element) by living organisms; in animals it is concentrated in
the thyroid gland as a constituent of
thyroid hormones. The element is
present in sea water and was formerly extracted from seaweed. It is
now obtained from oil-well brines
(displacement by chlorine). There is
one stable isotope, iodine–127, and
fourteen radioactive isotopes. It is
used in medicine as a mild antiseptic
(dissolved in ethanol as tincture of iodine), and in the manufacture of iodine compounds. Chemically, it is
less reactive than the other halogens
and the most electropositive (metallic) halogen. In solution it can be
determined by titration using thiosulphate solution:
I 2 + 25 2 O 3
2–
→ 2I
– + S u O 6
2– .
The molecule forms an intense blue
complex with starch, which is consequently used as an indicator. It was
discovered in 1812 by Courtois.
A
• Information from the WebElements site
iodine(V) oxide (iodine pentoxide)
A white solid, I 2 O 5 ; r.d. 4.799; decomposes at 300–350°C. It dissolves in
water to give iodic(V) acid and also
acts as an oxidizing agent.
iodine value A measure of the
amount of unsaturation in a fat or
vegetable oil (i.e. the number of double bonds). It is obtained by Ünding
the percentage of iodine by weight
absorbed by the sample in a given
time under standard conditions.
iodoethane (ethyl iodide) A colourless liquid *haloalkane, C 2 H 5 I; r.d.
1.9; m.p. –108°C; b.p. 72°C. It is made
by reacting ethanol with a mixture of
iodine and red phosphorus.
iodoform See triiodomethane.
iodoform test See haloform reaction.
iodomethane (methyl iodide) A
colourless liquid haloalkane, CH 3 I;
r.d. 2.28; m.p. –66.45°C; b.p. 42.4°C. It
can be made by reacting methanol
with a mixture of iodine and red
phosphorus.
ion An atom or group of atoms that
inversion
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