count of its reducing properties. It
has also been used for the production
of sodium thiosulphate (for the photographic industry) and as a depilatory agent in leather preparation. It
is a strong skin irritant.
sodium sulphite A white solid,
Na 2 SO 3 , existing in an anhydrous
form (r.d. 2.63) and as a heptahydrate
(r.d. 1.59). Sodium sulphite is soluble
in water and because it is readily oxidized it is widely used as a convenient reducing agent. It is prepared
by reacting sulphur dioxide with either sodium carbonate or sodium hydroxide. Dilute mineral acids reverse
this process and release sulphur dioxide. Sodium sulphite is used as a
bleaching agent in textiles and in
paper manufacture. Its use as an antioxidant in some canned foodstuffs
gives rise to a slightly sulphurous
smell immediately on opening, but
its use is prohibited in meats or foods
that contain vitamin B 1 . Sodium sulphite solutions are occasionally used
as biological preservatives.
sodium–sulphur cell A type of
*secondary cell that has molten electrodes of sodium and sulphur separated by a solid electrolyte consisting
of beta alumina (a crystalline form of
aluminium oxide). When the cell is
producing current, sodium ions Ûow
through the alumina to the sulphur,
where they form sodium polysulphide. Electrons from the sodium
Ûow in the external circuit. The opposite process takes place during
charging of the cell. Sodium–sulphur
batteries have been considered for
use in electric vehicles because of
their high peak power levels and relatively low weight. However, some of
the output has to be used to maintain the operating temperature
(about 370°C) and the cost of sodium
is high.
sodium superoxide (sodium dioxide) A whitish-yellow solid, NaO 2 ,
formed by the reaction of sodium
peroxide with excess oxygen at elevated temperatures and pressures. It
reacts with water to form hydrogen
peroxide and oxygen.
sodium thiosulphate (hypo) A
colourless efÛorescent solid, Na 2 S 2 O 3 ,
soluble in water but insoluble in
ethanol, commonly encountered as
the pentahydrate (monoclinic; r.d.
1.73; m.p. 42°C), which loses water at
100°C to give the anhydrous form
(r.d. 1.66). It is prepared by the reaction of sulphur dioxide with a suspension of sulphur in boiling sodium
hydroxide solution. Aqueous solutions of sodium thiosulphate are
readily oxidized in the presence of
air to sodium tetrathionate and
sodium sulphate. The reaction with
dilute acids gives sulphur and sulphur dioxide. It is used in the photographic industry and in analytical
chemistry.
soft acid See hsab principle.
soft base See hsab principle.
soft soap See soap.
soft water See hardness of water.
sol A *colloid in which small solid
particles are dispersed in a liquid
continuous phase.
solder An alloy used to join metal
surfaces. A soft solder melts at a temperature in the range 200–300°C and
consists of a tin–lead alloy. The tin
content varies between 80% for the
lower end of the melting range and
31% for the higher end. Hard solders
contain substantial quantities of silver in the alloy. Brazing solders are
usually alloys of copper and zinc,
which melt at over 800°C.
solid A state of matter in which
there is a three-dimensional regularity of structure, resulting from the
493
solid
s
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has also been used for the production
of sodium thiosulphate (for the photographic industry) and as a depilatory agent in leather preparation. It
is a strong skin irritant.
sodium sulphite A white solid,
Na 2 SO 3 , existing in an anhydrous
form (r.d. 2.63) and as a heptahydrate
(r.d. 1.59). Sodium sulphite is soluble
in water and because it is readily oxidized it is widely used as a convenient reducing agent. It is prepared
by reacting sulphur dioxide with either sodium carbonate or sodium hydroxide. Dilute mineral acids reverse
this process and release sulphur dioxide. Sodium sulphite is used as a
bleaching agent in textiles and in
paper manufacture. Its use as an antioxidant in some canned foodstuffs
gives rise to a slightly sulphurous
smell immediately on opening, but
its use is prohibited in meats or foods
that contain vitamin B 1 . Sodium sulphite solutions are occasionally used
as biological preservatives.
sodium–sulphur cell A type of
*secondary cell that has molten electrodes of sodium and sulphur separated by a solid electrolyte consisting
of beta alumina (a crystalline form of
aluminium oxide). When the cell is
producing current, sodium ions Ûow
through the alumina to the sulphur,
where they form sodium polysulphide. Electrons from the sodium
Ûow in the external circuit. The opposite process takes place during
charging of the cell. Sodium–sulphur
batteries have been considered for
use in electric vehicles because of
their high peak power levels and relatively low weight. However, some of
the output has to be used to maintain the operating temperature
(about 370°C) and the cost of sodium
is high.
sodium superoxide (sodium dioxide) A whitish-yellow solid, NaO 2 ,
formed by the reaction of sodium
peroxide with excess oxygen at elevated temperatures and pressures. It
reacts with water to form hydrogen
peroxide and oxygen.
sodium thiosulphate (hypo) A
colourless efÛorescent solid, Na 2 S 2 O 3 ,
soluble in water but insoluble in
ethanol, commonly encountered as
the pentahydrate (monoclinic; r.d.
1.73; m.p. 42°C), which loses water at
100°C to give the anhydrous form
(r.d. 1.66). It is prepared by the reaction of sulphur dioxide with a suspension of sulphur in boiling sodium
hydroxide solution. Aqueous solutions of sodium thiosulphate are
readily oxidized in the presence of
air to sodium tetrathionate and
sodium sulphate. The reaction with
dilute acids gives sulphur and sulphur dioxide. It is used in the photographic industry and in analytical
chemistry.
soft acid See hsab principle.
soft base See hsab principle.
soft soap See soap.
soft water See hardness of water.
sol A *colloid in which small solid
particles are dispersed in a liquid
continuous phase.
solder An alloy used to join metal
surfaces. A soft solder melts at a temperature in the range 200–300°C and
consists of a tin–lead alloy. The tin
content varies between 80% for the
lower end of the melting range and
31% for the higher end. Hard solders
contain substantial quantities of silver in the alloy. Brazing solders are
usually alloys of copper and zinc,
which melt at over 800°C.
solid A state of matter in which
there is a three-dimensional regularity of structure, resulting from the
493
solid
s
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