with the iron in haemoglobin in the
blood, so preventing oxygen reaching
the tissues of the body. It is used in
the extraction of precious metals and
in electroplating industries. Aqueous
solutions are alkaline due to salt hydrolysis.
sodium dichromate A red crystalline solid, Na 2 Cr 2 O 7 .2H 2 O, soluble
in water and insoluble in ethanol. It
is usually known as the dihydrate
(r.d. 2.52), which starts to lose water
above 100°C; the compound decomposes above 400°C. It is made by
melting chrome iron ore with lime
and soda ash and acidiÜcation of the
chromate thus formed. Sodium
dichromate is cheaper than the corresponding potassium compound but
has the disadvantage of being hygroscopic. It is used as a mordant in dyeing, as an oxidizing agent in organic
chemistry, and in analytical chemistry.
sodium dihydrogenorthophosphate See sodium dihydrogenphosphate(v).
sodium dihydrogenphosphate(V) (sodium dihydrogenorthophosphate) A colourless
crystalline solid, NaH 2 PO 4 , which is
soluble in water and insoluble in alcohol, known as the monohydrate
(r.d. 2.04) and the dihydrate (r.d.
1.91). The dihydrate loses one water
molecule at 60°C and the second
molecule of water at 100°C, followed
by decomposition at 204°C. The compound may be prepared by treating
sodium carbonate with an equimolar
quantity of phosphoric acid or by
neutralizing phosphoric acid with
sodium hydroxide. It is used in the
preparation of sodium phosphate
(Na 3 PO 4 ), in baking powders, as a
food additive, and as a constituent of
buffering systems. Both sodium dihydrogenphosphate and trisodium
phosphate enriched in
32 P have been
used to study phosphate participation in metabolic processes.
sodium dioxide See sodium superoxide.
sodium ethanoate (sodium acetate) A colourless crystalline compound, CH 3 COONa, which is known
as the anhydrous salt (r.d. 1.52; m.p.
324°C) or the trihydrate (r.d. 1.45;
loses water at 58°C). Both forms are
soluble in water and in ethoxyethane, and slightly soluble in
ethanol. The compound may be prepared by the reaction of ethanoic
acid (acetic acid) with sodium carbonate or with sodium hydroxide. Because it is a salt of a strong base and
a weak acid, sodium ethanoate is
used in buffers for pH control in
many laboratory applications, in
foodstuffs, and in electroplating. It is
also used in dyeing, soaps, pharmaceuticals, and in photography.
sodium Ûuoride A crystalline
compound, NaF, soluble in water and
very slightly soluble in ethanol;
cubic; r.d. 2.56; m.p. 993°C; b.p.
1695°C. It occurs naturally as villiaumite and may be prepared by the reaction of sodium hydroxide or of
sodium carbonate with hydrogen
Ûuoride. The reaction of sodium
Ûuoride with concentrated sulphuric
acid may be used as a source of hydrogen Ûuoride. The compound is
used in ceramic enamels and as a
preservative agent for fermentation.
It is highly toxic but in very dilute solution (less than 1 part per million) it
is used in the Ûuoridation of water
for the prevention of tooth decay on
account of its ability to replace OH
groups with F groups in the material
of dental enamel.
sodium formate See sodium
methanoate.
sodium hexaÛuoraluminate A
colourless monoclinic solid, Na 3 AlF 6 ,
489
sodium hexaÛuoraluminate
s
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blood, so preventing oxygen reaching
the tissues of the body. It is used in
the extraction of precious metals and
in electroplating industries. Aqueous
solutions are alkaline due to salt hydrolysis.
sodium dichromate A red crystalline solid, Na 2 Cr 2 O 7 .2H 2 O, soluble
in water and insoluble in ethanol. It
is usually known as the dihydrate
(r.d. 2.52), which starts to lose water
above 100°C; the compound decomposes above 400°C. It is made by
melting chrome iron ore with lime
and soda ash and acidiÜcation of the
chromate thus formed. Sodium
dichromate is cheaper than the corresponding potassium compound but
has the disadvantage of being hygroscopic. It is used as a mordant in dyeing, as an oxidizing agent in organic
chemistry, and in analytical chemistry.
sodium dihydrogenorthophosphate See sodium dihydrogenphosphate(v).
sodium dihydrogenphosphate(V) (sodium dihydrogenorthophosphate) A colourless
crystalline solid, NaH 2 PO 4 , which is
soluble in water and insoluble in alcohol, known as the monohydrate
(r.d. 2.04) and the dihydrate (r.d.
1.91). The dihydrate loses one water
molecule at 60°C and the second
molecule of water at 100°C, followed
by decomposition at 204°C. The compound may be prepared by treating
sodium carbonate with an equimolar
quantity of phosphoric acid or by
neutralizing phosphoric acid with
sodium hydroxide. It is used in the
preparation of sodium phosphate
(Na 3 PO 4 ), in baking powders, as a
food additive, and as a constituent of
buffering systems. Both sodium dihydrogenphosphate and trisodium
phosphate enriched in
32 P have been
used to study phosphate participation in metabolic processes.
sodium dioxide See sodium superoxide.
sodium ethanoate (sodium acetate) A colourless crystalline compound, CH 3 COONa, which is known
as the anhydrous salt (r.d. 1.52; m.p.
324°C) or the trihydrate (r.d. 1.45;
loses water at 58°C). Both forms are
soluble in water and in ethoxyethane, and slightly soluble in
ethanol. The compound may be prepared by the reaction of ethanoic
acid (acetic acid) with sodium carbonate or with sodium hydroxide. Because it is a salt of a strong base and
a weak acid, sodium ethanoate is
used in buffers for pH control in
many laboratory applications, in
foodstuffs, and in electroplating. It is
also used in dyeing, soaps, pharmaceuticals, and in photography.
sodium Ûuoride A crystalline
compound, NaF, soluble in water and
very slightly soluble in ethanol;
cubic; r.d. 2.56; m.p. 993°C; b.p.
1695°C. It occurs naturally as villiaumite and may be prepared by the reaction of sodium hydroxide or of
sodium carbonate with hydrogen
Ûuoride. The reaction of sodium
Ûuoride with concentrated sulphuric
acid may be used as a source of hydrogen Ûuoride. The compound is
used in ceramic enamels and as a
preservative agent for fermentation.
It is highly toxic but in very dilute solution (less than 1 part per million) it
is used in the Ûuoridation of water
for the prevention of tooth decay on
account of its ability to replace OH
groups with F groups in the material
of dental enamel.
sodium formate See sodium
methanoate.
sodium hexaÛuoraluminate A
colourless monoclinic solid, Na 3 AlF 6 ,
489
sodium hexaÛuoraluminate
s
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