the slow release of equally toxic hydrogen cyanide gas.
potassium dichromate (potassium bichromate) An orange-red
crystalline solid, K 2 Cr 2 O 7 , soluble in
water and insoluble in alcohol; monoclinic or triclinic; r.d. 2.68; monoclinic changes to triclinic at 241.6°C;
m.p. 396°C; decomposes above
500°C. It is prepared by acidiÜcation
of crude potassium chromate solution (the addition of a base to solutions of potassium dichromate
reverses this process). The compound
is used industrially as an oxidizing
agent in the chemical industry and in
dyestuffs manufacture, in electroplating, pyrotechnics, glass manufacture,
glues, tanning, photography and lithography, and in ceramic products.
Laboratory uses include application
as an analytical reagent and as an oxidizng agent. Potassium dichromate
is toxic and considered a Üre risk on
account of its oxidizing properties.
potassium dioxide See potassium
superoxide.
potassium hydride A white or
greyish white crystalline solid, KH;
r.d. 1.43–1.47. It is prepared by passing hydrogen over heated potassium
and marketed as a light grey powder
dispersed in oil. The solid decomposes on heating and in contact with
moisture and is an excellent reducing agent. Potassium hydride is a Üre
hazard because it produces hydrogen
on reaction with water.
potassium hydrogencarbonate
(potassium bicarbonate) A white
crystalline solid, KHCO 3 , soluble in
water and insoluble in ethanol; r.d.
2.17; decomposes about 120°C. It occurs naturally as calcinite and is prepared by passing carbon dioxide into
saturated potassium carbonate solution. It is used in baking, soft-drinks
manufacture, and in CO 2 Üre extinguishers. Because of its buffering capacity, it is added to some detergents
and also used as a laboratory reagent.
potassium hydrogentartrate
(cream of tartar) A white crystalline
acid salt, HOOC(CHOH) 2 COOK. It is
obtained from deposits on wine vats
(argol) and used in baking powders.
potassium hydroxide (caustic
potash; lye) A white deliquescent
solid, KOH, often sold as pellets,
Ûakes, or sticks, soluble in water and
in ethanol and very slightly soluble
in ether; rhombic; r.d. 2.044; m.p.
360.4°C; b.p. 1320°C. It is prepared
industrially by the electrolysis of concentrated potassium chloride solution but it can also be made by
heating potassium carbonate or sulphate with slaked lime, Ca(OH) 2 . It
closely resembles sodium hydroxide
but is more soluble and is therefore
preferred as an absorber for carbon
dioxide and sulphur dioxide. It is also
used in the manufacture of soft soap,
other potassium salts, and in Ni–Fe
and alkaline storage cells. Potassium
hydroxide is extremely corrosive to
body tissues and especially damaging
to the eyes.
potassium iodate A white crystalline solid, KIO 3 , soluble in water
and insoluble in ethanol; monoclinic;
r.d. 3.9; m.p. 560°C. It may be prepared by the reaction of iodine with
hot concentrated potassium hydroxide or by careful electrolysis of
potassium iodide solution. It is an
oxidizing agent and is used as an
analytical reagent. Some potassium
iodate is used as a food additive.
potassium iodide A white crystalline solid, KI, with a strong bitter
taste, soluble in water, ethanol, and
acetone; cubic; r.d. 3.13; m.p. 681°C;
b.p. 1330°C. It may be prepared by
the reaction of iodine with hot potassium hydroxide solution followed by
potassium dichromate
434
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potassium dichromate (potassium bichromate) An orange-red
crystalline solid, K 2 Cr 2 O 7 , soluble in
water and insoluble in alcohol; monoclinic or triclinic; r.d. 2.68; monoclinic changes to triclinic at 241.6°C;
m.p. 396°C; decomposes above
500°C. It is prepared by acidiÜcation
of crude potassium chromate solution (the addition of a base to solutions of potassium dichromate
reverses this process). The compound
is used industrially as an oxidizing
agent in the chemical industry and in
dyestuffs manufacture, in electroplating, pyrotechnics, glass manufacture,
glues, tanning, photography and lithography, and in ceramic products.
Laboratory uses include application
as an analytical reagent and as an oxidizng agent. Potassium dichromate
is toxic and considered a Üre risk on
account of its oxidizing properties.
potassium dioxide See potassium
superoxide.
potassium hydride A white or
greyish white crystalline solid, KH;
r.d. 1.43–1.47. It is prepared by passing hydrogen over heated potassium
and marketed as a light grey powder
dispersed in oil. The solid decomposes on heating and in contact with
moisture and is an excellent reducing agent. Potassium hydride is a Üre
hazard because it produces hydrogen
on reaction with water.
potassium hydrogencarbonate
(potassium bicarbonate) A white
crystalline solid, KHCO 3 , soluble in
water and insoluble in ethanol; r.d.
2.17; decomposes about 120°C. It occurs naturally as calcinite and is prepared by passing carbon dioxide into
saturated potassium carbonate solution. It is used in baking, soft-drinks
manufacture, and in CO 2 Üre extinguishers. Because of its buffering capacity, it is added to some detergents
and also used as a laboratory reagent.
potassium hydrogentartrate
(cream of tartar) A white crystalline
acid salt, HOOC(CHOH) 2 COOK. It is
obtained from deposits on wine vats
(argol) and used in baking powders.
potassium hydroxide (caustic
potash; lye) A white deliquescent
solid, KOH, often sold as pellets,
Ûakes, or sticks, soluble in water and
in ethanol and very slightly soluble
in ether; rhombic; r.d. 2.044; m.p.
360.4°C; b.p. 1320°C. It is prepared
industrially by the electrolysis of concentrated potassium chloride solution but it can also be made by
heating potassium carbonate or sulphate with slaked lime, Ca(OH) 2 . It
closely resembles sodium hydroxide
but is more soluble and is therefore
preferred as an absorber for carbon
dioxide and sulphur dioxide. It is also
used in the manufacture of soft soap,
other potassium salts, and in Ni–Fe
and alkaline storage cells. Potassium
hydroxide is extremely corrosive to
body tissues and especially damaging
to the eyes.
potassium iodate A white crystalline solid, KIO 3 , soluble in water
and insoluble in ethanol; monoclinic;
r.d. 3.9; m.p. 560°C. It may be prepared by the reaction of iodine with
hot concentrated potassium hydroxide or by careful electrolysis of
potassium iodide solution. It is an
oxidizing agent and is used as an
analytical reagent. Some potassium
iodate is used as a food additive.
potassium iodide A white crystalline solid, KI, with a strong bitter
taste, soluble in water, ethanol, and
acetone; cubic; r.d. 3.13; m.p. 681°C;
b.p. 1330°C. It may be prepared by
the reaction of iodine with hot potassium hydroxide solution followed by
potassium dichromate
434
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