The
chemical compound Potassium chloride (KCl) is a metal
halide salt composed of
potassium and
chlorine. In its pure state KCl
is odorless. KCl
has a white or colorless
vitreous crystal, with a crystal structure that cleaves
easily in three directions. KCl crystals are
face-centered cubic. It is also commonly known as "Muriate of
Potash" or MOP. MOP varies in color from pink or red to white
depending on the mining and recovery process used. White potash,
sometimes referred to as soluble potash, is usually higher in
analysis and is used primarily for making liquid starter
fertilizers. KCl is
used in medicine, scientific applications,
food processing and in judicial
execution through
lethal injection. KCl
occurs naturally as the
mineral
sylvite and in combination with
sodium chloride as
sylvinite.
The majority of this salt
produced is used for making
fertilizer, since the growth of many plants is limited by
their potassium intake. As a chemical feedstock KCl is used
for the manufacture of
potassium hydroxide and
potassium metal. KCl is also used in
medicine,
scientific applications,
food processing, as a sodium-free substitute for
table salt (sodium
chloride), and in
judicial
execution through
lethal injection. KCl is sometimes used in water as a
completion fluid in oil and gas operations. It is also used as an
alternative to
sodium chloride in household
water softener units. It is useful as a
beta radiation source for calibration of radiation monitoring
equipment because natural potassium contains 0.0118% of the isotope
40K. It is also used in
Dasani water. It was once used as a fire extinguishing
agent. It can be used as a salt substitute
for food, but due to its weak, bitter, un-salty flavor, it is
usually mixed with regular salt (sodium chloride), for this purpose
to improve the taste (for example, in Morton Lite Salt. It is used
in oil drilling fluid, muds and Chemicals.
KCl can react as a source of
chloride
ion. As with any other
soluble ionic chloride, it will precipitate insoluble
chloride
salts when added to a solution of an appropriate
metal ion:
KCl(aq)
+
AgNO3(aq) →
AgCl(s)
+
KNO3(aq)
Although potassium is more
electropositive than
sodium, KCl can be reduced to the metal by reaction with
metallic
sodium at 850 °C because the potassium is removed by
distillation (see
Le Chatelier's principle):
KCl(l) + Na(l) → NaCl(l) + K(g)
This method, replacing K with
Na in KCl is the main method for producing metallic
potassium.
Electrolysis (used for
sodium) fails because of the high solubility of potassium
in molten potassium chloride (KCl).
As with other compounds
containing potassium, KCl in powdered form gives a lilac
flame test result.
Physical properties
KCl has a crystalline structure
like many other salts. Its structure is
face-centered cubic. Its lattice constant is
roughly 630 picometers.
In chemistry and physics KCl
is a very commonly used as a standard,
for example as a calibration standard solution
in measuring electrical conductivity of (ionic)
solutions, since carefully prepared
potassium chloride (KCl)
solutions have well-reproducible and
well-repeatable measurable properties.
Solubility of KCl in various solvents
(g KCl / 100 g of solvent at 25 °C) |
| H2O |
36 |
| Liquid ammonia |
0.04 |
| Liquid sulfur dioxide |
0.041 |
| Methanol |
0.53 |
| Formic acid |
19.2 |
| Sulfolane |
0.004 |
| Acetonitrile |
0.0024 |
| Acetone |
0.000091 |
| Formamide |
6.2 |
| Acetamide |
2.45 |
| Dimethylformamide |
0.017–0.05 |
Reference:
Burgess, J. Metal Ions in Solution
(Ellis Horwood, New York, 1978) |
