Potassium is a chemical element in the
periodic table that has the symbol K
(Latin, Kalium) and atomic number 19. This is
a soft, silvery-white metallic alkali metal that occurs
naturally bound to other elements in seawater and many
minerals. It oxidizes rapidly in air, is very reactive,
especially in water, and resembles sodium chemically.
Potassium is the second lightest metal. It is a soft
solid that easily is cut with a knife and is silvery in
color on fresh surfaces. It oxidizes in air rapidly and
must be stored in mineral oil for preservation.
Similar to other alkali metals, potassium reacts violently
with water producing hydrogen. When in water it may catch
fire spontaneously. Its salts emit a violet color when
exposed to a flame.
- Potassium oxide, best known as potash, is primarily
used in fertilizer.
- Potassium nitrate is used in gunpowder.
- Potassium carbonate is used in glass manufacture.
- NaK an alloy of sodium and potassium is used as a
- This element is an essential component needed in plant
growth and is found in most soil types.
- In animal cells potassium ions are vital to keeping
cells alive (see Na-K pump)
- Potassium chloride is used as a substitute for table
salt and is also used to stop the heart, e.g. in cardiac
surgery and in executions by lethal injection.
Many potassium salts are very important, and include,
potassium; bromide, carbonate, chlorate, chloride, chromate,
cyanide, dichromate, hydroxide, iodide, nitrate, sulfate.
Potassium (English, potash L. kalium) was discovered
in 1807 by Sir Humphry Davy who derived it from caustic
potash (KOH. This alkali metal was the first metal that
was isolated by electrolysis.
This element makes up about 2.4% of the weight of the
Earth's crust and is the seventh most abundant element
in it. Due to its insolubility, it is very difficult to
obtain potassium from its minerals.
However, other minerals, such as carnallite, langbeinite,
polyhalite, and sylvite are found in ancient lake and sea
beds. These minerals form extensive deposits in these environments,
making extracting potassium and its salts more economical.
The principle source of potassium, potash is mined in California,
Germany, New Mexico, Utah, and in other places around the
world. At 3000 ft below the surface of Saskatchewan are
large deposits of potash which may become important sources
of this element and its salts in the future.
The oceans are another source of potassium but the quantity
present in a given volume of seawater is relatively low
compared to sodium.
Potassium can be isolated through electrolysis of its
hydroxide in a process that has changed little since Davy.
Thermal methods also are employed in potassium production.
Potassium is almost never found unbound in nature. However,
in living organisms K+ ions
are important in the physiology of excitable cells.
There are seventeen isotopes of potassium known to exist.
The non-synthetic form of potassium are composed of three
isotopes: K-39 (93.3%), K-40 (0.01%) and K-41 (6.7%).
Naturally occurring K-40 decays to stable Ar-40 (11.2%)
by electron capture and by positron emission, and decays
to stable Ca-40 (88.8%) by negatron emission; K-40 has
a half-life of 1.250 × 109 years.
The decay of K-40 to Ar-40 is commonly used as a method
for dating rocks. The conventional K-Ar dating method
depends on the assumption that the rocks contained no
argon at the time of formation and that all the subsequent
radiogenic argon (i.e., Ar-40) was quantitatively retained,
i.e., closed system. Minerals are dated by measurement
of the concentration of potassium, and the amount of radiogenic
Ar-40 that has accumulated. The minerals that are best
suited for dating include biotite, muscovite, and plutonic/high
grade metamorphic hornblende, and volcanic feldspar; whole
rock samples from volcanic flows and shallow instrusives
can also be dated if they are unaltered.