Potassium
Potassium is a Chemical element in the Periodic table. It has the symbol K (L. kalium) and Atomic number 19. The name "potassium" comes from the word "potash", as potassium was first isolated from Potash. Potassium 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.
Notable characteristics
With a density less than that of water, potassium is the second lightest metal after Lithium. It is a soft solid that can easily be cut with a knife and is silvery in color on fresh surfaces. It oxidizes in Air rapidly and must be stored in Mineral oil or Kerosene 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.
Applications
- Potassium oxide is primarily used in Fertilizer.
- Potassium hydroxide is an important industrial chemical used as a strong base.
- Potassium nitrate is used in Gunpowder and Black powder. An older term for KNO3 is Saltpeter.
- Potassium carbonate, known as Potash, is used in Glass manufacture.
- Glass treated with liquid potassium is much stronger than regular glass.
- NaK, an Alloy of Sodium and potassium, is used as a heat-transfer medium.
- Potassium 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 in liquid form.
- The Superoxide KO2 is used as a portable source of oxygen and as a carbon dioxide absorber. It is useful in portable respiration systems.
History
Potassium was discovered in 1807 by Sir Humphrey Davy, who derived it from caustic potash (KOH). Potassium was the first metal that was isolated by Electrolysis.Potassium was not known in Roman times, and its names are not Classical Latin.
The name kalium was taken from the word "Alkali", which came from Arabic al qalīy = "the calcined ashes".
The name potassium was made from the word "Potash", which is English, and originally meant an Alkali extracted in a pot from the ash of burnt wood or tree leaves.
Occurrence
Potassium makes up about 2.40% of the weight of the Earth's crust and is the seventh most abundant element in it. As it is very Electropositive, potassium metal is difficult to obtain from its minerals.Potassium salts 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 principal source of potassium, Potash, is mined in California, Germany, New Mexico, Utah, and in other places around the world. 3000 ft below the surface of Saskatchewan are large deposits of potash which are important sources of this element and its salts, with several large mines in operation since the 1980's. Saskatchewan pioneered the use of freezing of wet sands (the Blairmore fomation) in order to drive mine shafts through them. 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, using Potassium chloride. Potassium is almost never found unbound in nature. However, in living organisms K+ ions are important in the physiology of excitable cells.
Isotopes
There are seventeen known isotopes of potassium. Three isotopes occur naturally: 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 Beta decay; K-40 has a Half-life of 1.250 × 109 years.The decay of K-40 to Ar-40 enables a commonly used 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. 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, 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.
Outside of dating, potassium isotopes have been used extensively as tracers in studies of Weathering. They have also be used for nutrient cycling studies because potassium is a macro-nutrient required for life.
K-40 occurs in natural potassium (and thus in some commercial salt substitutes) in sufficient quantity that large bags of those substitutes can be used as a radioactive source for classroom demonstrations.