56 | The History and Use of Our Earth’s Chemical Elements Potassium bromide (KBr) is used in photography and as a medical sedative.
56 | The History and Use of Our Earth’s Chemical Elements Potassium bromide (KBr) is used in photography and as a medical sedative.
Potassium chloride (KCl) is used in drug preparations and as a food additive and chemical reagent. It is possible to reduce the sodium in your diet by substituting potassium chloride for table salt (sodium chloride), which may be healthier. Molten potassium chloride is also used in the electrolytic production of metallic potassium. KCl is also found in seawater brine and can be extracted from the mineral carnallite.
Potassium carbonate (K 2 CO 3 ), also known as potash or pearl ash, is the 33rd most produced chemical in the United States. It is a white, granular powder that becomes alkaline when dis- solved in water. It is produced by a chemical process involving magnesium oxide, potassium
chloride, and carbon dioxide, or by a laboratory process of bubbling CO 2 through a solution of KOH. Commercially, both the Haber-Bosch and the Solvay processes are employed in its manufacture. Potassium carbonate is used in the production of color TV tubes and other optical devices, as a food additive, for making paint and ink pigments, in the manufacture of some glass and soaps, and as an agent for dehydration (a material that will “dry out” or remove moisture from substances).
Potassium hydroxide (KOH) is commonly referred to as caustic potash or lye because of its extreme alkalinity (high pH value). It is produced in an electrolytic cell reaction (2KCl + 2H 2 O→H 2 + Cl 2 + 2KOH). It is used to manufacture soaps and as a caustic drain cleaner because it is strong enough to dissolve animal fats that clog household and restaurant drains. Potassium chromate (K 2 CrO 4 ) is soluble in water and is used to make bright yellow inks and paint pigments. It is also used as a reagent in chemical laboratories and as a mordant to “fix” dyes in colored textiles.
Potassium cyanide (KCN) is a white crystalline substance with a slight odor of bitter almonds. It is produced when hydrogen cyanide is absorbed in potassium hydroxide. It is used to extract gold and silver from their ores, in electroplating computer boards, and as an insecticide. Potassium cyanide is very toxic to the skin or when ingested or inhaled, and it is used as a source of cyanide (CN) gas in gas chambers.
Potassium permanganate (KMnO 4 ) is a dark purple-bluish sheen crystal with a slightly sweet taste. It is produced by oxidizing manganate in an electrolytic cell or by passing carbon dioxide through a hot solution of manganate and then cooling until permanganate crystals form. It is
a strong oxidizing agent, particularly with organic matter, which makes it a good disinfectant, deodorizer, bleach, and antiseptic. Potassium iodide (KI) is added to table salt (known as iodized salt) to help prevent enlarge- ment of the thyroid gland, a condition known as a goiter.
Hazards Elemental potassium as a metal is not found in its pure form in nature, but is derived from
its numerous compounds. The metal is very dangerous to handle. It can ignite while you are holding it with your hands or as you cut it. The metal must be stored in an inert gas atmosphere or in oil. Potassium fires cannot be extinguished with water—it only makes matters worse because it results in the formation of potassium hydroxide and hydrogen gas with enough heat to ignite the hydrogen. Dry chemicals such as soda ash, graphite, or dry sand can be used.
A particular hazard, which has been with humans since the beginning of time, is the radioactive isotope potassium-40 (K-40). Less than 1% of all potassium atoms on Earth are in the form of this radioactive isotope. It has a half-life of 1.25 billion years. Its decay process
Guide to the Elements | 57 ends with the formation of the noble gas argon, which can then be analyzed to determine the
age of rocks. This system (K-40 → argon) has been used to establish that the oldest rocks on Earth were formed about 3.8 billion years ago. Every living thing needs some potassium in its diet, including humans, who cannot escape this source of radiation, given that the human body cannot distinguish the radioactive potassium from the nonradioactive form. Along with cosmic rays and other naturally radioactive elements in the Earth’s crust, potassium-40 con- tributes to the normal lifetime accumulation of radiation. It makes up almost one-fourth of the total radiation the human body receives during a normal life span.
Many of the potassium “salts” mentioned are hazardous because they are explosive when either heated or shocked. Some are also toxic to the skin and poisonous when ingested. On the other hand, numerous compounds of potassium make our lives much more livable.
RUBIDIUM SYMBOL:Rb PERIOD:5 GROUP:1(IA) ATOMICNO:37
ATOMICMASS:85.4678amu VALENCE:1 OXIDATIONSTATE:+1 NATURALSTATE:Solid ORIGINOFNAME: RubidiumisnamedfortheLatinwordrubidus,meaning“reddish.” ISOTOPES:Thereare30isotopesofrubidium,rangingfromRb-75toRb-98.Rb-85isthe
onlystableformofrubidiumandconstitutes72.17%ofallrubidiumisotopesfoundin theEarth’scrust.Rb-87isradioactive(ahalf-lifeof4.9×10 10 years)andmakesupabout 27.83%oftheremainderofrubidiumfoundintheEarth’scrust.Alltheother28iso- topesmakeupatinyfractionofalltherubidiumfoundonEarthandareradioactivewith veryshorthalf-lives.
ELECTRONCONFIGURATION EnergyLevels/Shells/Electrons Orbitals/Electrons
s2,p6
3-M=18
s2,p6,d10
4-N=8