Prairie

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Prairie

 

Prairies are ecosystems considered part of the temperate grasslands, savannas, and shrublands biome by ecologists, based on similar temperate climates, moderate rainfall, and a composition of grasses, herbs, and shrubs, rather than trees, as the dominant vegetation type. Temperate grassland regions include the Pampas of Argentina, Brazil and Uruguay, and the steppe of Ukraine, Russia and Kazakhstan. Lands typically referred to as "prairie" tend to be in North America. The term encompasses the area referred to as the Interior Lowlands of Canada, the United States, and Mexico, which includes all of the Great Plains as well as the wetter, hillier land to the east.

In the U.S., the area is constituted by most or all of the states of North Dakota, South Dakota, Nebraska, Kansas, and Oklahoma, and sizable parts of the states of Montana, Wyoming, Colorado, New Mexico, Texas, Missouri, Iowa, Illinois, Indiana, Wisconsin, and western and southern Minnesota. The Palouse of Washington and the Central Valley of California are also prairies. The Canadian Prairies occupy vast areas of Manitoba, Saskatchewan, and Alberta. Prairies contain various lush flora and fauna, often contain rich soil maintained by biodiversity, with a temperate climate and a varied view.

Etymology

Approximate regional types of prairie in the United States

  Shortgrass prairie

  Mixed grass prairie

  Tallgrass prairie

According to Theodore Roosevelt:

We have taken into our language the word prairie, because when our backwoodsmen first reached the land [in the Midwest] and saw the great natural meadows of long grass—sights unknown to the gloomy forests wherein they had always dwelt—they knew not what to call them, and borrowed the term already in use among the French inhabitants.

Prairie (pronounced [pʁɛʁi]) is the French word for "meadow" formed ultimately from the Latin root word pratum (same meaning).

Formation

Tallgrass prairie flora (Midewin National Tallgrass Prairie)

The formation of the North American Prairies started with the uplift of the Rocky Mountains near Alberta. The mountains created a rain shadow that resulted in lower precipitation rates downwind.

The parent material of most prairie soil was distributed during the last glacial advance that began about 110,000 years ago. The glaciers expanding southward scraped the landscape, picking up geologic material and leveling the terrain. As the glaciers retreated about 10,000 years ago, they deposited this material in the form of till. Wind based loess deposits also form an important parent material for prairie soils.

Tallgrass prairie evolved over tens of thousands of years with the disturbances of grazing and fire. Native ungulates such as bison, elk, and white-tailed deer roamed the expansive, diverse grasslands before European colonization of the Americas. For 10,000-20,000 years, native people used fire annually as a tool to assist in hunting, transportation, and safety. Evidence of ignition sources of fire in the tall grass prairie are overwhelmingly human as opposed to lightning. Humans, and grazing animals, were active participants in the process of prairie formation and the establishment of the diversity of graminoid and forbs species. Fire has the effect on prairies of removing trees, clearing dead plant matter, and changing the availability of certain nutrients in the soil from the ash produced. Fire kills the vascular tissue of trees, but not prairie species, as up to 75% (depending on the species) of the total plant biomass is below the soil surface and will re-grow from its deep (upwards of 20 feet) roots. Without disturbance, trees will encroach on a grassland and cast shade, which suppresses the understory. Prairie and widely spaced oak trees evolved to coexist in the oak savanna ecosystem.

Fertility

In spite of long recurrent droughts and occasional torrential rains, the grasslands of the Great Plains were not subject to great soil erosion. The root systems of native prairie grasses firmly held the soil in place to prevent run-off of soil. When the plant died, the fungi and bacteria returned its nutrients to the soil. These deep roots also helped native prairie plants reach water in even the driest conditions. Native grasses suffer much less damage from dry conditions than many farm crops currently grown.

Geographical regions

Prairie grasses

Prairie in North America is usually split into three groups: wet, mesic, and dry. They are generally characterized by tallgrass prairie, mixed, or shortgrass prairie, depending on the quality of soil and rainfall.

Wet

In wet prairies the soil is usually very moist, including during most of the growing season, because of poor water drainage. The resulting stagnant water is conducive to the formation of bogs and fens. Wet prairies have excellent farming soil. The average precipitation is 10–30 inches (250–760 mm) a year.

Mesic

Mesic prairie has good drainage, but good soil during the growing season. This type of prairie is the most often converted for agricultural usage; consequently, it is one of the most endangered types of prairie.

Dry

Wheatfield intersection in the Southern Saskatchewan prairies, Canada.

Dry prairie has somewhat wet to very dry soil during the growing season because of good drainage in the soil. Often, this type of prairie can be found on uplands or slopes. Dry soil usually doesn't get much vegetation due to lack of rain. This is the dominant biome in the Southern Canadian agricultural and climatic region known as Palliser's Triangle. Once thought to be completely unarable, the Triangle is now one of the most important agricultural regions in Canada thanks to advances in irrigation technology. In addition to its very high local importance to Canada, Palliser's Triangle is now also one of the most important sources of wheat in the world as a result of these improved methods of watering wheat fields (along with the rest of the Southern prairie provinces which also grow wheat, canola and many other grains). Despite these advances in farming technology, the area is still very prone to extended periods of drought, which can be disastrous for the industry if it is significantly prolonged. An infamous example of this is the Dust Bowl of the 1930s, which also hit much of the United States Great Plains ecoregion, contributing greatly to the Great Depression.

Environmental history

Bison hunting

Main articles: plains tribes and bison hunting

Nomadic hunting has been the main human activity on the prairies for the majority of the archaeological record. This once included many now-extinct species of megafauna.

After the other extinctions, the main hunted animal on the prairies was the plains bison. Using loud noises and waving large signals, Native peoples would drive bison into fenced pens called buffalo pounds to be killed with bows and arrows or spears, or drive them off a cliff (called a buffalo jump), to kill or injure the bison en masse. The introduction of the horse and the gun greatly expanded the killing power of the plains Natives. This was followed by the policy of indiscriminate killing by European Americans and Canadians for both commercial reasons and to weaken the independence of plains Natives, and caused a dramatic drop in bison numbers from millions to a few hundred in a century's time, and almost caused their extinction.

Farming and ranching

Prairie Homestead, Milepost 213 on I-29, South Dakota (May 2010)

The very dense soil plagued the first European settlers who were using wooden plows, which were more suitable for loose forest soil. On the prairie, the plows bounced around, and the soil stuck to them. This problem was solved in 1837 by an Illinois blacksmith named John Deere who developed a steel moldboard plow that was stronger and cut the roots, making the fertile soils ready for farming. Former grasslands are now among the most productive agricultural lands on Earth.

The tallgrass prairie has been converted into one of the most intensive crop producing areas in North America. Less than one tenth of one percent (<0.09%) of the original landcover of the tallgrass prairie biome remains. Much of what persists is in cemetery prairies, railroad rights-of-way, or rocky/sandy/hilly places unsuitable for agriculture. States formerly with landcover in native tallgrass prairie such as Iowa, Illinois, Minnesota, Wisconsin, Nebraska, and Missouri have become valued for their highly productive soils and are included in the Corn Belt. As an example of this land use intensity, Illinois and Iowa rank 49th and 50th, out of 50 US states, in total uncultivated land remaining.

Drier shortgrass prairies were once used mostly for open-range ranching. With the development of barbed wire in the 1870s and improved irrigation techniques, this region has mostly been converted to cropland and small fenced pastures.

Biofuels

Main article: Biofuel

 

Sawgrass prairie in Everglades

Research by David Tilman, ecologist at the University of Minnesota, suggests that "Biofuels made from high-diversity mixtures of prairie plants can reduce global warming by removing carbon dioxide from the atmosphere. Even when grown on infertile soils, they can provide a substantial portion of global energy needs, and leave fertile land for food production." Unlike corn and soybeans, which are both directly and indirectly major food crops, including livestock feed, prairie grasses are not used for human consumption. Prairie grasses can be grown in infertile soil, eliminating the cost of adding nutrients to the soil. Tilman and his colleagues estimate that prairie grass biofuels would yield 51 percent more energy per acre than ethanol from corn grown on fertile land. Some plants commonly used are lupine, big bluestem (turkey foot), blazing star, switchgrass, and prairie clover.

Preservation

Because rich and thick topsoil made the land well suited for agricultural use, only 1% of tallgrass prairie remains in the U.S. today. Shortgrass prairie is more abundant.

See also: List of protected grasslands of North America

Significant preserved areas of prairie include:

• Alderville Black Oak Savanna; Rice Lake, Ontario
• American Prairie, Phillips and Blaine counties, Montana
• Clymer Meadow Preserve, Hunt County, Texas
• Cypress Hills Interprovincial Park, Alberta and Saskatchewan
• Goose Lake Prairie State Natural Area, Grundy County, Illinois
• Grasslands National Park, Saskatchewan
• Hoosier Prairie, Lake County, Indiana
• James Woodworth Prairie Preserve, a virgin prairie owned by University of Illinois, Glenview, Illinois
• Jennings Environmental Education Center, Pennsylvania
• Kissimmee Prairie Preserve State Park, Okeechobee County, Florida
• Konza Prairie, Manhattan, Kansas
• Midewin National Tallgrass Prairie, in Will County, Illinois
• Mnoké Prairie, Indiana Dunes National Park, Porter, Indiana
• Nachusa Grasslands, a Nature Conservancy preserve near Franklin Grove, Illinois
• Wichita Mountains Wildlife Refuge, in Comanche County, Oklahoma
• Neal Smith National Wildlife Refuge, Iowa
• Nine-Mile Prairie, Nebraska
• Ojibway prairie in Windsor, Ontario.
• Paynes Prairie Preserve State Park, Alachua County, Florida
• Richard Bong State Recreation Area, in Kenosha County, Wisconsin
• Russell R. Kirt Prairie, College of DuPage, Illinois
• Tallgrass Aspen Parkland, Manitoba & Minnesota
• Tallgrass Prairie National Preserve, Kansas
• Tallgrass Prairie Preserve 32,000 acres (130 km²), Oklahoma
• University of Wisconsin–Madison Arboretum, University of Wisconsin–Madison, Wisconsin
• Zumwalt Prairie, Wallowa County, Oregon

Virgin prairies

Virgin prairie refers to prairie land that has never been plowed. Small virgin prairies exist in the American Midwestern states and in Canada. Restored prairie refers to a prairie that has been reseeded after plowing or other disturbance.

Prairie garden

A prairie garden is a garden primarily consisting of plants from a prairie.

Physiography

Expansive fertile soil are good habitats for Prairie dogs.

The originally treeless prairies of the upper Mississippi basin began in Indiana, and extended westward and north-westward, until they merged with the drier region known as the Great Plains. An eastward extension of the same region, originally tree-covered, extended to central Ohio. Thus, the prairies generally lie between the Ohio and Missouri rivers on the south and the Great Lakes on the north. The prairies are a contribution of the glacial period. They consist for the most part of glacial drift, deposited unconformably on an underlying rock surface of moderate or small relief. Here, the rocks are an extension of the same stratified Palaeozoic formations already described as occurring in the Appalachian region and around the Great Lakes. They are usually fine-textured limestones and shales, lying horizontal. The moderate or small relief that they were given by mature preglacial erosion is now buried under the drift.

View of sand dunes and vegetation at Fossil Lake, with the Christmas Valley Sand Dunes, Feb. 21, 2017

The greatest area of the prairies, from Indiana to North Dakota, consists of till plains, that is, sheets of unstratified drift. These plains are 30, 50 or even 100 ft (up to 30 m) thick covering the underlying rock surface for thousands of square miles except where postglacial stream erosion has locally laid it bare. The plains have an extraordinarily even surface. The till is presumably made in part of preglacial soils, but it is more largely composed of rock waste mechanically transported by the creeping ice sheets. Although the crystalline rocks from Canada and some of the more resistant stratified rocks south of the Great Lakes occur as boulders and stones, a great part of the till has been crushed and ground to a clayey texture. The till plains, although sweeping in broad swells of slowly changing altitude, often appear level to the eye with a view stretching to the horizon. Here and there, faint depressions occur, occupied by marshy sloughs, or floored with a rich black soil of postglacial origin. It is thus by sub-glacial aggradation that the prairies have been levelled up to a smooth surface, in contrast to the higher and non-glaciated hilly country just to the south.

The great ice sheets formed terminal moraines around their border at various end stages. However, the morainic belts are of small relief in comparison to the great area of the ice. They rise gently from the till plains to a height of 50, 100 or more feet. They may be one, two or three miles (5 km) wide and their hilly surface, dotted over with boulders, contains many small lakes in basins or hollows, instead of streams in valleys. The morainic belts are arranged in groups of concentric loops, convex southward, because the ice sheets advanced in lobes along the lowlands of the Great Lakes. Neighboring morainic loops join each other in re-entrants (north-pointing cusps), where two adjacent glacial lobes came together and formed their moraines in largest volume. The moraines are of too small relief to be shown on any maps except of the largest scale. Small as they are, they are the chief relief of the prairie states, and, in association with the nearly imperceptible slopes of the till plains, they determine the course of many streams and rivers, which as a whole are consequent upon the surface form of the glacial deposits.

The complexity of the glacial period and its subdivision into several glacial epochs, separated by interglacial epochs of considerable length (certainly longer than the postglacial epoch) has a structural consequence in the superposition of successive till sheets, alternating with non-glacial deposits. It also has a physiographic consequence in the very different amount of normal postglacial erosion suffered by the different parts of the glacial deposits. The southernmost drift sheets, as in southern Iowa and northern Missouri, have lost their initially plain surface and are now maturely dissected into gracefully rolling forms. Here, the valleys of even the small streams are well opened and graded, and marshes and lakes are rare. These sheets are of early Pleistocene origin. Nearer the Great Lakes, the till sheets are trenched only by the narrow valleys of the large streams. Marshy sloughs still occupy the faint depressions in the till plains and the associated moraines have abundant small lakes in their undrained hollows. These drift sheets are of late Pleistocene origin.

When the ice sheets extended to the land sloping southward to the Ohio River, Mississippi River and Missouri River, the drift-laden streams flowed freely away from the ice border. As the streams escaped from their subglacial channels, they spread into broader channels and deposited some of their load, and thus aggraded their courses. Local sheets or aprons of gravel and sand are spread more or less abundantly along the outer side of the morainic belts. Long trains of gravel and sands clog the valleys that lead southward from the glaciated to the non-glaciated area. Later, when the ice retreated farther and the unloaded streams returned to their earlier degrading habit, they more or less completely scoured out the valley deposits, the remains of which are now seen in terraces on either side of the present flood plains.

When the ice of the last glacial epoch had retreated so far that its front border lay on a northward slope, belonging to the drainage area of the Great Lakes, bodies of water accumulated in front of the ice margin, forming glacio-marginal lakes. The lakes were small at first, and each had its own outlet at the lowest depression of land to the south. As the ice melted further back, neighboring lakes became confluent at the level of the lowest outlet of the group. The outflowing streams grew in the same proportion and eroded a broad channel across the height of land and far down stream, while the lake waters built sand reefs or carved shore cliffs along their margin, and laid down sheets of clay on their floors. All of these features are easily recognized in the prairie region. The present site of Chicago was determined by an Indian portage or carry across the low divide between Lake Michigan and the headwaters of the Illinois River. This divide lies on the floor of the former outlet channel of the glacial Lake Michigan. Corresponding outlets are known for Lake Erie, Lake Huron, and Lake Superior. A very large sheet of water, named Lake Agassiz, once overspread a broad till plain in northern Minnesota and North Dakota. The outlet of this glacial lake, called river Warren, eroded a large channel in which the Minnesota River evident today. The Red River of the North flows northward through a plain formerly covered by Lake Agassiz.

Certain extraordinary features were produced when the retreat of the ice sheet had progressed so far as to open an eastward outlet for the marginal lakes. This outlet occurred along the depression between the northward slope of the Appalachian plateau in west-central New York and the southward slope of the melting ice sheet. When this eastward outlet came to be lower than the south-westward outlet across the height of land to the Ohio or Mississippi river, the discharge of the marginal lakes was changed from the Mississippi system to the Hudson system. Many well-defined channels, cutting across the north-sloping spurs of the plateau in the neighborhood of Syracuse, New York, mark the temporary paths of the ice-bordered outlet river. Successive channels are found at lower and lower levels on the plateau slope, indicating the successive courses taken by the lake outlet as the ice melted farther and farther back. On some of these channels, deep gorges were eroded heading in temporary cataracts which exceeded Niagara in height but not in breadth. The pools excavated by the plunging waters at the head of the gorges are now occupied by little lakes. The most significant stage in this series of changes occurred when the glacio-marginal lake waters were lowered so that the long escarpment of Niagara limestone was laid bare in western New York. The previously confluent waters were then divided into two lakes. The higher one, Lake Erie, supplied the outflowing Niagara River, which poured its waters down the escarpment to the lower, Lake Ontario. This gave rise to Niagara Falls. Lake Ontario's outlet for a time ran down the Mohawk Valley to the Hudson River. At this higher elevation, it was known as Lake Iroquois. When the ice melted from the northeastern end of the lake, it dropped to a lower level, and drained through the St. Lawrence area. This created a lower base level for the Niagara River, increasing its erosive capacity.

In certain districts, the subglacial till was not spread out in a smooth plain, but accumulated in elliptical mounds, 100–200 feet. high and 0.5 to 1 mile (0.80 to 1.61 kilometres) long with axes parallel to the direction of the ice motion as indicated by striae on the underlying rock floor. These hills are known by the Irish name, drumlins, used for similar hills in north-western Ireland. The most remarkable groups of drumlins occur in western New York, where their number is estimated at over 6,000, and in southern Wisconsin, where it is placed at 5,000. They completely dominate the topography of their districts.

A curious deposit of an impalpably fine and unstratified silt, known by the German name bess (or loess), lies on the older drift sheets near the larger river courses of the upper Mississippi basin. It attains a thickness of 20 ft (6.1 m) or more near the rivers and gradually fades away at a distance of ten or more miles (16 or more km) on either side. It contains land shells, and hence cannot be attributed to marine or lacustrine submergence. The best explanation is that, during certain phases of the glacial period, it was carried as dust by the winds from the flood plains of aggrading rivers, and slowly deposited on the neighboring grass-covered plains. The glacial and eolian origin of this sediment is evidenced by the angularity of its grains (a bank of it will stand without slumping for years), whereas, if it had been transported significantly by water, the grains would have been rounded and polished. Loess is parent material for an extremely fertile, but droughty soil.

Southwestern Wisconsin and parts of the adjacent states of Illinois, Iowa, and Minnesota are known as the driftless zone, because, although bordered by drift sheets and moraines, it is free from glacial deposits. It must therefore have been a sort of oasis, when the ice sheets from the north advanced past it on the east and west, and joined around its southern border. The reason for this exemption from glaciation is the converse of that for the southward convexity of the morainic loops. For while they mark the paths of greatest glacial advance along lowland troughs (lake basins), the driftless zone is a district protected from ice invasion by reason of the obstruction which the highlands of northern Wisconsin and Michigan (part of the Superior upland) offered to glacial advance.

The course of the upper Mississippi River is largely consequent upon glacial deposits. Its sources are in the morainic lakes in northern Minnesota. The drift deposits thereabouts are so heavy that the present divides between the drainage basins of Hudson Bay, Lake Superior, and the Gulf of Mexico evidently stand in no very definite relation to the preglacial divides. The course of the Mississippi through Minnesota is largely guided by the form of the drift cover. Several rapids and the Saint Anthony Falls (determining the site of Minneapolis) are signs of immaturity, resulting from superposition through the drift on the under rock. Farther south, as far as the entrance of the Ohio River, the Mississippi follows a rock-walled valley 300 to 400 ft (91 to 122 m) deep, with a flood-plain 2 to 4 mi (3.2 to 6.4 km) wide. This valley seems to represent the path of an enlarged early-glacial Mississippi, when much precipitation that is today discharged to Hudson Bay and the Gulf of St Lawrence was delivered to the Gulf of Mexico, for the curves of the present river are of distinctly smaller radii than the curves of the valley. Lake Pepin (30 mi [48 km] below St. Paul), a picturesque expansion of the river across its flood-plain, is due to the aggradation of the valley floor where the Chippewa River, coming from the northeast, brought an overload of fluvio-glacial drift. Hence, even the father of waters, like so many other rivers in the Northern states, owes many of its features more or less directly to glacial action.

The fertility of the prairies is a natural consequence of their origin. During the mechanical transportation of the till, no vegetation was present to remove the minerals essential to plant growth, as is the case in the soils of normally weathered and dissected peneplains. The soil is similar to the Appalachian piedmont which though not exhausted by the primeval forest cover, are by no means so rich as the till sheets of the prairies. Moreover, whatever the rocky understructure, the till soil has been averaged by a thorough mechanical mixture of rock grindings. Hence, the prairies are continuously fertile for scores of miles together. The true prairies were once covered with a rich growth of natural grass and annual flowering plants, but today, they are covered with farms.

Base (chemistry)

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Base_(chemistry)

 

Soaps are weak bases formed by the reaction of fatty acids with sodium hydroxide or potassium hydroxide.

 

In chemistry, there are three definitions in common use of the word base, known as Arrhenius bases, Brønsted bases, and Lewis bases. All definitions agree that bases are substances that react with acids, as originally proposed by G.-F. Rouelle in the mid-18th century.

In 1884, Svante Arrhenius proposed that a base is a substance which dissociates in aqueous solution to form hydroxide ions OH⁻. These ions can react with hydrogen ions (H⁺ according to Arrhenius) from the dissociation of acids to form water in an acid–base reaction. A base was therefore a metal hydroxide such as NaOH or Ca(OH)₂. Such aqueous hydroxide solutions were also described by certain characteristic properties. They are slippery to the touch, can taste bitter and change the color of pH indicators (e.g., turn red litmus paper blue).

In water, by altering the autoionization equilibrium, bases yield solutions in which the hydrogen ion activity is lower than it is in pure water, i.e., the water has a pH higher than 7.0 at standard conditions. A soluble base is called an alkali if it contains and releases OH⁻ ions quantitatively. Metal oxides, hydroxides, and especially alkoxides are basic, and conjugate bases of weak acids are weak bases.

Bases and acids are seen as chemical opposites because the effect of an acid is to increase the hydronium (H₃O⁺) concentration in water, whereas bases reduce this concentration. A reaction between aqueous solutions of an acid and a base is called neutralization, producing a solution of water and a salt in which the salt separates into its component ions. If the aqueous solution is saturated with a given salt solute, any additional such salt precipitates out of the solution.

In the more general Brønsted–Lowry acid–base theory (1923), a base is a substance that can accept hydrogen cations (H⁺)—otherwise known as protons. This does include aqueous hydroxides since OH⁻ does react with H⁺ to form water, so that Arrhenius bases are a subset of Brønsted bases. However, there are also other Brønsted bases which accept protons, such as aqueous solutions of ammonia (NH₃) or its organic derivatives (amines). These bases do not contain a hydroxide ion but nevertheless react with water, resulting in an increase in the concentration of hydroxide ion. Also, some non-aqueous solvents contain Brønsted bases which react with solvated protons. For example in liquid ammonia, NH₂⁻ is the basic ion species which accepts protons from NH₄⁺, the acidic species in this solvent.

G. N. Lewis realized that water, ammonia, and other bases can form a bond with a proton due to the unshared pair of electrons that the bases possess. In the Lewis theory, a base is an electron pair donor which can share a pair of electrons with an electron acceptor which is described as a Lewis acid. The Lewis theory is more general than the Brønsted model because the Lewis acid is not necessarily a proton, but can be another molecule (or ion) with a vacant low-lying orbital which can accept a pair of electrons. One notable example is boron trifluoride (BF₃).

Some other definitions of both bases and acids have been proposed in the past, but are not commonly used today.

Properties

General properties of bases include:

• Concentrated or strong bases are caustic on organic matter and react violently with acidic substances.
• Aqueous solutions or molten bases dissociate in ions and conduct electricity.
• Reactions with indicators: bases turn red litmus paper blue, phenolphthalein pink, keep bromothymol blue in its natural colour of blue, and turn methyl orange-yellow.
• The pH of a basic solution at standard conditions is greater than seven.
• Bases are bitter.

Reactions between bases and water

The following reaction represents the general reaction between a base (B) and water to produce a conjugate acid (BH⁺) and a conjugate base (OH⁻):

$${\displaystyle {\text{B}}_{(\text{aq})}^{}+{{\text{H}}_2^{}\text{O}}_{(\text{l})}^{}\stackrel{-\rightharpoonup }{\leftharpoondown -}{{\text{BH}}^{+}}_{(\text{aq})}^{}+{{\text{OH}}^{-}}_{(\text{aq})}^{}}$$

The equilibrium constant, K_b, for this reaction can be found using the following general equation:

${\displaystyle K_b=\frac{[B{H}^{+}][O{H}^{-}]}{[B]}}$

In this equation, the base (B) and the extremely strong base (the conjugate base OH⁻) compete for the proton. As a result, bases that react with water have relatively small equilibrium constant values. The base is weaker when it has a lower equilibrium constant value.

Neutralization of acids

Ammonia fumes from aqueous ammonium hydroxide (in test tube) reacting with hydrochloric acid (in beaker) to produce ammonium chloride (white smoke).

Bases react with acids to neutralize each other at a fast rate both in water and in alcohol. When dissolved in water, the strong base sodium hydroxide ionizes into hydroxide and sodium ions:

${\displaystyle \text{NaOH}⟶{\text{Na}}^{+}+{\text{OH}}^{-}}$

and similarly, in water the acid hydrogen chloride forms hydronium and chloride ions:

${\displaystyle \text{HCl}+{\text{H}}_2^{}\text{O}⟶{\text{H}}_3^{}{\text{O}}^{+}+{\text{Cl}}^{-}}$

When the two solutions are mixed, the H
₃O⁺
and OH⁻
ions combine to form water molecules:

${\displaystyle {\text{H}}_3^{}{\text{O}}^{+}+{\text{OH}}^{-}⟶2{\text{H}}_2^{}\text{O}}$

If equal quantities of NaOH and HCl are dissolved, the base and the acid neutralize exactly, leaving only NaCl, effectively table salt, in solution.

Weak bases, such as baking soda or egg white, should be used to neutralize any acid spills. Neutralizing acid spills with strong bases, such as sodium hydroxide or potassium hydroxide, can cause a violent exothermic reaction, and the base itself can cause just as much damage as the original acid spill.

Alkalinity of non-hydroxides

Bases are generally compounds that can neutralize an amount of acid. Both sodium carbonate and ammonia are bases, although neither of these substances contains OH⁻
groups. Both compounds accept H⁺ when dissolved in protic solvents such as water:

${\displaystyle {\text{Na}}_2^{}{\text{CO}}_3^{}+{\text{H}}_2^{}\text{O}⟶2{\text{Na}}^{+}+{\text{HCO}}_3^{-}+{\text{OH}}^{-}}$

${\displaystyle {\text{NH}}_3^{}+{\text{H}}_2^{}\text{O}⟶{\text{NH}}_4^{+}+{\text{OH}}^{-}}$

From this, a pH, or acidity, can be calculated for aqueous solutions of bases.

A base is also defined as a molecule that has the ability to accept an electron pair bond by entering another atom's valence shell through its possession of one electron pair. There are a limited number of elements that have atoms with the ability to provide a molecule with basic properties. Carbon can act as a base as well as nitrogen and oxygen. Fluorine and sometimes rare gases possess this ability as well. This occurs typically in compounds such as butyl lithium, alkoxides, and metal amides such as sodium amide. Bases of carbon, nitrogen and oxygen without resonance stabilization are usually very strong, or superbases, which cannot exist in a water solution due to the acidity of water. Resonance stabilization, however, enables weaker bases such as carboxylates; for example, sodium acetate is a weak base.

Strong bases

A strong base is a basic chemical compound that can remove a proton (H⁺) from (or deprotonate) a molecule of even a very weak acid (such as water) in an acid–base reaction. Common examples of strong bases include hydroxides of alkali metals and alkaline earth metals, like NaOH and Ca(OH)
₂, respectively. Due to their low solubility, some bases, such as alkaline earth hydroxides, can be used when the solubility factor is not taken into account. One advantage of this low solubility is that "many antacids were suspensions of metal hydroxides such as aluminium hydroxide and magnesium hydroxide." These compounds have low solubility and have the ability to stop an increase in the concentration of the hydroxide ion, preventing the harm of the tissues in the mouth, oesophagus, and stomach. As the reaction continues and the salts dissolve, the stomach acid reacts with the hydroxide produced by the suspensions. Strong bases hydrolyze in water almost completely, resulting in the leveling effect." In this process, the water molecule combines with a strong base, due to the water's amphoteric ability; and, a hydroxide ion is released. Very strong bases can even deprotonate very weakly acidic C–H groups in the absence of water. Here is a list of several strong bases:

Lithium hydroxide	LiOH
Sodium hydroxide	NaOH
Potassium hydroxide	KOH
Rubidium hydroxide	RbOH
Cesium hydroxide	CsOH
Magnesium hydroxide	Mg(OH) 2
Calcium hydroxide	Ca(OH) 2
Strontium hydroxide	Sr(OH) 2
Barium hydroxide	Ba(OH) 2
Tetramethylammonium hydroxide	N(CH 3) 4OH
Guanidine	HNC(NH 2) 2

The cations of these strong bases appear in the first and second groups of the periodic table (alkali and earth alkali metals). Tetraalkylated ammonium hydroxides are also strong bases since they dissociate completely in water. Guanidine is a special case of a species that is exceptionally stable when protonated, analogously to the reason that makes perchloric acid and sulfuric acid very strong acids.

Acids with a pK_a of more than about 13 are considered very weak, and their conjugate bases are strong bases.

Superbases

Main article: Superbase

Group 1 salts of carbanions, amide ions, and hydrides tend to be even stronger bases due to the extreme weakness of their conjugate acids, which are stable hydrocarbons, amines, and dihydrogen. Usually, these bases are created by adding pure alkali metals such as sodium into the conjugate acid. They are called superbases, and it is impossible to keep them in aqueous solutions because they are stronger bases than the hydroxide ion (See the leveling effect.) For example, the ethoxide ion (conjugate base of ethanol) undergoes this reaction quantitatively in presence of water.

${\displaystyle {\text{CH}}_3^{}{\text{CH}}_2^{}{\text{O}}^{-}+{\text{H}}_2^{}\text{O}⟶{\text{CH}}_3^{}{\text{CH}}_2^{}\text{OH}+{\text{OH}}^{-}}$

Examples of common superbases are:

• Butyl lithium (n-C₄H₉Li)
• Lithium diisopropylamide (LDA) [(CH₃)₂CH]₂NLi
• Lithium diethylamide (LDEA) (C
  ₂H
  ₅)
  ₂NLi
• Sodium amide (NaNH₂)
• Sodium hydride (NaH)
• Lithium bis(trimethylsilyl)amide [(CH
  ₃)
  ₃Si]
  ₂NLi

Strongest superbases are synthesised in only gas phase:

• Ortho-diethynylbenzene dianion (C₆H₄(C₂)₂)²⁻ (This is the strongest superbase ever synthesized)
• Meta-diethynylbenzene dianion (C₆H₄(C₂)₂)²⁻ (second strongest superbase)
• Para-diethynylbenzene dianion (C₆H₄(C₂)₂)²⁻ (third strongest superbase)
• Lithium monoxide anion (LiO⁻) was considered the strongest superbase before diethynylbenzene dianions were created.

Weak bases

Main article: weak base

A weak base is one which does not fully ionize in an aqueous solution, or in which protonation is incomplete. For example, ammonia transfers a proton to water according to the equation

${\displaystyle N{H}_3(aq)+H_{2}O(l)\rightleftharpoons N{H}_4^{+}(aq)+O{H}^{-}(aq)}$

The equilibrium constant for this reaction at 25 °C is 1.8 x 10⁻⁵, such that the extent of reaction or degree of ionization is quite small.

Lewis bases

A Lewis base or electron-pair donor is a molecule with one or more high-energy lone pairs of electrons which can be shared with a low-energy vacant orbital in an acceptor molecule to form an adduct. In addition to H⁺, possible electron-pair acceptors (Lewis acids) include neutral molecules such as BF₃ and high oxidation state metal ions such as Ag²⁺, Fe³⁺ and Mn⁷⁺. Adducts involving metal ions are usually described as coordination complexes.

According to the original formulation of Lewis, when a neutral base forms a bond with a neutral acid, a condition of electric stress occurs. The acid and the base share the electron pair that formerly belonged to the base. As a result, a high dipole moment is created, which can only be decreased to zero by rearranging the molecules.

Solid bases

Examples of solid bases include:

• Oxide mixtures: SiO₂, Al₂O₃; MgO, SiO₂; CaO, SiO₂
• Mounted bases: LiCO₃ on silica; NR₃, NH₃, KNH₂ on alumina; NaOH, KOH mounted on silica on alumina
• Inorganic chemicals: BaO, KNaCO₃, BeO, MgO, CaO, KCN
• Anion exchange resins
• Charcoal that has been treated at 900 degrees Celsius or activates with N₂O, NH₃, ZnCl₂-NH₄Cl-CO₂

Depending on a solid surface's ability to successfully form a conjugate base by absorbing an electrically neutral acid, basic strength of the surface is determined. The "number of basic sites per unit surface area of the solid" is used to express how much basic strength is found on a solid base catalyst. Scientists have developed two methods to measure the amount of basic sites: one, titration with benzoic acid using indicators and gaseous acid adsorption. A solid with enough basic strength will absorb an electrically neutral acidic indicator and cause the acidic indicator's color to change to the color of its conjugate base. When performing the gaseous acid adsorption method, nitric oxide is used. The basic sites are then determined by calculating the amount of carbon dioxide that is absorbed.

Bases as catalysts

Basic substances can be used as insoluble heterogeneous catalysts for chemical reactions. Some examples are metal oxides such as magnesium oxide, calcium oxide, and barium oxide as well as potassium fluoride on alumina and some zeolites. Many transition metals make good catalysts, many of which form basic substances. Basic catalysts are used for hydrogenation, the migration of double bonds, in the Meerwein-Ponndorf-Verley reduction, the Michael reaction, and many others. Both CaO and BaO can be highly active catalysts if they are heated to high temperatures.

Uses of bases

• Sodium hydroxide is used in the manufacture of soap, paper, and the synthetic fiber rayon.
• Calcium hydroxide (slaked lime) is used in the manufacture of bleaching powder.
• Calcium hydroxide is also used to clean the sulfur dioxide, which is caused by the exhaust, that is found in power plants and factories.
• Magnesium hydroxide is used as an 'antacid' to neutralize excess acid in the stomach and cure indigestion.
• Sodium carbonate is used as washing soda and for softening hard water.
• Sodium bicarbonate (or sodium hydrogen carbonate) is used as baking soda in cooking food, for making baking powders, as an antacid to cure indigestion and in soda acid fire extinguisher.
• Ammonium hydroxide is used to remove grease stains from clothes

Monoprotic and polyprotic bases

Bases with only one ionizable hydroxide (OH⁻) ion per formula unit are called monoprotic since they can accept one proton (H⁺). Bases with more than one OH- per formula unit are polyprotic.

The number of ionizable hydroxide (OH⁻) ions present in one formula unit of a base is also called the acidity of the base. On the basis of acidity bases can be classified into three types: monoacidic, diacidic and triacidic.

Monoacidic bases

Sodium hydroxide

When one molecule of a base via complete ionization produces one hydroxide ion, the base is said to be a monoacidic or monoprotic base. Examples of monoacidic bases are:

Sodium hydroxide, potassium hydroxide, silver hydroxide, ammonium hydroxide, etc

Diacidic bases

When one molecule of base via complete ionization produces two hydroxide ions, the base is said to be diacidic or diprotic. Examples of diacidic bases are:

Barium hydroxide

Barium hydroxide, magnesium hydroxide, calcium hydroxide, zinc hydroxide, iron(II) hydroxide, tin(II) hydroxide, lead(II) hydroxide, copper(II) hydroxide, etc.

Triacidic bases

When one molecule of base via complete ionization produces three hydroxide ions, the base is said to be triacidic or triprotic. Examples of triacidic bases are:

Aluminium hydroxide, ferrous hydroxide, Gold Trihydroxide,

Etymology of the term

The concept of base stems from an older alchemical notion of "the matrix":

The term "base" appears to have been first used in 1717 by the French chemist, Louis Lémery, as a synonym for the older Paracelsian term "matrix." In keeping with 16th-century animism, Paracelsus had postulated that naturally occurring salts grew within the earth as a result of a universal acid or seminal principle having impregnated an earthy matrix or womb. ... Its modern meaning and general introduction into the chemical vocabulary, however, is usually attributed to the French chemist, Guillaume-François Rouelle. ... In 1754 Rouelle explicitly defined a neutral salt as the product formed by the union of an acid with any substance, be it a water-soluble alkali, a volatile alkali, an absorbent earth, a metal, or an oil, capable of serving as "a base" for the salt "by giving it a concrete or solid form." Most acids known in the 18th century were volatile liquids or "spirits" capable of distillation, whereas salts, by their very nature, were crystalline solids. Hence it was the substance that neutralized the acid which supposedly destroyed the volatility or spirit of the acid and which imparted the property of solidity (i.e., gave a concrete base) to the resulting salt.

— William B. Jensen, The origin of the term "base"