Limestone is a carbonate sedimentary rock, composed of the skeletal fragments of marine organisms such as coral and molluscs. Its major materials are the minerals calcite and aragonite, which are different crystal forms of calcium carbonate. A related rock is dolostone, which contains a high percentage of the mineral dolomite, CaMg2. In fact, in old USGS publications, dolostone was referred to as magnesian limestone, a term now reserved for magnesium-deficient dolostones or magnesium-rich limestones. About 10% of sedimentary rocks are limestones; the solubility of limestone in water and weak acid solutions leads to karst landscapes, in which water erodes the limestone over thousands to millions of years. Most cave systems are through limestone bedrock. Limestone has numerous uses: as a building material, an essential component of concrete, as aggregate for the base of roads, as white pigment or filler in products such as toothpaste or paints, as a chemical feedstock for the production of lime, as a soil conditioner, or as a popular decorative addition to rock gardens.
Like most other sedimentary rocks, most limestone is composed of grains. Most grains in limestone are skeletal fragments of marine organisms such as foraminifera; these organisms secrete shells made of aragonite or calcite, leave these shells behind when they die. Other carbonate grains composing limestones are ooids, peloids and extraclasts. Limestone contains variable amounts of silica in the form of chert or siliceous skeletal fragment, varying amounts of clay and sand carried in by rivers; some limestones do not consist of grains, are formed by the chemical precipitation of calcite or aragonite, i.e. travertine. Secondary calcite may be deposited by supersaturated meteoric waters; this produces speleothems, such as stalactites. Another form taken by calcite is oolitic limestone, which can be recognized by its granular appearance; the primary source of the calcite in limestone is most marine organisms. Some of these organisms can construct mounds of rock building upon past generations. Below about 3,000 meters, water pressure and temperature conditions cause the dissolution of calcite to increase nonlinearly, so limestone does not form in deeper waters.
Limestones may form in lacustrine and evaporite depositional environments. Calcite can be dissolved or precipitated by groundwater, depending on several factors, including the water temperature, pH, dissolved ion concentrations. Calcite exhibits an unusual characteristic called retrograde solubility, in which it becomes less soluble in water as the temperature increases. Impurities will cause limestones to exhibit different colors with weathered surfaces. Limestone may be crystalline, granular, or massive, depending on the method of formation. Crystals of calcite, dolomite or barite may line small cavities in the rock; when conditions are right for precipitation, calcite forms mineral coatings that cement the existing rock grains together, or it can fill fractures. Travertine is a banded, compact variety of limestone formed along streams where there are waterfalls and around hot or cold springs. Calcium carbonate is deposited where evaporation of the water leaves a solution supersaturated with the chemical constituents of calcite.
Tufa, a porous or cellular variety of travertine, is found near waterfalls. Coquina is a poorly consolidated limestone composed of pieces of coral or shells. During regional metamorphism that occurs during the mountain building process, limestone recrystallizes into marble. Limestone is a parent material of Mollisol soil group. Two major classification schemes, the Folk and the Dunham, are used for identifying the types of carbonate rocks collectively known as limestone. Robert L. Folk developed a classification system that places primary emphasis on the detailed composition of grains and interstitial material in carbonate rocks. Based on composition, there are three main components: allochems and cement; the Folk system uses two-part names. It is helpful to have a petrographic microscope when using the Folk scheme, because it is easier to determine the components present in each sample; the Dunham scheme focuses on depositional textures. Each name is based upon the texture of the grains. Robert J. Dunham published his system for limestone in 1962.
Dunham divides the rocks into four main groups based on relative proportions of coarser clastic particles. Dunham names are for rock families, his efforts deal with the question of whether or not the grains were in mutual contact, therefore self-supporting, or whether the rock is characterized by the presence of frame builders and algal mats. Unlike the Folk scheme, Dunham deals with the original porosity of the rock; the Dunham scheme is more useful for hand samples because it is based on texture, not the grains in the sample. A revised classification was proposed by Wright, it adds some diagenetic patterns and can be summarized as follows: See: Carbonate platform About 10% of all sedimentary rocks are limestones. Limestone is soluble in acid, therefore forms many erosional landforms; these include limestone pavements, pot holes, cenotes and gorges. Such erosion landscapes are known
Soil conservation is the prevention of soil loss from erosion or prevention of reduced fertility caused by over usage, salinization or other chemical soil contamination. Slash-and-burn and other unsustainable methods of subsistence farming are practiced in some lesser developed areas. A sequel to the deforestation is large scale erosion, loss of soil nutrients and sometimes total desertification. Techniques for improved soil conservation include crop rotation, cover crops, conservation tillage and planted windbreaks, affect both erosion and fertility; when plants trees, die they decay and become part of the soil. Code 330 defines standard methods recommended by the U. S. Natural Resources Conservation Service. Farmers have practiced soil conservation for millennia. In Europe, policies such as the Common Agricultural Policy are targeting the application of best management practices such as reduced tillage, winter cover crops, plant residues and grass margins in order to better address the soil conservation.
Political and economic action is further required to solve the erosion problem. A simple governance hurdle concerns how we name and value the land and what we call it and this can be changed by cultural adaptation. Contour ploughing orients furrows following the contour lines of the farmed area. Furrows move right to maintain a constant altitude, which reduces runoff. Contour ploughing was practiced by the ancient Phoenicians, is effective for slopes between two and ten percent. Contour ploughing can increase crop yields from 10 to 50 percent as a result of greater soil retention. Terracing is the practice of creating nearly level areas in a hillside area; the terraces form a series of each at a higher level than the previous. Terraces are protected from erosion by other soil barriers. Terraced farming is more common on small farms and in underdeveloped countries, since mechanized equipment is difficult to deploy in this setting. Keyline design is an enhancement of contour farming, where the total watershed properties are taken into account in forming the contour lines.
Tree and ground-cover are effective perimeter treatment for soil erosion prevention, by impeding surface flows. A special form of this perimeter or inter-row treatment is the use of a “grass way” that both channels and dissipates runoff through surface friction, impeding surface runoff and encouraging infiltration of the slowed surface water. Windbreaks are sufficiently dense rows of trees at the windward exposure of an agricultural field subject to wind erosion. Evergreen species provide year-round protection. Cover crops such as legumes plant, white turnip and other species are rotated with cash crops to blanket the soil year-round and act as green manure that replenishes nitrogen and other critical nutrients. Cover crops help suppress weeds. Soil-conservation farming involves no-till farming, “green manures” and other soil-enhancing practices; such farming methods attempt to mimic the biology of barren lands. They can revive damaged soil, minimize erosion, encourage plant growth, eliminate the use of nitrogen fertilizer or fungicide, produce above-average yields and protect crops during droughts or flooding.
The result is lower costs that increase farmers' profits. No-till farming and cover crops act as sinks for nitrogen and other nutrients; this increases the amount of soil organic matter. Repeated plowing/tilling degrades soil, killing its beneficial earthworms. Once damaged, soil may take multiple seasons to recover in optimal circumstances. Critics argue that no-till and related methods are impractical and too expensive for many growers because it requires new equipment, they cite advantages for conventional tilling depending on the geography and soil conditions. Some farmers claimed that no-till complicates weed control, delays planting and that post-harvest residues for corn, are hard to manage. Salinity in soil is caused by irrigating with salty water. Water evaporates from the soil leaving the salt behind. Salt breaks down causing infertility and reduced growth; the ions responsible for salination are: sodium, calcium and chlorine. Salinity is estimated to affect about one third of the earth’s arable land.
Soil salinity adversely affects crop metabolism and erosion follows. Salinity occurs in areas with shallow saline water tables. Over-irrigation deposits salts in upper soil layers as a byproduct of soil infiltration; the best-known case of shallow saline water table capillary action occurred in Egypt after the 1970 construction of the Aswan Dam. The change in the groundwater level led to high salt concentrations in the water table; the continuous high level of the water table led to soil salination. Use of humic acids may prevent excess salination given excessive irrigation. Humic acids can eliminate them from root zones. Planting species that can tolerate saline conditions can be used to lower water tables and thus reduce the rate of capillary and evaporative enrichment of surface salts. Salt-tolerant plants include saltbush, a plant found in much of North America and in the Mediterranean regions of Europe; when worms excrete egesta in the form of casts, a balanced selection of minerals and plant nutrients is made into a form accessible for root uptake.
Earthworm casts are five times richer in available nitrogen, seven times richer in available phosphates and eleven times richer in available potash than the surroundi
Freising is a town in Bavaria and the capital of the Freising district, with a population of 45,227. Freising is north of Munich, near Munich International Airport, on the Isar river and two hills, the cathedral hill with the bishop's castle and Freising cathedral, Weihenstephan Hill with Weihenstephan Abbey, the oldest working brewery in the world, it was the first recorded place of a European tornado. The city is 448 meters above sea level. Freising is located on the Isar halfway between Landshut in Upper Bavaria. Freising is one of the oldest settlements in Bavaria, becoming a major religious centre in the early Middle Ages, it is the centre of an important diocese. Some important historical documents were created between 900 and 1200 in its monastery: Freising manuscripts written in Slovenian, being the first Roman-script continuous text in a Slavic language Chronicle or history of the two cities by Otto of FreisingThe above and other scripts from that time can be found in the "Bayerische Staatsbibliothek" in Munich.
Though archaeological finds show that the area was settled in the Bronze Age, no proof has been found yet to suggest a continuous settlement until the 8th century AD Frigisinga. Saint Corbinian settled at a shrine that existed at Freising in 724, he was the forerunner of the diocese of Freising, established after his death by Saint Boniface. According to his Vita by Bishop Arbeo he ordered a bear to carry his luggage over the Alps after it had killed his packhorse; the saddled bear is still the symbol of the city, displayed in the coat of arms. Though the seat of the diocese was moved to Munich in 1821, including the elevation to an arch-diocese, Freising has remained the seat of diocese administration until today. Between 764-783, Bishop Arbeo founded a scriptorium at the abbey; the settlement started to become a religious centre. The earliest recorded tornado in Europe struck Freising in 788; the mortal remains of Pope Alexander I are said to have been transferred to Freising in 834. In 996, Freising received city rights from Emperor Otto III.
However, after the " destruction of the episcopal bridge, custom houses and salt works near Oberföhring by Duke Henry the Lion, who transferred the custom houses and bridge site to the upper part of Oberföhring, placing them in the village of Munich on the Isar" in 1158, Freising started to lose its economic significance. In 1159, the romanesque cathedral was constructed. In the secularization of 1803, the Roman Catholic Church lost most of its properties and authority over the city; the Lord Mayor of Freising is Tobias Eschenbacher. The majority of seats in the city council are held by the so-called "Free Voters"; the distribution of seats in Freising's city council can be seen in the following diagram: Schools include: Camerloher-Gymnasium Freising Dom-Gymnasium Freising Josef-Hofmiller-GymnasiumUniversities include: Hochschule Weihenstephan-Triesdorf TU-München Weihenstephan Prince-Bishopric of Freising Freising is twinned with: Obervellach, since 1963 Innichen, since 1969 Maria Wörth, since 1978 Waidhofen an der Ybbs, since 1986 Arpajon, since 1991 Škofja Loka, since 2004 Otto of Freising, bishop.
Mair von Landshut, late 15th-century artist, was a citizen and born in Freising. The Bavarian General and War Minister Benignus Ritter von Safferling was born in Freising. Georg Eder and historian Martin Ruland the Elder and alchemist Johann Stadlmayr, court music director and composer Benignus von Safferling, Bavarian General and Minister of War Ludwig Prandtl, physicist Ernst Kraus, a German geologist Karl Maria Demelhuber, SS-Obergruppenführer and General of the Waffen-SS Karl Lederer, 1933 to 1942 mayor of Freising. Karl Gustav Fellerer, a German musicologist Albrecht Obermaier, German naval officer, last deputy naval officer of the Bundesmarine Pope Benedict XVI, Pope from 2005-2013 Karl Huber, German painter and sculptor Heinrich Reinhardt, Roman Catholic priest and professor of philosophy Peter Neumair, wrestler Joseph Weiss, German diplomat Hans Pflügler, former clubs: Bayern Munich - World champion 1990 Alexander Kutschera, footballer Stefan Diez, German industrial designer Ferdinand Bader, ski jumper Brigitte Wagner, wrestler Maximilian Haas, footballer Maximilian Wittek, footballer Veit Arnpeck, Bavarian chronicler Benignus von Safferling, General of the Bavarian Army and War Minister Ludwig Petuel, Munich businessman Oskar Knight of Niedermayer and adventurer Simone Blum Show jumper Freising cathedral Sichtungsgarten Weihenstephan, a notable horticultural garden Freising travel guide from Wikivoyage Official website Bavarian state library Pictures of Freising
Soil test may refer to one or more of a wide variety of soil analysis conducted for one of several possible reasons. The most conducted soil tests are those done to estimate the plant-available concentrations of plant nutrients, in order to determine fertilizer recommendations in agriculture. Other soil tests may be done for geochemical or ecological investigations. In agriculture, a soil test refers to the analysis of a soil sample to determine nutrient content and other characteristics such as the acidity or pH level. A soil test can determine fertility, or the expected growth potential of the soil which indicates nutrient deficiencies, potential toxicities from excessive fertility and inhibitions from the presence of non-essential trace minerals; the test is used to mimic the function of roots to assimilate minerals. The expected rate of growth is modeled by the Law of the Maximum. Labs, such as those at Iowa State and Colorado State University, recommend that a soil test contains 10-20 sample points for every 40 acres of field.
Tap water or chemicals can change the composition of the soil, may need to be tested separately. As soil nutrients vary with depth and soil components change with time, the depth and timing of a sample may affect results. Composite sampling can be performed by combining soil from several locations prior to analysis; this should be used judiciously to avoid skewing results. This procedure must be done. A reference map should be created to record the location and quantity of field samples in order to properly interpret test results. Soil chemistry changes over time, as biological and which chemical processes break down or combine compounds over time; these processes change once the soil is removed from its natural environment. As a result, the chemical composition analysis accuracy can be improved if the soil is analysed soon after its extraction — within a relative time period of 24 hours; the chemical changes in the soil can be slowed during transportation by freezing it. Air drying can preserve the soil sample for many months.
Soil testing is performed by commercial labs that offer a variety of tests, targeting groups of compounds and minerals. The advantages associated with local lab is that they are familiar with the chemistry of the soil in the area where the sample was taken; this enables technicians to recommend the tests that are most to reveal useful information. Laboratory tests check for plant nutrients in three categories: Major nutrients: nitrogen and potassium Secondary nutrients: sulfur, magnesium Minor nutrients: iron, copper, boron, chlorineThe amount of plant available soil phosphorus is most measured with a chemical extraction method, different countries have different standard methods. Just in Europe, more than 10 different soil P tests are in use and the results from these tests are not directly comparable with each other. Do-it-yourself kits only test for the three "major nutrients", for soil acidity or pH level. Do-it-yourself kits are sold at farming cooperatives, university labs, private labs, some hardware and gardening stores.
Electrical meters that measure pH, water content, sometimes nutrient content of the soil are available at many hardware stores. Laboratory tests are more accurate than tests with electrical meters. Here is an example soil sample report from one laboratory. Soil testing is used to facilitate fertilizer composition and dosage selection for land employed in both agricultural and horticultural industries. Prepaid mail-in kits for soil and ground water testing are available to facilitate the packaging and delivery of samples to a laboratory. In 2004, laboratories began providing fertilizer recommendations along with the soil composition report. Lab tests are more accurate and utilize precise flow injection technology. In addition, lab tests include professional interpretation of results and recommendations. Always refer to all proviso statements included in a lab report as they may outline any anomalies and shortcomings in the sampling and/or analytical process/results; some laboratories analyze for all 13 mineral nutrients and a dozen non-essential toxic minerals utilizing the "universal soil extractant".
Common mineral soil contaminants include arsenic, cadmium, mercury and zinc. Lead is a dangerous soil component; the following table from the University of Minnesota categorizes typical soil concentration levels and their associated health risks. Six gardening practices to reduce the lead riskLocate gardens away from old painted structures and traveled roads Give planting preferences to fruiting crops Incorporate organic materials such as finished compost and peat moss Lime soil as recommended by soil test Discard old and outer leaves before eating leafy vegetables.
Aluminium or aluminum is a chemical element with symbol Al and atomic number 13. It is a silvery-white, soft and ductile metal in the boron group. By mass, aluminium makes up about 8% of the Earth's crust; the chief ore of aluminium is bauxite. Aluminium metal is so chemically reactive that native specimens are rare and limited to extreme reducing environments. Instead, it is found combined in over 270 different minerals. Aluminium is remarkable for its low density and its ability to resist corrosion through the phenomenon of passivation. Aluminium and its alloys are vital to the aerospace industry and important in transportation and building industries, such as building facades and window frames; the oxides and sulfates are the most useful compounds of aluminium. Despite its prevalence in the environment, no known form of life uses aluminium salts metabolically, but aluminium is well tolerated by plants and animals; because of these salts' abundance, the potential for a biological role for them is of continuing interest, studies continue.
Of aluminium isotopes, only 27Al is stable. This is consistent with aluminium having an odd atomic number, it is the only aluminium isotope that has existed on Earth in its current form since the creation of the planet. Nearly all the element on Earth is present as this isotope, which makes aluminium a mononuclidic element and means that its standard atomic weight equates to that of the isotope; the standard atomic weight of aluminium is low in comparison with many other metals, which has consequences for the element's properties. All other isotopes of aluminium are radioactive; the most stable of these is 26Al and therefore could not have survived since the formation of the planet. However, 26Al is produced from argon in the atmosphere by spallation caused by cosmic ray protons; the ratio of 26Al to 10Be has been used for radiodating of geological processes over 105 to 106 year time scales, in particular transport, sediment storage, burial times, erosion. Most meteorite scientists believe that the energy released by the decay of 26Al was responsible for the melting and differentiation of some asteroids after their formation 4.55 billion years ago.
The remaining isotopes of aluminium, with mass numbers ranging from 21 to 43, all have half-lives well under an hour. Three metastable states are known, all with half-lives under a minute. An aluminium atom has 13 electrons, arranged in an electron configuration of 3s23p1, with three electrons beyond a stable noble gas configuration. Accordingly, the combined first three ionization energies of aluminium are far lower than the fourth ionization energy alone. Aluminium can easily surrender its three outermost electrons in many chemical reactions; the electronegativity of aluminium is 1.61. A free aluminium atom has a radius of 143 pm. With the three outermost electrons removed, the radius shrinks to 39 pm for a 4-coordinated atom or 53.5 pm for a 6-coordinated atom. At standard temperature and pressure, aluminium atoms form a face-centered cubic crystal system bound by metallic bonding provided by atoms' outermost electrons; this crystal system is shared by some other metals, such as copper. Aluminium metal, when in quantity, is shiny and resembles silver because it preferentially absorbs far ultraviolet radiation while reflecting all visible light so it does not impart any color to reflected light, unlike the reflectance spectra of copper and gold.
Another important characteristic of aluminium is its low density, 2.70 g/cm3. Aluminium is a soft, lightweight and malleable with appearance ranging from silvery to dull gray, depending on the surface roughness, it is nonmagnetic and does not ignite. A fresh film of aluminium serves as a good reflector of visible light and an excellent reflector of medium and far infrared radiation; the yield strength of pure aluminium is 7–11 MPa, while aluminium alloys have yield strengths ranging from 200 MPa to 600 MPa. Aluminium has stiffness of steel, it is machined, cast and extruded. Aluminium atoms are arranged in a face-centered cubic structure. Aluminium has a stacking-fault energy of 200 mJ/m2. Aluminium is a good thermal and electrical conductor, having 59% the conductivity of copper, both thermal and electrical, while having only 30% of copper's density. Aluminium is capable of superconductivity, with a superconducting critical temperature of 1.2 kelvin and a critical magnetic field of about 100 gauss.
Aluminium is the most common material for the fabrication of superconducting qubits. Aluminium's corrosion resistance can be excellent due to a thin surface layer of aluminium oxide that forms when the bare metal is exposed to air preventing further oxidation, in a process termed passivation; the strongest aluminium alloys are less corrosion resistant due to galvanic reactions with alloyed copper. This corrosion resistance is reduced by aqueous salts in the presence of dissimilar metals. In acidic solutions, aluminium reacts with water to form hydrogen, in alkaline ones to form aluminates—protective passivation under these conditions is negligible; because it is corroded by dissolved chlorides, such as common sodium chloride, household plumbing is never made from aluminium. However, because
Soil is a mixture of organic matter, gases and organisms that together support life. Earth's body of soil, called the pedosphere, has four important functions: as a medium for plant growth as a means of water storage and purification as a modifier of Earth's atmosphere as a habitat for organismsAll of these functions, in their turn, modify the soil; the pedosphere interfaces with the lithosphere, the hydrosphere, the atmosphere, the biosphere. The term pedolith, used to refer to the soil, translates to ground stone in the sense "fundamental stone". Soil consists of a solid phase of minerals and organic matter, as well as a porous phase that holds gases and water. Accordingly, soil scientists can envisage soils as a three-state system of solids and gases. Soil is a product of several factors: the influence of climate, relief and the soil's parent materials interacting over time, it continually undergoes development by way of numerous physical and biological processes, which include weathering with associated erosion.
Given its complexity and strong internal connectedness, soil ecologists regard soil as an ecosystem. Most soils have a dry bulk density between 1.1 and 1.6 g/cm3, while the soil particle density is much higher, in the range of 2.6 to 2.7 g/cm3. Little of the soil of planet Earth is older than the Pleistocene and none is older than the Cenozoic, although fossilized soils are preserved from as far back as the Archean. Soil science has two basic branches of study: pedology. Edaphology studies the influence of soils on living things. Pedology focuses on the formation and classification of soils in their natural environment. In engineering terms, soil is included in the broader concept of regolith, which includes other loose material that lies above the bedrock, as can be found on the Moon and on other celestial objects as well. Soil is commonly referred to as earth or dirt. Soil is a major component of the Earth's ecosystem; the world's ecosystems are impacted in far-reaching ways by the processes carried out in the soil, from ozone depletion and global warming to rainforest destruction and water pollution.
With respect to Earth's carbon cycle, soil is an important carbon reservoir, it is one of the most reactive to human disturbance and climate change. As the planet warms, it has been predicted that soils will add carbon dioxide to the atmosphere due to increased biological activity at higher temperatures, a positive feedback; this prediction has, been questioned on consideration of more recent knowledge on soil carbon turnover. Soil acts as an engineering medium, a habitat for soil organisms, a recycling system for nutrients and organic wastes, a regulator of water quality, a modifier of atmospheric composition, a medium for plant growth, making it a critically important provider of ecosystem services. Since soil has a tremendous range of available niches and habitats, it contains most of the Earth's genetic diversity. A gram of soil can contain billions of organisms, belonging to thousands of species microbial and in the main still unexplored. Soil has a mean prokaryotic density of 108 organisms per gram, whereas the ocean has no more than 107 procaryotic organisms per milliliter of seawater.
Organic carbon held in soil is returned to the atmosphere through the process of respiration carried out by heterotrophic organisms, but a substantial part is retained in the soil in the form of soil organic matter. Since plant roots need oxygen, ventilation is an important characteristic of soil; this ventilation can be accomplished via networks of interconnected soil pores, which absorb and hold rainwater making it available for uptake by plants. Since plants require a nearly continuous supply of water, but most regions receive sporadic rainfall, the water-holding capacity of soils is vital for plant survival. Soils can remove impurities, kill disease agents, degrade contaminants, this latter property being called natural attenuation. Soils maintain a net absorption of oxygen and methane and undergo a net release of carbon dioxide and nitrous oxide. Soils offer plants physical support, water, temperature moderation and protection from toxins. Soils provide available nutrients to plants and animals by converting dead organic matter into various nutrient forms.
A typical soil is about 50% solids, 50% voids of which half is occupied by water and half by gas. The percent soil mineral and organic content can be treated as a constant, while the percent soil water and gas content is considered variable whereby a rise in one is balanced by a reduction in the other; the pore space allows for the infiltration and movement of air and water, both of which are critical for life existing in soil. Compaction, a common problem with soils, reduces this space, preventing air and water from reaching plant roots and soil organisms. Given sufficient time, an undifferentiated soil will evolve a soil profile which consists of two or more layers, referred to as soil horizons, that differ in one or more properties such as in their texture, density, consistency, temperature and reactivity; the horizons differ in thickness and gene
In chemistry, bases are substances that, in aqueous solution, release hydroxide ions, are slippery to the touch, can taste bitter if an alkali, change the color of indicators, react with acids to form salts, promote certain chemical reactions, accept protons from any proton donor or contain or displaceable OH− ions. Examples of bases are the hydroxides of the alkaline earth metals; these particular substances produce hydroxide ions in aqueous solutions, are thus classified as Arrhenius bases. For a substance to be classified as an Arrhenius base, it must produce hydroxide ions in an aqueous solution. Arrhenius believed; this makes the Arrhenius model limited, as it cannot explain the basic properties of aqueous solutions of ammonia or its organic derivatives. There are bases that do not contain a hydroxide ion but react with water, resulting in an increase in the concentration of the hydroxide ion. An example of this is the reaction between water to produce ammonium and hydroxide. In this reaction ammonia is the base.
Ammonia and other bases similar to it have the ability to form a bond with a proton due to the unshared pair of electrons that they possess. In the more general Brønsted–Lowry acid–base theory, a base is a substance that can accept hydrogen cations —otherwise known as protons. In the Lewis model, a base is an electron pair donor. 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 releases OH − ions quantitatively. However, it is important to realize. Metal oxides and alkoxides are basic, conjugate bases of weak acids are weak bases. Bases can be thought of as the chemical opposite of acids. However, some strong acids are able to act as bases. Bases and acids are seen as opposites because the effect of an acid is to increase the hydronium concentration in water, whereas bases reduce this concentration.
A reaction between an acid and a base is called neutralization. In a neutralization reaction, an aqueous solution of a base reacts with an aqueous solution of an acid to produce a solution of water and 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; the notion of a base as a concept in chemistry was first introduced by the French chemist Guillaume François Rouelle in 1754. He noted that acids, which at that time were volatile liquids, turned into solid salts only when combined with specific substances. Rouelle considered that such a substance serves as a "base" for the salt, giving the salt a "concrete or solid form". 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, turn methyl orange yellow.
The pH of a basic solution at standard conditions is greater than seven. Bases are bitter in taste; the following reaction represents the general reaction between a base and water to produce a conjugate acid and a conjugate base: B + H2O ⇌ BH+ + OH−The equilibrium constant, Kb, for this reaction can be found using the following general equation: Kb = /In this equation, both the base and the strong base compete with one another for the proton. As a result, bases that react with water have small equilibrium constant values; the base is weaker. Bases react with acids to neutralize each other at a fast rate both in alcohol; when dissolved in water, the strong base sodium hydroxide ionizes into hydroxide and sodium ions: NaOH → Na+ + OH−and in water the acid hydrogen chloride forms hydronium and chloride ions: HCl + H2O → H3O+ + Cl−When the two solutions are mixed, the H3O+ and OH− ions combine to form water molecules: H3O+ + OH− → 2 H2OIf equal quantities of NaOH and HCl are dissolved, the base and the acid neutralize leaving only NaCl 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, the base itself can cause just as much damage as the original acid spill. Bases are compounds that can neutralize an amount of acids. 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: Na2CO3 + H2O → 2 Na+ + HCO3− + OH− NH3 + H2O → NH4+ + OH−From this, a pH, or acidity, can be calculated for aqueous solutions of bases. Bases directly act as electron-pair donors themselves: CO32− + H+ → HCO3− NH3 + H+ → NH4+A base is 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