The name "acid" calls to mind vivid sensory images — of tartness, for instance, if the acid in question is meant for human consumption, as with the citric acid in lemons.
On the other hand, the thought of laboratory-and industrial-strength substances with scary-sounding names, such as sulfuric acid or hydrofluoric acid, carries with it other ideas — of acids that are capable of destroying materials, including human flesh. The name "base," by contrast, is not widely known in its chemical sense, and even when the older term of "alkali" is used, the sense-impressions produced by the word tend not to be as vivid as those generated by the thought of "acid.
As with acids, they have many household uses, in substances such as baking soda or oven cleaners. From a taste standpoint, as anyone who has ever brushed his or her teeth with baking soda knowsbases are bitter rather than sour.
How do we know when something is an acid or a base? Acid-base indicators, such as litmus paper and other materials for testing pH, offer a means of judging these qualities in various substances.
However, there are larger structural definitions of the two concepts, which evolved in three stages during the late nineteenth and early twentieth centuries, that provide a more solid theoretical underpinning to the "3 substances that contain bases of dating" of acids and bases.
From these observations, they could form general rules, but they lacked any means of "seeing" into the atomic and molecular structures of the chemical world. The phenomenological distinctions between acids and basesgathered by scientists from ancient times onward, worked well enough for many centuries. The word "acid" comes from the Latin term acidus, or "sour," and from an early period, scientists understood that substances such as vinegar and lemon juice shared a common acidic quality.
Eventually, the phenomenological definition of acids became relatively sophisticated, encompassing such details as the fact that acids produce characteristic colors in certain vegetable dyes, such as those used in making litmus paper.
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In addition, chemists realized that acids dissolve some metals, releasing hydrogen in the process. The word "alkali" comes from the Arabic al-qili, which refers to the ashes of the seawort plant. The latter, which typically grows in marshy areas, was often burned to produce soda ash, used in making soap.
In contrast to acids, bases — caffeine, for example — have a bitter taste, and many of them feel slippery to the touch. They also produce characteristic colors in the vegetable dyes of litmus paper, and can be used to promote certain chemical reactions. Note that today chemists use the word "base" instead of "alkali," the reason being that the latter term has a narrower meaning: Originally, "alkali" referred only to the ashes of burned plants, such as seawort, that contained either sodium or potassium, and from which the oxides of sodium and potassium could be obtained.
Eventually, alkali came to mean the soluble hydroxides of the alkali and alkaline earth metals. This includes sodium hydroxidethe active ingredient in drain and oven cleaners; magnesium hydroxide, used for instance in milk of magnesia ; potassium hydroxide, found in soaps and other substances; and other compounds. Broad as this range of substances is, it fails to encompass the wide array of materials known today as bases — compounds which react with acids to form salts and water. The reaction to form salts and water is, in fact, one of the ways that acids and bases can be defined.
In an aqueous solution, hydrochloric acid and sodium hydroxide react to form sodium chloride — which, though it
3 substances that contain bases of dating suspended in an aqueous solution, is still common table salt — along with water. In other words, the sodium Na ion in sodium hydroxide switches places with the hydrogen ion in hydrochloric acid, resulting in the creation of NaCl salt along with water. But why does this happen? Useful as this definition regarding the formation of salts and water is, it is still not structural — in other words, it does not delve into the molecular structure and behavior of acids and bases.
Credit for the first truly structural definition of the difference goes to the Swedish chemist Svante Arrhenius It was Arrhenius who, in
3 substances that contain bases of dating doctoral dissertation inintroduced the concept of an ion, an atom possessing an electric charge. His understanding was particularly impressive in light of the fact that it was 13 more years before the discovery of the electron, the subatomic particle responsible for the creation of ions.
Atoms have a neutral charge, but when an electron or electrons depart, the atom becomes a positive ion or cation. Similarly, when an electron or electrons join a previously uncharged atom, the result is a negative ion or anion. Not only did the concept of ions greatly influence the future of chemistry, but it also provided Arrhenius with the key necessary to formulate his distinction between acids and bases.
Arrhenius observed that molecules of certain compounds break into charged particles when placed in liquid.
In chemistry, bases are substances...
This was a good start, but two aspects of Arrhenius's theory suggested the need for a definition that encompassed more substances. First of all, his theory was limited to reactions in aqueous solutions. Though many acid-base reactions do occur when water is the solvent, this is not always the case. Second, the Arrhenius definition effectively limited acids and bases only to those ionic compounds, such as hydrochloric acid or sodium hydroxide, which produced either hydrogen or hydroxide ions.
However, ammonia, or NH 3acts like a base in aqueous solutions, even though it does not produce the hydroxide ion. The same is true of other substances, which behave like acids or bases without conforming to the Arrhenius definition. Nonetheless, Arrhenius's theory represented an important first step, and inhe was awarded the Nobel Prize in Chemistry for his work on the dissociation of molecules into ions.
These symbols indicate that an acid has a proton it is ready to give away, while a base, with its negative charge, is ready to receive the positively charged proton. It is thus really nothing more than a lone
3 substances that contain bases of dating, but this is the one and only case in which an atom and a proton are exactly the same thing. This tutorial introduces basics of...
In an acid-base reaction, a molecule of acid is "donating" a proton, in the form of a hydrogen ion. This should not be confused with a far more complex process, nuclear fusion, in which an atom gives up a proton to another atom. The first acid shown — which,
3 substances that contain bases of dating three of the four "players" in this equation, is dissolved in an aqueous solution — combines with water, which can serve as either an acid or a base.
In the present context, it functions as a base. Water molecules are polar, meaning that the negative charges tend to congregate on one end of the molecule with the oxygen atom, while the positive charges remain on the other end with the hydrogen atoms.
The hydronium ion produced here is an example of a conjugate acid, an acid formed when a base accepts a proton. These two products of the reaction are called a conjugate acid-base pair, a term that refers to two substances related to one another by the donating of a proton.
An example, mentioned earlier, is ammonia. As American chemist Gilbert N. Lewis recognized, this did not encompass the full range of acids and bases; what was needed, instead, was a definition that did not involve the presence of a hydrogen atom. Lewis is particularly noted for his work in the realm of chemical bonding.
The bonding of atoms is the result of activity on the part of the valence electrons, or the electrons at the "outside" of the atom. Electrons are arranged in different ways, depending on the type of bonding, but they always bond in pairs. According to the Lewis acid-base theory, an acid is the reactant that accepts an electron pair from another reactant in a chemical reaction, while a base is the reactant that donates an electron pair to another reactant.
Instead, the manner in which the compound reacts with another serves to identify it as an acid or base. The beauty of the Lewis definition lies in the fact that it encompasses all the situations covered by the others — and more.
In particular, Lewis theory can be used to differentiate the acid and base in bond-producing chemical reactions where ions are not produced, and in which there is no proton donor or acceptor.
An example is the reaction of boron trifluoride BF 3 with ammonia NH 3both in the gas phases, to produce boron trifluoride ammonia complex F 3 BNH 3. In this reaction, boron trifluoride accepts an electron pair and is therefore a Lewis acid, while ammonia donates the electron pair and is thus a Lewis base.
Though hydrogen is involved in this particular reaction, Lewis theory also addresses reactions involving no hydrogen.
Though chemists apply the sophisticated structural definitions for acids and bases that we have discussed, there are also more "hands-on" methods for identifying a particular substance including complex mixtures as an acid or base.
The term pH stands for "potential of hydrogen," and the pH scale is a means of determining the acidity or alkalinity of a substance. Though, as noted, the term "alkali" has been replaced by "base," alkalinity is still used as an adjectival term to indicate the degree to which a substance displays the properties of a base. There are theoretically no limits to the range of the pH scale, but figures for acidity and alkalinity are usually given with numerical values between 0 and A rating of 0 on the pH scale indicates a substance that is virtually pure acid, while a 14 rating represents a nearly pure base.
A rating of 7 indicates a neutral substance. The pH scale is logarithmic, or exponential, meaning that the numbers represent exponents, and thus an increased value of 1 represents not a simple arithmetic addition of 1, but an increase of 1 power. This, however, needs a little further explanation. The pH of a virtually pure acid, such as the sulfuric acid in car batteries, is 0, and this represents 1 mole mol of hydronium per liter l of solution.
It is interesting to observe that most of the fluids in the human body have pH values in the neutral range blood venous, 7. The most precise pH measurements are made with electronic pH meters, which can provide figures accurate to 0. However, simpler materials are also used. Best known among these is litmus paper made from an extract of two lichen species
3 substances that contain bases of dating turns blue in the presence of bases and red in the presence of acids.
The term "litmus test" has become part of everyday language, referring to a make-or-break issue — for example, "views on abortion rights became a litmus test for Supreme Court nominees. Litmus is just one of many materials used for making pH paper, but in "3 substances that contain bases of dating" case, the change of color is the result of the neutralization of the substance on the paper.
In chemistry, bases are substances...
For instance, paper coated with phenolphthalein changes from colorless to pink in a pH range from 8. Extracts from various fruits and vegetables, including red cabbages, red onions, and others, are also applied as indicators.
The tables below list a few well-known acids and bases, along with their formulas and a few applications. Of course these represent only a few of the many acids and bases that exist.
Selected substances listed above are discussed briefly below. As its name suggests, citric acid is found in citrus fruits — particularly lemons, limes, and grapefruits.
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It is also used as a flavoring agent, preservative, and cleaning agent. Produced commercially from the fermentation of sugar by several species of mold, citric acid creates a taste that is both tart and sweet. The tartness, of course, is a function of its acidity, or a manifestation of the fact that it produces hydrogen ions. The sweetness is a more complex biochemical issue relating to the ways that citric acid molecules fit into the tongue's "sweet" receptors.
Citric acid plays a role in one famous stomach remedy, or antacid. This in itself is interesting, since antacids are more generally associated with alkaline substances, used for their ability to neutralize stomach acid. The fizz in Alka-Seltzer, however, comes from the reaction of citric acids which also provide a more pleasant taste with sodium bicarbonate or
3 substances that contain bases of dating soda, a base.
This reaction produces carbon dioxide gas. As a preservative, citric acid prevents metal ions from reacting with, and thus hastening the degradation of, fats in foods. It is also used in the production of hair rinses and low-pH shampoos and toothpastes. The carboxylic acid family of hydrocarbon derivatives includes a wide array of substances — not only citric acids, but amino acids.
Amino acids combine to make up proteins, one of the principal components in human muscles, skin, and hair. Carboxylic acids are also applied industrially, particularly in the use of fatty acids for making soaps, detergents, and shampoos. As with acids, they have many household uses, in substances such as baking soda.
However, ammonia, or NH3, acts like a base in aqueous solutions, even. Acid–base reaction, a type of chemical process typified by the exchange of one or but do not donate hydrogen ions (aluminum chloride, AlCl3, and the silver ion AG+). Other properties associated at an early date with acids were their solvent, Not all substances that contain hydrogen, however, are acids, and the first. Weak acids usually have a pH close to 7 (). Bases are compounds that break up into hydroxide (OH-) ions and another compound when "3 substances that contain bases of dating" in an.
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