In acidic soils, the blossoms of Hydrangea macrophylla room blue; in alkaline soils, the flowers are pink.

You are watching: The word acid comes from the latin word

The indigenous "acid" comes from the Latin acidus an interpretation "sour." In chemistry, however, the term acid has a an ext specific meaning.

An acid (often stood for by the generic formula HA) is any substance the in solution tastes sour, produces a prickling or burning emotion on call with the skin, changes the color of indicators (e.g. Reddens blue litmus paper), reacts through some metals to liberate hydrogen, reacts through bases to kind salt and water, promotes particular chemical reaction (e.g. A chemical reaction accelerated by the addition of an acid; the acid itself not being spend in the reaction, dubbed acid catalysis), and gives a equipment with a pH of less than 7.0.

Acids and bases match each other. As soon as combined, lock neutralize each various other to form salts. Acids and bases and the reactions between them exemplify the ubiquitousness the complementary bag in the herbal world—plus and also minus, male and also female (the "yang" and "yin" of eastern philosophy)—whose interactions produce the dynamism and also multiform existences populating the universe.

Acids are vital for life, and also many take place naturally. Because that example, our stomach produce hydrochloric acid (HCl) to help digestion. Mountain are likewise widely provided in industries and also are in a large number that foods and also beverages. However, countless acids space poisonous, and can cause severe burns.

Examples that acids encompass the inorganic substances, also known as mineral acids—compounds composed of hydrogen and also a nonmetal aspect or radical the does no contain carbon atoms.(e.g. Sulfuric, hydrochloric, nitric, and phosphoric acids)—and the organic acids i beg your pardon are current in many fruits and other foods (e.g. Citric mountain in lemons, oranges, and grapefruits; malic acid, in apples; lactic acid, in sour-milk products; and acetic acid, in vinegar).

Acid-base extractionAcid dissociation constantAcidity functionProton affinitySelf-ionization the waterAcids:Mineral acidsOrganic acidsStrong acidsSuperacidsWeak acidsBases:Organic basesSuperbasesNon-nucleophilic basesWeak bases

Definitions of acids and bases

Acids and also bases kind complementary pairs, so their interpretations need to be taken into consideration together. There room three typical groups of definitons: the Arrhenius, the Brønsted-Lowry and also the Lewis definitions, in bespeak of raising generality.

Brønsted-Lowry: according to this definition, an acid is a substance the donates hydrogen ions in solution. Because the hydrogen ion (H+, hydrogen nucleus) is merely a proton, the Brønsted-Lowry mountain is also referred to as a proton donor. The acid is said to be dissociated after the proton is donated. The part of the acid that has actually lost a proton have the right to now act as a basic (or proton acceptor), and also it is dubbed the "conjugate base" the the acid. Brønsted and Lowry formulated this definition, which has water-insoluble building material not had in the Arrhenius definition.

The Brønsted-Lowry definition, although no the most basic one, is the many widely offered definition. The toughness of one acid may be construed using this an interpretation by the stability of hydronium and also the solvated conjugate base upon dissociation. Boosting stability the the conjugate base will rise the acidity of a compound. This principle of acidity is used frequently for organic acids such together acetic acid. The molecular orbit description, where the unfilled proton orbit overlaps with a lone pair, is linked to the Lewis definition.

Solutions of weak acids and also salts of your conjugate bases type buffer solutions, that is a equipment of a weak acid and also its conjugate base the resist readjust in pH.

Acid/base solution are different from oxidization (oxidation-reduction) reactions in the there is no readjust in oxidation state.


Generally, acids have the following properties:

Taste: Acids normally are cake when dissolved in water.Touch: Acids produce a stinging feeling, particularly strong acids.Litmus test: one acid transforms blue litmus paper red.


Acids are named according to their anions. That ionic suffix is dropped and replaced through a new suffix (and sometimes prefix), according to the table below. For example, HCl has chloride as its anion, so the -ide suffix provides it take it the type hydrochloric acid.

Anion PrefixAnion SuffixAcid PrefixAcid SuffixExample
perateperic acidperchloric acid (HClO4)
ateic acidchloric mountain (HClO3)
iteous acidchlorous mountain (HClO2)
hypoitehypoous acidhypochlorous mountain (HClO)
idehydroic acidhydrochloric acid (HCl)

Chemical characteristics

In water, the complying with equilibrium occurs between an mountain (HA) and also the water, which acts together a base:

HA(aq) + H2O(l) ⇌ H3O+(aq) + A-(aq)

The acidity continuous (or mountain dissociation constant) is the equilibrium consistent that suggests the level to which hydrogen ion dissociate native an acid.

Ka=\displaystyle K_a=<\mboxH_3\mboxO^+>\cdot \over
\cdot \over }}" />

Strong acids are those that almost fully dissociate in water. Castle have huge Ka values; hence, the acid dissociation equilibrium lies 100% come the right, which means that over there are mainly H3O+ and also A- ion in solution with a an extremely minute amount of undissociated HA molecules.

Common strong acids room perchloric acid (HClO4), hydrochloric acid (HCl), hydrobromic mountain (HBr), hydroiodic mountain (HI), nitric mountain (HNO3), and sulphuric mountain (H2SO4). For example, the Ka worth for hydrochloric mountain (HCl) is 107.

Weak acids space those that partly dissociate in water. They have tiny Ka values; therefore, only a small percent that protons room donated to water, keeping the mountain dissociation equilibrium come the left. The systems mainly consists of undissociated HA molecules with very small H3O+ and also A- ions. Typical weak acids are nitrous acid (HNO2), hydrofluoric mountain (HF), and also acetic mountain (CH3CO2H). For example, the Ka worth for acetic acid is 1.8 x 10-5.

Note on terms used:

In aqueous solution, the water is protonated to kind hydronium ion, H3O+(aq). This is often abbreviated together H+(aq) also though the price is not chemically correct.The term "hydroxide ion" (OH-) is also called hydroxyl ion.The strength of an acid is measure by its mountain dissociation constant (Ka) or equivalently that is pKa (pKa= - log(Ka)).

Polyprotic acids

Polyprotic acids are able come donate more than one proton per acid molecule, in comparison to monoprotic mountain that just donate one proton every molecule. Specific types of polyprotic acids have much more specific names, such together diprotic acid (two potential proton to donate) and also triprotic acid (three potential proton to donate).

A monoprotic acid can undergo one dissociation (sometimes dubbed ionization) as follows and also simply has actually one acid dissociation constant as presented above:

HA(aq) + H2O(l) ⇌ H3O+(aq) + A−(aq)         Ka

A diprotic mountain (here symbolized by H2A) can undergo one or two dissociations depending upon the pH. Each dissociation has its very own dissociation constant, Ka1 and also Ka2.

H2A(aq) + H2O(l) ⇌ H3O+(aq) + HA−(aq)       Ka1HA−(aq) + H2O(l) ⇌ H3O+(aq) + A2−(aq)       Ka2

The an initial dissociation continuous is commonly greater than the second; i.e., Ka1 > Ka2 . For example, sulfuric mountain (H2SO4) have the right to donate one proton to kind the bisulfate anion (HSO4−), for which Ka1 is an extremely large; then it have the right to donate a second proton to type the sulfate anion (SO42−), within the Ka2 is intermediate strength. The large Ka1 because that the an initial dissociation renders sulfuric a strong acid. In a comparable manner, the weak turbulent carbonic mountain (H2CO3) have the right to lose one proton to type bicarbonate anion (HCO3−) and also lose a second to kind carbonate anion (CO32−). Both Ka values room small, however Ka1 > Ka2 .

A triprotic acid (H3A) can undergo one, two, or 3 dissociations and has 3 dissociation constants, where Ka1 > Ka2 > Ka3 .

H3A(aq) + H2O(l) ⇌ H3O+(aq) + H2A−(aq)        Ka1H2A−(aq) + H2O(l) ⇌ H3O+(aq) + HA2−(aq)       Ka2HA2−(aq) + H2O(l) ⇌ H3O+(aq) + A3−(aq)         Ka3

An inorganic example of a triprotic mountain is orthophosphoric mountain (H3PO4), typically just called phosphoric acid. All 3 protons deserve to be successively shed to yield H2PO4−, climate HPO42−, and finally PO43− , the orthophosphate ion, typically just dubbed phosphate. An organic instance of a triprotic mountain is citric acid, which can successively lose three proton to finally kind the citrate ion. Also though the location of the proton on the original molecule may be equivalent, the succeeding Ka values will differ because it is energetically less favorable to lose a proton if the conjugate base is an ext negatively charged.


Neutralization is the reaction in between an acid and also a base, developing a salt and also water; because that example, hydrochloric acid and also sodium hydroxide form sodium chloride and water:

HCl(aq) + NaOH(aq) → H2O(l) + NaCl(aq)

Neutralization is the communication of titration, whereby a pH indicator shows an equivalence point when the same variety of moles the a base have been added to one acid.

Weak acid/weak basic equilibria

In bespeak to shed a proton, that is necessary that the pH of the mechanism rise above the pKa of the protonated acid. The reduced concentration the H+ in that simple solution move the equilibrium in the direction of the conjugate base form (the deprotonated kind of the acid). In lower-pH (more acidic) solutions, over there is a high sufficient H+ concentration in the equipment to reason the mountain to continue to be in its protonated form, or to protonate that conjugate base (the deprotonated form).

Acidification that the environment

Acidification is the process whereby a compound is added to a solution, resulting in a drop in the pH that the solution. One example is once the air pollution of air—mainly sulfur dioxide and also nitrogen oxides—is converted right into acidic substances.

This "acid rain" is best known for the damages it reasons to forests and also lakes. It likewise damages freshwater and seaside ecosystems, soils, and also even ancient historical monuments.

Sulfur dioxide and also the nitrogen oxides are largely emitted by burn fossil fuels. The 1990s witnessed these emissions drop substantially, many thanks to a mix of europe Directives forcing the installation of desulfurisation systems, the relocate away indigenous coal as a fossil fuel, and major economic restructuring in the brand-new German Lander.

See more: Where Did Communists Gain Power In Latin America, Communism In Latin America

Acidification is nonetheless still a significant environmental difficulty in Europe. It is a cross-border issue, requiring combination initiatives throughout countries and sectors. This section brings together the EEA’s reports ~ above the scale of the problem and also the efficiency of the options tried come date.<1>