Polyprotic acids
Polyprotic acids are able to donate more than one proton per acid molecule, in contrast to monoprotic acids that only donate one proton per molecule. Specific types of polyprotic acids have more specific names, such as diprotic acid (two potential protons to donate) and triprotic acid (three potential protons to donate).
A diprotic acid (here symbolized by H2A) can undergo one or two dissociations depending on the pH. Each dissociation has its own dissociation constant, Ka1 and Ka2.
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- H2A(aq) + H2O(l) H3O+(aq) + HA−(aq) Ka1
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- HA−(aq) + H2O(l) H3O+(aq) + A2−(aq) Ka2
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The first dissociation constant is typically greater than the second; i.e., Ka1 > Ka2. For example, sulfuric acid Sulfuric acid, H2SO4, is a strong mineral acid. It is soluble in water at all concentrations. Sulfuric acid has many applications, and is one of the top products of the chemical industry. World production in 2001 was 165 million tonnes, with an approximate value of US$8 billion. Principal uses include lead-acid batteries for cars and other (H2SO4) can donate one proton to form the bisulfate In inorganic chemistry, a sulfate is a salt of sulfuric acid anion (HSO4−), for which Ka1 is very large; then it can donate a second proton to form the sulfate In inorganic chemistry, a sulfate is a salt of sulfuric acid anion (SO42−), wherein the Ka2 is intermediate strength. The large Ka1 for the first dissociation makes sulfuric a strong acid. In a similar manner, the weak unstable carbonic acid Carbonic acid has the formula H2CO3. It is also a name sometimes given to solutions of carbon dioxide in water, which contain small amounts of H2CO3. The salts of carbonic acids are called bicarbonates (or hydrogen carbonates) and carbonates. It is a weak acid. Carbonic acid should never be confused with carbolic acid, an antiquated name for (H2CO3) can lose one proton to form bicarbonate In inorganic chemistry, bicarbonate is an intermediate form in the deprotonation of carbonic acid. Its chemical formula is HCO3− anion (HCO3−) and lose a second to form carbonate In chemistry, a carbonate is a salt or ester of carbonic acid, characterized by the presence of the carbonate ion, CO2−3 or a carbonate functional group O=C2 anion (CO32−). Both Ka values are small, but Ka1 > Ka2 .
A triprotic acid (H3A) can undergo one, two, or three dissociations and has three dissociation constants, where Ka1 > Ka2 > Ka3.
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- H3A(aq) + H2O(l) H3O+(aq) + H2A−(aq) Ka1
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- H2A−(aq) + H2O(l) H3O+(aq) + HA2−(aq) Ka2
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- HA2−(aq) + H2O(l) H3O+(aq) + A3−(aq) Ka3
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An inorganic Traditionally, inorganic compounds are considered to be of a mineral, not biological, origin. Complementarily, most organic compounds are traditionally viewed as being of biological origin. Over the past century, the precise classification of inorganic vs organic compounds has become less important to scientists, primarily because the majority of example of a triprotic acid is orthophosphoric acid (H3PO4), usually just called phosphoric acid Phosphoric acid, also known as orthophosphoric acid or phosphoric acid, is a mineral (inorganic) acid having the chemical formula H3P . All three protons can be successively lost to yield H2PO4−, then HPO42−, and finally PO43−, the orthophosphate ion, usually just called phosphate A phosphate, an inorganic chemical, is a salt of phosphoric acid. Inorganic phosphates are mined to obtain phosphorus for use in agriculture and industry. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry. An organic An organic compound is any member of a large class of chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of compounds such as carbonates, simple oxides of carbon and cyanides, as well as the allotropes of carbon, are considered inorganic. The division between "organic" and " example of a triprotic acid is citric acid, which can successively lose three protons to finally form the citrate ion. Even though the positions of the protons on the original molecule may be equivalent, the successive Ka values will differ since it is energetically less favorable to lose a proton if the conjugate base is more negatively charged.
See also: Acid dissociation constant#Polyprotic acids An acid dissociation constant, Ka, is a quantitative measure of the strength of an acid in solution. It is the equilibrium constant for a chemical reaction known as dissociation in the context of acid-base reactions. The equilibrium can be written symbolically as:<<Table of Contents An acid is traditionally considered any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion activity greater than in pure water, i.e. a pH less than 7.0. That approximates the modern definition of Johannes Nicolaus Brønsted and Martin Lowry, who independently defined an acid as a compound which donates a hydrogen | Next>> | Show All>>
