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A weak acid is an acid
Acid

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....
 that dissociates incompletely and does not release all of its hydrogen
Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the chemical symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly combustion and explosive Diatomic molecule gas with the molecular formula H2....
s in a solution i.e it does not completely donate all of its proton
Proton

The proton is a subatomic particle with an electric charge of +1 elementary charge. It is found in the nucleus of each atom but is also stable by itself and has a second identity as the hydrogen ion, H+....
s. These acids have higher pKa
PKA

PKA or pKa may be:* Protein kinase A, a cAMP activated protein kinase* pKa, the symbol for Acid dissociation constant...
 compared to strong acids, which release all of their hydrogens when dissolved in water.

While strong acid
Strong acid

A strong acid is an acid that ionizes completely in an aqueous solution , or in other terms, with a acid dissociation constant < -1.74. This generally means that in aqueous solution at standard temperature and pressure, the concentration of hydronium ions is equal to the concentration of strong acid introduced to the solution....
s are generally assumed to be the most corrosive
Corrosive

A corrosive substance is one that will destroy or irreversibly damage another substance with which it comes in contact. The main hazards to people include damage to eyes, skin and tissue under the skin, but inhalation or ingestion of a corrosive substance can damage the respiratory and gastrointestinal tracts....
, this is not always true. The carborane
Carborane

A carborane is a cluster composed of boron and carbon atoms. Like many of the related boranes, these clusters are polyhedra and are similarly classified as closo-, nido-, arachno-, hypho-, etc....
 superacid
Superacid

A superacid is an acid with an acidity greater than that of 100% sulfuric acid, which has a Hammett acidity function of -12. Commercially available superacids include trifluoromethanesulfonic acid , also known as triflic acid, and fluorosulfuric acid , both of which are about a thousand times stronger than sulfuric acid....
 (H(CHB11Cl11), which is one million times stronger than sulfuric acid
Sulfuric acid

Sulfuric acid, hydrogen2sulfuroxygen4, 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....
, is entirely non-corrosive, whereas the weak acid hydrofluoric acid
Hydrofluoric acid

Hydrofluoric acid is a solution of hydrogen fluoride in water. While it is extremely corrosive and dangerous to handle, it is technically a weak acid....
 (HF) is extremely corrosive and can dissolve, among other things, glass and all metals except iridium
Iridium

Iridium is the chemical element with atomic number 77, and is represented by the symbol Ir. A very hard, brittle, silvery-white transition metal of the platinum group, iridium is the second densest element and is the most corrosion-resistant metal, even at temperatures as high as 2000 ?C....
.

acids do not ionize
Ionization

Ionization is the physics process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or other ions....
 in a solution
Solution

In chemistry, a solution is a homogeneous mixture composed of two or more substances. In such a mixture, a solute is dissolved in another substance, known as a solvent....
 to a significant extent; that is, if the acid was represented by the general formula HA, then in aqueous solution a significant amount of undissociated HA still remains.






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Encyclopedia


A weak acid is an acid
Acid

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....
 that dissociates incompletely and does not release all of its hydrogen
Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the chemical symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly combustion and explosive Diatomic molecule gas with the molecular formula H2....
s in a solution i.e it does not completely donate all of its proton
Proton

The proton is a subatomic particle with an electric charge of +1 elementary charge. It is found in the nucleus of each atom but is also stable by itself and has a second identity as the hydrogen ion, H+....
s. These acids have higher pKa
PKA

PKA or pKa may be:* Protein kinase A, a cAMP activated protein kinase* pKa, the symbol for Acid dissociation constant...
 compared to strong acids, which release all of their hydrogens when dissolved in water.

While strong acid
Strong acid

A strong acid is an acid that ionizes completely in an aqueous solution , or in other terms, with a acid dissociation constant < -1.74. This generally means that in aqueous solution at standard temperature and pressure, the concentration of hydronium ions is equal to the concentration of strong acid introduced to the solution....
s are generally assumed to be the most corrosive
Corrosive

A corrosive substance is one that will destroy or irreversibly damage another substance with which it comes in contact. The main hazards to people include damage to eyes, skin and tissue under the skin, but inhalation or ingestion of a corrosive substance can damage the respiratory and gastrointestinal tracts....
, this is not always true. The carborane
Carborane

A carborane is a cluster composed of boron and carbon atoms. Like many of the related boranes, these clusters are polyhedra and are similarly classified as closo-, nido-, arachno-, hypho-, etc....
 superacid
Superacid

A superacid is an acid with an acidity greater than that of 100% sulfuric acid, which has a Hammett acidity function of -12. Commercially available superacids include trifluoromethanesulfonic acid , also known as triflic acid, and fluorosulfuric acid , both of which are about a thousand times stronger than sulfuric acid....
 (H(CHB11Cl11), which is one million times stronger than sulfuric acid
Sulfuric acid

Sulfuric acid, hydrogen2sulfuroxygen4, 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....
, is entirely non-corrosive, whereas the weak acid hydrofluoric acid
Hydrofluoric acid

Hydrofluoric acid is a solution of hydrogen fluoride in water. While it is extremely corrosive and dangerous to handle, it is technically a weak acid....
 (HF) is extremely corrosive and can dissolve, among other things, glass and all metals except iridium
Iridium

Iridium is the chemical element with atomic number 77, and is represented by the symbol Ir. A very hard, brittle, silvery-white transition metal of the platinum group, iridium is the second densest element and is the most corrosion-resistant metal, even at temperatures as high as 2000 ?C....
.

Explanation

Weak acids do not ionize
Ionization

Ionization is the physics process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or other ions....
 in a solution
Solution

In chemistry, a solution is a homogeneous mixture composed of two or more substances. In such a mixture, a solute is dissolved in another substance, known as a solvent....
 to a significant extent; that is, if the acid was represented by the general formula HA, then in aqueous solution a significant amount of undissociated HA still remains. Weak acids in water dissociate as

The equilibrium concentrations of reactants and products are related by the Acidity constant expression, (Ka):

The greater the value of Ka, the more the formation of H+ is favored, and the lower the pH
PH

pH is a measure of the Acid or Base of a solution. It is defined as the cologarithm of the Activity of dissolved hydrogen ions . Hydrogen ion activity coefficients cannot be measured experimentally, so they are based on theoretical calculations....
 of the solution. The Ka of weak acids varies between 1.8×10-16 and 55.5. Acids with a Ka less than 1.8×10-16 are weaker acids than water.

Examples

The vast majority of acids are weak acids. Organic acids are a large subset of weak acids. However, there are some mineral acid
Mineral acid

A mineral acid is an acid derived from one or more inorganic chemistry compounds. A mineral acid does not contain any carbon atoms and all mineral acids release hydrogen ions when dissolved in water....
s in this field.
  • acetic acid
    Acetic acid

    Acetic acid, CH3COOH, also known as ethanoic acid, is an organic acid which gives vinegar its sour taste and pungent smell. Pure, water-free acetic acid is a colourless liquid that absorbs water from the environment , and freezes at 16.7 Celsius to a colourless crystalline solid....
  • citric acid
    Citric acid

    Citric acid is a weak organic chemistry acid, and it is a natural preservative and is also used to add an acidic, or sour, taste to foods and soft drinks....
  • boric acid
    Boric acid

    Boric acid, also called boracic acid or orthoboric acid or Acidum Boricum, is a weak acid often used as an antiseptic, insecticide, flame retardant, in nuclear power plants to control the fission rate of uranium, and as a precursor of other chemical compounds....
  • phosphoric acid
    Phosphoric acid

    Phosphoric acid, also known as orthophosphoric acid or phosphoric acid, is a mineral acid having the chemical formula Hydrogen3PhosphorusOxygen4....
  • hydrofluoric acid
    Hydrofluoric acid

    Hydrofluoric acid is a solution of hydrogen fluoride in water. While it is extremely corrosive and dangerous to handle, it is technically a weak acid....


See also

  • Strong acid
    Strong acid

    A strong acid is an acid that ionizes completely in an aqueous solution , or in other terms, with a acid dissociation constant < -1.74. This generally means that in aqueous solution at standard temperature and pressure, the concentration of hydronium ions is equal to the concentration of strong acid introduced to the solution....
  • Weak base
    Weak base

    In chemistry, a weak base is a chemical base that does not ionize fully in an aqueous solution. As Bronsted-Lowry bases are proton acceptors, a weak base may also be defined as a chemical base in which protonation is incomplete....


External links

  • on weak acids and bases