Skip to main content
Select Source:

dissociation

dissociation, in chemistry, separation of a substance into atoms or ions. Thermal dissociation occurs at high temperatures. For example, hydrogen molecules (H2) dissociate into atoms (H) at very high temperatures; at 5,000°K about 95% of the molecules in a sample of hydrogen are dissociated into atoms. Electrolytic dissociation occurs when an electrolyte is dissolved in a polar solvent. For example, when hydrogen chloride, HCl, is dissolved in water to form hydrochloric acid, most of its molecules dissociate into hydrogen ions (H+) and chloride ions (Cl-). Some pure substances spontaneously dissociate. For example, in pure water some of the molecules dissociate to form hydrogen ions and hydroxyl ions. Dissociation is generally reversible; when the atoms or ions of the dissociated substance are returned to the original conditions, they recombine in the original form of the substance. The dissociation constant is a measure of the extent of dissociation. It is represented by the symbol K. In the simplest case, if a substance AB dissociates into two parts A and B and the concentrations of AB, A, and B are represented by [AB], [A], and [B], then K=[A]×[B]/[AB]. The dissociation constant is measured at equilibrium, and its value is usually affected by changes in temperature.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"dissociation." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. 11 Nov. 2018 <https://www.encyclopedia.com>.

"dissociation." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. (November 11, 2018). https://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/dissociation

"dissociation." The Columbia Encyclopedia, 6th ed.. . Retrieved November 11, 2018 from Encyclopedia.com: https://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/dissociation

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

dissociate

dis·so·ci·ate / diˈsōshēˌāt; -ˈsōsē-/ • v. [tr.] 1. disconnect or separate (used esp. in abstract contexts) : voices should not be dissociated from their social context. ∎  (dissociate oneself from) declare that one is not connected with or a supporter of (someone or something): he took pains to dissociate himself from the religious radicals. ∎  [intr.] become separated or disconnected: the area would dissociate from the country. ∎  (usu. be dissociated) Psychiatry split off (a component of mental activity) to act as an independent part of mental life. 2. (usu. be dissociated) Chem. cause (a molecule) to split into separate smaller atoms, ions, or molecules, esp. reversibly: these compounds are dissociated by solar radiation to yield atoms of chlorine. ∎  [intr.] (of a molecule) undergo this process. DERIVATIVES: dis·so·ci·a·tive / -ˌātiv; -shətiv/ adj.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"dissociate." The Oxford Pocket Dictionary of Current English. . Encyclopedia.com. 11 Nov. 2018 <https://www.encyclopedia.com>.

"dissociate." The Oxford Pocket Dictionary of Current English. . Encyclopedia.com. (November 11, 2018). https://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/dissociate-0

"dissociate." The Oxford Pocket Dictionary of Current English. . Retrieved November 11, 2018 from Encyclopedia.com: https://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/dissociate-0

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

dissociation

dissociation (dis-soh-si-ay-shŏn) n. (in psychiatry) the process whereby thoughts and ideas can be split off from consciousness and may function independently, allowing conflicting opinions to be held at the same time about the same object. Dissociation may be the main factor in cases of dissociative fugue and multiple personalities (see dissociative disorder).
dissociative (dis-soh-shă-tiv) adj.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"dissociation." A Dictionary of Nursing. . Encyclopedia.com. 11 Nov. 2018 <https://www.encyclopedia.com>.

"dissociation." A Dictionary of Nursing. . Encyclopedia.com. (November 11, 2018). https://www.encyclopedia.com/caregiving/dictionaries-thesauruses-pictures-and-press-releases/dissociation

"dissociation." A Dictionary of Nursing. . Retrieved November 11, 2018 from Encyclopedia.com: https://www.encyclopedia.com/caregiving/dictionaries-thesauruses-pictures-and-press-releases/dissociation

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

dissociate

dissociate XVII. f. pp. stem of L. dissociāre, f. DIS- 1 + sociāre join together, f. socius companion; see -ATE 3.
So dissociation XVII.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"dissociate." The Concise Oxford Dictionary of English Etymology. . Encyclopedia.com. 11 Nov. 2018 <https://www.encyclopedia.com>.

"dissociate." The Concise Oxford Dictionary of English Etymology. . Encyclopedia.com. (November 11, 2018). https://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/dissociate-1

"dissociate." The Concise Oxford Dictionary of English Etymology. . Retrieved November 11, 2018 from Encyclopedia.com: https://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/dissociate-1

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

dissociate

dissociate •labiate •irradiate, radiate •mediate • ideate • repudiate •palliate, retaliate •affiliate, ciliate, conciliate, humiliate •exfoliate, foliate •nucleate • permeate • delineate •calumniate • expiate •expatriate, repatriate •recreate • inebriate •aureate, excoriate •procreate •appropriate, expropriate, impropriate, misappropriate •infuriate, luxuriate •asphyxiate • nauseate •annunciate, enunciate •instantiate, substantiate, transubstantiate •differentiate, potentiate •expatiate, ingratiate, satiate •appreciate, depreciate •initiate, officiate, propitiate, vitiate •associate, dissociate, negotiate •excruciate • aviate •abbreviate, alleviate, deviate •obviate • exuviate • inchoate •actuate • perpetuate • effectuate •habituate • fluctuate • punctuate •graduate • individuate • menstruate •accentuate, eventuate •evacuate •evaluate, valuate •superannuate • infatuate •attenuate, extenuate •insinuate • situate

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"dissociate." Oxford Dictionary of Rhymes. . Encyclopedia.com. 11 Nov. 2018 <https://www.encyclopedia.com>.

"dissociate." Oxford Dictionary of Rhymes. . Encyclopedia.com. (November 11, 2018). https://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/dissociate

"dissociate." Oxford Dictionary of Rhymes. . Retrieved November 11, 2018 from Encyclopedia.com: https://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/dissociate

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

Dissociation

Dissociation

Dissociation of water

Dissociation of acid and bases

Dissociation of salts

Resources

Dissociation is the process by which a molecule separates into ions. It may also be called ionization, but because there are other ways to form ions, the term dissociation is preferred. Substances dissociate to different degrees, ranging from substances that dissociate very slightly, such as water, to those that dissociate almost completely, such as strong acids and bases. The extent to which a substance dissociates is directly related to its ability to conduct an electric current. A substance that dissociates only slightly (as in the case of a weak acid like vinegar) is a weak electrolyte, as it conducts electricity poorly. A substance that is almost completely dissociated (such as table salt, NaCl, or hydrochloric acid, HCl) conducts electricity very well. The ability to conduct electricity is based on the ionic makeup of a substance. The more ions a substance contains, the better it will conduct electricity.

Dissociation of water

Pure water dissociates only slightly. About one water molecule out of every 10 million is dissociated and the rest remain in nondissociated (or molecular) form. This ionization of water (sometimes called self-or auto-ionization) can be summarized by the following formula. Pure water produces very few ions from its dissociation and so is a poor electrolyte, or conductor of electricity.

The following equation describes the process in which a water molecule ionizes (separates into ions) to form a hydrogen ion (proton) and a hydroxide ion.

H2O H+ + OH

Another way to describe the dissociation of water is as follows:

H2O + H2O H3O+ + OH

where two water molecules form a hydronium ion (essentially a water molecule with a proton attached) and a hydroxide ion.

Dissociation of acid and bases

Acids are molecules that can donate protons (hydrogen or H+ ions) to other molecules. An alternate view is that an acid is a substance that will cause an increase in the concentration of hydrogen ions in a solution.

The dissociation of a strong acid (such as hydrochloric acid, HCl) is essentially 100%.

HCI H+ + CI

In this case, nearly every HCl molecule is dissociated (separated into ions). When any substance dissociates, both positive and negative ions will be formed. In this case, the positive ion (cation) is a proton, and the negative ion (anion) is the chloride ion. A strong acid is a strong electrolyte and a good conductor of an electric current. In the case of a strong base, nearly 100% of the molecules are dissociated as well, and

strong bases (such as sodium hydroxide, NaOH) are also strong electrolytes.

NaOH Na+ + OH

A weak acid, such as hydrofluoric acid is only slightly dissociated. Many more of the molecules exist in the molecular (undissociated or unionized) form than in the ionized form. Since it forms fewer ions, a weak acid will be a weak electrolyte.

HFH+ + F-

In the case of a weak base, such as aluminum hydroxide, Al(OH)3, only a small percent of molecules ionize, producing few ions, and making weak bases weak electrolytes as well.

Al(OH)3 Al+ 3 + 3OH

In any dissociation reaction, the total charges will mathematically cancel each other out. The case above has a positive three charge on the aluminum ion and a negative one charge on each of the three hydroxide ions, for a total of zero.

Dissociation of salts

Salts are the product of the neutralization reaction between an acid and a base (the other product of this neutralization reaction being water). Salts that are soluble in water dissociate into their ions and are electrolytes. Salts that are insoluble or only slightly soluble in water form very few ions in solution and are nonelectrolytes or weak electrolytes. Sodium chloride, NaCl, is a water-soluble salt that dissociates totally in water.

NaClNa+ + Cl-

The process by which this takes place involves the surrounding of each positive sodium ion and each negative chloride ion by water molecules. Water molecules are polar and have two distinct ends, each with a partial positive or negative charge. Since opposite charges attract, the negative end of the water molecule will face the positive sodium ion and the positive end will face the negative ion. This process, illustrated in Figure 1, is known as solvation.

Resources

PERIODICALS

Carafoli, Ernest, and John Penniston. The Calcium Signal, Scientific American 253 (November 1985).

Ezzell, Carol. Salts Technique for Tickling the Taste Buds, Science News 140 (November 2, 1991).

OTHER

Shodor Education Foundation, Inc. AcidBase Chemistry <http://www.shodor.org/UNChem/basic/ab/> (accessed November 18, 2006).

Purdue University, College of Science, Chemical Education Division Groups Water, Acids, and Bases <http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch17/water.php> (accessed November 1, 2006).

Louis Gotlib

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Dissociation." The Gale Encyclopedia of Science. . Encyclopedia.com. 11 Nov. 2018 <https://www.encyclopedia.com>.

"Dissociation." The Gale Encyclopedia of Science. . Encyclopedia.com. (November 11, 2018). https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/dissociation

"Dissociation." The Gale Encyclopedia of Science. . Retrieved November 11, 2018 from Encyclopedia.com: https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/dissociation

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

Dissociation

Dissociation

Dissociation is the process by which a molecule separates into ions. It may also be called ionization, but because there are other ways to form ions, the term dissociation is preferred. Substances dissociate to different degrees, ranging from substances that dissociate very slightly, such as water , to those that dissociate almost completely, such as strong acids and bases . The extent to which a substance dissociates is directly related to its ability to conduct an electric current . A substance that dissociates only slightly (as in the case of a weak acid like vinegar) is a weak electrolyte , as it conducts electricity poorly. A substance that is almost completely dissociated (such as table salt , NaCl, or hydrochloric acid, HCl) conducts electricity very well. The ability to conduct electricity is based on the ionic makeup of a substance. The more ions a substance contains, the better it will conduct electricity.

Dissociation of water

Pure water dissociates only slightly. About one water molecule out of every 10 million is dissociated and the rest remain in non-dissociated (or molecular) form. This ionization of water (sometimes called self- or auto-ionization) can be summarized by the following formula. Pure water produces very few ions from its dissociation and so is a poor electrolyte, or conductor of electricity.

The following equation describes the process in which a water molecule ionizes (separates into ions) to form a hydrogen ion (proton ) and a hydroxide ion.

Another way to describe the dissociation of water is as follows:

where two water molecules form a hydronium ion (essentially a water molecule with a proton attached) and a hydroxide ion.

Dissociation of acid and bases

Acids are molecules that can donate protons (hydrogen or H+ ions) to other molecules. An alternate view is that an acid is a substance that will cause an increase in the concentration of hydrogen ions in a solution .

The dissociation of a strong acid (such as hydrochloric acid, HCl) is essentially 100%.

In this case, nearly every HCl molecule is dissociated (separated into ions). When any substance dissociates, both positive and negative ions will be formed. In this case, the positive ion (cation ) is a proton, and the negative ion (anion ) is the chloride ion. A strong acid is a strong electrolyte and a good conductor of an electric current. In the case of a strong base, nearly 100% of the molecules are dissociated as well, and strong bases (such as sodium hydroxide , NaOH) are also strong electrolytes.

A weak acid, such as hydrofluoric acid is only slightly dissociated. Many more of the molecules exist in the molecular (undissociated or unionized) form than in the ionized form. Since it forms fewer ions, a weak acid will be a weak electrolyte.

In the case of a weak base, such as aluminum hydroxide , Al(OH)3, only a small percent of molecules ionize, producing few ions, and making weak bases weak electrolytes as well.

In any dissociation reaction, the total charges will mathematically cancel each other out. The case above has a positive three charge on the aluminum ion and a negative one charge on each of the three hydroxide ions, for a total of zero .


Dissociation of salts

Salts are the product of the neutralization reaction between an acid and a base (the other product of this neutralization reaction being water). Salts that are soluble in water dissociate into their ions and are electrolytes. Salts that are insoluble or only slightly soluble in water form very few ions in solution and are nonelectrolytes or weak electrolytes. Sodium chloride , NaCl, is a water-soluble salt that dissociates totally in water.

The process by which this takes place involves the surrounding of each positive sodium ion and each negative chloride ion by water molecules. Water molecules are polar and have two distinct ends, each with a partial positive or negative charge. Since opposite charges attract, the negative end of the water molecule will face the positive sodium ion and the positive end will face the negative ion. This process, illustrated in Figure 1, is known as solvation.

Resources

periodicals

Carafoli, Ernest, and John Penniston. "The Calcium Signal." Scientific American 253 (November 1985).

Ezzell, Carol. "Salt's Technique for Tickling the Taste Buds." Science News 140 (November 2, 1991).


Louis Gotlib

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Dissociation." The Gale Encyclopedia of Science. . Encyclopedia.com. 11 Nov. 2018 <https://www.encyclopedia.com>.

"Dissociation." The Gale Encyclopedia of Science. . Encyclopedia.com. (November 11, 2018). https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/dissociation-0

"Dissociation." The Gale Encyclopedia of Science. . Retrieved November 11, 2018 from Encyclopedia.com: https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/dissociation-0

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.