dissociation

Examples of dissociation in the following topics:

• Dissociation

  • The major characteristic of all dissociative phenomena involves a detachment from reality.
  • Although some dissociative experiences involve memory loss, others do not.
  • At the pathological end of the dissociation spectrum are the dissociative disorders.
  • Psychoactive drugs can often induce a state of temporary dissociation.
  • Pathological dissociation involves the dissociative disorders, including dissociative fugue and depersonalization disorder.

• Acid Dissociation Constant (Ka)

  • The acid dissociation constant (Ka) is the measure of the strength of an acid in solution.
  • Acid dissociation constants are most often associated with weak acids, or acids that do not completely dissociate in solution.
  • The larger the value of pKa, the smaller the extent of dissociation.
  • Acetic acid is a weak acid with an acid dissociation constant $K_a=1.8\times 10^{-5}$ .
  • The acetic acid partially and reversibly dissociates into acetate and hydrogen ions.

• Calculating Percent Dissociation

  • To determine percent dissociation, we first need to solve for the concentration of H+.
  • However, because the acid dissociates only to a very slight extent, we can assume x is small.
  • As we would expect for a weak acid, the percent dissociation is quite small.
  • However, for some weak acids, the percent dissociation can be higher—upwards of 10% or more.
  • Calculate percent dissociation for weak acids from their Ka values and a given concentration.

• Dissociative Disorders

  • More pathological dissociation involves dissociative disorders.
  • These are both examples of dissociation.
  • Dissociation of this sort is fairly normal from time to time; however, there are five types of dissociative disorders which are considered psychopathological: dissociative identity disorder, disociative amnesia, depersonalization/derealization disorder, other specified dissociative disorder, and unspecified dissociative disorder.
  • Dissociative fugue, while it used to be its own diagnosis in the previous DSM-IV-TR, is now subsumed under dissociative amnesia as a specifier (i.e., dissociative amnesia with or without dissociative fugue).
  • The old category of dissociative disorder not otherwise specified is now split into two according to the DSM-5 (2013): other specified dissociative disorder and unspecified dissociative disorder.

• Diprotic and Polyprotic Acids

  • With any polyprotic acid, the first amd most strongly acidic proton dissociates completely before the second-most acidic proton even begins to dissociate.
  • Dissociation does not happen all at once; each dissociation step has its own Ka value, designated Ka1 and Ka2:
  • This first dissociation step of sulfuric acid will occur completely, which is why sulfuric acid is considered a strong acid; the second dissociation step is only weakly dissociating, however.
  • A triprotic acid (H3A) can undergo three dissociations and will therefore have three dissociation constants: Ka1 > Ka2 > Ka3.
  • The following formula shows how to find this fractional concentration of HA-, in which pH and the acid dissociation constants for each dissociation step are known:

• Calculating Equilibrium Concentrations of Polyprotic Acids

  • The first proton's dissociation may be denoted as Ka1 and the constants for successive protons' dissociations as Ka2, etc.
  • Because the first dissociation is so strong, we can assume that there is no measurable H2SO4 in the solution, and the only equilibrium calculations that need be performed deal with the second dissociation step only.
  • At a pH equal to the pKa for a particular dissociation, the two forms of the dissociating species are present in equal concentrations, due to the following mathematical observation.
  • When a weak diprotic acid such as carbonic acid, H2CO3, dissociates, most of the protons present come from the first dissociation step:
  • The above concentration can be used if pH is known, as well as the two acid dissociation constants for each dissociation step; oftentimes, calculations can be simplified for polyprotic acids, however.

• Specialized Equilibrium Constants

  • The value of the dissociation constant of water, KW, is $1.0\times 10^{-14}$.
  • An acid dissociation constant, Ka, is the equilibrium constant for the dissociation of an acid in aqueous solution.
  • Recall that strong acids dissociate completely or almost completely into their ions.
  • The base dissociation constant, Kb, is analogous to the acid dissociation constant.
  • A ball-and-stick model of the dissociation of acetic acid to acetate.

• Weak Acids

  • On average, only about 1 percent of a weak acid solution dissociates in water in a 0.1 mol/L solution.
  • The generalized dissociation reaction is given by:
  • The strength of a weak acid is represented as either an equilibrium constant or a percent dissociation.
  • The first Ka refers to the first dissociation step:
  • The second Ka is 4.69×10−11 (pKa2 = 10.329) and refers to the second dissociation step:

• The Acid Dissociation Constant

  • The acid dissociation constant measures the strength of an acid and is essential for understanding acid-base equilibria in solution.
  • This gives rise to a special equilibrium constant known as theacid dissociation constant, Ka.
  • It is the equilibrium constant for a chemical reaction known as dissociation in the context of acid-base reactions.
  • Therefore, the larger the value of pKa, the smaller the extent of dissociation.
  • A ball-and-stick model of the dissociation of acetic acid to acetate.

• Hallucinogens

  • Hallucinogens affect the levels of serotonin or glutamate in the brain and are divided into psychedelics, dissociatives, and deleriants.
  • Most dissociative drugs simulate a dream-like experience.
  • Primary dissociatives are NMDA antagonists, which block glutamate from entering its receptors and regulating brain function.
  • When used in excess of specified maximum dosages, dextromethorphan acts as a dissociative.
  • It can produce effects similar to the dissociative states created by other dissociative anaesthetics such as ketamine and phencyclidine.