Greetings Savants and Dilettante of the CS art, To continue:
The degree of dissociation refers to the fraction of solute molecules which yields completely free ions. It is these free ions which contribute to the conductivity of a solution. Since the degree of dissociation is less than one, either the solute did not completely dissociate into ions or some of the dissociated ions were not free to conduct the current, or both. The latter effect occurs because ions of opposite charge may be in the vicinity of one another and, due to electrostatic interaction, may stay in the vicinity of one another to form units called "ion-pairs". This concept was introduced by Bjerrum in 1926. These ion-pairs are not molecules, but behave in solution as discrete units. Strong electrolytes may be completely dissociated into ions, but may have ion-pairs as well as free ions in solution. A solution of a weak electrolyte may contain not only non-ionized solute molecules and solute ions, but ion-pairs of solute. It should be emphasized that these ion-pairs behave in solution as discrete neutral units and do not contribute to the conductivity. The fraction of undissociated solute, (1-alfa), includes both non-ionized solute molecules and solute ion-pairs. It is found that the extent of formation of ion-pairs depends on the concentration of solute, the charge on the ions, and the dielectric constant of the solvent. As the concentration is increased, the number of oppositely charged ions about a given ion is greater, so the chance for ion-pair formation is increased. The larger the charge on an ion, the greater the coulombic force between oppositely charged ions, so ion-pair formation is favored. The lower the dielectric constant of a solvent, the greater the coulombic force between oppositely charged ions, so the greater the probability of ion-pair formation. A look at acids and bases ( acids and alkalines). Some theories. The classification of substances into acids and bases has undergone many revisions over the years, the classifications have been refined and polished as it were by adding useful changes and additions to reflect the continuing improvement in our understanding of acids and bases. The properties first noted for acidic substances were that their water solutions had a sour taste, changed the color of litmus dye from blue to red, neutralized bases, and reacted with active metals to form hydrogen gas. The properties of basic substances in water solution have a bitter taste, change the color of litmus dye from red to blue, neutralize acids, and feel slippery. Arrhenius defined an acid as a substance that would dissociate to yield a hydrogen ion, and a base as one that would dissociate to yield a hydroxyl ion in a water solution. So according to Arrhenius, neutralization would be represented by H+1 + OH-1 >>>>H2O . Arrhenius's ideas had to be extended for several reasons. As mentioned previously, the proton is nonexistent in aqueous solutions. It conbines with a molecule of water to form a hydronium ion, H3O+1. Also some acids are capable of dissociating a proton in solvents other than water. In addition, compounds other than hydrogen-containing compounds are capable of releasing hydronium ions by reacting with water. Such compounds are called acid anhydrides. To broaden Arrhenius's concept of acids and bases, Bronsted and Lowry, in 1923 noted that an acid reacted with water in a manner opposite to that of a base. Hydrogen chloride, an acid, donates a proton to a water molecule, while ammonia, a base, accepts a proton from a water molecule. On this basis they defined an acid as any substance that can donate a proton to another substance and a base as any substance that can accept a proton from another substance. This means that water can be an acid or a base, depending on the properties of the substance being added to the water. This leads us to the concept that when an acid reacts with a base there will be two conjugate acid-base pairs (ion-pairs). The strength of an acid is a measure of its tenency to donate a proton, and the strength of a base is a measure of its tendency to accept a proton. Since a strong acid completely dissociates into a proton, its conjugate base cannot hold onto the proton and hence it is a weak base. In general, the stronger the acid, the weaker its conjugate base, and the stronger the base, the weaker its conjugate acid. -- to be continued-- Bless you Bob Lee -- oozing on the muggy shore of the gulf coast [email protected] -- The silver-list is a moderated forum for discussion of colloidal silver. To join or quit silver-list or silver-digest send an e-mail message to: [email protected] -or- [email protected] with the word subscribe or unsubscribe in the SUBJECT line. To post, address your message to: [email protected] Silver-list archive: http://escribe.com/health/thesilverlist/index.html List maintainer: Mike Devour <[email protected]>
