Man's physical universe

xanabras

588 MAN IS MASTERING HIS MATERIAL WORLD

cules of electrolytes dissociate in water solution to form atoms or

groups of atoms which are electrically charged and carry the current

in electrolysis. The metallic ions are positively charged, and the

nonmetallic ions are negatively charged, the charge on the ion being

proportional to its valence.

Electrolytes whose solutions are poor conductors of electricity are

called weak electrolytes, and those whose solutions are good conductors

of electricity are called strong electrolytes.

Since Arrhenius' time many observations have been made that can be

explained best by assuming that strong electrolytes are completely

ionized under all conditions and that weak electrolytes consist of

covalent compounds that are in equilibrium with electrovalent modifications

of these compounds.

The Theory of Electrolytic Dissociation Explains the Properties of

Electrolytes.

1. Properties of Acids, Bases, and Salts Are Due to the Properties

of Their Ions. Solutions of acids have only one thing in common,

that is, hydronium ions, H30+.^ It is concluded, therefore, that the

properties of acids are due to the hydronium ions present in their

solutions. Solutions of those acids which have strongly acid properties

have more hydronium ions present in a given volume than do solutions

of weak acids.

What has been said of acids applies to bases, except that in this case

the characteristic ions are hydroxyl ions, 0H~.

The ionization theory also accounts for the properties of solutions

of acid and basic salts, by stating that such salts dissociate to form

H3O+ ions and 0H~ ions, respectively, in addition to the ions of the

corresponding normal salts.

2. Precipitation. The formation and separation of an insoluble

substance as a product of a chemical reaction is

called precipitation,

the substance thus formed being called a precipitate.

Every solid has a definite solubility, and, if the concentration of

ions of any substance exceeds that present in a saturated solution,

precipitation will

take place.

3. Why Reactions Go to Completion. Many reactions do not go to

completion; that is, they are reversible.

The products of such reactions

react with each other to form the original reactants, and before long a

condition of equilibrium between the original reaction and the reverse

reaction is set up.

When such an equilibrium exists, the reactants are

'

HsO"*" ions are formed by the combining of protons, H"*", with water, H2O. Thus:

H+ + H2O > H3O+

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