104 THE THEORY OF IONIZATIONacquired, he will be able to interpret ordinary single equations in
terms of the ionic theory.Rules for Writing Equations in Ionic Form:- Solid substances are underlined: e.g., NaCl.
- The un-ionized part of substances in solution is shown by
the molecular formula without ionic charges: e.g., HC2H3O2. - Ionized substances in solution are shown by the formulas
of the ions: e.g., Na+ Cl". - All salts, strong acids and strong bases (that is, those which
are as much as 45 per cent ionized in 0.1 equivalent solution) are
to be treated, as far as equation writing is concerned, as if they
were completely ionized: e.g., Na+Cl"; H+Cl"; Na+OH";
2H+SO4"". - In equations showing the reactions of weak acids and bases,
the un-ionized parts cannot be neglected. Both the un-ionized
and ionized parts must be shown, e.g.:
HC 2 H 3 O 2 ^ H+ + C 2 H 3 O 2 -
NH4OH ^ NH 4 + + OH"- Solid substances formed in a reaction and thus precipitated
are indicated by an arrow pointing downward: e.g., AgCl J, - Gaseous substances formed in a reaction and thus escaping
from the solution are indicated by an arrow pointing upward: e.g.,
co 2 t - Intersecting equations. To represent a reaction which takes
place between two ionized substances, the formulas of the ions
should be arranged so that positive will always be adjacent to neg-
ative in either the horizontal or vertical direction. An arrow
then should be inserted to point toward the formula of the new
combination.
Ag+ NOr
Cl~ Na+
1
AgClj
When weak electrolytes are brought together a series of reactions
ensues. First the ionization of these electrolytes is shown in hori-
zontal equations as in Rule 5, but the ionic products must be placed
with positive ion above negative so that, if either new pair of ions