Ions and Molecules in Aqueous Solution
Expt 7 Electrolytes.wpd
Electrical Conductivities of Pure Substances
The ability of any substance to conduct electricity often provides great insight into its chemical and
Since electric current involves the flow of electrical charge, a conducting substance
must provide a source of mobile, charged particles.
The excellent conductivity of the metals, for
example, involves the movement of the loosely held valence electrons of the metal atoms through the
solid crystal lattice of the metal.
In this case, there is no need for the atoms themselves to move.
Ionic compounds are usually recognized by inspection of their chemical formulas which are likely to
contain both metals and nonmetals,
, KCl and Mg(NO ) .
Ionic solids consist of a highly ordered
crystal lattice of positively and negatively charged ions, but these charged particles are locked into their
positions within the crystal and are unable to transport charge.
Ionic compounds do become conductors,
however, in the molten or liquid state since the ions are now free to migrate.
Molecular compounds generally have chemical formulas that contain only nonmetals,
, H S and
C H O .
Molecular solids consist of discrete molecules which have no overall charge; that is, the
molecules are neutral and cannot transfer charge even if they become mobile in the liquid state.
If one were to investigate a
series of solids by measuring
their relative conductivities in
both the solid and molten states,
it may be possible to classify
each into one of three broad
categories: metals, ionic
are compounds which dissolve or react in water to
produce mobile ions in
, and these solutions, therefore,
Many ionic compounds and some
molecular compounds are capable of being solution electrolytes.
The electrolytic behavior of five
representative compounds (CaBr , HBr , HCO H , NH , and CH OH) will be contrasted in the following