proximity of the component atoms,
ions, or molecules and the strength
of the forces between them. True
solids are crystalline (see also amorphous). If a crystalline solid is
heated, the kinetic energy of the
components increases. At a speciÜc
temperature, called the melting
point, the forces between the components become unable to contain
them within the crystal structure. At
this temperature, the lattice breaks
down and the solid becomes a liquid.
solid solution A crystalline material that is a mixture of two or
more components, with ions, atoms,
or molecules of one component replacing some of the ions, atoms, or
molecules of the other component in
its normal crystal lattice. Solid solutions are found in certain alloys. For
example, gold and copper form solid
solutions in which some of the copper atoms in the lattice are replaced
by gold atoms. In general, the gold
atoms are distributed at random, and
a range of gold–copper compositions
is possible. At a certain composition,
the gold and copper atoms can each
form regular individual lattices (referred to as superlattices). Mixed crystals of double salts (such as alums)
are also examples of solid solutions.
Compounds can form solid solutions
if they are isomorphous (see isomorphism).
solidus A line on a phase diagram
below which a substance is solid.
solubility The quantity of solute
that dissolves in a given quantity of
solvent to form a saturated solution.
Solubility is measured in kilograms
per metre cubed, moles per kilogram
of solvent, etc. The solubility of a
substance in a given solvent depends
on the temperature. Generally, for a
solid in a liquid, solubility increases
with temperature; for a gas, solubility decreases. See also concentration.
solubility product Symbol K s . The
product of the concentrations of ions
in a saturated solution. For instance,
if a compound A x B y is in equilibrium
with its solution
A x B y (s) ˆ xA
+ (aq) + yB
–
(aq)
the equilibrium constant is
K c = [A
+ ]
x
[B
– ]
y /[A x B y ]
Since the concentration of the undissolved solid can be put equal to 1,
the solubility product is given by
K s = [A
+ ]
x [B
– ]
y
The expression is only true for sparingly soluble salts. If the product of
ionic concentrations in a solution exceeds the solubility product, then
precipitation occurs.
solute The substance dissolved in a
solvent in forming a *solution.
solution A homogeneous mixture
of a liquid (the *solvent) with a gas
or solid (the solute). In a solution, the
molecules of the solute are discrete
and mixed with the molecules of solvent. There is usually some interaction between the solvent and solute
molecules (see solvation). Two liquids that can mix on the molecular
level are said to be miscible. In this
case, the solvent is the major component and the solute the minor component. See also solid solution.
solvation The interaction of ions of
a solute with the molecules of solvent. For instance, when sodium
chloride is dissolved in water the
sodium ions attract polar water molecules, with the negative oxygen
atoms pointing towards the positive
Na
+ ion. Solvation of transition-metal
ions can also occur by formation of
coordinate bonds, as in the hexaquocopper(II) ion [Cu(H 2 O) 6 ]
2+
. Solvation
is the process that causes ionic solids
to dissolve, because the energy released compensates for the energy
necessary to break down the crystal
solid solution
494
s
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ions, or molecules and the strength
of the forces between them. True
solids are crystalline (see also amorphous). If a crystalline solid is
heated, the kinetic energy of the
components increases. At a speciÜc
temperature, called the melting
point, the forces between the components become unable to contain
them within the crystal structure. At
this temperature, the lattice breaks
down and the solid becomes a liquid.
solid solution A crystalline material that is a mixture of two or
more components, with ions, atoms,
or molecules of one component replacing some of the ions, atoms, or
molecules of the other component in
its normal crystal lattice. Solid solutions are found in certain alloys. For
example, gold and copper form solid
solutions in which some of the copper atoms in the lattice are replaced
by gold atoms. In general, the gold
atoms are distributed at random, and
a range of gold–copper compositions
is possible. At a certain composition,
the gold and copper atoms can each
form regular individual lattices (referred to as superlattices). Mixed crystals of double salts (such as alums)
are also examples of solid solutions.
Compounds can form solid solutions
if they are isomorphous (see isomorphism).
solidus A line on a phase diagram
below which a substance is solid.
solubility The quantity of solute
that dissolves in a given quantity of
solvent to form a saturated solution.
Solubility is measured in kilograms
per metre cubed, moles per kilogram
of solvent, etc. The solubility of a
substance in a given solvent depends
on the temperature. Generally, for a
solid in a liquid, solubility increases
with temperature; for a gas, solubility decreases. See also concentration.
solubility product Symbol K s . The
product of the concentrations of ions
in a saturated solution. For instance,
if a compound A x B y is in equilibrium
with its solution
A x B y (s) ˆ xA
+ (aq) + yB
–
(aq)
the equilibrium constant is
K c = [A
+ ]
x
[B
– ]
y /[A x B y ]
Since the concentration of the undissolved solid can be put equal to 1,
the solubility product is given by
K s = [A
+ ]
x [B
– ]
y
The expression is only true for sparingly soluble salts. If the product of
ionic concentrations in a solution exceeds the solubility product, then
precipitation occurs.
solute The substance dissolved in a
solvent in forming a *solution.
solution A homogeneous mixture
of a liquid (the *solvent) with a gas
or solid (the solute). In a solution, the
molecules of the solute are discrete
and mixed with the molecules of solvent. There is usually some interaction between the solvent and solute
molecules (see solvation). Two liquids that can mix on the molecular
level are said to be miscible. In this
case, the solvent is the major component and the solute the minor component. See also solid solution.
solvation The interaction of ions of
a solute with the molecules of solvent. For instance, when sodium
chloride is dissolved in water the
sodium ions attract polar water molecules, with the negative oxygen
atoms pointing towards the positive
Na
+ ion. Solvation of transition-metal
ions can also occur by formation of
coordinate bonds, as in the hexaquocopper(II) ion [Cu(H 2 O) 6 ]
2+
. Solvation
is the process that causes ionic solids
to dissolve, because the energy released compensates for the energy
necessary to break down the crystal
solid solution
494
s
www.AzShimi.ir www.AzShimi.com