Mr. Gibson – Chemistry II – Spring 2011
w/o February 14th
The Formula for a Hydrate
Chemistry II
Unit IX(e): Hydrates
w/o-Feb. 14, 2011
During your lab
exercise LIII-02:
Crystal Formation
& Crystal Lattices;
You learned about
the process of
drawing
compounds out of
solution to form
crystal lattices.
Chemistry II
Unit IX(e): Hydrates
w/o-Feb. 14, 2011
And during your
lab exercise –
aqueous solutions
containing those
cations and anions
(of a given unit
formula) fell out of
the solution – as
crystalline solids.
Chemistry II
Unit IX(e): Hydrates
w/o-Feb. 14, 2011
In your Chemistry
studies you will see
there are times
when these
crystalline solids –
as they form to fall
out of a solution will
have some of the
water molecules
adhere (hang on) to
the ions .
Chemistry II
Unit IX(e): Hydrates
w/o-Feb. 14, 2011
In general… Solids,
in which water
molecules are
trapped are called –
Hydrates.
For Chemists we are
more specific when
talking about
“Hydrates”
Chemistry II
Unit X: Hydrates
w/o-Feb. 14, 2011
To a Chemist a
“Hydrate” is a
compound that has
a specific number of
water molecules
bound to [its]
atoms.
Chemistry II
Unit IX(e): Hydrates
w/o-Feb. 14, 2011
For example: the
semi-precious
gemstone “opal”
(shown at the right)
is the solid “silicon
dioxide” (SiO2) that
has water molecules
bound to its atoms
giving rise to the
unique colors in the
opal stones.
Chemistry II
Unit IX(e): Hydrates
w/o-Feb. 14, 2011
And since, the
instances of this
occurring is regular
and specific;
Hydrates are named
in a certain way and
written in a certain
way [as to]
communicate their
structure &
composition.
Chemistry II
Unit IX(e): Hydrates
w/o-Feb. 14, 2011
Formulas for
Hydrates
The solid’s
Unit Formula is
written first.
Example:
the solid -- Calcium Chloride
has a unit formula written
[as]:
CaCl2
Chemistry II
Unit IX(e): Hydrates
w/o-Feb. 14, 2011
Formulas for
Hydrates
The solid’s
Unit Formula is
written first.
Example:
the solid -- Calcium Chloride
has a unit formula written
[as]:
CaCl2
Chemistry II
Unit X: Hydrates
w/o-Feb. 14, 2011
Formulas for
Hydrates
This is followed by
a raised “dot”
CaCl2
Chemistry II
Unit X: Hydrates
w/o-Feb. 14, 2011
Formulas for
Hydrates
This is followed by
a raised “dot”
CaCl2
Chemistry II
Unit IX(e): Hydrates
w/o-Feb. 14, 2011
Formulas for
Hydrates
The number of
associated water
molecules is then
written after the
raised “dot”
CaCl2 2H2O
Chemistry II
Unit IX(e): Hydrates
w/o-Feb. 14, 2011
Formulas for
Hydrates
The number of
associated water
molecules is then
written after the
raised “dot”
CaCl2 2H2O
Chemistry II
Unit IX(e): Hydrates
w/o-Feb. 14, 2011
Naming Hydrates
To indicate the
number of
associated water
molecules in a
Hydrate --- a set of
names has been
adopted from the
field of
mathematics.
Chemistry II
Unit IX(e): Hydrates
w/o-Feb. 14, 2011
Naming Hydrates
The table of names
shown at the right
is used to indicate
the number of
water molecules
associated with the
crystal’s unit
formula.
Name Prefix
Molecules of
Water
Mono -
1
Di-
2
Tri-
3
Tetra-
4
Penta-
5
Hexa-
6
Hepta-
7
Octa-
8
Nona-
9
Deca-
10
Chemistry II
Unit X: Hydrates
w/o-Feb. 14, 2011
Naming Hydrates
Using our previous
calcium chloride
hydrate example &
this table… we can
name this particular
hydrate.
CaCl2 2H2O
Name Prefix
Molecules of
Water
Mono -
1
Di-
2
Tri-
3
Tetra-
4
Penta-
5
Hexa-
6
Hepta-
7
Octa-
8
Nona-
9
Deca-
10
Chemistry II
Unit IX(e): Hydrates
w/o-Feb. 14, 2011
Naming Hydrates
Remember the “2”
in front of water?
This means the
calcium chloride
solid has two water
molecules
associated with its
base formula unit.
CaCl2 2H2O
Name Prefix
Molecules of
Water
Mono -
1
Di-
2
Tri-
3
Tetra-
4
Penta-
5
Hexa-
6
Hepta-
7
Octa-
8
Nona-
9
Deca-
10
Chemistry II
Unit IX(e): Hydrates
w/o-Feb. 14, 2011
Naming Hydrates
Therefore; looking
at the table to the
right we look for
molecules of water
= “2”
CaCl2 2H2O
Name Prefix
Molecules of
Water
Mono -
1
Di-
2
Tri-
3
Tetra-
4
Penta-
5
Hexa-
6
Hepta-
7
Octa-
8
Nona-
9
Deca-
10
Chemistry II
Unit IX(e): Hydrates
w/o-Feb. 14, 2011
Naming Hydrates
We then look at the
name of the prefix
that goes with that
number.
CaCl2 2H2O
Name Prefix
Molecules of
Water
Mono -
1
Di-
2
Tri-
3
Tetra-
4
Penta-
5
Hexa-
6
Hepta-
7
Octa-
8
Nona-
9
Deca-
10
Chemistry II
Unit IX(e): Hydrates
w/o-Feb. 14, 2011
Naming Hydrates
And since “prefix”
means “before”…
The name of this
hydrate would be
calcium chloride
dihydrate.
CaCl2 2H2O
Name Prefix
Molecules of
Water
Mono -
1
Di-
2
Tri-
3
Tetra-
4
Penta-
5
Hexa-
6
Hepta-
7
Octa-
8
Nona-
9
Deca-
10
Chemistry II
Unit IX(e): Hydrates
w/o-Feb. 14, 2011
Molar Masses of
Hydrates
And… still using
our calcium
chloride dihydrate
example;
Given your
previous experience
in this unit:
CaCl2 2H2O
Name Prefix
Molecules of
Water
Mono -
1
Di-
2
Tri-
3
Tetra-
4
Penta-
5
Hexa-
6
Hepta-
7
Octa-
8
Nona-
9
Deca-
10
Chemistry II
Unit IX(e): Hydrates
w/o-Feb. 14, 2011
Molar Masses of
Hydrates
CP0214: find the
molar mass of this
compound, and
then send your
answer via
Schoolrack’s
message board to
me. Just put it in
the message text as
g/mol. [value = 3 pts]
CaCl2 2H2O
Name Prefix
Molecules of
Water
Mono -
1
Di-
2
Tri-
3
Tetra-
4
Penta-
5
Hexa-
6
Hepta-
7
Octa-
8
Nona-
9
Deca-
10