Water and aqueous systems
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Transcript Water and aqueous systems
Water and aqueous
systems
Water is unique
High
polarity
Forms extensive hydrogen bonds with other
molecules
High surface tension
Low vapor pressure
High specific heat
High heat of vaporization
High melting point
All
because of hydrogen bonds!
Properties of water
Specific heat of water:
Evaporization and condensation:
4.184 J/g°C
∆Hevp = 2.26 kJ/g
∆Hcond = -2.26 kJ/g
High boiling point: 100°C
Most molecules with a low molecular mass have low
boiling points.
Ex: CH4 boils at -164°C, and ammonia at -33.3°C
Why does ice float?
When
most liquids cool they contract and
become more dense.
Water does this until about 4°C, then
arranges itself like a honey comb.
Ice is less dense than water so it floats.
Aqueous solutions
Anything
dissolved in water.
Solvent: what does the dissolving
Ex: water, paint thinners, mineral spirits.
Solute:
what gets dissolved
Ex: salt, the paint, etc.
Solvation:
the process that occurs when a
solute dissolves in a solution.
How does this work?
Water
is polar (positive on one end and
negative on the other)
The positive part of the water is attracted
to the negative part of the solute and vise
versa.
It surrounds the solute and breaks it apart.
Why can’t I dissolve oil in water?
I
can dissolve it in gasoline.
“like dissolves like”
Water is polar, it will only dissolve polar
molecules and ionic compounds (because
of the difference of charges.
Gasoline is non-polar, and so is oil.
Electrolytes
Electrolytes
conduct electricity when
dissolved in water. All ionic compounds
are electrolytes.
Nonelectrolytes do not.
Water of hydration
Water
of hydration: Water is an important
part of many different crystals. This is the
water in the crystal.
Hydrate: any compound that contains
water.
Effloresce: when a hydrate has a higher
vapor pressure, and loses it’s water
Water of hydration (cont)
Hydroscopic:
remove moisture from the
air.
Desiccants: hydroscopic substances used
to keep things dry. (the little packet that
says “do not eat”)
Deliquescent: remove enough water from
the air to dissolve completely
Heterogenous systems
Suspensions:
mixtures from which particle
settle out upon standing
Colloids: Particles are smaller than a
suspension, but larger than a solution.
These cannot be filtered out and will not
settle out.
Tyndall effect: Scattering of visible light in
all directions
More!
Brownian
Motion: Chaotic movement of
colloidal particles, it keeps them from
settling.
Emulsions: colloidal dispersions of liquids
on liquids. There must be an emulsifying
agent to form the mixture and keep it
stable.
Solubility
Saturated
solution: contains the maximum
amount of solute for a given amount of
solvent at a constant temperature.
You can’t add any more sugar to your koolaid, because it won’t dissolve.
Unsaturated
solution: Contains less solute
than a saturated solution.
You could still add more sugar to your koolaid if you wanted to.
Solubility:
the amount of substance that
will dissolve in a given quantity of solvent
at a given temperature to produce a
saturated solution.
How much sugar can you possibly put in your
kool-aid?
Miscible:
two liquids that can dissolve in
each other.
Ex: oil & gas
Immiscible:
two liquids that are insoluble
with each other (won’t dissolve)
Ex: oil & water