4 Solutions

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Solute
A solute is the dissolved substance in a
solution.
Salt in salt water
Sugar in soda drinks
Carbon dioxide in soda drinks
Solvent
A solvent is the dissolving medium in a
solution.
Water in salt water
Water in soda
“Like Dissolves Like”
Nonpolar solutes dissolve best in nonpolar
solvents
Fats
Steroids
Benzene
Hexane
Waxes
Toluene
Polar and ionic solutes dissolve best in polar
solvents
Inorganic Salts
Sugars
Water
Small alcohols
Acetic acid
Solubility Trends
 The solubility of MOST solids increases
with temperature.
 The rate at which solids dissolve increases
with increasing surface area of the solid.
 The solubility of gases decreases with
increases in temperature.
 The solubility of gases increases with the
pressure above the solution.
Therefore…
Solids tend to dissolve best when:
o Heated
o Stirred
o Ground into small particles
Gases tend to dissolve best when:
o The solution is cold
o Pressure is high
Solubility Chart
Saturation of Solutions
 A solution that contains the maximum amount of
solute that may be dissolved under existing
conditions is saturated.
 A solution that contains less solute than a
saturated solution under existing conditions is
unsaturated.
 A solution that contains more dissolved solute
than a saturated solution under the same
conditions is supersaturated.
Definition of Electrolytes and
Nonelectrolytes
An electrolyte is:
A substance whose aqueous solution
conducts an electric current.
A nonelectrolyte is:
A substance whose aqueous solution
does not conduct an electric current.
Electrolytes vs. Nonelectrolytes
The ammeter measures the flow of electrons (current)
through the circuit.
If the ammeter measures a current, and the bulb
glows, then the solution conducts.
If the ammeter fails to measure a current, and the
bulb does not glow, the solution is non-conducting.
Try to classify the following substances
as electrolytes or nonelectrolytes…
1.Pure water
2.Tap water
3.Sugar solution
4.Sodium chloride solution
5.Hydrochloric acid solution
6.Lactic acid solution
7.Ethyl alcohol solution
8.Pure sodium chloride
Answers to Electrolytes
ELECTROLYTES:
NONELECTROLYTES:
Tap water (weak)
Pure water
NaCl solution
Sugar solution
HCl solution
Ethanol solution
Lactate solution (weak)
Pure NaCl
Ionic Compounds “Dissociate”
NaCl(s)  Na+(aq) + Cl-(aq)
AgNO3(s)  Ag+(aq) + NO3-(aq)
MgCl2(s)  Mg2+(aq) + 2 Cl-(aq)
Na2SO4(s)  2 Na+(aq) + SO42-(aq)
AlCl3(s)  Al3+(aq) + 3 Cl-(aq)
Ions tend to stay in solution where they can
conduct a current rather than re-forming a
solid.
The reason for this is
the polar nature of
the water molecule…
Positive ions associate with the negative
end of the water dipole (oxygen).
Negative ions associate with the positive
end of the water dipole (hydrogen).
Some covalent compounds IONIZE in solution
Covalent acids form ions in solution, with the
help of the water molecules.
For instance, hydrogen chloride molecules,
which are polar, give up their hydrogens to
water, forming chloride ions (Cl-) and
hydronium ions (H3O+).
Strong acids such as HCl are completely
ionized in solution.
Other examples of strong acids include:
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Sulfuric acid, H2SO4
Nitric acid, HNO3
Hydriodic acid, HI
Perchloric acid, HClO4
Weak acids such as lactic
acid usually ionize less than
5% of the time.
Many of these weaker acids
are “organic” acids that contain
a “carboxyl” group.
The carboxyl group does not easily give up its
hydrogen.
Because of the carboxyl group, organic acids
are sometimes called “carboxylic acids”.
Other organic acids and their sources include:
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Citric acid – citrus fruit
Malic acid – apples
Butyric acid – rancid butter
Amino acids – protein
Nucleic acids – DNA and RNA
Ascorbic acid – Vitamin C
This is an enormous group of compounds;
these are only a few examples.