Intro and Definitions
Mr. Shields
Regents Chemistry
U12 L01
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We make or use solutions everyday in our lives.
So… what are some of these everyday examples?
-Making coffee / hot chocolate /tea
-Dissolving the flavors of spices into our foods
-Putting additives into our gasoline
-Adding anti-freeze to our cars cooling system
-Dissolving salt or sugar in our food and drinks
-Medicine dissolved in liquids to make them easier to take
-Drinking liquids with dissolved Carbon dioxide
-Dissolving chemicals in drinking and recreational water to
make them safe
-Breathing air into our lungs
-Our bodies dissolving nutrients in our blood for nourishment
AND THERE ARE MANY MANY OTHER EXAMPLES AS WELL
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Mixtures
Recall that in the classification of matter there were 2 major
categories. Do you remember what were they?
- Pure Substances (elements & compounds)
- Mixtures
Mixtures are further divided into 2 categories. What are they?
- Heterogeneous mixtures (What’s the definition? Examples?)
- Homogeneous mixtures (What’s the definition? Example?)
- Solutions (All kinds )
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Solutions
There are several different kinds of solutions. Can you name some?
We’re going to
Discuss these 4
Sterling silver (Cu/Ag)
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Solutions
Solutions we said are homogeneous mixtures. There are
Two components that make up a solution…
-The Solute
&
-The Solvent
In solutions one substance is usually considered to be “broken
down” into individual ions or molecules and dissolved into
the other.
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Solutions
The substance being dissolved is called the SOLUTE
ex: NaCl is the solute when dissolved in water
The substance that does the dissolving (what the solute
Dissolves in) is called the SOLVENT
ex: When Sugar is dissolved in
water, water is the solvent
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Solvent vs Solute
The distinction between solute and solvent is not
Always so clear. For example consider the following…
A solution that is 5% ethanol & 95% water.
Which is the solvent?
If you said water you would be correct …
But now consider what happens if I kept increasing
the ethanol until the solution contained 60% ethanol
and 40% water.
Which one is the solvent?
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Some rules
1) If the solute and solvent are present in the Same Physical
state then the Solvent is considered to be the one
present in the larger amount.
Ex: Ethanol Water
35%
65%
55%
45%
water is the solvent
ethanol is the solvent
2) If the solute being dissolved in a solvent is present
in a Different Physical State from the solvent it is always
considered the solute no matter how much of each is present.
Ex: 5g or 120g of KNO3(s) in 100ml of H2O; KNO3 is always the solute
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Solution Concentration
The Words UNSATURATED, SATURATED and SUPERSATURATED
can be used to describe the amount of solute in the solvent.
A SATURATED solution is one in which the solvent can no longer
Dissolve any additional solute.
An UNSATURATED solution is the opposite. It is one in which
More solute can be dissolved in the solvent.
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Unsat & Saturated solutions
Sol’n can dissolve more solute
Solubility of Sucrose in 100ml
Of water at 20º C
Sol’n can’t dissolve any
More solute
If I add 50 g to a sat. Sol’n
It just sits at the bottom 10
Supersaturated
Besides saturated and unsaturated there are also
SUPERSATURATED SOLUTIONS
A supersaturated solution is a solution that contains MORE
SOLUTE in solution than the SOLVENT can normally dissolve
At a given temperature.
So how do we put more solute into solution than the solvent
Can dissolve???
In other words how is a supersaturated solution formed?
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Making a supersaturated sol’n
1. The solute is dissolved at some high temperature
2. The sol’n is then very slowly cooled
3. As the sol’n cools it has more solute in it than it can normally
dissolve at that temperature
- Decreasing temperature decreases solubility
4. The solute concentration does not
decrease so we end up
with an unstable situation
5. If a single crystal is added
to the supersaturated solution…
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Supersaturated
The addition of a small crystal will cause excess solute to
crystallize out of a supersaturated solution immediately!
The solution remaining behind is SATURATED!
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Liquid Sol’n terms
Two other terms used when both solute and solvent are Liquids –
Miscible and Immiscible
A liquid is MISCIBLE in another liquid if it is…
SOLUABLE in one another IN ALL PROPORTIONS
Example: Alcohol in Water
A liquid is IMMISCIBLE in another liquid if it is…
NOT SOLUBLE in one another IN ANY PROPORTION
Example: Oil in Water
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Liquid Solubility
The general rule of thumb is the following:
“LIKE DISSOLVES LIKE”
So What does this mean in terms of solubility?
1- Polar liquids will dissolve polar liquids
2- Non-polar liquids will dissolve Non-polar liquids
3- But Polar and non-polar liquids tend to be immiscible
Remember Polar and non-polar?
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Measuring Concentration
All the terms we’ve used so far to discuss solution concentrations
Are subjective terms.
We’ll next discuss ways to specify solution concentrations in
More objective terms
The methods we’ll look at for specifying the concentration of
solutions are:
1- Molarity (M) – most common method
2- Percent (%)
- mass/mass & volume/volume
3- Parts per Million (ppm) – Used for very dilute solutions
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