Definition: SOLUTION

A system in which one or more substances are
homogenously mixed or dissolved in another
substance.

In other words: two chemicals mixed together
completely.

Can result in a solid, liquid, or gas
What are some examples?





Shampoo
Soft drinks
Air
Gasoline
steel
What do you need to make a
solution?

Example: Kool-aid, basically sugar water
+


=
1) solute—part being dissolved (sugar)
2) solvent—part doing dissolving (water)
A True Solution
5 Properties of True Solutions

1) mixture is homogenous and the ratios of
solvent to solute can be varied.

In Kool-aid example, more or less sugar could be
added to make the solution more or less
concentrated.
A True Solution
Properties

2) The dissolved solute is molecular or ionic in
size.

The sugar in the packet dissolves into separate sugar
molecules
A True Solution
Properties

3) It is either colorless
or transparent (not cloudy)
A True Solution
 Properties

4) The solute is uniformly distributed and
doesn’t settle out over time.

After an hour, the solution should still look the
same. No chunks at the bottom or top…think of
hot chocolate when it sits for a while
A True Solution
 Properties

5) The solute can be separated from the solvent
by physical means (evaporation, filtration,
boiling, etc)

Recall the first lab where we boiled salt water, after
the water evaporated, the salt was left at the bottom.
Dissolving

How do substances dissolve?
Diffusion


Molecules travel from areas of high
concentration to areas of low concentration.
Solubility describes how likely one substance will
dissolve in another.
Solubility


Amount of solute that can dissolve in the
solvent.
Solubility varies with temperature.
4 ways to make a solute dissolve
faster?

(1)INCREASE THE TEMPERATURE


(2) AGITATION OR STIRRING


for liquids, this causes the solvent molecules to
move faster and bump into the solute particles more
often and harder, breaking them apart faster.
this physically helps the solute particles diffuse by
distributing them to all parts of the solvent.
(3)BREAK IT DOWN

The smaller the particle, the faster it dissolves
How can I make a solute dissolve
faster?

(4) CONCENTRATION
The closer you get to the saturation point, the slower
the dissolving occurs
 The solute dissolves quickly at first because there is a
lot of area to dissolve into
 As more of the solute dissolves, the area shrinks and
dissolving slows down.

What Affects a Substance’s
Solubility?

Question:
When making Jell-o, why do the directions
tell you to pour the packet into hot water and
then cool it?
Why can’t you just pour it in cold water and
then drink it right away?
What 3 factors affect the Solubility of
substances?
(1) Temperature
 For LIQUIDS:

 More
solute can be dissolved if you use warm
solvents.
 Why?
 The
KMT of course
Which one would dissolve more salt?
100 C
50 C
How much more would
the first cup dissolve?
Solubility Curves



Can use a graph to represent solubility
Y-axis = grams of solute per 100g H2O
X-axis = temperature

Different substances will have different curves on
the graph.
What’s
happening
with HCl,
NH3, and
SO2
(dotted
lines)
Solubility of Gases


The solubility of gases decreases with increasing
temperatures.
Can you think of a situation where this principle
is illustrated? (hint: many of you have one at
lunch time)
SODA
SODA


Cold soda is more fizzy because more gas is
dissolved in the soda.
Why does soda become flat as it warms to room
temperature? (remember the KMT)

As the soda becomes warm, the gas molecules begin
to move faster and evaporate out of the soda.
(2) Solubility & Pressure
Changes in pressure have the largest effect on
gases dissolved in liquids.

Pressure and solubility vary directly.

As the pressure increases, the solubility
increases.
Back to the Soda

Why does a can of soda fizz when it’s opened?

Canned at high pressures.

When it’s opened, the pressure inside is reduced to
the atmospheric pressure, and the excess dissolved
CO2 bubbles out of the sol’n.
(3) The Nature of the
Solute and the Solvent
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Explain why water and oil do not mix?
Like dissolves like
Polar substances dissolve in other polar
substances and nonpolar dissolve in nonpolar.
Oil is nonpolar and water is polar.
Nonpolar vs. Polar


When nonpolar substances dissolve in one
another, they simply mix.
When polar substances dissolve, electrical
reactions pull apart the molecules.
Saturated, Unsaturated, & Supersaturated
Sol’ns

SATURATED
Holds the maximum amount of solute in the
dissolved state
 No more solute can be added and still dissolve.


UNSATURATED


More solute could be added and still dissolve.
SUPERSATURATED
Holds more solute than the max.
 Very unstable and have to be prepared in a special
way.

Supersaturated Solutions




Hand/foot warmer packs used for cold weather
are examples.
Activated when they are crushed
The heat generated is a result of the
supersaturated solution coming out of
supersaturation. This reaction is exothermic.
Cold packs work the same way but are
endothermic reactions.

Will a solution made by adding 2.5g of
CuSO4 to 10g of H2O be saturated or
unsaturated at 20°C?
Use the curve on slides
 Find the solubility of CuSO4 at 20°
 It is 21g per 100g H2O
 This is equivalent to 2.1g CuSO4 per 10g H2O
 Since 2.5 is greater than 2.1, the sol’n will be
saturated. How much will be undissolved?
 .4g

You Try


Will a sol’n made by adding 9.0g NH4Cl to 20g
of H2O be saturated or unsaturated at 50°C?
unsaturated
Solution Concentration


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Equations to learn
(1) Molarity
(2) Dilution
Molarity
Molarity describes a solution’s concentration by
telling you how many moles of solute exist in
one liter of solution. (symbol is a capital M)
 M = moles
L
A 6 M HCl solution contains 6 moles of HCl for
every Liter of solution.

What does a 5.7 M solution contain?
5.7 moles of HCl for every Liter of solution.
Dilutions

Sometimes the available solution might be to
concentrated for our purposes; therefore we
must dilute the solution.
In other words, we reduce the concentration of
our solution. To find out how much solvent we
must add to reduce the concentration, we use
the following formula:

M1V1 = M2V2

where M=molarity
Dilution
100mL water
200mL water
6 moles NaCl
6 moles NaCl
The moles are the same in each glass

Because they contain the same amount of moles,
we can use:
 M1V1 = M2V2
M=molarity
or
 C1V1 = C2V2 C=concentration
Examples

Calculate the molarity of a solution prepared by
diluting 125 mL of 0.400 M K2Cr2O7 with 875
mL of water.

(125)(.400) = (1000) M2
.05 M
