A solution is a mixture with its particles uniformly
spread throughout a solvent
 A solvent is the part of the solution that dissolves
other substances
 The solute is a substance that is dissolved by the
solvent


A solution has the same properties throughout

It contains solute particles (molecules) that are too
small to see and are suspended in the solvent

Sugar dissolved in coffee is an example of a solution

The coffee is the solvent and the sugar is the solute
Solvent is water
Solutes are sugar
and flavoring

Salutes in a solution seem to disappear when they
are mixed in a solvent

When a solution forms, particles of the solvent
surround and separate the particles of the solute

Solutes and solvents have different physical properties such as
boiling point, melting point, color, size, density, and others

Physical changes do not change the
chemical properties of a substances

Physical changes can often be undone
to recover the original materials
• Dissolving a solute into a solvent is an example of a
physical change
• Physical properties can be used to recover the solute
from the solvent
• Suppose you dissolve salt into water
• Because water has a lower boiling point than salt, the
water can be boiled off leaving the salt behind

Solutes have various affects on solvents

The addition of solutes to a solvent can lower its
freezing point or raise its boiling point

Ordinarily, the freezing point of water is 0°C

By adding salt to water, the freezing point can be
lowered to -4oC (That’s why salt is spread on roads to lower
the freezing point in the winter…Oh! That’s right…California
doesn’t have icy roads!

When liquid water freezes with the solute particles
(salt) in it, the solute particles make it harder for the
water molecules to form ice crystals

The temperature must drop lower than 0°C for The
solution to freeze

Therefore, the
presence of
a solute
in water
lowers the
freezing point
of the water





The same is true for increasing the
boiling point
Solutes like salt raise the boiling point
of water
In a water solution, some of the
molecules are water and others are
particles of the solute
The water molecules in a
solution now need more
energy to reach the boiling
point
By adding salt to the water
decreases cooking time for
food because the water is hotter

Car manufacturers make use of solutes to protect
engines from heat and cold

The coolant in a car’s radiator is a solution of water
and another liquid called anti-freeze

The mixture of the two liquids has a higher boiling
point and lower freezing point then water alone

The solution can reduce the risk of damage to the car
from freezing and overheating

In many common solutions, the solvent is water

Water dissolves so many
substances that it is called
The "universal solvent"
 For example, water is the
solvent for sodas
 Food coloring, carbon
dioxide, sugar, and
flavoring are the
solutes

Life depends on water solutions
Nutrients used by plants and animals are dissolved
in water within the cells
 Water is the solvent in
blood, saliva, and tears


Many solutions are made with solvents other than
water

A solution may be a combination of gases, liquids, or
solids

For example
 Gasoline is the solution of several different
liquid fuels
 Alloys are solutions of different metals
 Air is a solution of different gases

Not all mixtures are solutions

Colloids and suspensions are
mixtures that have different
properties than solutions
 A colloid is a mixture that contains
small, undissolved particles too
small to be easily seen , but big
enough to scatter light trying to
pass through it
 Because the particles scatter the
light, it is impossible to see
through the mixture
 A suspension is a mixture in
which particles can be seen
suspended (held up) in a liquid or gas
 The particles can be easily
separated by settling or filtration
 The particles are visible and larger
than the particles in solutions or colloids
 Snow globes and salad dressings are examples of suspensions

When an ionic compound mixes with water, the
positive and negative ions are attracted
to the polar water molecules

Water molecules surround each
ion as the ions leave the surface
of the compound

As each layer of the compound
is exposed, more ions can
dissolve
Water molecule
-
Ions
- -
- +
+
+
O + + +
+ O
+
- --

Not every substance breaks into ions when
dissolved in water

A molecular compound, such as sugar, breaks up
into individual neutral molecules

The polar water molecules attract the slightly taller
sugar molecules

This causes the sugar
molecules to move
away from each other

The covalent bonds
within the molecules
remain unbroken

Supposed to have a water
solution, but you don't know
if the solute is salt or sugar

A solution of ionic
compounds (salt) conducts
electricity
Salt or Sugar?

A solution molecular
compounds (sugar) does not

If the solution does not
conduct electricity, no ions
are present which means
you have a sugar solution
Concentration
 Concentration is the amount of
solute in a solvent
 The more solute, the greater the
concentration
 It takes approximately 43 gallons of maple
sap to make 1 gallon of maple syrup
 In order to get the sap sweet enough for
pancake syrup, the water (solvent) in the sap
must be removed to make a sweeter solution
 Fruit juices are sometimes packaged as concentrates
 To make the concentrate, water
(solvent) is removed from the
natural juice
 When you prepare the juice to drink,
you dilute the concentrate by adding
back the water
Measuring Concentration
 To measure concentration, you compare the amount
of solute to the total amount of the solution
 Concentration is measured as a percent of solute in
the solution by volume or mass
 The mass of a solute or solvent is measured in grams
 The volume of a solute or solvent is measured in
milliliters or liters
Solubility
 Solubility is the measure of how
much solute can dissolve in a
solvent at a given temperature
 There is a maximum amount of solute that can be
dissolved in a solvent before the solvent
becomes saturated and
no more solute can
dissolve
Working with Solubility
You can identify a substance
by its solubility
 Solubility is a property of
matter
 If you had a white powder
and could not tell if it was
salt or sugar, you could identify it by its solubility
 Salt dissolves faster
because salt molecules
are smaller than sugar
molecules

Sugar
Factors Affecting Solubility
 The solubility of solutes change when
conditions change
 The factors that affect solubility of a
substance include PRESSURE, the TYPE
of SOLVENT, and TEMPERATURE
 Example: Sugar will dissolve faster in
hot tea than ice tea
 A sugar solution will become
saturated (no more sugar will dissolve)
in ice tea faster than hot tea
 Hot tea will dissolve much more sugar
than ice tea before becoming saturated
Pressure
 Increasing the pressure
increases the solubility of gases
 Soda water contains dissolved
carbon dioxide gas
 To increase the carbon dioxide
concentration in the solution,
the gas is added under highpressure
 Opening the bottle releases the
pressure and makes the hissing
sound you hear

Scuba divers must be aware of the effects of pressure
on gases
When divers breath compressed air, nitrogen from the
air dissolves in their blood
 More dissolves as they go deeper
 If divers return to the surface too quickly, nitrogen
bubbles form in the blood and block blood flow and
divers double over in pain, which is why this condition is
sometimes called “The Bends"

Solvents
 Some solvents and solutes are not
compatible
 Your vinegar and oil salad dressing
has to be shaken because vinegar
and oil do not mix
 When you stop shaking the
dressing, it quickly
separates into layers of
vinegar and oil

For liquid solutions, the solvent affects how well a solute
dissolves
Polar compounds are molecules that have a positive
charge on one side and a negative charge on the other
side
 Polar compounds dissolve in polar solvents
 Nonpolar compounds do not dissolve in polar solvents
Example—

Polar water-based paints
clean up with soap and
polar water
Nonpolar oil-based paints
require a nonpolar solvents
such as turpentine

Waterand oil do not mix because
water is a polar compound and oil
is nonpolar

Polar compounds a nonpolar
compounds do not mix
Temperature
 Solubility increases as the
temperature increases
 Example— At room
temperature, not much
sugar can dissolve in water
 The solubility of sugar in
100g of water changes
from 180g at 0°C, to
231g at 25°C, to
487g at 100°C

Unlike most solids, gas in a liquid becomes less soluble
when the temperature of the liquid increases

Example— More carbon dioxide
will dissolve in cold water than hot
water

Warm soda taste "flat“ because warm
soda contains less carbon dioxide

Fish love cold water because cold
water can hold more oxygen

Properties of Acids
Acids are compounds whose properties include the
kinds of reactions they undergo
 An acid tastes sour, reacts with
metals, carbonates, and turns blue litmus paper red


Reactions with Indicators
Litmus paper is called an indicator
It is made by coating strips of paper with Litmus which
is made from plants
 Acids turn blue litmus paper red
 Other color litmus papers are used to indicate other
substances



Some common acids are hydrochloric acid, nitric acid,
sulfuric acid, carbonic acid, and acetic acid

Sour taste

Citrus fruitslemons, grapefruit,
oranges, and limes
all contain citric acid

Other fruits (cherries,
tomatoes, apples) and
many other types of
foods contain acids, too

Scientists never taste chemicals in order to identify
them

You should never taste a substance unless you know it
is safe to eat
Reactions with Metals

Acids react with certain
metals, such as magnesium,
zinc, and iron, to produce
hydrogen gas

When they react, the metals seem to disappear in the
acid solution

This observation is one
reason acids are described
as corrosive, meaning they
"wear away" other materials
Reactions with Carbonates
A product of an acid's reaction
with a carbonate is carbon
dioxide
 Geologists use this property of
acids to identify rocks
containing limestone
 Limestone is a compound that
contains the carbonate ion
 If you pour hydrochloric acid on
limestone, bubbles of carbon
dioxide appear on the rock's
surface

Properties of Bases

Bases are another group of compounds that can be
identified by their properties

A base tastes bitter, feels slippery,
and turn red litmus paper blue

Common bases include sodium
hydroxide, calcium hydroxide and
ammonia
Red = Acid
Blue = Base
Bitter Taste

Bases are bitter

The slight bitterness of
soda is caused by the base quinine

Soaps, shampoos and detergents are
bitter too, but they
are NOT safe to
taste

Slippery Feel

The slippery
characteristic
bases

Remember, don’t touch anything that you don’t know
what it is

Strong bases can irritate or burn your skin

A safer way to identify bases is by using an indicator like
litmus paper
feel is a
of

Reactions with Inhibitors

Since litmus paper can be used to test acids it can also
be used to test bases

Bases turn red litmus paper blue

Litmus paper gives a reliable, safe test
Uses of Acids and Bases

Acids and bases are almost everywhere

Manufacturers, farmers, and builders are only some
people who depend on acids and bases in their work

Some acids are vitamins, including vitamin C and folic acid

Vitamins are essential in small amounts to normal
growth and functioning of the body

Many cell processes also produce acids as waste products
for example— Lactic acid builds up in your muscles
when you make
them work too hard
Acids in solution
 A hydrogen ion (H+) is an atom of a hydrogen that
has lost its electron
 Hydrogen ions are the key to the reaction of acids

Acids in a water solution produce positive hydrogen
ions
 These hydrogen ions form the properties of acids
for example— When acid interacts with certain
metal atoms, hydrogen gas (H2) is produced

Hydrogen ions also react with blue litmus paper,
turning it red
Bases in solution

Not all bases contain hydroxide ions
for example— the gas ammonia does not, but in
solution, ammonia will react with water to form hydroxide
ions

A base produces hydroxide ions in water

Hydroxide ions are responsible for the bitter taste and
slippery feel of bases, and turn red litmus paper blue
Strength of acids and bases
 The strength of acids and bases refers to how well
an acid or a base produces ions in water
 With a weak acid, very few ions form in solution
 At the same concentration, a strong acid produces
more hydrogen ions
 Examples of strong acids include hydrochloric acid,
sulfuric acid, and nitric acid
 Most other acids, such as acetic acids are weak
Measuring pH
 Knowing the concentration of hydrogen ions is the key
to knowing how acidic or basic a solution is
 To describe the concentration of ions, chemist use a
numeric scale called the pH scale
 The pH scale is a range of values from 0 to 14

Most acidic items are at the low-end of the pH scale

A pH lower than 7 is acidic

The most basic items are at the high-end of the scale

A pH higher than 7 is basic

If the pH is 7, the solution is neutral

That means it's neither an acid nor a base

Pure water has a
pH of 7

A low pH indicates that the concentration of
hydrogen ions is big

In contrast, a high pH indicates that the
concentration of hydrogen ions is low

If you keep these ideas in mind, you can make sense
of how the scale works

The pH of a solution can be determined by use of pH
paper

pH paper turns a different color for each pH value

Matching the color the paper with the color of the test
scale indicates how acidic or basic the solution is

Some indicator solutions will change color over the
entire pH scale other indicators solutions only
change color within a range of approximately two
pH units

Knowing the pH range
over which this color
change occurs gives you
a rough estimate of pH

Most chemistry
laboratories contain a
pH meter that makes
rapid pH measurements
Using acids and bases safely
 Even a dilute solution of hydrochloric acid can eat a
hole in your clothing
 In order to handle
acids and bases
safely, you need to
know both their
strengths and their
concentration
Acid-base reactions
 After neutralization, an acid or base solution is less
acidic or basic than either of the starting solutions
 The pH depends on the type, the volume, and the
concentration of the reactants
 A solution with a small amount of strong base
reacting with a much larger amount of strong acid
will remain acidic
 When mixing a solution of strong acid containing
hydrogen ions and a solution of strong base
containing an equal amount of hydroxide ions a
neutral solution will be the result

"Salt" may be a familiar name of the stuff you sprinkle
on food

But to a chemist a salt is any compound made from the
neutralization of an acid with a base

A salt is made from the positive ions of a base and the
negative ions of an acid

One product of a reaction of
nitric acid with potassium
hydroxide (base) is neutral
water

The other products is potassium nitrate,
and salt

Potassium nitrate is soluble in water

Some salts are insoluble and form
precipitates