Substances, Mixtures & Solutions
Substances

Atoms are the basic building blocks of matter.

A compound is a type of matter made from atoms of two or more
elements that are combined chemically. For example, two atoms of the
element hydrogen (H) and one atom of the element oxygen (O) combine
to form one molecule of water (H2O).

Compounds always contain the same ratio of the different atoms. For
example there are always 2 atoms of hydrogen for every one atom of
oxygen in water. So if there were 6 atoms of hydrogen, there would be 3
atoms of oxygen. The same ratio of 2:1 is used.

Elements and compounds are called substances and CANNOT be broken
down to simpler parts by ordinary physical processes. Only a chemical
process can change a substance into one or more new substances. For
example, you cannot separate a molecule of water into hydrogen and
oxygen by ordinary means. It takes a chemical process to do that.
Mixtures

Mixtures are combinations of substances that CAN be separated by
physical means. For example, you can use boiling to separate salt from
water in saltwater and you can use a magnet to separate metal from sand.

Unlike compounds, mixtures do not always contain the same ratio of the
different substances used in them.

Heterogeneous mixtures are not mixed evenly, so different parts of the
mixture have different compositions. The different parts of a
heterogeneous mixture are usually easy to tell apart. An example of a
heterogeneous mixture would be a cantaloupe. It is a mixture of rind,
flesh and seeds which you can easily tell apart.

Homogeneous mixtures are the same throughout. The substances that
make up a heterogeneous mixture are not usually easy to tell apart. An
example of a homogeneous mixture would be salt water. Another name
for a homogeneous mixture is a solution.
Solutions

A solution is made up of two or more substances. One of the substances
seems to disappear into the other. This process is called dissolution.

A solute is the substance that seems to disappear or dissolve. A solvent
is the substance that dissolves the solute. In the solution salt water, salt
is the solute and water is the solvent.

If a substance is soluble, it means it dissolves in the solvent. If a
substance is insoluble, it means that this substance does not dissolve in
the solvent. Salt is soluble in water, but oil is insoluble in water.

Some soluble substances can fall out of a liquid solution. When this
happens, the solid formed is called a precipitate. Soap scum is an
example of a precipitate that falls out of a solution of soap and water.

Solutions can be solid, liquid or gas.
o Gaseous solution: Air is a gaseous solution of nitrogen, oxygen,
argon, carbon dioxide, neon, helium, krypton, hydrogen, xenon and
ozone. Nitrogen is the solvent and the other gases are the solutes.
o Liquid solution: Vinegar is a liquid solution of water and acetic acid.
Water is the solvent and the acetic acid is the solute.
o Solid solution: Brass is a solid solution. It is a combination of
copper and zinc. Zinc is the solvent and copper is the solute.
Aqueous solutions

If water is the solvent in a liquid solution, it is called an aqueous solution.

Water is called the universal solvent because of its ability to dissolve so
many different solutes.

Water is a good solvent because of the way the hydrogen atoms bond with
the oxygen atom. Because the hydrogen atoms don’t share electrons
equally with the oxygen atom, the atom of water formed has a region that
has a slight positive charge and a region that has a slight negative charge.
Because of this, when the water meets a solute, the different regions of
the water molecule pull apart of the solute.
Solubility

Solubility describes how much solute dissolves in a given amount of
solvent.

“Like dissolves like” is a term scientist use as a rule of thumb. For
example, water has regions that are charged and sugar has regions that
are charged. They are alike. This means that sugar will be soluble in
water. However, baby oil does not have a charge. Since water does have
a charge, baby oil will not dissolve in water because they are unlike.

Solubility can be affected by temperature. For example in the liquid
solution of sugar water, if the temperature of the water is increased, it will
be able to dissolve more sugar.

Solubility can be affected by pressure. For example in the gas-liquid
solution of soda (a mixure of carbon dioxide and water), if the pressure of
the carbon dioxide is increased, it will be more soluble in the water.

Solubility can also be affected by the amount of solute or the amount
of solvent.

Saturated solutions are solutions in which the solvent CANNOT hold any
more solute. If any more solute is added to the solvent, it will not
dissolve.

The concentration of a solution tells you how much solute is present in a
given amount of solvent. If the amount of solute is high, then the solution
is called concentrated. If the amount of solution is low, then the
sollution is called dilute.
Acids and Bases

Acids are substances that contain hydrogen and produce hydronium ions
when they dissolve in water. If a substance contains acids, it is called
acidic.

Hydronium ions ( H3O+) are positively charged.

Properties of Acids:
o sour
o conduct electricity
o react strongly with metals
o can cause burns
o can damage body tissue
o corrosive

Acids
o
o
o
o
o
o

Bases are substances that contain hydrogen and produce hydroxide ions
when they dissolve in water. If a substance contains bases, it is called
basic.
are found in:
citrus fruit
vinegar
digestive juices
car batteries
industrial cleaners
insect stings

Hydroxide ions (OH-) are negatively charged.

Properties of bases:
o bitter-tasting
o slippery
o corrosive
o conduct electricity
o can cause burns
o can damage body tissue
o do not react with metal

Bases are found in:
o soaps
o other cleaning products
o antacids
o chalk
o fertilizers
o plastics
o fibers
o blood
o drain cleaner
pH

A solution’s pH is a measure of how acidic or basic the solution is.

The pH range is from 0 to 14 with 0 being highly acidic, 14 being highly
basic and 7 being neutral (neither an acid or a base).

Neutral solutions have equal numbers of hydronium ions and hydroxide
ions.

Indicators are compounds that react with acids and bases to produce
certain colors. Litmus paper and cabbage juice are two such indicators.
With these indicators, the paper and juice turn blue if there is a base
present and pink or red if there is an acid present. If a neutral solution is
present, the indicator will remain unchanged.

Neutralization is the interaction between acids and bases in which the
properties of the acids and bases are canceled out because of the presence
of the other.