Grade 7 Science: Pure Substances and
Mixtures
By: Michelle and Rawan
I
can explain the components of a solution.
 I can identify solutes and solvents in various
kinds of solutions (liquid, solid and gas).
 I can explain why water is referred to as the
universal solvent.
 Key
terms: solute, solvent, dissolve
Recall from our last lesson:
 Solution: a mixture that looks like a
single pure substance; a uniform
mixture of two or more pure
substances also known as a
homogenous mixture.
 Today
we will be taking a closer look
at solutions.
 Solute:
The smaller part of a solution; the
part of a solution that dissolves in the
solvent.
Example: Kool-Aid powder mix
 Solvent:
The larger part of a solution; the
part of a solution into which the solutes
dissolve.
Example: Water (the most common
solvent.)
When the kool-aid powder mix (solute) is mixed
in the water (solvent), it dissolves and
becomes Kool-Aid (solution).
We are most familiar with solutions that are liquids.
 Liquid
solutions all have liquid
solvents.
 Solutes
that dissolve in liquids may
be solids (e.g. salt, sugar), liquids
(e.g. acetic acid to from vinegar), or
gases (e.g. CO2 and nitrogen gases
dissolve in our blood and are carried
around our body).
The Universal Solvent is water.
 Water
dissolves more different
substances than any other solvent. It is
the solvent for many important solutions.
 This is why it is called “The Universal
Solvent”.
o
o
o
Tap water usually looks and tastes like pure
water but, did you know, that water is a solution
that contains many solutes?
These solutes include iron, aluminum, salt,
fluorine, calcium, magnesium, and chlorine.
As water flows in rivers and lakes and
underground, it comes into contact with many
types of matter.
Example: Gases from the air and minerals from the rocks
and soil, all dissolve in the water. Pollutants may also
dissolve in the water.

Before water reaches your tap it is cleaned so it is
safe for drinking (Chlorine and fluorine are
sometimes added to the water. Chlorine kills
bacteria and fluorine may help keep your teeth
healthy).
Water in your body:
 70% of your body is water. This water
dissolves many different solutes, making a
variety of solutions. The solutes are salt,
oxygen, sugars, and mineral components
(calcium and potassium). Because they are
dissolved in water they have the ability to
travel around your body.

Some of the solutions produced by your body
are blood plasma, sweat, urine, and tears.
The solvent of all of these solutions is water.
70% of the Earth’s surface is water. As water
moves around Earth, it dissolves many
different solutes which are transported
around the world as the water cycle occurs.
 Solutes in water can be absorbed by living
things. Plants absorb the minerals and
nutrients dissolved in water through their
roots.


Discuss why it is important to know this in
terms of pollution.

A pollutant is any pure substance or mixture that can
contaminate or harm the natural environment.

Polluted water is a mixture of pure water and
pollutants. Pollutants can enter water from various
sources such as fertilizers and pesticides from farms,
waste from mining, fertilizers and pesticides from
lawns, industrial waste, and sewage and household
products put down the drains.

It’s always important to keep our water clean so
that organisms can grow and live normally in the
lakes, rivers and oceans. We have to be careful not
to let contaminants get into our water.
Solutions that are solids have both solid
solutes and solid solvents.
 Example: The gold that is used to make
jewelry often is called “14 karat” gold. Pure
gold is 24 karat gold. This means that the
jewelry gold is 14 parts gold and 10 parts of
other metals(silver, copper, nickel, or
palladium). Gold is the solvent and the other
metals are the solutes in this case.
 Remember, the solutes are the smaller part
of the solution and they are dissolved into
the solvent.

 Solid
solutions are called “alloys” when
they contain two or more metals. To
make them, the metals are heated until
they melt, and then mixed together and
allowed to cool.
Brass is an
alloy of copper
and tin.
 In
any gas solution, the solvents and
solutes are always gases.

An example of a gas solution is the air we
breathe. It is 78% nitrogen gas, 21% oxygen
gas and 1% argon gas. It also has small
amounts of other gases like carbon dioxide.
Can you tell what the solvent is of this gas
solution is? How about the solutes?