CHEMISTRY 30S – MODULE 4
SOLUTIONS
LESSON 1  MIXTURES
Introduction to Solutions
Solutions are all around us, and an important part of our everyday lives. Two-thirds
of our bodies' mass is water and most of the chemical reactions involved in the
body's processes take place in solution. In industry, most chemical processes take
place in solution. The metal in chairs is usually a solution of metals. The water we
drink is a mixture of gases and solids and the air we breathe is a mixture of gases.
In this module, we will examine the characteristics of solutions and how to make
solutions.
Matter is made of pure substances and mixtures. This lesson will examine the
different types of mixtures and focus on the terminology used to describe mixtures.
Outcomes
When you have completed this lesson, you will be able to:

Describe the properties of a solution (e.g., homogeneous, saturated, etc.).

Identify the solute and solvent in the preparation of a solution.

Describe and give examples of various types of solutions (e.g., solidliquid, solid-solid, liquid-liquid).

Differentiate between the terms homogeneous and heterogeneous
mixtures, and soluble and insoluble compounds.
Mixtures
If you recall from Module 1, we defined matter as anything that has mass and volume. We
can use the flowchart below to show the different kinds of matter.
CHEM 30S
Mod 3 Chemical Reactions Lesson 6
1
TALC
2010
So far, we have studied the properties of pure substances – substances in which all particles
have the same properties.
Mixtures are different from pure substances in that a mixture contains more than one kind of
particle. In mixtures, the individual components of the mixture retain their properties. The
difference between pure substances and mixtures is illustrated below.
Mixtures can be heterogeneous and homogeneous. The particles in a heterogeneous
mixture are not evenly distributed and individual particles are often distinguishable. For
example, a mixture of sand and water or salt and pepper are heterogeneous. The individual
particles of a homogeneous mixture are evenly distributed and cannot be easily separated.
For example, when salt or sugar are dissolved in water the salt or sugar spreads out evenly
and is not easily separated from the water.
The components of a mixture can be separated by physical means, like evaporation or
filtration. The components of a compound (elements) can only be separated by chemical
means, that is, by using a chemical reaction.
Heterogeneous Mixtures
Heterogeneous mixtures will often settle out if left to stand. For example, solid dust
particles in the air are easily seen when a beam of sunlight shines in the room or when a
projector is on in a dark room. The dust eventual settles out (why does it always seem to
settle out just in our bedrooms?). Another example of a heterogeneous mixture is sand in
water. The sand mixes with the water, but eventually settles out. The individual grains of
sand are easily distinguished from the water. These two are examples of mixtures called
suspensions. We can use filters to separate the components of a suspension.
Suspensions of solids in liquids do not usually allow much light to pass through; they are
usually opaque or translucent. This is due to the light reflecting off the solid particles rather
than passing through the mixture. This is what is known as the Tyndall Effect.
Another heterogeneous mixtures can occur between two or more liquids. Mayonnaise is and
example of a mixture of several liquids, like oil, lemon juice and egg. Mayonnaise is a
fragile mixture that has the oil suspended as tiny droplets within the lemon juice. Lemon
juice is made mostly of water and we know that oil does not dissolve in water, so egg is
added to help keep the oil suspended. A suspension of liquids, like mayonnaise, is called an
emulsion. Another example of an emulsion is milk. Most milks, other than skim, consist of
CHEM 30S
Mod 3 Chemical Reactions Lesson 3
2
TALC
2010
tiny droplets of butter fat suspended in water with dissolved proteins. Homogenized milk
uses a special process to break up the fat so it doesn't separate from the water and rise to the
top.
If we let emulsions sit, they will eventually separate, or what is known as "break" in the
cooking world. Just add some vegetable oil and water together in a bottle. Shake the mixture
vigorously. The oil breaks apart into small droplets and is distribute throughout the water.
When you stop shaking, the oil and water separate. You can also try this with sand, or
pepper, or any other substance that will not dissolve in water.
Homogeneous Mixtures
As mentioned, homogeneous mixtures have their components evenly distributed. Most
homogeneous mixtures are known as solutions. Common examples of homogeneous
mixtures include salt dissolved in water and sugar dissolved in water. If you dissolve sugar
in a cup of tea or coffee, the tea or coffee tastes just as sweet at the beginning as at the end
of the cup (unless there is some left undissolved at the bottom). This is what we mean by
homogeneous, the sugar is evenly distributed throughout the cup.
Solutions do not settle out if left to stand, just as mixtures of salt or sugar and water do not
settle out. Carbonated beverages are examples of homogeneous mixtures of carbon dioxide
gas, sugar and water. If left undisturbed, carbonated beverages will sit on store shelves for
months or even years without any of the components separating out. Try this at home. Let
me know if they separate out in a couple of years
We also notice that a homogeneous mixture of salt or sugar in water is clear or transparent.
A beam of light can be shone directly through a solution without reflecting off other
particles. A solution can still have colour, like cranberry or apple juice. The particles of salt
or sugar are not distinguishable from the particles of water.
Solutions cannot be easily filtered. If salt water were easily filtered there would not be
shortages of drinking water in many parts of the world.
These are all what are characteristics of solutions. We also call this an operational definition
of solutions because we can use the characteristics to know if we have a solution.
Defining Solutions
A solution is defined as a homogeneous mixture of two or more substances where all
substances are distributed as individual molecules or ions.
TERMINOLOGY
Since science has its own language, we must learn the terminology to communicate in
science. The chemistry of solutions has its own terms.
A solution is made up of one or more solutes and a solvent. Generally speaking, the solvent
CHEM 30S
Mod 3 Chemical Reactions Lesson 3
3
TALC
2010
is the substance that does the dissolving and the solute is the substance dissolved. When the
solution is a mixture of substances in the same state, the solvent is the substance present in
the larger amount. For example, when we dissolve sugar in water, water is the solvent and
sugar is the solute. Solutions which have water as the solvent are known as aqueous
solutions.
If a substance is able to dissolve in a solvent, we call the substance soluble. For example,
sugar is soluble in water because it dissolves in water. If a substance does not dissolve in a
solvent, that substance is said to be insoluble. For example, chalk is insoluble in water. It
should be noted that the terms soluble and in soluble are relative terms. This means that
even though small amounts of chalk can dissolve in water, compared to how much sugar
can dissolve in an equal amount of water, a very insignificant amount of chalk dissolves.
Often times substances said to be insoluble are found to be soluble in a solvent in very small
amounts by using very sensitive instruments. However, the amounts able to dissolve are not
significant.
When two liquids dissolve in each other, like alcohol and water, we say the liquids are
miscible. When they do not dissolve, like oil and water, we say they are immiscible.
Types of Solutions
We can describe the types of solutions in terms of the state or phase of the solute and
solvent.
Solvent Solute
liquid
solid
Examples
sugar in water
salt in water
liquid
liquid alcohol in water
ethylene glycol (radiator antifreeze) in water
liquid
gas
solid
solid
Carbon dioxide in water (carbonated beverages)
brass (copper and zinc)
14 karat gold
solid
liquid dental amalgams (mercury in tin)
solid
gas
hydrogen in palladium
gas
solid
gas
liquid gasoline in air
mothballs in air
water in air
gas
CHEM 30S
gas
air (oxygen, carbon dioxide, etc.in nitrogen)
Mod 3 Chemical Reactions Lesson 3
4
TALC
2010
The solutions using liquids as the solvent are quite common, however there are other
solutions that are not quite as obvious. Solutions of metals, like brass, are called alloys.
Alloys are formed by mixing molten metals and allowing them to solidify. Metals are
mixed to take advantage of their individual properties like malleability, density, strength
and resistance to oxidation.
Steel is a mixture of carbon and iron. Pure iron, which is quite brittle, can be mixed with
carbon to give it greater strength. Stainless steel has metals like chromium can be added
to the steel to decrease the rate the steel rusts. Metals such as copper are added to gold for
jewellery so the gold is not so soft. Aluminum alloys are used in bikes and other
equipment the require strength but must be lightweight as well.
Another solution mentioned in the table above is the amalgam. Amalgams are the silver
dental fillings. An amalgam is a mixture of mercury and an alloy of tin, silver and
copper. The mercury binds these metals together in a way that enables them to be
manipulated into the cavity in a tooth.
All mixtures of gases are solutions. All gases mix to form homogeneous mixtures. Gases
such as hydrogen will dissolve in some metals. Palladium metal, a solid, is useful in
purifying hydrogen gas since palladium can dissolve as much as 900 times its volume in
hydrogen.
Exercise
Answer the following questions:
1. What are the properties of a solution?
2. Define what is meant by a solution.
3. Compare (how are they the same) and contrast (how are they different) solutions,
suspensions and colloids.
4. Distinguish between homogeneous and heterogeneous mixtures.
Source: WebCT Manitoba http://webct.merlin.mb.ca
CHEM 30S
Mod 3 Chemical Reactions Lesson 3
5