Science Tests and You
Volume 3 Issue 3
Pure Substances and Mixtures
Chapter 10 - HEAT CAUSES CHANGES IN SOLIDS, LIQUIDS, AND GASES (S,L,G)
7.1 - Classification of Matter by Composition
- Everything that we see is made of matter.
- Matter can be classified as a pure substance.
- Mixtures can be classified as solutions or mechanical mixtures.
Matter is anything that has mass and takes up space.
Mass is the amount of matter in an object.
A solid is matter that has a definite shape and volume.
Volume is the amount of space that matter occupies.
A liquid is matter that does not have a definite shape but does have a definite volume.
A gas is matter that does not have a definite shape or volume. Air is made up of different types of gaseous
matter, such as oxygen and nitrogen.
A pure substance is made up of only one type of matter.
Pure substances appear uniform, or homogeneous, throughout.
A mixture is made up of two or more different substances.
When you look at mechanical mixtures closely, they do not have the same appearance throughout. They are
heterogeneous.
Mechanical mixtures are also called heterogeneous mixtures. This means that they are made up of many
different substances, each with different appearances and properties.
Solutions have the same appearance throughout, but are made up of two or more substances.
When you mix one substance in another to form a solution, you dissolve one substance in the other.
All solutions are homogeneous mixtures because they look the same throughout even though they are made
up of different substances.
7.2 The Particle Theory of Matter
- The particle theory of matter describes the characteristics of matter.
- The spaces between particles are small in solids, larger in liquids, and largest in gases.
- Energy changes accompany changes of state.
Everything that you see is made of particles. Particles are very small portions of matter.
The Particle Theory of Matter
The particle theory of matter is a theory that describes matter. It explains the behaviour of solids, liquids, and
gases.
1. All matter is made up of particles.
2. All particles of one substance are identical.
3. The particles of matter are in constant motion.
4. Temperature affects the speed at which particles move.
5. Particles have forces of attraction between them.
6. There are spaces between particles.
Kinetic energy is the energy of movement. In solids, the particles vibrate and wiggle in one place. In liquids,
the particles slide around and over each other.
Temperature is the measure of the average kinetic energy of the particles in a substance.
Heat is the energy that transfers from a substance at a higher temperature to one at a lower temperature.
There are spaces between particles. There are also forces of attraction between particles.
Changes in temperature can also cause changes of state. A change of state is a change from one physical
state of matter (solid, liquid, gas) to another.
Melting - The change of state from a solid to a liquid. TEMP INCREASE
Evaporation - The change of state from liquid to gas. TEMP INCREASE
Condensation - The change of state from gas to liquid. TEMP INCREASE
Freezing or Solidifcation- The change of state from liquid to solid TEMP DECREASE
Sublimation - The change of state from solid to gas. TEMP DECREASE
Deposition - The change of state from gas to solid. TEMP DECREASE
8.1 Solutions: Concentration and Solubility
- The concentration of a solution can be described in qualitative and quantitative terms.
- Solutes and solvents can be identified in various kinds of solutions.
- Water is sometimes referred to as the universal solvent.
Solutions
Alloys - Solid solutions are called alloys.
Solute - A solute is the substance that dissolves.
Solvent - A solvent is the substance into which the solute dissolves.
Water is often referred to as the universal solvent because many different solids, liquids, and gases dissolve in
it to form solutions.
Solubility - Solubility is the relative ability of a solute to form a solution when added to a certain solvent.
Insoluble - When a substance does not dissolve in a solvent, that substance is insoluble in that solvent.
Concentrated - A concentrated solution is a solution that contains a large amount of dissolved solute and very
little solvent.
Dilute - Solutions are dilute when very little solute is dissolved in the solvent.
Concentration - The concentration of a solution is the amount of solute dissolved in a specific amount of
solvent.
Saturation - The maximum amount of solute that can be dissolved in a given amount of solvent at a given
temperature.
A solution is saturated when it has been formed from the maximum amount of solute for a given amount of
solvent at a given temperature.
Every solution has a saturation point at a given temperature. That means that no more solute can be dissolved
in a fixed volume of solvent at that temperature.
Unsaturated - If more solute can be dissolved in a solvent at a given temperature.
In same cases, a saturated solution can be cooled below a certain temperature to form a supersaturated
solution. This contains more solute than would normally be dissolved in the solution.
8.2 Factors Affecting Solubility
• The particle theory of matter explains how solutes dissolve in solvents.
• Solubility is affected by temperature, type of solute or solvent, particle size, and stirring.
The constant motion of particles and the attraction of water particles to salt particles cause salt to dissolve in water.
How quickly a substance dissolves in a solvent is variable. The rate of dissolving is affected by stirring
(agitating the particles), temperature, and particle size.
Stirring - stirring the solvent pushes some of the solute particles surrounded by the solvent particles around
and increases the number of solvent particles that are able to interact with solute particles. Thus, more solute
particles are exposed to and come in contact with more solvent particles. This speeds up the dissolving process.
Temperature - Particles move more rapidly at higher temperatures, as heat is transferred by the movement of
the particles. Since the rate of dissolving depends on solute particles bumping into solvent particles, when the
particles move more rapidly, more solvent and solute particles will bump into one another.
Particle Size -Large particles take longer to dissolve than smaller particles of the same
substance. Particles of a solvent will contact solute particles at the surface of a clump or crystal of solute
particles. Therefore, large pieces of a solute must be broken apart to enable solvent particles to come in contact
with solute particles.
8.3 Separating
Solutions and Mechanical Mixtures
• Solutions can be separated by filtration, paper chromatography, evaporation, or distillation.
• Mechanical mixtures can be separated by sorting, sifting, or magnetism.
Paper Chromatography - A method of separating a solution into its components using paper.
Evaporation - Evaporating the solvent will leave greater concentration of the solute (This is how maple syrup is made)
Distillation - A method of separating a solution into its components that involves boiling and condensation. This is
useful for substances with large differences in boiling points.
Filtration - A mechanical process of separating solids from liquids or gases using porous article or mass, such as paper
or sand.
Sorting - A technique that involves separating substances on the basis of appearance, which may involve colour, size,
texture, or composition.
Sifting - The means of separating solids by component size, involves shaking or agitating a solid material while passing
it through a screen or mesh.
Magnetism - Using magnet, and the magnetic properties of some compounds to separate different materials.
9.1 Industrial Methods of Separating Components of Mixtures
• There are different methods of separating components from mixtures.
• There are many industrial applications of the different methods of separating solutions
and mechanical mixtures.
Fractional Distillation - Fractional distillation is used to separate different substances
or fractions that make up crude petroleum oil based on
differences in their boiling points. For example, Crude petroleum is separated into different parts based on the
boiling point. (See figure 9.4 on page 243)
Separation using evaporation - See SALT PAN
Salt Pan - A large low-lying area surrounded by dykes into which seawater flows, used in the evaporation of
seawater to obtain salt.
Separation using filtering - Water purification uses very fine filters to separate dirt and
some bacteria from water. Water filters can be used to improve the taste and purity of tap water. AIr filters are
often used in buildings to trap dust particles to improve air quality.
Separation using Magnetism - Recyclers of solid waste often use magnets to separate metals (e.g., iron, steel)
from other waste products. Steel and iron recovered by this process can be melted down and remanufactured
into other useful products.
Separation using Sifting - Rocks containing metals (ore) are sifted before metal is
extracted from ore by melting. This sifting process separates the denser metal-containing rocks from lighter
rock material (which has very little metal content) to make it easier to
remove the metals from the rocks.
Sifting flour is also an important process in baking.
9.2 Impact
of Industrial Methods of Separating
Mixtures and Solutions
• Some methods of separating mixtures often have a negative impact on the environment.
• Some methods of separating mixtures, such as filtering, can be positive for the environment.
Many commonly used commercial products, including gasoline and plastics, are produced in refineries. A
refinery is an industrial plant that purifies crude substances, such as petroleum or sugar.
Surface Mining - Surface mining involves removing a large amount of soil and rock on the surface in order to
access the valuable material underneath.
Open Pit Mining - Open pit mining involves the removal of all materials in a large pit.
Strip Mining - Strip mining involves removal of long strips of overburden in areas where the material being
mined is concentrated in veins.
Mountaintop Removal - The mountaintop removal process starts with clear-cutting
and removal of the mountaintop forest, as none of the vegetation can survive this coal extraction process. Next,
all soil on top of the mountain is removed and set aside for possible reclamation. Explosives are used to blast
away the land and rock above the coal. This overburden is then pushed into a nearby valley to fill the hollow.
Large trucks or draglines are used to transport coal to washing and processing plants. During this process,
millions of litres of waste water are stored in nearby pools created by the construction of earthen dams. After
the coal is removed, the stored topsoil may be deposited on the exposed surface, and steps can be taken to
replant trees to ensure revegetation.
Tailings Ponds - A large pool where cyanide compounds (mixed with crushed rock) break down in sunlight.
Gas Flaring - Waste gases produced by the refining process, such as methane or natural gas, are released and
sometimes set aflame in a process known as gas flaring.
Evaporation and the environment - To make 1L of maple syrup, 40L of water must be evaporated. This takes a
lot of energy and can result in the production of a considerable amount of carbon dioxide being produced.
- Some methods of separating mixtures can have a positive impact on the environment. Filtering is an example
of a separation method with positive consequences. Air and water filters are the two most common types of
filters.
- Waste water treatment involves the use of filters that separate impurities from water. This process helps to
make it possible for municipalities to provide large amounts of pure treated water for domestic use.
- Many people suffer from asthma or allergies that are made worse by breathing air contaminated with dust,
pollen, and other matter produced by combustion of fuels. Air filters are used in furnaces and air purification
devices to help clean the air inside the home. This is another industrial process (air filtration) that has a
positive impact on society and the environment.
9.3 Effects of Use and Disposal of Pure Substances and Mixtures on the Environment
• Careless use and disposal of pesticides has a harmful effect on the environment.
• The release of raw sewage has a negative effect on waterways.
• Disposal of industrial substances and mixtures, as well as by-products of industrial processes, has a
negative impact on the environment.
Sewage - Sewage is the liquid waste water from toilets, baths, showers,
and sinks.
STUDY THE WASTE WATER TREATMENT ILLUSTRATION Figure 9.17 on page 254
Primary Treatment - involves separation of a mechanical mixture, including removal
of suspended solids, rocks, sand, and grit. It allows heavy matter in the mixture to settle to the bottom of a
sedimentation tank before moving on to secondary treatment. The solid
matter that settles at the bottom of the tank is called sludge.
Secondary Treatment - Secondary treatment is a biological process involving aeration, which mixes waste
water and sludge with large volumes of air. Living organisms, such as bacteria and protozoa, help to break
apart larger clumps.
Tertiary Treatment - Tertiary treatment involves the application of chemicals, such as chlorine, to disinfect
and kill remaining germs, and to remove phosphates. Other treatments include exposure to high-intensity
ultraviolet (UV) light and treatment with ozone gas, which also kill germs.
Completely treated waste water is usually safe to return to the environment. However, sometimes during periods of
heavy use, of very rainy weather, water treatment plants become overwhelmed and waste water is not retained
long enough to ensure purity. This
commonly leads to the release of contaminated water.
Pesticides - (insecticides and herbicides) Farmers use these to protect their crops by killing insects and
controlling weed growth.
These percolate into the ground where they eventually enter the water.
They also evaporate into the atmosphere and come back as acid rain.
Landfill - A landfill is an area where garbage is disposed of and buried under layers of soil.
Radioactive - A radioactive substance releases energy in the form of radiation.
Uranium is highly radioactive and poses a hazard for 10 000 years. Uranium fuel is stored in a special manner.
First it is sealed in dry storage casks made of steel and further encased in concrete containers, which would be
moved to a final storage location, possibly kilometres underground.