Pure Substances and Mixtures

Grade 7

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

A liquid is matter that does not have a definite shape, but has a definite volume

A gas is matter that does not have a definite shape or volume

(but you knew that already didn’t you )

Classification of Matter

All matter can also be grouped into two basic categories: pure substances, and mixtures

Classifying Matter by Composition

A Pure Substance is made up of only one type of matter.

Sugar, distilled water, and copper wire are all types of pure substances.

For example, all the parts in a packet of sugar are the same.

Pure Substances

Pure substances appear homogeneous. This means that every part of that substance has the same composition as every other part.

When you look at a container of salt, or distilled water, every part of that substance looks the same.

The prefix “homo” comes from the Greek work “homos” which means “same”.

Pure Substances

A mixture is made up of two or more different substances.

For example, a pizza is a mixture of different types of edible ingredients placed on flat dough. Mmm.

Each substance in a mixture keeps its particular properties even though they may be hard to see.

For example, you can not always see the sugar that is in a soft drink – even if you can taste it.

Mixtures

Mixtures can also be grouped into two basic categories: mechanical mixtures and solutions.

When you look at mechanical mixtures closely they do not have the same appearance throughout. They are heterogeneous. You can see the differences with the naked eye.

The prefix “hetero” comes from the Greek work “heteros” which means “different”

Classifying Mixtures

Mechanical Mixtures are also called heterogeneous mixtures.

This means they are made up of many different substances, each with different appearances and properties.

Classifying Mixtures

Solutions have the same appearance throughout but are made of two or more substances.

When you mix one substance in another to form a solution, you dissolve one substance in the other.

Classifying Mixtures

All solutions are homogeneous mixtures because they look the same throughout, even through they are made up of different solutions.

For example, when you dissolve sugar in tea, the tea looks the same throughout.

Classifying Mixtures

Categorize each item as a pure substance or a mixture on the chart in your booklet.

chocolate pudding

gold necklace

Bleach

helium gas

unfiltered tap water

Gatorade

a diamond

pepper

The Particle Theory of Matter is a theory that describes matter. It explains the behaviour of solids, liquids and gasses.

Copy the 6 postulates of the theory into your booklet form page 200 in your textbook.

The Partical Theory of Matter

All matter is made of particles. The particles in matter are in constant motion. They move and vibrate constantly.

Particles move because they have kinetic energy. Kinetic energy is the energy of movement.

Temperature is the average kinetic energy of the particles in a substance. It measures how hot a substance is.

The Particle Theory of Matter

Heat is the energy that transfers from a substance at a higher temperature to one at a lower temperature.

Temperature affects the speed at which particles move.

the higher the temperature: the more the movement of energy in the particle. the lower the temperature: the less the movement of energy in the particle.

The Particle Theory of Matter

There are spaces between particles. There is also a force of action between particles.

These forces have differing strengths in solids, liquids and gasses.

Space and Attraction between Particles

Solutions can occur as solids, liquids or gasses.

Solid solutions are called alloys. Liquid and gaseous solutions are simply

called solutions.

This brass door knocker is a mixture of copper and zinc.

Soloutions

Solutions consist of solutes and solvents.

A solute is the substance that dissolves. A solvent is the substance into which the solution dissolves.

For example, in seawater, salt and other substances (solutes) dissolve in water (solvent)

Water is often referred to as the Universal Solvent, because many different solids, liquids and gasses dissolve into it to form solutions.

Soloutions

Solubility refers to the ability of a solute to form a solution when added to a certain solvent.

To form a solution the solute must be attracted to the solvent particles, which allows the particles to spread evenly throughout the solution.

For example, salt dissolves in water because the salt particles are attracted to the water particles.

Solubility

Salt water does not dissolve in olive oil because the salt particles are not attracted to the oil particles.

When a substance does not dissolve in a solvent, that substance is insoluble in that solvent.

A solution does not form when one of the substances is insoluble to another.

Solubility

A concentrated solution is a solute that has a large amount of dissolved solute and very little solvent.

A diluted solution has very little solute dissolved in the solvent.

Concentration

The concentration of a solution is the amount of solute dissolved in a specific amount of solvent.

For example, if 5g of salt are dissolved in 500ml of water, the concentration of the solution is 5g/500ml

Concentration

A saturated solution is one that has been formed from the maximum amount of solute for a given amount of solvent at a certain temperature.

Saturation In all solutions, there is a maximum

amount of solute that can be dissolved in a given solvent at a given temperature – this is called saturation

Every solution has a saturation point, which means no more solute can be dissolved into a fixed volume of solvent at that temperature.

That is why there is sometimes extra undissolved delicious Kool Aid powder at the bottom of your class.

Yummm.

Saturation

If more solute can be dissolved in a solvent at a given temperature, then the solution is unsaturated. You can dissolve more solute in an unsaturated solution.

Saturation

Under certain circumstances, a saturated solution can be cooled enough to form a supersaturated solution, which has more solute than would normally be dissolved in the solution.

The particle theory of matter explains how solutes dissolve in solvents

The rate of dissolving is affected by stirring, temperature and particle size

Solubility and the Particle Theory

Stirring a solution increasesthe rate in which a solute dissolves in a solvent

Stirring

Temperature Temperature affects the speed at which

particles move. When particles move faster, more solvents and solute particles will bump into each other. This will quickly spread the solute particles throughout the solvent.

Large particles take longer to dissolve than smaller particles of the same substance.

For example, sugar cubes dissolve more slowly than granular sugar.

Particle Size

Last topic – Separating solutions and mixtures! Aren’t Pure Substances and Mixtures fun! ....all these delicious sugary pictures are making me hungry...

Seperating Solutions The components of a solution have very

similar properties and characteristics, which make them difficult to separate.

The most common strategy involves making the solvent or solute change state so that it can be removed from the solution.

In paper chromatography a highly concentrated solution is placed on a single spot and is absorbed by the paper. The paper is dipped in a solvent so that the spot is above the solvent. The solvent moves through the paper because the solvent particles are attracted to the paper particles and to one another. Different compounds travel different distances from the starting point and become separated.

Paper Chromatography

When you heat up an object, eventually all of the water particles leave the solution, leaving the solute particles behind.

Maple syrup is made by boiling maple sap. This causes the water in maple sap to evaporate, which leaves behind a concentrated solution of maple syrup.

Evaporation

Distillation enables you to retain both the solute and the solvent from a solution.

During the distillation process, the solution is boiled, which vaporizes the solvent. The solute remains in the original container, but the solvent condenses and is collected.

This process removes salt from water so it can be drank.

Distillation

Generally speaking, separating mechanical mixtures is easier, because the components of the mechanical mixture are usually quite different from each other.

Separating Mechanical Mixtures

Filtration is the mechanical process of separating solids from liquids or gases using a porous article or mass, such as paper or sand.

When the mixture is poured into the filter, the solid parts are trapped in the filter, and the liquid passes through.

Filtrations is used to separate solids from liquids or gases.

Filtration

Sorting is a technique that involves separating substances on the basis of appearance (e.g. Size, colour, composition)

We should practice this technique to ensure our garbage is put where it belongs!

Sorting

Sifting is a means of separating solids by component size. It involves shaking a solid material while it passes through a screen or mesh.

Componenets of the solid materials that are small enough to pass through do, separating them from larger components.

Sifting is used to separate solids from solids.

Sifting

Some metals are magnetic because their component particles are attracted to the particles within magnets

Iron, steel, and nickel are highly attracted to magnets, whereas most other substances are not. Therefore, you can use a magnet to separate magnetic materials from ones which are not.

Magnetism