8F Compounds and mixtures

© OUP: To be used solely in purchaser’s school or college

8F Compounds and mixtures

Element or compound

Mixtures


Changing state


Element or compound



8F Element or compound – how are they different?

Decide if these statements describe an element or a compound.

contain only one type of atomsodium chloride is an examplethere are just over 100 different typescan be broken down into their separate elementscannot be broken down into anything smallercontain more than one type of atom that are chemically joinedthere are millions of different typeshydrogen gas is an example


8F Element or compound – how are they different?

Check your answers.

contain only one type of atom

sodium chloride is an example

there are just over 100 different types

can be broken down into their separate elements

cannot be broken down into anything smaller

contain more than one type of atom that are chemically joined

there are millions of different types

hydrogen gas is an example

Elements

Compounds


8F Fabulous formulae

A chemical formula can be very informative.It shows the numbers and types of elements in a compound.What is the formula of the compound described by these compositions?

One copper to one oxygen

One carbon to two oxygen

One calcium to one carbon to three oxygen

CuO

CO2

CaCO3

Hydrogen and oxygen in the ratio 2:1 H2O

Carbon and hydrogen in the ratio 4:1 CH4

Potassium, nitrogen and oxygen in the ratio 1:1:3 KNO3


8F Comparing properties

Does a compound have the same properties as the elements it is made of?

Substance Appearance Is it magnetic? Reaction with hydrochloric acid

iron shiny metal yes bubbles - hydrogen gas

sulphur yellow powder no no bubbles

iron-sulphur mixture

shiny metal + yellow powder

only the iron is attracted to the magnet

bubbles from the iron only – hydrogen gas

iron sulphide brown solid no bubbles – not hydrogen gas


8F Comparing properties

The word equation for the chemical reaction between iron and sulphur is

Compare the particles of the elements, the mixture and the compound.

Why does iron sulphide have different properties to the elements it is made of?


8F Signs of a chemical reaction

How do you know when a chemical reaction is taking place?

colour changes gives out a gas

cools down

produces a solid

glowsheats up

produces smokeflashes


8F Compounds in chemical reactions

Compounds can be the products of chemical reactions but can they also be reactants?Take a look at these chemical reactions and match the reactants and products.

hydrochloric + magnesiumacid carbonate

copper + carbonoxide dioxide

sodium + ironcarbonate chloride

carbon + water

coppercarbonate

iron + sodiumcarbonate chloride

sucrose carbon + water + magnesiumdioxide chloride

carbon + water + magnesiumdioxide chloride

iron + sodiumcarbonate chloride

copper + carbonoxide dioxide

carbon + water


1. In an element, the atoms are all the same.

2. A compound contains atoms of different elements joined together.

3. Carbon is a compound.

4. Elements in a compound are easy to separate.

5. A chemical formula shows what elements are in a compound.

8F Element or compound?

True or false?

TRUE

TRUE

FALSE

FALSE

TRUE


Mixtures



8F Is it pure or impure? What is a mixture?

A pure substance is not mixed with anything else.

A material that contains more than one substance is ‘impure’.

A mixture contains more than one substance mixed up, but not chemically joined, so they can be separated.

So mixtures are impure.

Is mineral water pure?

Is tap water pure?

How would you describe pure water?


8F

Can you remember the three lab methods for separating mixtures?

filtering

chromatography

distillation

Which of these does each method do?

A separates a solvent from a solution

B separates a solid from a liquid

C separates substances with different solubilities

8F Separating mixtures


8F Mixtures – composition of air

Air is not a pure substance, it is a mixture of gases.

What gases are present in air?

Which gas do we need to inhale to stay alive?

Is the composition of air always the same?


8F Mixtures – composition of air

But is inhaled air the same as exhaled air?

What’s the formula for air?It’s a trick question – there isn’t a formula for air. Why not?


1. Substances in a mixture are easier to separate than substances in a compound.

2. Pure water is a mixture.

3. Pure air is a mixture.

4. Substances in mixtures are not chemically joined.

5. Pure copper oxide is a mixture.

8F Mixtures – true or false?

True or false?

TRUE

FALSE

TRUE

TRUE

FALSE


Changing state



8F Melting points and boiling points

Reminder:If a substance is heated to its melting point it changes from a ?? to a ??.If a substance is cooled to its melting point it changes from a ?? to a ??.If a substance is heated to its boiling point it changes from a ?? to a ??.

If a substance is cooled to its boiling point it changes from a ?? to a ??.

Pure substances have fixed melting points and boiling points.

Do mixtures have fixed melting points and boiling points?


8F Mixtures

Why do we put salt on roads and paths to melt ice?

Because mixing salt with water:

a) raises the freezing point to a higher temperature

b) lowers the freezing point to a lower temperature

c) raises the boiling point to a higher temperature?


8F Mixtures

Mixtures, like salt and water, do not have fixed melting points or boiling points.Increasing the amount of salt added to water:

Increases the boiling point

Decreases the freezing point

Boiling potatoes: what is the effect of adding salt to the water?


8F Element, compound, or mixture?

How would you classify the following: element, compound, or mixture?• air • iron • lemonade • sugar • soil

Use the flow chart to help you.

Element, compound or mixture?

Are all the particles in this substance the same?

Are all the atoms in these particles the same?

It must be a mixture!A mixture is a collection of

substances made of different particles that are not chemically joined

It must be an element.An element is a substance that contains just one type of atom.

It must be a compound.A compound contains different atoms

that are chemically bonded

yes no

yes no

Documents

8F Compounds and mixtures