8 f compounds & mixtures (boardworks)

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KS3 Chemistry
8F Compounds
and Mixtures

8F Compounds and Mixtures
Mixtures
Summary activities
Comparing elements and compounds
Compound names and formulae
Contents
Word equations

Properties of elements and compounds
Why is it safe to put sodium chloride on fish and chips…
…but not safe to use sodium and chlorine?

Compounds contain two or more different types of atom.
Elements are materials made up of one type of atom only.
Atoms in elements and compounds
The element, hydrogen, exists
as molecules.
Each hydrogen molecule is
made up of two hydrogen atoms
joined together.
The compound, water, exists
as molecules.
Each water molecule consists
of two hydrogen atoms joined
to one oxygen atom.
H H

Element or compound?

A compound is made when atoms of different elements
react and join together.
For example, water is produced from the chemical reaction
between hydrogen and oxygen.
Making a compound – water
Two hydrogen molecules react with one oxygen molecule
to produce two molecules of water.
+
H H
H H
O O
hydrogen oxygen water+
Why does water have different properties to its elements?

Properties of a compound–carbon dioxide
A compound has different properties to the elements from
which it is made because the atoms are joined differently.
Black solid
used as fuel.
Colourless gas in
which many
substances burn.
Colourless gas used
in fizzy drinks and
fire extinguishers.
+
+ O OC
carbon oxygen carbon dioxide+

A compound is not a mixture
The atoms in water, the
compound made when
hydrogen and oxygen react
and their atoms become
chemically joined to each
other, look like this…
The atoms in a mixture of
hydrogen gas and oxygen
gas, which have not reacted
with each other, look like this…

Mixtures
Summary activities
Contents
Word equations

To name simple compounds of metals and non-metals:
Naming simple compounds
2. Write down the name of the non-metal,
changing the ending of the word to “-ide”.
1. Write down the name of the metal.
What is the name of the compound made when the
following elements combine?
 magnesium and oxygen
 sodium and chlorine
 oxygen and iron
magnesium oxide
sodium chloride
iron oxide

What is the name of each compound formed by these
metal and non-metal elements?
nitrogenlithium
sulphurzinc
iodinenickel
brominealuminium
oxygentin
chlorinesodium
nitrogenmagnesium
sulphuriron
Name of compoundElement 2Element 1
iron sulphide
magnesium nitride
sodium chloride
tin oxide
aluminium bromide
nickel iodide
zinc sulphide
lithium nitride
Naming simple compounds

Many compounds contain more than two elements.
oxygenbrominealuminium
oxygensulphurcopper
oxygen
oxygen
oxygen
Element 3
nitrogensodium
magnesium nitratenitrogenmagnesium
nickel sulphatesulphurnickel
Name of compoundElement 2Element 1
sodium nitrate
copper sulphate
aluminium bromate
Naming further compounds
For compounds containing two elements plus oxygen,
the ending of the other non-metal usually changes to “--ate”.

A compound always contains a particular amount of
each element. It has a fixed composition.
Composition of compounds
A compound contains atoms from different elements that
are chemically joined together.
Compound names can get quite long and complicated,
so the symbols of the elements are used as a shorthand.
The symbols of the elements in a compound are
combined to give the formula of the compound.
What is the formula of
carbon dioxide?

carbon dioxide
A formula uses the symbols of the elements in a compound.
When there is more than one atom of each element, the
number is always written after the symbol.
Writing a formula
carbon atom = 1
formula =
hydrogen atoms = 2
formula =
The formula shows the ratio of atoms in a compound.
water
CO2
H2O
oxygen atoms = 2
oxygen atom = 1

1. Titanium oxide
For every titanium atom there are two oxygen atoms.
Formula =
2. Lithium oxide
For every two lithium atoms there is one oxygen atom.
Formula =
3. Aluminium chloride
For every aluminium atom there are three chlorine atoms.
Formula =
What is the formula of each of these compounds?
What is the formula?
TiO2
Li2O
AlCl3
(In a formula put the metal first as when naming a compound.)

1. Silicon chloride
For every silicon atom there are four chlorine atoms.
Formula =
2. Manganese oxide
For every manganese atom there are two oxygen atoms.
Formula =
3. Aluminium oxide
For every two aluminium atoms there are three oxygen atoms.
Formula =
What is the formula of each of these compounds?
What is the formula?
SiCl4
MnO2
Al2O3
(In a formula put the metal first as when naming a compound.)

What is the ratio of atoms?

What does a formula show?

Mixtures
Summary activities
Contents
Word equations

Writing a word equation
A word equation can be used to describe any chemical
reaction, i.e. any process in which atoms become joined
in different ways.
The steps for writing a word equation are:
1. On the right-handside, put the name of the reactant(s).
If there are two or more reactants, link them with a ++ sign.
2. In the middle, write down an arrow ( ).
3. On the right-handside, put the name of the product(s).
If there are two or more products, link them with a ++ sign.

The lead and oxygen don’t mix, they react to form lead oxide.
This means that the lead and oxygen atoms in the product
are joined differently to the atoms in the reactants .
Lead reacts with oxygen to form lead oxide.
lead + oxygen lead oxide
Why is lead oxide so different to both lead and oxygen?
What is the word equation?
What is the word equation for this reaction?

1. Limestone (calcium carbonate) is heated to make
calcium oxide and carbon dioxide.
2. Magnesium reacts with hydrochloric acid to make
magnesium chloride and hydrogen.
3. Methane is burnt to make carbon dioxide and water.
calcium carbonate calcium oxide +carbon dioxide
magnesium + hydrochloric acid magnesium chloride + hydrogen
methane + oxygen carbon dioxide + water
What is the word equation?
Write out word equations for the following chemical reactions.

Mixtures
Summary activities
Contents
Word equations

A mixture is not the same as a compound:
1. The proportions of the substances in a mixture are not fixed.
2. The properties of a mixture are often an “average” of the
properties of its ingredients (e.g. a mixture of a black and
white powder is grey).
3. The substances in a mixture are just mixed, not chemically
joined, and so it is usually quite easy to separate the
A mixture contains two or more
substances that are mixedmixed together
but have not reacted with each other.
Sea water is a mixture of salts, water
and other substances.
What is a mixture?
ingredients (e.g. it is easy to get salt from sea water).

Element, compound or mixture?

Liquids that do not mix are described as immiscible.
Examples of immiscible liquids are water with oil and
water with petrol.
On a small scale, immiscible liquids can be separated
by simply removing the top layer using a pipette.
oil
water water oil
Separating immiscible liquids

Liquids that do mix are described as miscible.
Examples of miscible liquids are water with alcohol and
petrol with kerosine.
Miscible liquids can be separated by heating them to boiling.
The components of the mixture have different boiling points
and so will boil off at different temperatures.
A condenser is used to recover the liquids as they boil off.
This piece of apparatus is a tube that has cold water
circulating around the outside. It cools down vapours and
condenses them back to a liquid.
Substances with low boiling points are collected first, while
those with higher boiling points are collected later.
Separating miscible liquids

Distillation apparatus

How can each mixture be separated?
alcoholalcohol and water
cooking oilcooking oil and water
watersea water
saltsea water
glassglass and water
MethodWantedMixture
filter
evaporate
distil
pipette
distil
Separating mixtures

Reggie has been given a mixture
of salt, sand and water.
He needs to separate these three
substances but cannot remember
how, so Reggie needs your help!
Experiment to separate a mixture
Write an experimental plan for Reggie to follow so that he
will end up with the sand, salt and water in separate
containers.
Start your plan with a list of the equipment that is needed
for separating this mixture. Then write a step by step plan
that is easy for Reggie or anyone else to follow.

Mixtures
Summary activities
Contents
Word equations

Glossary
atom – The smallest particle that can exist on its own.
boiling point – Temperature at which a pure liquid
becomes a gas.
compound – Substance made up of two or more
different types of atoms that are chemically joined together.
element – Substance made up of only one type of atom.
formula – The symbols and numbers that represent the
ratio of different atoms in a substance.
immiscible – Liquids which do not mix.
miscible – Liquids which do mix.
mixture – Two or more substances that are mixed but
not chemically joined together.

Anagrams

True or false?

Multiple-choice quiz

8 f compounds & mixtures (boardworks)

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