© OUP: To be used solely in purchaser’s school or college 8F Compounds and mixtures Element or...
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Transcript of © OUP: To be used solely in purchaser’s school or college 8F Compounds and mixtures Element or...
© OUP: To be used solely in purchaser’s school or college
8F Compounds and mixtures
Element or compound
Mixtures
8F Compounds and mixtures
Changing state
© OUP: To be used solely in purchaser’s school or college
Element or compound
8F Compounds and mixtures
© OUP: To be used solely in purchaser’s school or college
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
© OUP: To be used solely in purchaser’s school or college
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
© OUP: To be used solely in purchaser’s school or college
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
© OUP: To be used solely in purchaser’s school or college
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
© OUP: To be used solely in purchaser’s school or college
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?
© OUP: To be used solely in purchaser’s school or college
8F Signs of a chemical reaction
How do you know when a chemical reaction is taking place?
colour changesgives out a gas
cools down
produces a solid
glowsheats up
produces smokeflashes
© OUP: To be used solely in purchaser’s school or college
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
© OUP: To be used solely in purchaser’s school or college
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
© OUP: To be used solely in purchaser’s school or college
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?
© OUP: To be used solely in purchaser’s school or college
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
© OUP: To be used solely in purchaser’s school or college
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?
© OUP: To be used solely in purchaser’s school or college
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?
© OUP: To be used solely in purchaser’s school or college
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
© OUP: To be used solely in purchaser’s school or college
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?
© OUP: To be used solely in purchaser’s school or college
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?
© OUP: To be used solely in purchaser’s school or college
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?
© OUP: To be used solely in purchaser’s school or college
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