8F Compounds and Mixtures (2)

7/22/2019 8F Compounds and Mixtures (2)

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Elements and Compounds

It follows that

compounds contain twoor more types of atom.

The water molecule contains two

hydrogen atoms bonded to one

oxygen atom, so the formula is H2O.

Elements are materialsmade up of one type of

atom only. Hydrogen molecule contains

two hydrogen atoms bonded

together, so the formula is H2.


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Compounds: Water

Compounds are produced when elements combine. For

example, water is produced in the following reaction.

Word Equation

Hydrogen + Oxygen Water

+ +

Two water molecules react with one oxygen molecule to give water.


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Compoundsnot mixtures

The atoms in compounds are NOT

mixed together. A mixture of hydrogenand oxygen would look like:

They become bondedtogether during a chemical

reaction. Because of this compounds have properties that

are verydifferent to the elements that they are made from.

HYDROGEN

Flammable gas.

OXYGEN

Gas in which many

substances burn.

WATER

Liquid that extinguishes

most fires.

+


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Compoundsnot mixtures

Black solid

used as

barbecue

fuel

Gas in

which

many

substancesburn

Gas used in

fizzy drinks and

fire

extinguishers

carbon + oxygen carbon dioxide


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Naming Simple compounds.

It is easy to name simple compounds of metals and non-metals.

1. Write down the name of the metal2. Write down the name of the non-metal but change

the ending to ide.

oxygencalcium

sulphursilver

brominecopper

Name of compoundElement 2Element 1

copper bromide

silver sulphide

calcium oxide

1) magnesium 2) oxygen =magnesium

oxide

1) sodium 2) chlorine =sodium

chloride


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Name the compound formed from these elements

nitrogenlithium

sulphurzinc

iodinenickel

brominealuminium

oxygentin

chlorinesodium

nitrogenmagnesium

sulphuriron


iron sulphide

magnesium nitride

sodium chloride

tin oxide

aluminium bromide

nickel iodide

zinc sulphide

lithium nitride

Naming Simple compounds.


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Naming more complicated Compounds

Many compounds contain more than twoelements. Naming them can get complicated butfor those containing two elements plusoxygenthe name ending usually changes to ate.

oxygenbrominealuminium

oxygensulphurcopperoxygen

oxygen

oxygen

Element 3

nitrogensodium

magnesium nitratenitrogenmagnesium

nickel sulphatesulphurnickel


sodium nitrate

copper sulphate

aluminium bromate



The composition of compounds.

Compounds are very different to the elements from

which they are made but there is another way inwhich compounds are different to mixtures.

In a mixture you can add any amount of the

ingredients.

Compounds always contain a definite amount of eachelement. They have a fixed composition.

This is not really surprising as looking at the word

equations you will have seen they always have adefinite number of element atoms joined together.

Na Cl O OC Mg OO

H

H



The formula of compounds

This means that every compound can have a

formula that tells us how many of each type of atom

are present. We include small slightly dropped

numbers if there are more of one atom than the

other.

Water

One oxygen atom

Two hydrogen atoms

Formula H2O

O

H

H

Carbon dioxide

One carbon

atom

Two oxygen

atoms

FormulaCO2

O OC



What is the formulae

of each of thecompounds shown?

(As with names, put

the metal first.)

2. Lithium Oxide

LiO

Li

? oxygen atom

? lithium atoms

Formula

?

3. Aluminium chloride

? aluminium atom

? chlorine atomsFormula

Al ClCl

Cl

1. Titanium oxide

? titanium atom

? oxygen atomsFormula

Ti OO

1 titanium atom

2 oxygen atoms

Formula

TiO2

1 oxygen atom

2 lithium atoms

Formula

Li2O

1 aluminium atom

3 chlorine atomsFormula

AlCl3

Activity




What is the formulaeof each of the compounds

shown?

Silicon chloride

? silicon atom

? chlorine atomsFormula

Si ClCl

Cl

Manganese oxide

? manganese atom

? oxygen atomsFormula

Mn OO

1 manganese atom

2 oxygen atoms

Formula

MnO2

1 silicon atom

4 chlorine atoms

Formula

SiCl4

Cl

Aluminium oxide

? aluminium atom

? oxygen atoms

Formula

Al

OO O

2 aluminium atom

3 oxygen atoms

Formula

Al2O3

Al

Activity




Word equations can be used to describe anychemical change. (i.e. any process where the atoms

become joined (bonded) in different ways).

The steps are:

1. Write down the name of the reactant(s) linking

them with a +sign if there is more than one.

2. Write down an arrow

3. Write down the names of the products linkingthem with a +sign if there is more than one

Word Equations



It hasnt just mixed.

It has reacted and atoms are joined differently.

Write out word equations for this reaction

Lead reacts with oxygen to form lead oxide

Lead + oxygen lead oxide

Lead Lead oxide

Why is lead oxide so different to both lead and oxygen?

Activity

Word Equations

A ti it



Write out word equations for the following

reactions.1. Limestone (calcium carbonate) is heated to make

calcium oxide and carbon dioxide.

2. Magnesium reacts with hydrochloric acid to makemagnesium chloride and hydrogen.

3. Methane is burnt to make carbon dioxide andwater.

calcium carbonatecalcium oxide +carbon dioxide

magnesium + hydrochloric acid magnesium chloride + hydrogen

methane + oxygencarbon dioxide + water

Activity

Word Equations



Mixtures

Mixtures are, as the name indicates, mixedrather thanreacted together.

This means that, unlike compounds:1 They do not have to have any particularproportions of the various ingredients.

2 Their properties are often an average of theproperties of their ingredients. (eg. a mixture of ablack and white powder is grey!)

sea water: a mixture

of salts and water

3 They are mixed, not bonded, and

so are usually not too hard toseparate back into their ingredients.

(For example, it is easy to get salt

from sea water.)



S i Mi



Immiscible liquids

Immiscible means doesnt mix and so we are talkingabout mixtures like water with cooking oil or water with

petrol.

On a small scale you can simply remove the top layer

using a pipette.

oil

water

water oil

Separating Mixtures

S ti Mi t



Miscible liquidsMiscible means does mix and so we are talking about

mixtures like water and alcohol or petrol with kerosine.

These are separated by boiling them as it is unlikely that

they will boil at exactly the same temperature.

In order to get back the liquids we use a condenser. This

is a tube that has cold water circulating through the

outside. It cools down vapours and condenses them back

to a liquid. Substances with low boiling points collect first,

while those with higher boiling points collect later.

Separating Mixtures

Mi ibl li id



condenser

electric

heatercollection

beaker

water in

water out

thermometer

Distillation Equipment

Miscible liquids

S ti



Separations

How would you get this?

Mixture Wanted Method

Glass and water glass

Sea water saltSea water water

Cooking oil & water cooking oil

Alcohol and water alcohol

filter

evaporate

distil

pipette

distil

S ti E i t



John has been given a mixture of salt, sand and water.He needs to separate them but cannot remember how.

Can you help him?

Write an experimental plan for John to follow so that hecan have the sand, salt and water in separate

containers.

Make sure you start off by telling him what equipmenthe will need.

Then he will need a step by step plan that is easy to

follow.

Separation Experiment

S ti iti



Summary activities



1. Which of these is a compound?

A. bromine

B. copperC. carbon dioxide

D. uranium



2. Which of these best describes a

compound?

A. Two or more atoms bonded together.

B. Two or more elements mixed together.C. Two or elements bonded together.

D. Two or more types of molecule mixed

together.



3. Which of these could best describe compounds?

Substances that:

A. are similar to the elements that they are made

from.

B. can be formed when elements react together.

C. can be formed when elements decompose into

two or more new substances.

D. substances with symbols in the Periodic Table.


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4. What would be the name of acompound formed from sulphur, oxygenand zinc?

A. sulphur zincideB. sulphur zincate

C. zinc sulphide

D. zinc sulphate


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5. What would be the formula of acompound containing two aluminium

atoms for every three sulphur atoms?

A. Al2S3 B. Al3S2

C.Al2S3 D.Al3S2


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6. How would you separate a mixture ofwater and alcohol. (Two miscible liquids)

A. filteringB. chromatography

C. evaporation

D. distillation


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7. What is the main technique you woulduse when separating a mixture of saltand sand?

A. filtering

B. chromatography

C. evaporation

D. distillation


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8. Use the chromatogram to decide

which dyes are in the ink.

A B C D Ink

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8F Compounds and Mixtures (2)