Chemistry c3


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  • Created on: 17-05-12 15:22

Tests for water

Qualitative analysis, investigates chemicals present in a sample

Quantitative analysis , measures the amount of each chemical present

Pollution that can contaminate the water comes from

Industry- discharges toxic chemicals in it's waste

Fertilisers: contaminate rivers and lakes

Detergents- washed down the drain contaminates water systems

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Test for ions

Ions are atoms that have lost or gained electrons

Ionic bonds are formed between metals and non metals

Metals form positive ions called cations by losing electrons

Non metals usually form negative ions called anions

Flame tests - this is qualitative analysis technique

1 Clean piece of wire dipped in a solution and put in a hot bunson flame

2 Colour produced indicates the metal ions present

3 colours produced as the electrons in the atoms move between energy levels

4 different metals have different electron arrangement so they have different energy levels

5 so the different metals give different colours of light

Calcium ca2+ is brick red

Sodium na+. Is yellow

Potassium k+ is lilac

Copper cu2+ is green

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Looking for cations

Add sodium hydroxide solution to a solution that is unknown

Metal ions are often unsolube so a precipitation reaction is likely to occur

Precipitate that is formed can identify the ion present

1 ammonium nh4+ there is no precipitate

2 aluminium al3+ a White precipitate is formed

3 calcium ca2+ White precipitate is formed

4. Copperii cu2+ blue precipitate is formed

5 ironiii fe3+ brown precipitate is formed (rust)

Precipitate will be a solid hydroxide of the cation

Aluminium and calcium can be distinguished by added excess sodium hydroxide

In excess sodium hydroxide , calcium precipitate is not changed

Aluminium precipitate does not change

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Ammonium test and looking for anions

To test for the ammonium ion :

Heat the unknown sample with concentrated sodium hydroxide

If the ions are present the smelly alkaline gas called ammonia will be given off

This is detected if it turns universal indicater blue

Looking for anions

If indicater turns blue or purple than hydroxide solution is present

If they are not present add hydrochloric acid

Bubbles of gas will be given off of carbonate or sulphide ions are present.

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Hydrochloric acid + sodium carbonate give off sodium chloride + co2 +h20

hydrochloric acid + sodium sulpite gives sodium cloride + so2 +h2o

You can identify which gas is formed by these tests

Gas turns limewater milky if it is carbon dioxide and carbonate

Gas Is acidic and choking smell it is sulpar dioxide sulphite

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Detecting acids

Sulphur dioxide and nitrogen dioxide realised by burning fossil fuels makes water acidic

Acidic solutions contain eccess h+ ions which is detected by using indicaters

Litmus and universal indicater both turn red in acids

all acids react with reactive metals ( alkali metals)

Hydrogen and salt is made

Test for hydrogen is squeaky pop

Acids also react with metal carbonates

Acid + metal carbonate gives a salt water and carbon dioxide

Carbon dioxide is tested for by lime water as it turns it cloudy

Formulae of common acids

Hydrochloric acid is hcl

Sulphuric acid is h2so4

Nitric acid is hno3

Phosphoric acid is h3po4

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Looking for anions

Test for sulphate ions uses precipitation reaction

Barium chloride solution added to sulphate

White precipitate of barium sulphate forms from this

Carbonates and sulphites also produce precipitates with barium chloride

To be sure what ion that is present you add hydrochloric acid

There is no effect on sulphates

However it dissolves the White precipitate of carbonate and sulphides

Halide atoms such as chlorine is identified using silver nitrate solution acidified with nitric acid

A different colour precipitate of the silver halide forms due to this

Cl- White

Bromine- cream

Iodine - yellow

Dilute nitric acid used remove any carbon sulphite hydroxide ions as they also produce precipitate with silver nitrate

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Hard water

Hard water won't easily form a other with a soap. It makes scum instead

Hard water also forms limescale on the sides of pipes boilers and kettles

Hard water contains calcium ions and magnesium ions and this is gotten from the soils

The concentration of calcium carbonate in milligrams per cubic dice meter are converted into clarks degrees to see how hard the water is

0 to 99.99 ( 0 to 6.9 clarks) is soft water

400 to 499.9 ( 28 to 34.9 clarks ) is very hard water

Qauntitive analysis

1dm3 = 1000cm3

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electroysis is the breaking down of a substance using electricity

it requires a liquid to coduct electricity� this is called the electrolyte

electrolytes are usally free ions dissolved in water eg dissolved salts or molten ionic substances

it is the free ions that conduct electricity and allow the electroysis to work

for an electrical curcuit to work there has to be a flow of electrons

1 electrons are taken qaway from the postive anode and given to other ions at the negative cathod this happens because opposites attract� so the negative atoms goes to the positive anode and postive goes to the cathode this means that in giving the electronss to the postive atoms all the ions become neutral

2 as ions gain or lose electrons they become atoms or molecules and are released

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electroysis and copper

the pureer copper is the better it conducts electricity. so electroysis is used to purify copper

1 The electrons are pulled off the copper atoms at the anode causing them to go into soulution as ca2+ ions

2 ca2+ ions near the cathode gain electrons and turn back into copper ions

3 The impurities are dropped at the anode as sludge where pur copper bond to the cathode

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electrolysis of salts and half equations

positive ions are called cations because they are attracted to the negative cathode

negative ions are called anions as they are attracted to the �positive anode

1 at the cathode two hydrogen atoms accept two electrons� to become a hydrogen molecule 2h+ +2e- > h2

�2 at the anode two cloride cl- ions lose thier electrons� and become one chlorine molecule 2cl - >cl2 + 2e-

3 naoh is left in the solution

the number in the half equations has to be the same on both sides

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Calculating formulae moles

Relative atomic masses tell us aproximately how much heavier one atom of the element is compared to a hydrogen atom

Relative formula mass of an element is found by adding the relative atomic masses of all the atoms in the formula together

Mass = number of moles *mr

M= n of moles * mass of one mole

Mole is equal to 6 *10to the 23

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Reaction if alkali metals with water

Alkali metals get more reactive as you go down the group. This is because as The atoms get bigger the force of attraction between the Nucleus and the outermost electrons get smaller. This means the electron will be easier to lose

The alkali metals are stored under oil because they react vigorously with oxygen and water

When alkali metals react with water a metal hydroxide and hydrogen gas is formed

The metal hydroxide dissolves in water to form an alkali solution

2k(s) + 2h2o(l) > 2koh (aq) + h2(g)

A stands for aquras which means in solution

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Reaction of alkali metals with non metals

When alkali metals react with non metals to form ionic compounds. The metal atoms lose one electron each to form metal ions with a positive charge . The products are White solids that dissolve in water to form colourless solutions


2na + cl2 > 2nacl

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The halogens

As we go down group 7 the netting and the boiling points increase . The group 7 elements become less reactive as you go down the group

The elements become less reactive down the group because it becomes harder for them to gain an electron . This is due to there not being as big a pull from the nucleus in order to draw the new electron in.

At room temperature florine and chlorine are gases and bromine is liquid . They are all coloured vapours. The cases of bromine and chorine they have an extremely strong smell.

They are all diatomic which means that they are made up of pairs of atoms

Halogens are brittle and crumbly as solids and are very poor conductors of electricity

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Reaction of halogens

Halogens react with metals to produce ionic salts

2li. + cl2 > 2licl

Reaction of halogens with other non metallic elements

Halogen rections with other non metallic elements

Halogens react with other non matalic elements to produce molecular compounds

H2(g) + cl2( g) > 2hcl(g)

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Displacement reaction of halogens

A more reactive halogen will displace a less reactive halogen from a solution version of it's salt chorine will displace both bromine and iodine but bromine will displace displace iodine and not chlorine 2kl + cl2 > kCl + I2

Trends in group one

Alkali metals all have one electron in their outer shell

They get more reactive as you go down the group as the outer electron is lost more easily

The transition metals properties

1 They have high melting points

2 they are more dense

3 they are strong and hard

4 ductile can be made easily into copper wires

5 sonorous

6 form positive ions

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Hard water

There are too types of hard water permanent and temporary

Perminant hard water always contains a calcium salt that is not removed by boiling

Tempory hard water can be softened by boiling

Temporary hard water contains a salt called hydrogen hydrocarbonate that decompose upon heating to form carbonate ions . These react with magnesium or calcium ions to form precipitates . The precipitate is known as limescale

The hardness can be measured by titration with a salt solution . The more soup solution needed to firm a permanent lather the harder the water

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Advantages of hard water

Contains calcium needed for healthy bones and teeth

May help to reduce heart disease

Lime scale build up in pipes can prevent corrosion and stop dangerous metals from dissolving in the water


Can cause a build up of limescale

Can cause pipes to become blocked

More soap is needed for washing

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It is used to find out how much acid is needed to neutralise an alkali

1 a pipette which has been carefully washed and rinsed with an alkali - this is used to measure out a known and accurate measure of an alkali

2 the alkali is put in a clean conical flask and a suitable indicater is added

3 the acid is placed in a burette which has been rinsed out with alkali - an initial measurement of the volume of acid in the burrete is made

4 the acid is carefully added to the alkali until the indicater changes colour

This is called the end point

You must find a suitable indicater to find the volume of different strengths of acid and alkalis

For example when a strong acid and alkali react any acid based indicted such as methyl orange can be used.

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Making sulphuric acid

1 the first stage is too make sulphuric acid - this I made by burning sulphur in the air by roasting sulphur ores

S+ o2 > so2

2 the sulphur dioxide is than oxidised to make sulphur trioxide this is reversible

2so2 + o2 > 2so3

3 next the sulphur troxide is dissolved in concentrated sulphuric acid to form oleum

So3 + h2so4 >. h2s2o7

4 finally the oluem is diluted with water to form concentrated sulphuric acid

h2s2o7 +h2o > 2h2so4

It is exothermic ( gives out heat)

To get more product the temperature should be reduced

Temperature decreasing causes the reaction to slow down

This means that the optimum temperature is 450 degrees as a compromise

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The naming of alcohols is the same s the alkanes cn h2n+1 exept it has. Oh on the end

Methanol - ch3oh

Ethanol -c2h5oh

Propane- c3h7oh

Butonal- c4h9oh

Pentonal- c5h11oh


Alcohol are made by two methods


Hydration of ethene

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In fermentation the fungi yeast changes sugar into ethanol and carbon dioxide

C6 h12 o6 > 2c2 h5oh + 2co2

The process is anaerobic without oxygen and occurs at about 35 degrees

Hydration of ethene is made by reacting ethene using steam

The conditions

Phosphoric acid is the catalyst

Temperature of 300 degrees

Pressure of 6.5 *10^3 kpa

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Uses of alcohols

1 they react with oxygen to produce carboxylic acids

2 these carboxylic react with oxygen to produce esters esters are flamabol and extremely volatile ( evaporate easily)

3 methylated spirit is made from a mix of alcohol and other chemicals and is used to clean paintbrushes

4 used to drink

5 carboxylic acids can be used to make soaps and fabrics


1 first 3 alcohols mix completely with water

2 alcohols can disolve hydrocarbons, oils and fats

3 solvent for perfumes and aftershave solutions

4 ethanol can e mixed with water to make fuel

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Carboxylic acid

General formula is

CnH2n+1 cooh

They are often called organic acids

They all end with anoic acid

The names start with normal meth/eth/prop/but

Methanoic acid hcooh

Ethanoic acid ch3cooh

Propanoic acid c2c5cooh

Butanoic acid c3h7cooh

Organic acids mix with water and with solvents like alchols and alkanes

Ethonic acids are the acid in vinegar

Aspirin is a man made organic acid

They are used to make esters

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Acid catalyst is used to make it

Used to make flavouring , ointment, aromas and used as a solvent like in paint

Mixes with alcohol and organic substances but not water

Esters are in the functional group coo

They are formed from an alcohol and a carboxylic acid

The reaction is known as esterification

Sulphuric acid is used as a catalyst

Naming esters

Name of alcohol is written first

The acid part is written next

The oil ending of the carboxylic acid is changed to oate

Methanol + ethanoc acid > methyloate + water

They are used as flavourings , solvents and perfumes

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Concentration = amount of soulute/ volume of solvent

Concentration is dm ^3 which is 1000cm^3

Moles = mass over rfm

Con = moles 1000/volume

Moles= con volume/1000

1 calculate no moles of reactant

2 determine mole ratio of recant to product and make it balanced

3 calculate no moles of product

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