Chemistry c3
C3
- Created by: bambi
- 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
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
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
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.
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
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
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
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
electroysis
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
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
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
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
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
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
Example
2na + cl2 > 2nacl
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
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)
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
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
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
Disadvantages
Can cause a build up of limescale
Can cause pipes to become blocked
More soap is needed for washing
Titrations
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.
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
Alcohols
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
Hexonal-c6h13oh
Alcohol are made by two methods
Fermentation
Hydration of ethene
Alcohols
Fermentation
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
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
Solubility
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
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
Esters
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
Equations
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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