review of chemistry
TRANSCRIPT
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Chemistry Revision
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AtomsAll chemical elements are made up of atoms
Every atom is made up of smaller particles; neutronsandprotonsin the atoms nucleus which is
surrounded by electrons
Atoms become ions when they gain/lose an electron
The atomic numberis the number of protons in the
nucleus ( which is the same as the number of
electrons)The mass number is the protons + neutrons in the
nucleus, the mass of an electron is so small it is
considered to be negligible
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Atom Mass
A is the relative atomic mass
M is the relative molecular mass,
For example- HO has a relative
molecular mass of 18 [(2x1) + 16)
For ionic compounds the term relativeformula mass is used as there is no
separate molecules
r
r
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Isotopes
Isotopes are different forms of the same
element
If an isotope has more neutrons than protons,
it can sometimes be unstable and is likely to
decay
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Alkali MetalsGroup 1 in the periodic table
More reactive as you go down the group
Low densities
Ionic compounds +1 charge
Alkaline solution
Soft shiny metals
React with the oxygen in the air and become tarnishedso they
are stored in oil
React vigorously with water, they fizz and produce hydrogen gasIdentifying Alkali Metals- identified using the flame test
Lithium burns with a red colour
Sodium burns with a yellow/orange colour
Potassium burns with a lilac/purple colour
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HalogensGroup 7 in the periodic table
More reactive as you go up the group
Reacts with alkali metals
Halogens react with iron- iron wool bursts into flames when
it reacts with fluorine gasHalogen displacement reactions mean the more reactive
halogen displaces the less reactive halogen
Identifying Halides- identified using the precipitation test
using silver nitrate
Chlorine- white/silver
Bromine- Pale yellow/cream
Iodine- yellow
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MetalPhysical PropertiesThe following properties applies to copper
High electrical conductivity
High thermal conductivity
High melting point and boiling point
DuctileCorrosion resistant
Antibacterial
Malleable (can be hammered/squashed into differentshapes)
Easy to alloy
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Metallic Structure
positive
The structure can
easily pass the
vibration of hot
particles along andthe free electrons
move faster which
is why metals aresuch good
conductors
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Ionic Compound- Physical Properties
The following properties applies to Sodium Chloride
High melting point- because they have strong attractiveforces ( lot of energy to separate)
Solid sodium chloride does not conduct electricitybecause the lattice holds to sodium and chloride ions infixed positions ( Not free to move)
but it can conduct electricity does if dissolved in water
as the lattice breaks down so the ions move freelyBrittle- if a stress is applied will make the layers move
Soluble in water
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Ionic Structure
The sodium lost an electron andthe chlorine gained an electron
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Simple Covalent Molecule- Physical properties
Low melting point( strong bonds
but weak attractive forces)
Liquid at room temperature
Poor conductor of electricity
Water soluble
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Simple Covalent Structure
A covalent bond
happens when
electrons are
shared betweento atoms
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Giant Covalent SubstanceDiamond
Transparent + crystalline (used for jewellery)
Extremely hard ( lot of energy needed to breakdown lattice)
Electrical insulator
High melting point
Graphite
Grey/black shiny solid
Very soft- used in pencils
Conducts electricity( along the layer aselectrons are free to move but does notconduct across the layers)High melting point
Slippery( hexagonal layers slide across eachother
Both different forms of carbon
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Structure of diamond and graphite
Carbon atoms each connected to
4 other atoms
3-d Lattice based on a tetrahedral
unit cell
graphite Diamond
Made up of layers
Arranged in hexagonal ringsEach carbon atom is connected
to 3 other atoms
Bonds between layers are weak
Layers can slide over each other
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Carbon Nanotubes
One of the stiffest and strongest fibres knownHigh electrical conductivity
Formed when graphite layers are rolled up intotubes
Covalently bonded hexagonal carbon sheetsmake it very strong
Proposed uses for electrical connections insmaller circuits
Used in bike components, boat hulls andbonding of things like wind-turbines
Could be used for cancer treatment
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Smart MaterialsSmart materials are materials that change when there is a change
in their surroundingsThermochromic PigmentsSpecial paints which change
colour when there is a change in
temperature
Most are base on liquid crystal
technology
Used in mugs to see hot
temperatures
Also used in T-shirts
Photochromic PigmentsContain organic molecules which will
change colour when exposed to light,
especially ultraviolet light
Used in T-shirts and glasses
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Smart Materials
Shape-memory
polymersPlastics that regain their
shape when heated
Somewhere betweenthermoplastics and
thermosets
Used for sealing around
window framesCould be used for car
bodies (fix the dent)
or stitches which will adjust
to tension
Shape-memory alloysMetal alloys that regain
their shape when heated
Used for spectacle frames,
surgical plates and wires
HydrogelsPolymers that absorb or
expel water and swell or
shrink the size itswells/shrinks to depends
on changes in PH or
temperature
Used in artificial muscles
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Rates of reaction
We can measure the rate of reaction by :
-Capturing & measuring the volume of gas
produced by a reaction
- Measuring the change in mass
- Measuring the amount of light passing
through a reaction that is producing a
precipitate
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Chemical Reactions
Chemical reactions occur when molecules/atoms/ionscollide but it only happens there is enough energy forthe bonds to break and be reformed.
Successful collisions per second = collision frequency
Factors that affect the rate of reaction
1. Temperature
2. Surface Area
3. Concentration
4. Use of a catalyst
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Catalysts
These aresubstances that
increase the rate of
reaction but remain
chemicallyunchanged
It reduces the
amount of energyneeded which will
increase the
collision frequency
Used in the production of
bulk materials eg. Sulphuric
acid and food processing
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Percentage Composition of Compounds
Calculate the % of copper in copper sulphate,CuSO4 Relative atomic masses: Cu = 64, S = 32and O = 16
relative formula mass = 64 + 32 + 4x16 = 160
only one copper atom of relative atomic mass 64
% Cu = 64 x 100 / 160 = 40% copper by mass inthe compound
Example
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Masses of reactants and products
The total mass of the reactants equals the totalmass of the products
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The Yield of a Chemical reaction
Yield= What was obtainedWhat was expected
X 100 %
Example: Mass of carbon monoxide you would expect to reduce 1000g of iron oxide
FeO + 3CO 2Fe + 3CO
FeO CO
Mass(g) 1000 ? = 525
Mr 160 40
Mass/Mr 6.25 18.75 (3x6.25)
1 : 3
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Combustion of methane
The breaking of the bong is endothermic (gives
out heat
The formation of the bond is exothermic (takesin heat)
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Oil
Crude oil is a mixture ofhydrocarbons
Fractional distillation is
how you separatedifferent fractions of oil
The larger the molecule
the higher the boilingpoint
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Alkanes and Alkenes
Alkanes are saturated hydrocarbons which
means they only contain single bonds
Alkenes are unsaturated hydrocarbons they
have a double bond
Alkenes can be produced from alkanes by
cracking ( heating the alkane with a catalyst)
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Polymers
Examples: polythene , polypropene
Monomers (ie ethene) are used to form
polymers
Ethene can become polyethene by heating it
under pressure
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Thermosets and thermoplastics
Thermosetsare plastics that are resistant toheat. Used for kettles, saucepan handles etc.Have strong cross linkages which hold the
structure together and make them resistant toheat make them resistant to heat
Thermoplasticsare plastics that soften whenheated. Used for packaging, containers. Madeup of polymer chains not linked together so theycan slide over each other
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Water TreatmentWhen the water is inthe reservoir, the largeparticles will sink tothe bottom(sedimentation), the
smaller particles willbefiltered.
The water ischlorinated to kill the
bacteria to make itsafe to drink. Fluorideis also added
It is then stored until it
is needed
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DesalinationDefinition: The removal of salt from sea water so it can be
used for drinkingThis is usually done by reverse osmosis which goes through a
membrane that lets water molecules through but not salt
Problems
- Lots of energy required
- Produces a lot more greenhouse gases
- Expensive
- Very salty water is left when fresh water is used
- Poor countries that have droughts cannot afford this
- Some countries dont have access to the sea
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Extracting waterIf something is dissolved in water,
you can extract it by evaporating
& condensing
To separate a liquid from water
you need to use distillation.
Different liquids have differentboiling points . If you heat an
ethanol and water mixture, the
boiling point of ethanol is 78C so
by heating the mixture at thistemperature the ethanol will
evaporate and when the ethanol
vapour reaches the condenser it
will be cooled and become a
liquid
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Chromatography
Paper Chromatography- a drop of mixtureis placed on the Chromatography paperand placed in a solvent used to dissolvepigment. The solvent soaks into the paperand moves upwards. The more soluble willtravel with the solvent and move furtherup the paper.
The R value is used to measure this
(distance substance travelled/ distance solvent travelled)f
Gas Chromatography- can be used to detect pollutants in water or
air and it is also used to test for banned substances in sports
players. The mixture must be in the form of a gas (vaporised or
naturally occurring.) The gas passes through a column and different
substances are absorbed into an inert solid or liquid. The position
the chemical moves along the column is detected electronically
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Hard water
Hard water contains dissolved calcium and magnesium ions.Can be temporary or permanent
Temporary hard water contains magnesium/calcium hydrogencarbonates . When heated the hardness is removed but it formscalcium carbonate (scale) which clogs up pipes.
Permanent hard water contains chlorides/sulphates of calciumand magnesium which does not soften when heated
Advantages of hard water
-Some people prefer the taste
-Calcium is good for teeth and bones-Helps reduce heart illness
- Some brewers use hard water in beer
Disadvantages of hard water
-Difficult to form lather with
soap-Scum forms with soap
- Scale forms, clogs pipes
and kettles
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How to soften hard water
1. Boiling- easy and cheap but doesnt work forpermanent hardness
2. Adding Sodium Chloride- prevents calcium and
magnesium ions bonding with washing detergent.
Cheap, removes permanent hardness but deposits
are still formed
3. Ion exchange column- Column filled with resin
which has sodium ions. The calcium/magnesiumions are swapped for the sodium ions and come out
of the tube with the water where as the calcium
ions remain in the resin. Can treat a large amount of
t b t i