Chemistry

Separating Mixtures

Filtration - Separating small pieces of solid from a solution or a liquid

DecantingSeparating large pieces of solid from a solution or a liquid

Evaporation/Crystallisation - Separating a solute from a solvent

Simple Distillation  - Separating a solvent from a solution

Fractional Distillation - Separating a mixture of miscible liquids

Separating Funnel - Separating a mixture of immiscible liquids

Chromotography - Separating a mixture of soluble dyes

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Crude Oil

Industrial Fractional Distillation of Crude Oil 

  • Crude oil is a complex mix of hydrocarbons.
  • A hydrocarbon is a compound containing hydrogen and carbon atoms only.
  • Crude oil is (pre)heated.
  • The vapour is passed into a fractionating column which is cooler at the top and hotter at the bottom.
  • The fractions condense at different heights.
  • The crude oil is split into various fractions which have different boiling point ranges.
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Uses of the Fractions

Refinery Gas - LPG (for domestic heating and cooking)

Gasoline (petrol) - Fuels for cars

Kerosine - Fuel for jet aircraft, for domestic heating and as paraffin for small heaters and lamps

Diesel - Fuels for buses, lorries, some cars and railway engines

Fuel Oil -  Fuel in ships' boilers and for industrial heating

Bitumen - Mixed with rock chippings to make the top surfaces of roads

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Complete and Incomplete Combustion

Complete Combustion

Burning of a fuel in a plentiful supply of oxygen

Forms water and carbon dioxide

Dangers of products = greenhouse gases which lead to global warming

Incomplete Combustion

Burning of a fuel in a limited supply of oxygen

Forms water and carbon or carbon monoxide

Dangers of products = carbon monoxide is poisonous because it reduces the capacity of the blood to carry oxygen

 

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Pollutants in the Environment

Factories burn fossil fuels with sulfur impurities which form sulfur dioxide.

In car engines, the temperature reached is high enough to allow nitrogen and oxygen, forming nitrogen oxides.

Sulfur dioxide and nitrogen oxides are pollutant gases which contribute to acid rain.

This causes:

  • the corrosion of buildings made of limestone 
  • the killing of plants
  • the killing of aquatic animals and aquatic life
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Pollutants - Formation and Effects

Carbon Dioxide 

  • Formed by the complete combustion of hydrocarbon fuels.
  • Negative Impact = Greenhouse gas which cause global warming.

Sulfur Dioxide 

  • Formed by the combustion of fuels containing sulfur impurities.
  • Negative Impact = Reacts with water in the atmosphere to form an acid leading to acid rain.

Oxides of Nitrogen

  • Formed by the reaction of O  and N  from the air at high temperatures.
  • Negative Impact = Reacts with water in the atmosphere to form an acid leading to acid rain.
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Pollutants - Formation and Effects

Carbon Monoxide

  • Formed by the incomplete combustion of hydrocarbon fuels.
  • Negative Impact = Poisonous gas; reduces capacity of the blood to carry oxygen.

Carbon

  • Formed by the complete incombustion of hydrocarbon fuels.
  • Negative Impact = Asthma, respiratory irritant.

Water

  • Formed by the complete and incomplete combustion of hydrocarbon fuels.
  • Negative Impact = Greenhouse gas which causes global warming.
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Alkanes - Definitions

Alkane - A saturated hydrocarbon with the general formula 

General Formula - A formula that states the ratio of atoms of each element in the formula of ever compound in a homologous series

Homologous Series - A group of organic compounds with the same general formula and whose members differ from the next by a CH  group. Memebers of the same homologous series have a trend in physical properties and similar chemical properties.

Isomers - Componds with the same molecular formula but different displayed structural formulae

Saturated - A compound containing single bonds only

Unsaturated - A compound containing one or more double (or multiple) bonds

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Substitution Reaction

Alkanes undergo a substitution reaction with halogens in the presence of light. In UV light, methane reacts with bromine. For example: methane + bromine → bromomethane + hydrogen bromide           CH4 + Br2 → CH3Br + HBr

This reaction is a substitution reaction because one of the hydrogen atoms from the methane is replaced by a bromine atom.

Methane is added to bromine to produce methylbromine and hydrogen bromide.

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Cracking

Catalytic cracking is the thermal decomposition method used to convert long chain alkanes into shorter, more useful alkanes and alkenes. Heated at 600 - 700 and the catalysts required are either aluminia or silica.

Cracking is required because the fractional distillation of crude oil produces more long-chain hydrocarbons than can be used directly and fewer short-chain hydrocarbons than required. Therefore in order to produce enough short-chain hydrocarbons to meet the demand the longer-chain hydrocarbons are cracked to produce alkanes and alkenes.

The alkenes then undergo additional polymerisation

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Addition Reaction

Alkenes added to Bromine water causes colour change from ORANGE to COLOURLESS.

It is also a test for alkenes and unsaturation.

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Addition Polymerisation

Addition polymerisation is the process of joininh many small monomers to form one long polymer chain. The monomers are small alkenes and many of these join together to make the long polymer chain.

When the monomers join together, the double bond breaks. This allows for one carbon atom in the first monomer to join to a second carbon atom in the second monomer, and so on.

The repeat unit of a polymer is the structure that is repeated many times in the overall structure. The number of times that this is repeated is equal to the number of monomers that are joined together.

When naming polymers, we take the name of the monomer and add the word 'poly' to the start of it. The name of the monomer must also be in brackets.

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Disposing of Polymers

  • Polymers are inert - this means they are unreactive
  • This also means that they are not biodegradable - they cannot be broken down by microorganisms
  • This means that polyers are hard to dispose of - landfills are filling up, burning them releases toxic gases etc.
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Kinetics (rates of reactions) - Variable: Surface

Effect:

The larger the surface area the faster the rate of reaction..

Reason:

When you increase the surface area you are making more particles accessible to react meaning there are more successful collisions per second.

 

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Kinetics (rates of reactions) - Variable: Concentr

Effect:

The higher the concentration the higher the rate of reaction.

Reason:

Increasing the concentration means there are more particles in a set volume. This means there will be more collisions between the reactant particles and therefore more successful collisions per second.

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Kinetics (rates of reactions) - Variable: Temperat

Effect:

The higher the temperature the faster the rate of reaction.

Reason:

The particles are given more energy therefore more particles have the minimum energy needed for a reaction to occur (more particles have more energy than the activation energy). More collisions are successful meaning there are more successful collision per second.

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Kinetics (rates of reactions) - Variable: Add a Ca

Effect:

When you add a catalyst the rate of reaction is faster.

Reason:

Catalyst provides an alternative route of lower activation energy. This means there are more successful collisions per second.

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Activation Energy

Activation energy is the minimum amount of energy required by colliding particles for a reaction to occur.

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Reactivity Series

  • Potassium
  • Sodium
  • Lithium
  • Calcium
  • Magnesium
  • Aluminium
  • Zinc
  • Iron
  • Tin
  • Copper
  • Silver
  • Gold
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Oxidation and Reduction

Oxidation

Is

Loss of electrons

Reduction

Is

Gain of electrons

Redox Reaction - A reaction in which both reduction and oxidation are happening

Oxidising Agent - A substance that can cause another substance to be oxidised. The oxidising agent undergoes reduction in this process.

Reducing Agent - A substance that can cause another substance to be reduced. The reducing agent undergoes oxidation  in this process.

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