Chemistry HT1

Crude oil is a complexx mixture of compounds called HYDROCARBONS. 

COMPOUND- a substance which contains 2 or more elements CHEMICALLY BONDED together.

MIXTURE- this substance contains 2 or more elements/compounds that are NOT CHEMICALLY BONDED together.

The compounds in crude oil are called HYDROCARBONS. Hydrocarbons are compouds made up of CARBON and HYDROGEN ONLY. Crude oil is described as a FOSSIL FUEL.

Crude oil is formed from the remains of organisms, which lived  MILLIONS of years ago Fossil fuels are described as NON-RENEWABLE because once we have used up the supplies, they have gone forever. They are a finite source found in rocks. 

Fossil fuels like coal,oil and natural gas, have resulted from the action of heat and pressure over millions of years in the absence of air on animal and plant material, mainly plankton. They have been covered by layers of mud and sedimentary rock. 

Most of the hydrocarbons in crude oil are ALKANES. Alkanes are an example of a HOMOLOGOUS SERIES that have single C-C covalent bond. The covalent bonds are represented by a single line (-) in their display formula. 

Alkalines have the general formula  C2 H2n+2. Alkanes are descibed as SATURATED MOLECULES. This means they only contain a carbon carbon single bond.

Methane                                             CH4                                            H-C-H

Crude oil is useless as it comes out of the ground, it is too complex. It needs to be refined and the first stage in oil refining is DISTILATION. Distilation used the idea that each hydrocarbon has a different beoiling oint and as the chain length gets longer, the boiling point increases. 

Fractional distilation separates the crude oil into FRACTIONS. Fractions contain hydrocarbons  of SIMILAR chain length.

 About 2cm3  of crude oil was added to the side-armed test tube. Mineral wool was then added to soak up the crude oil. the mixture was gently heated and FRACTIONS collected. 

LOW CARBON LENGTGH 

Increasing boiling point therefore longer chain length

Darker in colour

More viskous  (THICKER)  

Less flamable and more smokier flame

Less volatile

 HIGH CARBON LENGTH

A partial separation of crude oil can be achieved by simple distilation. As the boiling point range of the fraction increases, the compounds in the fraction become DARKER in colour More viscous, LESS volatile, LESS flammable and burns with a MORE smoky flame.

The crude oil is heated and enters as a hot vapour. The fractionating colomn is cooler at the top and hot at the bottom. The different fractions now CONDENSE at different temperatures. At high temperatures the smaller hydrocarbons stay as gases and rise up the column. This means the larger hydrocarbons with the high boiling points turn back to liquids nearer the bottom. The very small hydrocarbons never condense and remain as a gas and are piped off at the top. 

We obtain many useful products from fractional distilation of crude oil. 

FUEL (petrol, disel, kerosine,heavy fuel oil and liquified petrolium gas)

FEED STOCK for the petrochemical industry

Many useful products are important in everyday life are produced by the petrochemical industry. You can get; ORGANIC SOLVENT- chemicals which are liquid and dissolves other substances         (solute).

                     LUBRICANTS- oils which are used to reduce friction between two moving parts.

                     POLYMERS- large chain molecules made by iorning many small molecules together. Polymers are essentially plastics.

                     DETERGENTS- a surfactant or a mixture of surfactancts with cleaning properties in dilute solutions.

A SERFACTANT reduces the surface tension between two liquids.

The vast array of synthetic aand natural carbon compounds occur due to the ability of carbon atoms to bond  with itself and because it can bond four times. Due to these families of similar comounda e.g. alkanes are produced. Theses similar compounds can be described as a HOMOLOGOUS SERIES. 

A homologous series of compounds contain compounds with,

SIMILAR properties, DIFFER by a CH2 unit, SAME general formua.

The more lighter fractions obtained from the distilation of crude oil are used as fuels. When fuels burn they react with oxogen in the air. The carbon and hydrogen are OXODISED to form carbon dioxide and water. 

This type of combustion is called COMPLETE COMBUSTION. 

Propane + Oxogen = Carbon doixide + water + energy 

The pump was swiched on before the candle was ignited to draw AIR through the apparatus. After a few minutes it was noted that the colbalt chloride paper remained BLUE and the limewater remained CLEAR suggesting that the air passing through was not responsible for any changes to the limewater or blue cobalt chloride paper.

Once the candle was ignited the cobalt chloride paper changed from a blue colour to a PINK colour. this means that water was produced. The limewater changed froma clear solution to form a WHITE preceipitate. It went CLOUDY. This showed that CARBON DIOXIDE was produced. The candle was undergoing COMPLETE COMBUSTION. Ther were signs of a black solid on the funnel. This was CARBON  and was a result of INCOMPLETE COMBUSTION.

 INCOMPLETE COMBUSTION is when the fuel is burned in a LIMITED supply of oxogen to produce carbon monoxide or carbon INSTEAD of carbon dioxide. Water is still produced. 

Examples, 

Propane + Oxogen = Carbon + Water  (C3H8 +2O2 = 3C + 4H20)

Propane + Oxogen = Carbon Monoxide + Water (2C3H8 +7O2 = 6CO + 8H2O)

CARBON DIOXIDE - A green house gas, absorbeds energy released as radiation from the earths       surface, causes global warming, results in sevear weathering (flooding), causes climate change.

NITROGEN OXIDES - This is produced inside engines at high temperatures, this temperature is high enough for nitrogen and oxogen from the air to react to form nitrogen oxides, nitrogen oxided are acidic gasses, acid gasses kills trees, kills aquatic life, reacts with limestone buildings and statues. 

WATER - A greenhouse gas

CARBON MONOXIDE - (INCOMPLETE COMBUSTION)  toxic gas, colourless and odourless, combines with the hymoglobin in red blood cells irreversibly instead of binding with oxogen. 

SULFUR DIOXIDE - All fossil fuels contain sulfur (an impurity) and when the fuel is burnt sulfure dioxide is formed. Toxic gas which causes acid rain which damages trees, kills aquatic life, sulfur impurities can be removed before burning e.g.  in petrol and desil. Sulfur dioxide can be removed from waste gasses using  Calcium oxide or Calcium hydroxide. 

UNBURNT HYDROCARBONS - Causes global warming

CARBON PARTICLES - (INCOMPLETE COMBUSTION) more likely when burning larger hydrocarbons, these particles travel up into upper atmosphere and reflect sunlight back into space causing global dimming. Can damage cells and cause cancer. 

Crude oil is speratared into different fractions. Each  contains hydrocarcarbons of SIMILAR chain legth. There are fractions which conatin chained hyrdocarrbons and others which contain long chained hydrocarbons. These long and short chained fractions are not produced in the propon ion that the market requires. There is  a surplus of long chain molecules (HYDROCARBONS)

Larger hydrocarbons are cracked into smaller hydrocarbons. These smaller hydrocarbons are of more use to us us than the larger hydrocarbons. Cracking involves a CATALYST like alluminuim oxide and heat. it is an eample of THERMAL DECOMPOSITION. the breaking down of a compound using heat. 

Ethane = Ethene + hydrogen 

Ethane can be cracked into ethene and hydrogen. 

Paraffin = Heptane + ethene + propene 

TEST                                                            GAS                                                 OIL

In industry, cracking can be achieved by various methods, e.g. Catalytic cracking and steam cracking.

CATALYTIC  CRACKING - it involves passing the hot vapour over a hot catalyst

STEAM CRACKING - It involves mixing the hydrocarbon with stem and heating to a very high temperature.

Alkenes are another example or a HOMOLOGOUS SERIES. Alkenes are always produced when saturated hydrocarbons (alkanes) are cracked. Dmall alkanes are also formed.

Alkenes posses at least one C=C double bond. They are described as UNSATURATED due to the possesion of the C=C double bond.

Ethene, C2H4                                   C=C

Alkenes have the general formula CN H2N. They are more reaactive than alkanes because they contain a C=C double bond (this is the functional group)

Alkenes react with Bromine water (test for Alkenes)

Ethene + bromine = 1,2 DIBROMOETHANE 

           C=C          +          Br-Br    =                   H-C-C-H

Unstaturated        orange/yellow/brown           colourless saturated

ALKENES ARE MORE REACTIVE THAN ALKANES

-Alkenes react with hydrogen at 60 degrees in the prescence of a nickle catalyst.

Ethene + Hydrogen = Ethane

          C=C          +           H-H                       =      H-C-C-H

    unsaturated               no colour change           saturated

-Alkenes react with water (steam) to produce ethanol in the prescence of heat and a catalyst. 

Ethene + Steam = Ethanol

         C =C           +         O                              =      H-C-C=C-H

This is a REVERSABLE REACTION so ethanol can break down to produce ethene and steam. These can be recycled over the catalyst.

Alkenes burn in air. Alkenes under go IMCOMPLETE COMBUSTION with alkanes.  Howver alkanes tend to burn with a more smoky flame due to MORE incomplete combustion.

COMPLETE COMBUSTION                                         C2H4 (g) + 3O2 (g) = 2CO2 (g) + 2H2O (l)

INCOMPLETE COMBUSTION TO PRODUCE CO2              C2H4 (g)   +  2O2 (g)   = 2CO (g)   + 2H2O (l)   

INCOMPLETE COMBUSTION TO PRODUCE C          C2H4 (g) + 02 (g)   = 2C (s) + 2H2O (l)

- Alkenes can join together to form polymers.                        C=C      +       C=C 

                                                                                             monomer       monomer

                                                                                                        C-C-C-C

                                                                                      Part of the poly(ethene) molecule