C7 Organic Chemistry
Different hydrocarbons
Hydrocarbon - Compounds only made up of hydrogen and carbon.
Alkanes - general formula:Cn+H2n+2
Hydrocarbon properties
The shortrer the chain the more runny it is (less viscous)
The shorter the chain the more volatile it is (lower boiling points)
The shorter the chain the more flammable it is.
Saturated compounds (single covalent bonds)
Meth, Eth, Prop, But
Reactions of hydrocarbons
Alkenes - general formula: Cn+H2n
Unsaturated (double covalent bonds)
They can open up this double bond meaning they are more reactive then alkanes.
Alkenes - Alkenes react by Addition reactions (something is added where the double bond is broken)
Complete combustion - releases a lot of energy and carbon dioxide and water. When there is enough oxygen. Because of complete combustion hydrocarbons can be used as fuels.
Alkenes and hydrogenation - Alkenes can react with H2 to form an alkane as they gain the extra two hydrogens. They need a catalyst to do so.
Alkenes and steam - Alkenes react with water vapour (steam) and an alcohol is formed. When they react they gain H2O which measn they become alcohols becasue of the extra OH gained.
This is on easy way of making ethanol industrially.
Alkenes and halogens (group 7 elements) - Alkenes react with halogens like Br2 which join across the double bond. If ethene and bromine react the result is called DIBROMOETHANE
Testing for alkanes or alkenes
The test is to add orange bormine water to the compund and if it stays orange this indicates a saturated compound (alkane) Whereas if it ges colourless this shows a alkene.
Alkenes burn with a smokey flame because they dont combust completely so carbon dioxide and water are still produced but you can also get poisenous gasses like carbon monoxide and carbon.
Alcohols - general formula: CnH2n+1OH
Alcohols are flammable, they undergo complete combustion to produce carbon dioxide and water. This is why they can be used as fuels in industry
All soluble in water. With a neutral pH. This is why they can be used as solvants in industry.
Alcohols can be oxidised by reacting with oxygen to produce carboxylic acids.
Alcohols react with sodium, one of the products is hydrogen.
Carboxylic acids - COOH group
Ethanol is used in alcoholic drinks. It can be made through fermentation where this equation applies - SUGAR + YEAST = ETHANOL + CARBON DIOXIDE
They can react with carbonates to produce a specific salt, water and carbon dioxide . For example if ethanoic acid reacted with sodium carbonate it would produce sodium ethanoate, water and CO2
Carboxylic acids can make esters when they react with alcohols when an acid catalyst is used. Ester group: COO
Esters - LOOK FOR THE 'COC' IN THE MIDDLE
H2O Is the extra product given off during the reaction
Carboxylic acids are 'weak' acids because they do not ionise completely (not all of the molecules loose their H+ ions) unlike other acids with a lower pH.
Fractional distillation
Method of separating hydrocarbons to get crude oil. produces different fractions which have different purposes shorter chains can be used for petrol and small gases like Bunsen burners and longer chains are used for diesel.
Crude oil cycle: Fossil fuel formed from the remains of dead animal and plant matter that has been buried under mud and compressed due to high temps and pressures where it turns to crude oil.
Method: 1) The oil is heated till it evaporates (turns to a gas) The gas enters the functioning column. 2) At the bottom of the collum the temp is really high however at the top the temps ar cooler 3) The longer hydrocarbons have higher boiling points (equal to the temp they will condense at) So they condense near to the bottom of the column. But ones with lower boiling points will rise higher and condense at cooler temps. Some hydrocarbons have much high boiling points that they are drained out as a liquid as waste product.
Cracking
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