Carbon compounds definition and study guide

 

 

 

Carbon compounds definition and study guide

 

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Carbon compounds definition and study guide

 

Unit 2: Carbon Compounds

 

(a)Fuels

 

(i) Combustion

  • A fuel is a chemical which is burned to produce energy.
  • Combustion is another word for burning.
  • When a substance burns it reacts with oxygen.
  • The chemical compounds which are found in oil and natural gas are mainly hydrocarbons.
  • A hydrocarbon is a compound which contains hydrogen and carbon only.
  • Hydrocarbons burn in a plentiful supply of air to produce carbon dioxide and water.
  • The test for carbon dioxide is that it turns lime water milky.
  • Carbon, and carbon monoxide, a poisonous gas, are produced when the hydrocarbons burn in a supply of oxygen which is insufficient for complete combustion.
  • Nitrogen and oxygen from the air react inside a petrol engine to form nitrogen oxides which are poisonous gases.
  • The burning of some fuels releases sulphur dioxide, a poisonous gas, into the atmosphere.
  • Soot particles produced by the incomplete combustion of diesel are harmful.
  • Air pollution from the combustion of hydrocarbons can be reduced by the use of catalytic converters which speed up the conversion of pollutant gases to harmless gases.

 

(ii) Fractional distillation

  • Crude oil is a mixture of chemical compounds, mainly hydrocarbons.
  • Fractional distillation is the process used to separate crude oil into fractions according to the boiling points of the components of the fractions.
  • A fraction is a group of hydrocarbons with boiling points within a given range.
  • Ease of evaporation, viscosity, flammability and boiling point range of the fractions are properties related to molecular sizes of the molecules within the fractions.
  • The uses of the fractions are related to the ease of evaporation, viscosity, flammability and boiling point range of the fractions.

 

b) Nomenclature and structural formulae

 

(i) Hydrocarbons

  • The alkanes are a subset of the set of hydrocarbons.
  • An alkane can be identified from the ‘-ane’ ending.
  • Straight-chain alkanes can be named from molecular formulae, shortened and full structural formulae (only C1 to C8).
  • Molecular formulae can be written and shortened and full structural formulae can be drawn, given the names of straight-chain alkanes (only C1 to C8).
  • Branched-chain alkanes can be systematically named from shortened and full structural formulae (only C4 to C8).
  • Molecular formulae can be written and shortened and full structural formulae can be drawn, given the systematic names of branched-chain alkanes (only C4 to C8).
  • The alkenes are a subset of the set of hydrocarbons.
  • An alkene can be identified from the carbon to carbon double bond and the ‘-ene’ ending.
  • Straight-chain alkenes can be named, incorporating the position of the double bond, from shortened and full structural formulae (only C2 to C8).
  • Molecular formulae can be written and shortened and full structural formulae can be drawn, given the names of alkenes (only C2 to C8).
  • The cycloalkanes are a subset of the set of hydrocarbons.
  • A cycloalkane can be identified from the name.
  • Cycloalkanes can be named from molecular formulae, shortened and full structural formulae (only C3 to C8; isomers are not required, eg only cyclohexane is expected, not methylcyclopentane).
  • Molecular formulae can be written and shortened and full structural formulae can be drawn, given the names of cycloalkanes (only C3 to C8).
  • A homologous series is a set of compounds with the same general formula and similar chemical properties.

 

(ii) Isomers

  • Isomers are compounds with the same molecular formulae but different structural formulae.
  • Isomers can be drawn for given molecular formulae, shortened and full structural formulae.
  • The alkenes are a subset of the set of hydrocarbons.
  • An alkene can be identified from the carbon to carbon double bond and the ‘-ene’ ending.
  • Straight-chain alkenes can be named, incorporating the position of the double bond, from shortened and full structural formulae (only C2 to C8).
  • Molecular formulae can be written and shortened and full structural formulae can be drawn, given the names of alkenes (only C2 to C8).
  • The cycloalkanes are a subset of the set of hydrocarbons.
  • A cycloalkane can be identified from the name.
  • Cycloalkanes can be named from molecular formulae, shortened and full structural formulae (only C3 to C8; isomers are not required, eg only cyclohexane is expected, not methylcyclopentane).
  • Molecular formulae can be written and shortened and full structural formulae can be drawn, given the names of cycloalkanes (only C3 to C8).
  • A homologous series is a set of compounds with the same general formula and similar chemical properties.

 

(ii) Isomers

  • Isomers are compounds with the same molecular formulae but different structural formulae.
  • Isomers can be drawn for given molecular formulae, shortened and full structural formulae.

 

c) Reactions of carbon compounds

 

(i) Addition reactions

  • The alkanes and the cycloalkanes are saturated hydrocarbons.
  • Saturated hydrocarbons contain only carbon to carbon single covalent bonds.
  • The alkenes are unsaturated hydrocarbons.
  • Unsaturated hydrocarbons contain at least one carbon to carbon double covalent bond.
  • It is possible to distinguish an unsaturated hydrocarbon from a saturated hydrocarbon using bromine solution.
  • An alkene reacts with hydrogen to form the corresponding alkane.
  • The reactions of an alkene with bromine, hydrogen and water are addition reactions.

 

(ii) Cracking

  • Fractional distillation of crude oil yields more long-chain hydrocarbons than are useful for present-day industrial purposes.
  • Cracking is an industrial method for producing a mixture of smaller, more useful molecules, some of which are unsaturated.
  • The catalyst allows the reaction to take place at a lower temperature.
  • Cracking can be carried out in the laboratory using an aluminium oxide or silicate catalyst.

 

(iii) Ethanol

  • Ethanol, for alcoholic drinks, can be made by fermentation of glucose derived from any fruit or vegetable.
  • An enzyme in yeast acts as a catalyst for the reaction.
  • There is a limit to the ethanol concentration of fermentation products.
  • Distillation is a method of increasing the ethanol concentration of fermentation products in the manufacture of ‘spirit’ drinks.
  • Alcoholic drinks, if taken in excess, can have damaging affects to health and mind.
  • To meet market demand ethanol is made by means other than fermentation.
  • Industrial ethanol is manufactured by the catalytic hydration of ethene.
  • Ethanol can be converted to ethene by dehydration.
  • Ethanol, mixed with petrol, can be used as a fuel for cars.
  • The ethanol is obtained from sugar cane, a renewable source of energy.

 

(iv) Making and breaking esters

  • Esters are formed by the condensation reaction between a carboxylic acid and an alcohol.
  • In a condensation reaction, the molecules join together by the reaction of the functional groups to make water.
  • The ester link is formed by the reaction of a hydroxyl group with a carboxyl group.
  • The parent carboxylic acid and the parent alcohol can be obtained by hydrolysis of an ester.
  • The formation and hydrolysis of an ester is a reversible reaction.

 

d) Plastics and synthetic fibres

 

(i) Uses

  • Synthetic materials are made by the chemical industry.
  • Most plastics and synthetic fibres are made from chemicals derived from oil.
  • Examples of plastics include polythene, polystyrene, perspex, PVC, nylon, bakelite, formica and silicones.
  • Kevlar, which is very strong, and poly(ethenol), which readily dissolves in water, are recently developed plastics.
  • The everyday uses of plastics are related to their properties.
  • Examples of synthetic fibres include polyesters, eg Terylene, and nylon.
  • For some uses, synthetic materials have advantages over natural materials and vice versa.
  • Biopol is a recently developed degradable plastic.
  • Most plastics are not biodegradable and their low density and durability can cause environmental problems.
  • Some plastics burn or smoulder to give off toxic fumes, including carbon monoxide.
  • The toxic gases given off during burning or smouldering can be related to the elements present in the plastic.
  • Plastics can be either thermoplastic or thermosetting.
  • A thermoplastic is one which can be reshaped on heating.
  • A thermosetting plastic cannot be reshaped by heating.

 

(ii) Addition polymerisation

  • Plastics are made up of long chain molecules called polymers.
  • Polymer molecules are made from many small molecules called monomers.
  • Addition polymers are made from small unsaturated molecules produced by cracking by a process called addition polymerisation.
  • The small unsaturated molecules join together by the opening of the carbon to carbon double bond.
  • The name of the addition polymer is related to the name of the monomer.
  • The repeating unit or the structure of an addition polymer can be drawn given the monomer structure and vice versa.

 

(iii) Condensation polymerisation

  • Condensation polymers are made from monomers with two functional groups per molecule.
  • The repeating unit or the structure of a condensation polymer can be drawn given the monomer structures and vice versa.
  • Polyesters are examples of condensation polymers.
  • An amine can be identified from the functional group.
  • Polyamides are examples of condensation polymers.
  • The amide link is formed by the reaction of an amine group with a carboxyl group.

 

e) Natural products

 

(i) Carbohydrates

  • Carbohydrates form an important class of food made by plants.
  • Carbohydrates supply the body with energy.
  • Carbohydrates are compounds which contain carbon, hydrogen and oxygen with the hydrogen and oxygen in the ratio of two to one.
  • Carbohydrates can be divided into sugars and starches.
  • Examples of sugars include glucose, fructose, maltose and sucrose (table sugar).
  • Most sugars can be detected by the Benedict’s test; sucrose is an exception.
  • Starch can be distinguished from other carbohydrates by the iodine test.
  • Sugars are carbohydrates with small molecules.
  • Starch is a natural condensation polymer made of many glucose molecules linked together.
  • Plants convert the glucose into starch for storing energy.
  • During digestion starch is hydrolysed to glucose which is carried by the blood stream to body cells.
  • Starch can be hydrolysed by acid and by enzymes.
  • Body enzymes function best at body temperature and are destroyed at higher temperature.

 

(ii) Proteins

  • Proteins form an important class of food made by plants.
  • Proteins are the major structural materials of animal tissue and are involved in the maintenance and regulation of life processes and include enzymes, many hormones, eg insulin and haemoglobin.
  • Proteins are condensation polymers made of many amino acid molecules linked together.
  • The structure of a section of protein is based on the constituent amino acids.
  • Condensation of amino acids produces the peptide (amide) link.
  • The peptide link is formed by the reaction of an amine group with a carboxyl group.
  • Proteins specific to the body’s needs are built up within the body.
  • During digestion enzyme hydrolysis of dietary proteins produces amino acids.
  • The structural formulae of amino acids obtained from the hydrolysis of proteins can be identified from the structure of a section of the protein.

 

(iii) Fats and oils

  • Natural fats and oils can be classified according to their origin as animal, vegetable or marine.
  • The lower melting points of oils compared to those of fats is related to the higher unsaturation of oil molecules.
  • The conversion of oils into hardened fats involves the partial removal of unsaturation by addition of hydrogen.
  • Fats and oils in the diet supply the body with energy and are a more concentrated source of energy than carbohydrates.
  • Fats and oils are esters.
  • The hydrolysis of fats and oils produces fatty acids and glycerol in the ratio of three moles of fatty acid to one mole of glycerol.
  • Fatty acids are saturated or unsaturated straight chain carboxylic acids, usually with long chains of carbon atoms.

 

 

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