IGCSE CHEMISTRY SECTION 3 LESSON 2

Content The iGCSE Chemistry course Section 1 Principles of Chemistry Section 2 Chemistry of the Elements Section 3 Organic Chemistry Section 4 Physical Chemistry Section 5 Chemistry in Society

Content Section 3 Organic Chemistry a)Introduction b)Alkanes c)Alkenes d)Ethanol

Lesson 2 c) Alkenes d) Alcohols c) Alkenes 3.6 recall that alkenes have the general formula CnH2n 3.7 draw displayed formulae for alkenes with up to four carbon atoms in a molecule, and name the straight-chain isomers (knowledge of cis- and transisomers is not required) 3.8 describe the addition reaction of alkenes with bromine, including the decolourising of bromine water as a test for alkenes. d) Ethanol 3.9 describe the manufacture of ethanol by passing ethene and steam over a phosphoric acid catalyst at a temperature of about 300°C and a pressure of about 60–70 atm 3.10 describe the manufacture of ethanol by the fermentation of sugars, for example glucose, at a temperature of about 30°C 3.11 evaluate the factors relevant to the choice of method used in the manufacture of ethanol, for example the relative availability of sugar cane and crude oil 3.12 describe the dehydration of ethanol to ethene, using aluminium oxide.

Organic Chemistry It’s the chemistry of carbon-containing compounds

Hydrocarbon = compound containing hydrogen and carbon only

The alkanes are saturated hydrocarbons – they form single covalent bonds only

The alkanes have the general formula of C n H 2n+2

Compounds exhibit isomerism when they have the same molecular formula but different structural formulae.

Alkenes C X X X X X X

C X X X X X X C X X X X X X

C X X X X X X C X X X X X X

C X X X X X X C X X X X X X Ethane

Alkenes C X X X X X X C X X X X X X

C X X X X X X C X X X X X X C H H C H H Ethene

Alkenes C X X X X X X C X X X X X X C H H C H H Ethene Double bond

Alkenes C X X X X X X C X X X X X X C H H C H H Ethene Double bond Alkenes are known as unsaturated hydrocarbons because they contain a double bond.

Alkenes C X X X X X X C X X X X X X C H H C H H Alkenes form a homologous series with the general formula C n H 2n Double bond Alkenes are known as unsaturated hydrocarbons because they contain a double bond.

Alkenes Namen Molecular formula Structural formula Ethene2 C2H4C2H4 Propene3 C3H6C3H6 Butene4 C4H8C4H8 Pentene5 C 5 H 10

Alkenes Namen Molecular formula Structural formula Ethene2 C2H4C2H4 Propene3 C3H6C3H6 Butene4 C4H8C4H8 Pentene5 C 5 H 10 H H H H CC

Alkenes Namen Molecular formula Structural formula Ethene2 C2H4C2H4 Propene3 C3H6C3H6 Butene4 C4H8C4H8 Pentene5 C 5 H 10 H H H H CC CCC H HHH H H

Alkenes Namen Molecular formula Structural formula Ethene2 C2H4C2H4 Propene3 C3H6C3H6 Butene4 C4H8C4H8 Pentene5 C 5 H 10 H H H H CC CCC H HHH H H

Alkenes Namen Molecular formula Structural formula Ethene2 C2H4C2H4 Propene3 C3H6C3H6 Butene4 C4H8C4H8 Pentene5 C 5 H 10 H H H H CC CCC H HHH H H

Chemical properties of alkenes

1. Alkenes are generally more reactive than alkanes.

Chemical properties of alkenes 1.Alkenes are generally more reactive than alkanes. 2.Ethene burns with a smoky flame. This is because it contains a relatively high percentage of carbon: C 2 H 4 + 3O 2  2CO 2 + 2H 2 O Other alkenes do not burn with a smoky flame

Chemical properties of alkenes 3. Alkenes and unsaturated compounds undergo addition reactions.

Chemical properties of alkenes 3. Alkenes and unsaturated compounds undergo addition reactions. An addition reaction is one in which two molecules combine to form a single molecule.

Chemical properties of alkenes 3.Alkenes and unsaturated compounds undergo addition reactions. For example: alkenes react with bromine to form 1,2-dibromoethane: H H H H C C + Br Br  H C C H H H Br Br

Chemical properties of alkenes 3.Alkenes and unsaturated compounds undergo addition reactions. For example: alkenes react with bromine to form 1,2-dibromoethane: H H H H C C + Br Br  H C C H H H Br Br Test for an alkene. Alkenes will decolourise bromine water as the alkene reacts with it. Eg. Ethene + Bromine Water  Colourless solution (colourless) (yellow-brown)

Ethanol

Ethanol belongs to the group of organic compounds known as the alcohols.

Ethanol Ethanol belongs to the group of organic compounds known as the alcohols. Alcohols contain the hydroxyl group, -OH

Ethanol Ethanol belongs to the group of organic compounds known as the alcohols. Alcohols contain the hydroxyl group, -OH The alcohols form a homologous series with the general formula C n H 2n+1 OH

Ethanol Ethanol belongs to the group of organic compounds known as the alcohols. Alcohols contain the hydroxyl group, -OH The alcohols form a homologous series with the general formula C n H 2n+1 OH Eg. Ethanol C 2 H 5 OH H H H C C O H H

Manufacture of Ethanol

Ethanol may be produced in two ways: 1)Industrial preparation Ethanol is made on a large scale by the hydration of ethene at a temperature of 300 o C and a pressure of about 65 atmospheres.

Manufacture of Ethanol Ethanol may be produced in two ways: 1)Industrial preparation Ethanol is made on a large scale by the hydration of ethene at a temperature of 300 o C and a pressure of about 65 atmospheres. A hydration reaction is a chemical reaction in which the hydroxyl group (-OH) and a proton (H + ) are added to a compound

Manufacture of Ethanol Ethanol may be produced in two ways: 1)Industrial preparation Ethanol is made on a large scale by the hydration of ethene at a temperature of 300 o C and a pressure of about 65 atmospheres. C 2 H 4 (g) + H 2 O (l)  C 2 H 5 OH (g) Phosphoric acid is used as a catalyst.

Manufacture of Ethanol Ethanol may be produced in two ways: 2)Preparation by fermentation Sugars are carbohydrates which can be broken down in the presence of yeast to form ethanol and carbon dioxide.

Manufacture of Ethanol Ethanol may be produced in two ways: 2)Preparation by fermentation Sugars are carbohydrates which can be broken down in the presence of yeast to form ethanol and carbon dioxide. Oil layer Yeast in glucose solution Lime water

Manufacture of Ethanol Ethanol may be produced in two ways: 2)Preparation by fermentation Sugars are carbohydrates which can be broken down in the presence of yeast to form ethanol and carbon dioxide. Oil layer Yeast in glucose solution Lime water C 6 H 12 O 6  2C 2 H 5 OH + 2CO 2 sugar ethanol

Manufacture of Ethanol Ethanol may be produced in two ways: 2)Preparation by fermentation Sugars are carbohydrates which can be broken down in the presence of yeast to form ethanol and carbon dioxide. Oil layer Yeast in glucose solution Lime water C 6 H 12 O 6  2C 2 H 5 OH + 2CO 2 sugar ethanol This process is known as fermentation

Manufacture of Ethanol Ethanol may be produced in two ways: 2)Preparation by fermentation Sugars are carbohydrates which can be broken down in the presence of yeast to form ethanol and carbon dioxide. Oil layer Yeast in glucose solution Lime water C 6 H 12 O 6  2C 2 H 5 OH + 2CO 2 sugar ethanol This process is known as fermentation Fermentation is used in wine and beer making. The reaction is carried out at a temperature of about 30 o C. The reaction is known as anaerobic respiration as air must be excluded.

Manufacture of Ethanol Ethanol may be produced in two ways: 2)Preparation by fermentation Sugars are carbohydrates which can be broken down in the presence of yeast to form ethanol and carbon dioxide. Oil layer Yeast in glucose solution Lime water C 6 H 12 O 6  2C 2 H 5 OH + 2CO 2 sugar ethanol This process is known as fermentation Fermentation is used in wine and beer making. The reaction is carried out at a temperature of about 20 o C. The reaction is known as anaerobic respiration as air must be excluded. If air does come into contact with the wine, the wine becomes sour due to the oxidation of ethanol to ethanoic acid. Vinegar means ‘bad wine’ and it contains ethanoic acid. Bacteria in the air may also kill the yeast.

Manufacture of Ethanol Ethanol may be produced in two ways: 2)Preparation by fermentation Sugars are carbohydrates which can be broken down in the presence of yeast to form ethanol and carbon dioxide. Oil layer Yeast in glucose solution Lime water C 6 H 12 O 6  2C 2 H 5 OH + 2CO 2 sugar ethanol This process is known as fermentation. The reaction requires an enzyme in yeast (zymase)

Manufacture of Ethanol Ethanol may be produced in two ways: 2)Preparation by fermentation Sugars are carbohydrates which can be broken down in the presence of yeast to form ethanol and carbon dioxide. Oil layer Yeast in glucose solution Lime water C 6 H 12 O 6  2C 2 H 5 OH + 2CO 2 sugar ethanol The yeast eventually dies when the alcohol content reaches about 15% or when the sugar is used up

Manufacture of Ethanol Which method? Industrial preparation Preparation by fermentation

Manufacture of Ethanol Which method? Industrial preparation Preparation by fermentation Depends upon the relative availability of the raw products.

Manufacture of Ethanol Which method? Industrial preparation Preparation by fermentation Depends upon the relative availability of the raw products. In countries where land is scarce or not easy to cultivate and there are oil reserves, hydration of ethene will be the favoured process

Manufacture of Ethanol Which method? Industrial preparation Preparation by fermentation Depends upon the relative availability of the raw products. In countries where land is scarce or not easy to cultivate and there are oil reserves, hydration of ethene will be the favoured process In countries with no crude oil reserves, ethanol is more likely to be made by the fermentation method; in particular if the climate allows sugar cane to grow well and there is plenty of land available.

Uses of Ethanol

Ethanol is used as a solvent. Many organic compounds are insoluble in water, but soluble in ethanol.

Uses of Ethanol Ethanol is used as a solvent. Many organic compounds are insoluble in water, but soluble in ethanol. Ethanol is used as a fuel. In Brazil, ethanol is produced by the fermentation of cane sugar, and then added to petrol (biofuel).

Uses of Ethanol Ethanol is used as a solvent. Many organic compounds are insoluble in water, but soluble in ethanol. Ethanol is used as a fuel. In Brazil, ethanol is produced by the fermentation of cane sugar, and then added to petrol (biofuel). Ethanol is used in the production of wines, beers and spirits.

Dehydration of Ethanol

A dehydration reaction is defined as a chemical reaction that involves the loss of water from the reacting molecule.

Dehydration of Ethanol Ethanol can be dehydrated by heating it in the presence of a catalyst, aluminium oxide.

Dehydration of Ethanol Ethanol soaked in mineral wool Heat from a Bunsen burner Aluminium oxide catalyst (or porcelain pieces) Ethene gas Water trough Delivery tube

Dehydration of Ethanol Ethanol soaked in mineral wool Heat from a Bunsen burner Aluminium oxide catalyst (or porcelain pieces) Ethene gas Water trough Delivery tube Ethanol  Ethene + Water C 2 H 5 OH  C 2 H 4 + H 2 O

End of Section 3 Lesson 2 In this lesson we have covered: The Chemistry of Alkenes Manufacture and reactions of Ethanol