11.2 Organic Families

The alkenes are unsaturated hydrocarbons. They form a homologous series, the members of which have similar chemical properties

   ● easily oxidised
   ● addition reactions
   ● polymerisation
   ● combustion.

All the alkenes have the same empirical formula.

Alkenes can be oxidised to carboxylic acids by boiling with aqueous potassium manganate(VII).

Complete the following equations for the addition reactions of propene.

CH₃–CH=CH₂ + Br₂ → .................................... 

CH3–CH=CH₂ + H₂O → ....................................

Draw the structural formula of poly(propene).

0.01 moles of an alkene needed 2.4 g of oxygen for complete combustion. 2.2 g of carbon dioxide were formed.

Determine the following mole ratio.

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   Write an equation for the complete combustion of this alkene.

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Many organic compounds which contain a halogen have chloro, bromo or iodo in their name.

The following diagram shows the structure of 1-chloropropane.

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Organic halides react with water to form an alcohol and a halide ion.

CH₃–CH₂–I + H₂O → CH₃–CH₂–OH + I^–

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The speed (rate) of reaction between an organic halide and water can be measured by the following method.
A mixture of 10 cm³ of aqueous silver nitrate and 10 cm³ of ethanol is warmed to 60 °C.
Drops of the organic halide are added and the time taken for a precipitate to form is measured.
Silver ions react with the halide ions to form a precipitate of the silver halide.

Ag⁺ (aq) + X^- (aq) → AgX (s)

Typical results for four experiments, A, B, C and D, are given in the table.

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Petroleum is a source of many important chemicals.

Name two industrial processes which must take place to produce alkenes from petroleum.

Ethene, CH₂=CH₂, and propene, CH₂=CHCH₃, can both be converted into polymers.

Ethene will react with steam to form ethanol.

Propene will react with steam to form two isomers, both of which are alcohols.

Suggest the structures of these alcohols.

Esters are organic chemicals noted for their characteristic smells. Ethanoic acid and methanol will react to form an ester.

Propanoic acid is a carboxylic acid. Its formula is CH₃–CH₂–COOH.

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Carboxylic acids can be made by the oxidation of alcohols.

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Complete the following equations for some of the reactions of propanoic acid.

The salts of this acid are called propanoates.

A piece of magnesium was added to 100 cm³ of an aqueous acid. The time taken for the metal to react completely was measured.

This experiment was repeated using different aqueous acids. The same volume of acid was used in each experiment and the pieces of magnesium used were identical.

In one experiment the reaction was carried out at a different temperature.

Explain the following in terms of collision rate between reacting particles.

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Plants can make complex molecules from simple starting materials, such as water, carbon dioxide and nitrates. Substances produced by plants include sugars, more complex carbohydrates, esters, proteins, vegetable oils and fats.

The fermentation of glucose can be carried out in the apparatus shown below. After a few days the reaction stops. A 12% aqueous solution of ethanol has been produced.

The ester methyl butanoate is found in apples. It can be made from butanoic acid and methanol. Their structural formulae are given below.

butanoic acid	methanol

Use the information given above to deduce the structural formula of methyl butanoate showing all the bonds.

Proteins are natural macromolecules. Draw the structural formula of a typical protein. Include three monomer units. You may represent amino acids by formulae of the type drawn below.

Methanol can be made from a mixture of carbon monoxide and hydrogen.

CO (g) + 2H₂ (g) CH₃OH (g)

The forward reaction is exothermic.

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Petroleum-based diesel is a mixture of hydrocarbons, such as octane and octene.

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Structural formulae are an essential part of Organic Chemistry.

Draw the structural formula of each of the following. Show all the bonds in the structure.

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Ethanoic acid and ethanol react to form an ester.

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Two macromolecules have the same amide linkage.
Nylon, a synthetic polymer, has the following structure.

Protein, a natural macromolecule, has the following structure.

How are they different?

Carboxylic acids contain the group

Ethanoic acid is a typical carboxylic acid. It forms ethanoates.

sodium hydroxide + ethanoic acid → ........................  ........................ + ........................

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Maleic acid is an unsaturated acid. 5.8 g of this acid contained 2.4 g of carbon, 0.2 g of hydrogen and 3.2 g of oxygen.

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Alkenes are unsaturated hydrocarbons. They undergo addition reactions.

Two of the methods of making alkenes are cracking and the thermal decomposition of chloroalkanes.

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The following alkenes are isomers.

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Give the name of the product when but-1-ene reacts with each of the following.

steam .........................................................
hydrogen ....................................................
bromine ......................................................

Alkenes can polymerise.

   name of monomer .......................................................
    structural formula

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Butan-1-ol is used as a solvent for paints and varnishes, to make esters and as a fuel.
Butan-1-ol can be manufactured from but-1-ene, which is made from petroleum.

Biobutanol is a fuel of the future. It can be made by the fermentation of almost any form of biomass - grain, straw, leaves etc.

But-1-ene can be obtained from alkanes such as decane, C₁₀H₂₂, by cracking.

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...... C₄H₉OH + ...... O₂ → ...... CO₂ + ...... H₂O

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The fermentation of biomass by bacteria produces a mixture of products which include biobutanol, propanol, hydrogen and propanoic acid.

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How could you show that butanol made from petroleum and biobutanol are the same chemical?

The alkanes are generally unreactive. Their reactions include combustion, substitution and cracking.

The complete combustion of an alkane gives carbon dioxide and water.

The equation for a substitution reaction of butane is given below.

Alkenes are more reactive and industrially more useful than alkanes.

They are made by cracking alkanes.

Esters, fats and polyesters all contain the ester linkage.

The structural formula of an ester is given below.

Name two chemicals that could be used to make this ester and draw their structural formulae. Show all bonds.

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   structural formulae

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The alkenes are a series of unsaturated hydrocarbons. They have the general molecular formula C_nH_2n.

Deduce the molecular formula of an alkene which has a relative molecular mass of 126.

Show your working.

The structural formula of propene is drawn below. 

This question is concerned with some of the addition reactions of but-1-ene.

The alcohols form a homologous series.

Explain why the following two alcohols are isomers.

This question is based on typical reactions of butan-1-ol.

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Alcohols can be made by fermentation or from petroleum.

Ethanol can be made by the fermentation of glucose.

C₆H₁₂O₆ (aq) 2C₂H₅OH (aq) + 2CO₂ (g)       exothermic reaction

Yeast are living single-cell fungi which ferment glucose by anaerobic respiration. This reaction is catalysed by enzymes from the yeast.

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The following observations were noted.

• When a small amount of yeast was added to the aqueous glucose the reaction started and the solution went slightly cloudy.
• The reaction rate increased and the solution became cloudier and warmer.
• After a while, the reaction rate decreased and eventually stopped, leaving a 14% solution of ethanol in water.

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One use of ethanol is in alcoholic drinks.

Give two other uses of ethanol.

Alcohols can be made from petroleum by the following sequence of reactions.

alkanes from petroleum → alkene → alcohol

Describe the manufacture of ethanol from hexane, C₆H₁₄. Include in your description an equation and type of reaction for each step.

The ester linkage showing all the bonds is drawn as

or more simply it can be written as –COO–.

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Draw the structural formula of the polyester formed from the following monomers.

HOOCC₆H₄COOH and HOCH₂CH₂OH

You are advised to use the simpler form of the ester linkage.

Esters can be used as solvents in chromatography. The following shows a chromatogram of plant acids.

An ester was used as the solvent and the chromatogram was sprayed with bromothymol blue.

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The alcohols form a homologous series. The first member of this series is methanol, CH₃OH.

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Methanol is manufactured using the following method.

CH₄ (g) + H₂O (g) → CO (g) + 3H₂ (g)   reaction 1

CO (g) + 2H₂ (g) CH₃OH (g)    reaction 2

The conditions for reaction 2 are:

The forward reaction is exothermic.

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Methanol is oxidised by atmospheric oxygen. This reaction is catalysed by platinum.

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Propenoic acid is an unsaturated carboxylic acid. The structural formula of propenoic acid is given below.

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Propenoic acid reacts with ethanol to form an ester. Deduce the name of this ester. Draw its structural formula.

Name of ester:

Structural formula showing all bonds:

An organic compound has a molecular formula C₆H₈O₄. It is an unsaturated carboxylic acid. One mole of the compound reacts with two moles of sodium hydroxide.

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Alkanes and alkenes are both series of hydrocarbons.

Alkenes and simpler alkanes are made from long-chain alkanes by cracking.

Complete the following equation for the cracking of the alkane C₂₀H₄₂.

Alkenes such as butene and ethene are more reactive than alkanes.

Alkenes are used in the petrochemical industry to make a range of products, which includes polymers and alcohols.

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20 cm³ of a hydrocarbon was burnt in 175 cm³ of oxygen. After cooling, the volume of the remaining gases was

125 cm³. The addition of aqueous sodium hydroxide removed carbon dioxide leaving 25 cm³ of unreacted oxygen.

The structural formula of a butanol is given below.

CH₃—CH₂—CH₂—CH₂—OH

Butanol can be made from petroleum and also by fermentation.

petroleum → butene → butanol

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Butanol can be oxidised to a carboxylic acid by heating with acidified potassium manganate(VII). Give the name and structural formula of the carboxylic acid.

Butanol reacts with ethanoic acid to form a liquid, X, which has the sweet smell of bananas. Its empirical formula is C₃H₆O and its M_r is 116.

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But-1-ene is a typical alkene. It has the structural formula shown below.

CH₃–CH₂–CH=CH₂

The structural formula of cyclobutane is given below.

These two hydrocarbons are isomers.

Describe how alkenes, such as but-1-ene, can be made from alkanes.

Name the product formed when but-1-ene reacts with:

The alcohols form an homologous series.

Give three characteristics of a homologous series.

The following two alcohols are members of the series and they are isomers.

CH₃—CH₂—CH₂—CH₂—OH and (CH₃)₂CH—CH₂OH

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Copper(II) oxide can oxidise butan-1-ol to liquid X whose pH is 4.

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The alcohol ethanol can be made by fermentation. Yeast is added to aqueous glucose.

C₆H₁₂O₆ (aq) → 2C₂H₅OH (aq) + 2CO₂ (g)

Carbon dioxide is given off and the mixture becomes warm as the reaction is exothermic.
The graph shows how the rate of reaction varies over several days.

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The alcohols form a homologous series. Two characteristics of a homologous series are that the physical properties of the members vary in a predictable way and they have similar chemical properties.

Complete the table.

Give two other characteristics of a homologous series.

Draw a diagram showing the arrangement of the valency electrons in one molecule of the covalent compound methanol.

Use x to represent an electron from a carbon atom.
Use ● to represent an electron from an oxygen atom.
Use o to represent an electron from a hydrogen atom.

Alcohols can be oxidised to carboxylic acids by heating with acidic potassium manganate(VII).

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Propan-1-ol and ethanoic acid react together to form an ester. Give its name and structural formula.

The alkenes are a homologous series of unsaturated hydrocarbons.

The table below gives the names, formulae and boiling points of the first members of the series.

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Describe a test that will distinguish between the two isomers, but-2-ene and cyclobutane.

test ..............................................................................................................................................................................

result with but-2-ene  ..........................................................................................................................................

result with cyclobutane  ......................................................................................................................................

Alkenes undergo addition reactions.

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Two homologous series of hydrocarbons are the alkanes and the alkenes.

One general characteristic of a homologous series is that the physical properties vary in a predictable way.

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Cracking is the thermal decomposition of alkanes into smaller hydrocarbons and possibly hydrogen.

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C₇H₁₆ → ................ + ................ 

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C₇H₁₆  →................ + ................ + H₂

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Hydrocarbons burn in excess oxygen to form carbon dioxide and water. 20 cm³ of a gaseous hydrocarbon burned in an excess of oxygen, 200 cm³. After cooling, the volume of the residual gas at r.t.p. was 150 cm³, 50 cm³ of which was
oxygen.

The fractional distillation of crude oil usually produces large quantities of the heavier fractions. The market demand is for the lighter fractions and for the more reactive alkenes. The heavier fractions are cracked to form smaller alkanes and alkenes as in the following example.

Alkenes are more reactive than alkanes and are used to make a range of organic chemicals. Propene, CH₃–CH=CH₂, is made by cracking. Give the structural formula of the addition product when propene reacts with the following.

Propene reacts with hydrogen iodide to form 2-iodopropane.

CH₃−CH=CH₂ + HI → CH₃−CHI−CH₃

1.4 g of propene produced 4.05 g of 2-iodopropane.

Calculate the percentage yield.

moles of CH₃–CH=CH₂ reacted = ..................................................

maximum moles of CH₃–CHI–CH₃ that could be formed = ..................................................

mass of one mole of CH₃–CHI–CH₃ = 170 g

maximum mass of 2- iodopropane that could be formed = ..................................................

percentage yield .................................................. %

The alcohols form a homologous series. The first four members are methanol, ethanol, propan-1-ol and butan-1-ol.

One characteristic of a homologous series is that the physical properties vary in a predictable way. The table below gives the heats of combustion of the first three alcohols.

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Give the name and structural formula of an isomer of propan-1-ol.

Methanol is made from carbon monoxide.

CO (g) + 2H₂(g) CH₃OH (g) the forward reaction is exothermic

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For each of the following predict the name of the organic product.

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A hydrocarbon has the following structural formula.

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Alkenes can be made from alkanes by cracking.

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Alkenes are used in polymerisation reactions and addition reactions.

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The fractional distillation of crude oil usually produces large quantities of the heavier fractions.

The market demand is for the lighter fractions and for the more reactive alkenes. The heavier fractions are cracked to form smaller alkanes and alkenes as in the following example.

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Alkenes are more reactive than alkanes and are used to make a range of organic chemicals. Propene, CH₃–CH=CH₂, is made by cracking. Give the structural formula of the addition product when propene reacts with the following.

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Propene reacts with hydrogen iodide to form 2-iodopropane.

CH₃−CH=CH₂ + HI →  CH₃−CHI−CH₃

1.4 g of propene produced 4.0 g of 2-iodopropane.

Calculate the percentage yield.

moles of CH₃–CH=CH₂ reacted = .........................................

maximum moles of CH₃–CHI–CH₃ that could be formed = .........................................

mass of one mole of CH₃–CHI–CH₃ = 170 g

maximum mass of 2- iodopropane that could be formed = .........................................

percentage yield ......................................... %