Dales Exam

Question 1

What is petroleum?

Answer 1

What is petroleum?

A mixture that consists mainly of alkanes are hydrocarbons

Question 2

Why are alkanes described as saturated hydrocarbons

Answer 2

Why are alkanes described as saturated hydrocarbons

They only contain carbon and hydrogen atoms, and each of their carbon atoms form is for single bonds – there are no C=C double bonds present

Question 3

Fractional distillation separates hydrocarbons.what property are they separated by?

Answer 3

Fractional distillation separates hydrocarbons.what property are they separated by?

Bpt

Question 4

Explain why some fractions are drawn off higher up the fractional distillation column than others

Answer 4

Explain why some fractions are drawn off higher up the fractional distillation column than others

Some fractions have lower boiling points than others this means they condense further up the column, so are drawn off higher up

Question 5

What is cracking

Answer 5

What is cracking

Breaking long chain alkanes into smaller hydrocarbons

Question 6

Why do we crack heavier petroleum fractions?

Answer 6

Why do we crack heavier petroleum fractions?

There is more demand for lighter petroleum fractions so, to meet the demand, the heavier fractions are cracked into lighter fractions

Question 7

Why does using a catalyst for catalytic cracking cut costs

Answer 7

Why does using a catalyst for catalytic cracking cut costs

Using a catalyst cut costs because the reaction can be done at a lower temperature and pressure and at an increased speed

Question 8

Complete combustion products

Answer 8

Complete combustion products

CO2 and H2O

Question 9

Incomplete combustion reaction products

Answer 9

Incomplete combustion reaction products

CO and H2O

Question 10

Give three pollutants produced by vehicle exhausts

Answer 10

Give three pollutants produced by vehicle exhausts

Carbon monoxide, carbon dioxide and unburned hydrocarbons

Question 11

What can be used to remove pollutants from vehicle exhausts

Answer 11

What can be used to remove pollutants from vehicle exhausts

A catalytic converter

Question 12

Explain how acid rain is caused by burning fossil fuels containing sulfur

Answer 12

Explain how acid rain is caused by burning fossil fuels containing sulfur

The sulphur burns to produce sulphur dioxide gas if sulfur dioxide enters the atmosphere, it can dissolve in the moisture and form sulfuric acid

Question 13

Describe one method for removing sulphur dioxide from flue gases

Answer 13

Describe one method for removing sulphur dioxide from flue gases

Powdered calcium carbonate can be mixed with water to make an alkaline slurry.
when the fluegases mix with the alkaline slurry, the acidic sulphur dioxide gas reacts with the calcium compounds to form a harmless salt

CaO(s) + SO2(g) —> CaSO3

Question 14

What’s a photochemical reaction

Answer 14

What’s a photochemical reaction

Reactions that are started by light

Question 15

Write an equation for the initiation step of the synthesis of chloromethane by a photochemical reaction

Answer 15

Write an equation for the initiation step of the synthesis of chloromethane by a photochemical reaction

Cl2 —-> 2Cl•

Question 16

describe what takes place in the termination step of a free radical substitution mechanism

Answer 16

describe what takes place in the termination step of a free radical substitution mechanism

To free radicals join together to make a stable molecule.
this terminates the chain reaction

Question 17

Why is ozone in the upper atmosphere beneficial

Answer 17

why is ozone in the upper atmosphere beneficial

It acts as a chemical sunscreen by absorbing a lot of ultraviolet radiation from the Sun, and stopping it from reaching us this helps to prevent sunburn and even skin cancer

Question 18

describe how chlorine free radicals are formed in the upper atmosphere

Answer 18

describe how chlorine free radicals are formed in the upper atmosphere

Chlorine free radicals, Cl• are formed in the upper atmosphere when the C – Cl bonds in chlorofluorocarbons are broken down by ultraviolet radiation

Question 19

Write two equations to show how chlorine atoms catalyse decomposition of ozone

Answer 19

Wright two equations to show how chlorine atoms catalyse decomposition of ozone

Cl• (g) + O3 (g) —-> O2(g) + ClO•(g)
ClO• (g) + O3 (g) —-> 2O2 (g) + Cl•(g)

Question 20

Explain why Chlorofluorocarbons were band from use as a solvent and refrigerants

Answer 20

Explain why Chlorofluorocarbons were band from use as a solvent and refrigerants

Research by several different scientific groups demonstrated that chlorofluorocarbons were causing damage to the ozone layer the advantages of chlorofluorocarbons couldn’t outweigh the environmental problems they were causing, so they were banned

Question 21

What is a halogenoalkane

Answer 21

What is a halogenoalkane

An alkane with at least one halogen atom in place of a hydrogen atom

Question 22

Explain why halogen – carbon bonds are polar

Answer 22

Explain why halogen – carbon bonds are polar

Halogen atoms are generally more electronegative than carbon atoms and so they withdraw electron density from carbon atoms

this leaves the carbon atoms with a partial positive charge and the halogen atoms with a partial negative charge – resulting in a polar bond

Question 23

What is a nucleophile

Answer 23

What is a nucleophile

An electron pair donor

Question 24

Give two examples of nucleophiles that will react with halogenoalkanes

Answer 24

Give two examples of nucleophiles that will react with
Halogenoalkanes

A cyanide ions, ammonia and hydroxide ions

Question 25

What does a pair of dots represent on a nucleophile

Answer 25

What does a pair of dots represent on a nucleophile A lone pair of electrons

Question 26

Why does the C-I bond easiest to break

Answer 26

Why does the C-I bond easiest to break Lowest bond enthalpy

Question 27

Draw the mechanism for the reaction of Iodopropane with ammonia the reaction is done in a sealed tube in warm ethanol

Answer 27

Draw the mechanism for the reaction of Iodopropane with ammonia the reaction is done in a sealed tube in warm ethanol

Question 28

Draw the mechanism for the hydrolysis of chloroethane by warm aqueous sodium hydroxide

Answer 28

Draw the mechanism for the hydrolysis of chloroethane by warm aqueous sodium hydroxide

Question 29

What happens in a nucleophilic substitution reaction

Answer 29

What happens in a nucleophilic substitution reaction In nucleophilic substitution, one functional group is substituted for another

Question 30

What chemical would you react bromoethane with to get ethanol

Answer 30

What chemical would you react bromoethane with to get ethanol Aqueous sodium hydroxide or potassium hydroxide

Question 31

Name the nucleophile that is present when the bromoethane reacts with ethanolic potassium cyanide under reflux

Answer 31

Name the nucleophile that is present when the bromoethane reacts with ethanolic potassium cyanide under reflux Cyanide ion

Question 32

Under what reaction conditions do you react bromoethane with ammonia to form ethylamine

Answer 32

Under what reaction conditions do you react bromoethane with ammonia to form ethylamine Warm in ethanol in a sealed tube

Question 33

Explain why Fluoroalkanes are substituted more slowly than other Halogenoalkanes

Answer 33

Explain why Fluoroalkanes are substituted more slowly than other Halogenoalkanes The C – F bond is the strongest – it has the highest bond enthalpy so Fluoroalkanes are substituted more slowly than other halogenoalkanes

Question 34

Draw the mechanism for the main reaction of 1-bromopropane with ethanol under reflux

Answer 34

Draw the mechanism for the main reaction of 1-bromopropane with ethanol under reflux

Question 35

Briefly describe an elimination reaction

Answer 35

Briefly describe an elimination reaction an elimination reaction happens when a molecule loses atoms or groups of atoms from two neighbouring carbon atoms and forms a carbon-carbon double bond

Question 36

Reacting bromoethane with water under reflux will produce mainly ethanol (a) what type of reagent does the sodium hydroxide ion act as in this reaction (b) name the type of reaction that’s happening

Answer 36

Reacting bromoethane with water under reflux will produce mainly ethanol (a) what type of reagent does the sodium hydroxide ion act as in this reaction As a nucleophile (b) name the type of reaction that’s happening Nucleophilic substitution

Question 37

Reacting bromoethane with ethanol under reflux will produce mainly ethene. (a) What type of reagent does the sodium hydroxide ion act as in this reaction (b) name the type of reaction that is occurring

Answer 37

Reacting bromoethane with ethanol under reflux will produce mainly ethene. (a) What type of reagent does the sodium hydroxide ion act as in this reaction As a base (b) name the type of reaction that is occurring Elimination reaction

Question 38

Chloroethane reacts with ethanolic potassium cyanide under reflux describe the following steps in this mechanism

Answer 38

Chloroethane reacts with ethanolic potassium cyanide under reflux describe the following steps in this mechanism The slightly positive Carbon attracts a lone pair of electrons from the cyanide ion The cyanide ion acts as a nucleophile attacking the slightly positive carbon atom A new bond forms between the carbon and the cyanide ion, making a nitrile The C-Cl bond breaks and both the electrons from the bond are taken by the Cl

Question 39

Chlorine and methane react in ultraviolet light to form the halogenoalkane chloromethane this reaction is initiated by the breaking of the Cl – Cl bond Wright two equations to show the propagation steps for this reaction write an equation of a termination reaction showing the formation of chloromethane

Answer 39

Chlorine and methane react in ultraviolet light to form the halogenoalkane chloromethane this reaction is initiated by the breaking of the Cl – Cl bond Wright two equations to show the propagation steps for this reaction Cl• + CH4 —-> •CH3 + HCl •CH3 + Cl2 —> CH3Cl + Cl• write an equation of a termination reaction showing the formation of chloromethane •CH3 + Cl• —> CH3Cl

Question 40

When chlorofluorocarbons enter the upper atmosphere, ultraviolet light breaks the C – Cl bonds to form chlorine free radicals. use equations to show how this leads to the decomposition of ozone and explain why this is a problem

Answer 40

When chlorofluorocarbons enter the upper atmosphere, ultraviolet light breaks the C – Cl bonds to form chlorine free radicals. use equations to show how this leads to the decomposition of ozone and explain why this is a problem The chlorine free radicals act as catalysts. They react with ozone to form an intermediate (ClO•) and an oxygen molecule in the following reaction Cl• (g) + O3(g) —> O2(g) + ClO•(g) the ClO then reacts with more ozone to regenerate the chlorine free radical in this reaction: ClO•(g) + O3(g) —> 2O2(g) + •Cl(g) because the chlorine free free radical is regenerated, just one chlorine free radical can destroy lots of ozone molecules this is a problem as ozone absorbs ultraviolet radiation, and acts as a chemical sunscreen When ozone is destroyed it will increase peoples risk of getting sunburn and skin cancer

Question 41

Heptane is an alkane which is found in petroleum fractional distillation can be used to separate out heptane explain how fractional distillation allows the fractions in petroleum to be seperated

Answer 41

Heptane is an alkane which is found in petroleum fractional distillation can be used to separate out heptane explain how fractional distillation allows the fractions in petroleum to be seperated Because the boiling point of alkanes increase as the molecules get bigger each fraction condenses a different temperature as the crude oil vapour goes up the fractionating column it gets cooler so the fractions are drawn off at different levels in the column depending on where they condense

Question 42

Petroleum fractions can be burnt to generate energy write an equation for the incomplete combustion of heptane Explain why the incomplete combustion of heptane can be dangerous

Answer 42

Petroleum fractions can be burnt to generate energy write an equation for the incomplete combustion of heptane C7H16(g) + 7 1/2O2(g) —-> 7CO(g) + 8H2O(g) Explain why the incomplete combustion of heptane can be dangerous Because carbon monoxide gas is poisonous

Question 43

Heptane can be cracked to form smaller chain hydrocarbons explain why it is necessary to crack heptane into smaller chain hydrocarbons Write an equation for the cracking of heptane into smaller chain hydrocarbons

Answer 43

Heptane can be cracked to form smaller chain hydrocarbons explain why it is necessary to crack heptane into smaller chain hydrocarbons There is more demand for light fractions Write an equation for the cracking of heptane into smaller chain hydrocarbons C7H16—-> C2H4 + C5H12

Question 44

In industry, a catalyst can be used to crack heptane | explain why a catalyst is used

Answer 44

In industry, a catalyst can be used to crack heptane explain why a catalyst is used Using a catalyst cuts costs because the reactions can be done at a lower temperature and pressure catalysts also speeds up the rate of reactions

Question 45

Ethanol is a simple alcohol that be can be used as a fuel, in alcoholic beverages, as a solvent and also as a starting molecule for many organic synthesis reactions ethanol can be created by a nucleophilic substitution reaction of bromoethane with aqueous sodium hydroxide write the equation for this reaction and draw out the mechanism by which it proceeds

Answer 45

Ethanol is a simple alcohol that be can be used as a fuel, in alcoholic beverages, as a solvent and also as a starting molecule for many organic synthesis reactions ethanol can be created by a nucleophilic substitution reaction of bromoethane with aqueous sodium hydroxide write the equation for this reaction and draw out the mechanism by which it proceeds CH3CH2Br + OH- —> CH3CH2OH + Br-

Question 46

Sodium hydroxide can be dissolved in warm ethanol instead of water how will this affect the type of reaction that occurs with bromoethane. explain your answer.

Answer 46

Sodium hydroxide can be dissolved in warm ethanol instead of water how will this affect the type of reaction that occurs with bromoethane. explain your answer. It will undergo an elimination reaction instead of a nucleophilic reaction this is because the sodium hydroxide ion acts as a base and removes a hydrogen atom from bromoethane

Question 47

Draw the mechanism for the reaction of but-2-ene with bromine.

Answer 47

Draw the mechanism for the reaction of but-2-ene with bromine.

Question 48

Explain why Alkenes are unsaturated

Answer 48

Explain why Alkenes are unsaturated Because they can make more bonds with extra atoms in addition reactions across the C=C double bond

Question 49

Explain why alkenes undergo electrophilic addition reactions

Answer 49

Explain why alkenes undergo electrophilic addition reactions As they have a double bond which has a high electron density and is easily attacked by electrophiles

Question 50

What’s an electrophile? Give two examples

Answer 50

What’s an electrophile? Electron-pair acceptors Give two examples NO2+, H+, CH3CH2Br

Question 51

What can you use bromine water to test for

Answer 51

What can you use bromine water to test for Alkenes

Question 52

Draw the mechanism for the reaction between but-2-ene and hydrogen bromide

Answer 52

Draw the mechanism for the reaction between but-2-ene and hydrogen bromide

Question 53

Hydrogen bromide reacts with but-1-ene to form either 1-bromobutane or 2-bromobutane Explain why 2-bromobutane is the major product of the reaction

Answer 53

Hydrogen bromide reacts with but-1-ene to form either 1-bromobutane or 2-bromobutane Explain why 2-bromobutane is the major product of the reaction The reaction mechanism for the production of 2-bromobutane contains a secondary carbocation, which is more stable than the primary carbocation formed in the reaction mechanism for 1-bromobutane More stable carbocations are more likely to form so 2-bromobutane is the major product of this reaction

Question 54

What could you react ethene with in order to produce bromoethane?

Answer 54

What could you react ethene with in order to produce bromoethane? Hydrogen bromide

Question 55

Write a reaction for the addition polymerisation of the monomer fluoroethene Name the polymer that is formed

Answer 55

Write a reaction for the addition polymerisation of the monomer fluoroethene Name the polymer that is formed Polyfluoroethene

Question 56

Describe addition polymerisation

Answer 56

Describe addition polymerisation The double bonds in alkenes open up and join together to make long chains called polymers

Question 57

Why are poly(alkenes) unreactive?

Answer 57

Why are poly(alkenes) unreactive? They have lost their C=C double bond (they are saturated and non-polar)

Question 58

Elimination reaction definition

Answer 58

Elimination reaction definition in which a pair of atoms or groups of atoms are removed from a molecule

Question 59

Give one condition necessary for a high yield of product in elimination reactions

Answer 59

Give one condition necessary for a high yield of product in elimination reactions High temperature and ethanol

Question 60

Hydrogen bromide (HBr) could be used in the overall conversion of P into R, instead of using HCl Hydrogen bromide is made by the reaction of NaBr with concentrated phosphoric acid. Concentrated sulfuric acid is not used to make HBr from NaBr Identify two toxic gases that are formed, together with HBr, when NaBr reacts with concentrated H2SO4 State the role of H2SO4 in the formation of these toxic gases

Answer 60

Hydrogen bromide (HBr) could be used in the overall conversion of P into R, instead of using HCl Hydrogen bromide is made by the reaction of NaBr with concentrated phosphoric acid. Concentrated sulfuric acid is not used to make HBr from NaBr Identify two toxic gases that are formed, together with HBr, when NaBr reacts with concentrated H2SO4 SO2 and Br2 State the role of H2SO4 in the formation of these toxic gases * is an oxidising agent * oxidises the bromide

Question 61

The haloalkane produced in Reaction 1 can be converted back into propene in an elimination reaction using ethanolic potassium hydroxide. CH3CHBrCH3 —-> H2C=CHCH3 Outline a mechanism for this conversion.

Answer 61

The haloalkane produced in Reaction 1 can be converted back into propene in an elimination reaction using ethanolic potassium hydroxide. CH3CHBrCH3 —-> H2C=CHCH3 Outline a mechanism for this conversion.

Question 62

Structural isomers

Answer 62

Structural isomers Compounds with the) same molecular formula but different structural / displayed / skeletal formula

Question 63

2-bromo-2-methylpentane is heated with potassium hydroxide dissolved in ethanol. Two structural isomers are formed. Name and draw the mechanism for the formation of one of the isomers. Name of mechanism Mechanism

Answer 63

2-bromo-2-methylpentane is heated with potassium hydroxide dissolved in ethanol. Two structural isomers are formed. Name and draw the mechanism for the formation of one of the isomers. Name of mechanism Mechanism

Question 64

Explain the term addition reaction.

Answer 64

Explain the term addition reaction. An addition reaction is one in which two molecules join together to make a bigger one with all the original atoms being present in the new molecule.