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Chemistry A Level > Dales Exam > Flashcards

Dales Exam Flashcards

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1
Q

What is petroleum?

A

What is petroleum?

A mixture that consists mainly of alkanes are hydrocarbons

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2
Q

Why are alkanes described as saturated hydrocarbons

A

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

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3
Q

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

A

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

Bpt

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4
Q

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

A

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

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5
Q

What is cracking

A

What is cracking

Breaking long chain alkanes into smaller hydrocarbons

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6
Q

Why do we crack heavier petroleum fractions?

A

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

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7
Q

Why does using a catalyst for catalytic cracking cut costs

A

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

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8
Q

Complete combustion products

A

Complete combustion products

CO2 and H2O

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9
Q

Incomplete combustion reaction products

A

Incomplete combustion reaction products

CO and H2O

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10
Q

Give three pollutants produced by vehicle exhausts

A

Give three pollutants produced by vehicle exhausts

Carbon monoxide, carbon dioxide and unburned hydrocarbons

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11
Q

What can be used to remove pollutants from vehicle exhausts

A

What can be used to remove pollutants from vehicle exhausts

A catalytic converter

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12
Q

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

A

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

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13
Q

Describe one method for removing sulphur dioxide from flue gases

A

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

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14
Q

What’s a photochemical reaction

A

What’s a photochemical reaction

Reactions that are started by light

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15
Q

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

A

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

Cl2 —-> 2Cl•

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16
Q

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

A

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

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17
Q

Why is ozone in the upper atmosphere beneficial

A

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

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18
Q

describe how chlorine free radicals are formed in the upper atmosphere

A

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

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19
Q

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

A

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)

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20
Q

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

A

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

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21
Q

What is a halogenoalkane

A

What is a halogenoalkane

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

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22
Q

Explain why halogen – carbon bonds are polar

A

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

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23
Q

What is a nucleophile

A

What is a nucleophile

An electron pair donor

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24
Q

Give two examples of nucleophiles that will react with halogenoalkanes

A

Give two examples of nucleophiles that will react with
Halogenoalkanes

A cyanide ions, ammonia and hydroxide ions

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25
Q

What does a pair of dots represent on a nucleophile

A

What does a pair of dots represent on a nucleophile

A lone pair of electrons

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26
Q

Why does the C-I bond easiest to break

A

Why does the C-I bond easiest to break

Lowest bond enthalpy

27
Q

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

A

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

28
Q

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

A

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

29
Q

What happens in a nucleophilic substitution reaction

A

What happens in a nucleophilic substitution reaction

In nucleophilic substitution, one functional group is substituted for another

30
Q

What chemical would you react bromoethane with to get ethanol

A

What chemical would you react bromoethane with to get ethanol

Aqueous sodium hydroxide or potassium hydroxide

31
Q

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

A

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

Cyanide ion

32
Q

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

A

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

Warm in ethanol in a sealed tube

33
Q

Explain why Fluoroalkanes are substituted more slowly than other Halogenoalkanes

A

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

34
Q

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

A

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

35
Q

Briefly describe an elimination reaction

A

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

36
Q

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

A

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

37
Q

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

A

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

38
Q

Chloroethane reacts with ethanolic potassium cyanide under reflux

describe the following steps in this mechanism

A

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

39
Q

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

A

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

40
Q

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

A

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

41
Q

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

A

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

42
Q

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

A

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

43
Q

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

A

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

44
Q

In industry, a catalyst can be used to crack heptane

explain why a catalyst is used

A

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

45
Q

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

A

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-

46
Q

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.

A

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

47
Q

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

A

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

48
Q

Explain why Alkenes are unsaturated

A

Explain why Alkenes are unsaturated

Because they can make more bonds with extra atoms in addition reactions across the C=C double bond

49
Q

Explain why alkenes undergo electrophilic addition reactions

A

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

50
Q

What’s an electrophile?

Give two examples

A

What’s an electrophile?

Electron-pair acceptors

Give two examples

NO2+, H+, CH3CH2Br

51
Q

What can you use bromine water to test for

A

What can you use bromine water to test for

Alkenes

52
Q

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

A

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

53
Q

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

A

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

54
Q

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

A

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

Hydrogen bromide

55
Q

Write a reaction for the addition polymerisation of the monomer fluoroethene

Name the polymer that is formed

A

Write a reaction for the addition polymerisation of the monomer fluoroethene

Name the polymer that is formed

Polyfluoroethene

56
Q

Describe addition polymerisation

A

Describe addition polymerisation

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

57
Q

Why are poly(alkenes) unreactive?

A

Why are poly(alkenes) unreactive?

They have lost their C=C double bond (they are saturated and non-polar)

58
Q

Elimination reaction definition

A

Elimination reaction definition

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

59
Q

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

A

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

High temperature and ethanol

60
Q

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

A

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
61
Q

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.

A

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.

62
Q

Structural isomers

A

Structural isomers

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

63
Q

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

A

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

64
Q

Explain the term addition reaction.

A

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.

Chemistry A Level (11 decks)

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