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chemistry > >>3.3 - Alkanes✔ > Flashcards

>>3.3 - Alkanes✔ Flashcards

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1
Q

What affect does the UV light have on the mechanism for chlorination of alkanes?

A

*Frequency of UV light causes Cl₂ bond to break apart (homolytic fission.)

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2
Q

In general terms describe the process of chlorination of alkanes:

A

*Alkanes react with halogens in the presence of UV light to produce halogenoalkanes.
*The UV light breaks down the halogen bonds producing reactive intermediates called free radicals, these attack the alkanes resulting in a series of reactions: Initiation, propagation and termination.

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3
Q

Explain how photochemical smog is caused:

A

*Caused by pungent, toxic gasses and minute solid particles suspended in the air.
*Smog is formed when NOₙ, SO₂ and unburnt hydrocarbons react with sunlight, also includes carbon atoms produced from combustion with a very limited O₂ supply.

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4
Q

What is the name of the mechanism for chlorination of alkanes?

A

*Free radical substitution (only ever happens with alkanes.)

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5
Q

What are the conditions and reagents for the mechanism for chlorination of alkanes?

A

*UV Light.

*Alkane + Chlorine OR Alkane + Bromine.

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6
Q

How are free radicals shown and what is a radical?

A

*Using a dot e.g: Cl *

*Radicals are very reactive species.

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7
Q

Chlorine and Methane:
What takes place in initiation in the mechanism of chlorination of alkanes?

A
  • The halogen is broken down into 2 radicals.
  • Cl₂ → 2Cl *
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8
Q

Chlorine and Methane:
What takes place in propagation in the mechanism of chlorination of alkanes?

A
  • Chain reaction, P1 makes hydrogen halide, P2 makes halogenoalkane.
  • P1: CH₄ + Cl* → *CH₃ + HCl
  • P2: *CH₃ + Cl₂ → Cl * + CH₃Cl
  • Overall Equation: CH₄ + Cl₂ → CH₃Cl + HCl
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9
Q

Chlorine and Methane:
What takes place in termination in the mechanism of chlorination of alkanes?

A

*Two radicals join to end the chain reaction and form a stable product.

  • *CH₃ + *CH₃ → C₂H₆
  • Cl* + Cl* → Cl₂
  • Cl* + *CH₃ → CH₃Cl
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10
Q

Give the order of substances extracted as you go down the fractionating column:

A

*Refinery gases.
*Petrol.
*Naphtha (petrochemicals, chemical feedstock.)
*Kerosene (jet fuel.)
*Diesel.
*Heavy fuel oil (boat fuel.)
*Waxes.
*Bitumen.

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11
Q

What is cracking?

A

*A process where less useful long chain hydrocarbons are broken down into more useful products that lack availability and are in high demand.
*Involves breaking c-c bonds.

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12
Q

What is a benzene group?

A

*C₆H₆
*Aromatic compound.

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13
Q

Thermal Cracking:
What is the raw material, temperature, pressure, time, catalyst, products and use of products?

A
  • Crude oil.
  • 1000-1200K.
  • 70atms.
  • 1s.
  • None.
  • Alkenes and short chain alkanes.
  • Manufacture of chemicals e.g: naphtha and manufacture of polymers from alkenes.
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14
Q

Catalytic Cracking:
What is the raw material, temperature, pressure, time, catalyst, products and use of products?

A

*Crude oil.
*800K.
*1atms.
*2-4s.
*Aluminium silicate zeolite.
*Branched and cyclo-alkanes and aromatic compounds.
*Fuel for motor vehicles.

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15
Q

What is the test for unsaturated hydrocarbons and what are the results for alkenes and alkanes?

A

*Add bromine water and shake.
*For alkenes the orange solution turns colourless.
*For alkanes the orange solution remains orange.

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16
Q

What are the health issues surrounding photochemical smog?

A

*Irritation to eyes and severe lung disease.

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17
Q

Explain the structure of a catalytic converter and what do they do?

A

*Honeycomb (giving large SA) clay structure coated in one of three metals: platinum, rhodium or palladium acting as catalysts.
*Thin layer makes it cheaper and uses less natural resources and increases SA.
*CO and NOₙ can both be removed from systems by converting them to more stable products such as CO₂ or H₂O.

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18
Q

What can CO₂ / SO₂ / NO₂ / NO all be classified as?

A

*Acidic non-metal oxides.

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19
Q

How can SO₂ be removed from flue gasses?

A

*Needs to be reacted with a base, either CaO or CaCO₃

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20
Q

Give the two possible equations for the removal of SO₂ from fumes:

A
  • CaO + SO₂ → CaSO₃
  • CaCO₃ + SO₂ → CaSO₃ + CO₂
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21
Q

What can calcium sulphite be used for?

A

*CaSO₃ can be used to make plaster boards.

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22
Q

Deduce the equations for the formation of: CO₂, CO, NO and NO₂

A
  • C + O₂ → CO₂
  • 2C + O₂ → 2CO
  • N₂ + O₂ → 2NO
  • N₂ + 2O₂ → 2NO₂ (2NO + O₂ → 2NO₂)
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23
Q

What is the origin, conditions causing it to form and the pollution caused of the following?
≫CO₂:
≫CO:
≫C:
≫NOₙ:
≫SO₂:
≫Hydrocarbons:
≫H₂O:

A

*C in fuel, excess O₂, global warming.
*C in fuel, limited O₂, toxic gas.
*C in fuel, very limited O₂, particles exacerbate asthma.
*N₂ in air, extremely high temperatures, acid rain + photochemical smog causing respiratory problems.
*S from fuel impurities, acid rain.
*Fuel compounds that remain unburned, react with NOₙ to form ground level ozone which causes respiratory issues.
*H in fuel.

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24
Q

Deduce the equations for the formation of: HNO₃ and H₂SO₄, both of which are acid rain:

A
  • 2NO₂ + H₂O + 0.5O₂ → 2HNO₃
  • SO₂ + H₂O + 0.5O₂ → H₂SO₄
25
Q

Deduce the equation for converting carbon monoxide into safer carbon dioxide:

A
  • 2CO + O₂ → 2CO₂
26
Q

Deduce the equation for turning carbon + nitrogen monoxides into safer products in a catalytic converter:

A
  • 2CO + 2NO → 2CO₂ + N₂
27
Q

Deduce the equation for turning unburnt octane and nitrogen (II) oxide into safer products in a catalytic converter:

A
  • C₈H₁₈ + 25NO → 8CO₂ + 9H₂O + 12.5N₂
28
Q

What are the affects of acid rain?

A

*pH of soil.
*pH of waterways.
*Corrosion of CaCO₃ and metals.

29
Q

Deduce the equations for H₂SO₄ on limestone, HNO₃ on limestone and H₂SO₄ on iron:

A
  • H₂SO₄ + CaCO₃ → CaSO₄ + H₂O + CO₂
  • 2HNO₃ + CaCO₃ → Ca(NO₃)₂ + H₂O + CO₂
  • H₂SO₄ + Fe → FeSO₄ + H₂
30
Q

What are the conditions for complete combustion and incomplete combustion?

A

*Plentiful O₂
*Lack of O₂

31
Q

What is the equation for complete combustion of ethane?

A
  • C₂H₆ + 3.5O₂ → 2CO₂ + 3H₂O
32
Q

Complete Combustion:
As we increase chain length by 1 carbon what happens to the amount of O₂?

A

*Increases by 1.5 moles.

33
Q

Incomplete Combustion (CO):
As we increase chain length by 1 carbon what happens to the amount of O₂?

A

*Increases by 1 mole.

34
Q

Incomplete Combustion (C):
As we increase chain length by 1 carbon what happens to the amount of O₂?

A

*Increases by 0.5 moles.

35
Q

What is the equation for incomplete combustion of ethane?

A
  • C₂H₆ + 2.5O₂ → 2CO + 3H₂O
36
Q

What are the two possible products for incomplete combustion?

A
  • CO + H₂O
    OR
  • C + H₂O
37
Q

Why is CO dangerous?

A

*Carbon monoxide is a toxic gaseous product that has no odour or colour.

38
Q

Briefly describe how the internal combustion engine works:

A

*A small amount of fuel with a large excess of air is drawn into a combustion chamber, the mixture is compressed and ignited with an extreme temperature spark, the mixture burns explosively forcing movement of the engine parts.

39
Q

How are NOₙ’s formed in the internal combustion engine?

A

*Due to the pressure and extreme temperatures the nitrogen in the air combines with oxygen producing a series of nitrogen oxides.

40
Q

What is the equation for the formation of nitrogen (II) oxide?

A
  • N₂ + O₂ → 2NO
41
Q

What is the equation for the formation of nitrogen (IV) oxide?

A
  • N₂ + 2O₂ → 2NO₂
42
Q

How is SO₂ formed in the internal combustion engine?

A

*Sulphur originates from impurities in crude oil which end up in the fuel, when burned with oxygen it reacts to form sulphur dioxide.

43
Q

What is the equation for the formation of sulphur dioxide?

A
  • S + O₂ → SO₂
44
Q

What is the general formula of an alkane?

A

*CₙH₂ₙ₊₂

45
Q

Why do unbranched alkanes have a higher melting point?

A

*Molecules can pack closer together so there are more and stronger VDW forces.

46
Q

Why do branched alkanes have a lower melting point?

A

*Molecules can’t pack close so VDW forces have to act over a greater distance so they are weaker and less of them.

47
Q

What are the states of matter up to hexane?

A

*CH₄ (g)
*C₂H₆ (g)
*C₃H₈ (g)
*C₄H₁₀ (g)
*C₅H₁₂ (l)
*C₆H₁₄ (l)

48
Q

What is crude oil?

A

*A mixture of hydrocarbons.
*It can be separated into separate molecules by fractional distillation.

49
Q

What is the definition of a fraction?

A

*A group of compounds which have similar boiling points and are removed from the same level of the fractionating column.

50
Q

Describe the process of fractional distillation:

A

*Crude oil is heated until it boils.
*The molecules evaporate.
*The gas particles rise up the fractionating column.
*A range of compounds of similar BP’s condense at different parts of the column.
*The temperature gradient of the column means that fractions of the lowest BP condense higher up the column except for the gasses.

51
Q

What happens as you move down the fractionating column?

A

*Temperature increases.
*Size of hydrocarbons increases/MP+BP of hydrocarbons increases.
*Viscosity increases.
*Flammability decreases.

52
Q

Describe the solubility of alkanes:

A

*Alkanes are insoluble in water but are soluble in organic solvents.

53
Q

What is petroleum?

A

*A mixture consisting mainly of alkane hydrocarbons that can be separated by fractional distillation.

54
Q

Suggest one important substance manufactured on a large scale from propene

A

Polypropylene

55
Q

Define hydrocarbons

A

A compound of carbons and hydrogens ONLY

56
Q

What is the equation for Pb in free radical substitution?

A

*h/c radical + halogen -> hydrogen radical + halogenoalkane

57
Q

What is the equation for Pa in free radical substitution?

A

*Alkane + Halogen radical -> hydrogen halide + h/c radical

58
Q

What is Homolytic fission?

A

*It is a reaction where 1 molecule breaks into 2 of the same molecule

59
Q

What is free radical substitution?

A

*It is a series of reactions which allows Alkanes to react with halogens or halogenoalkanes to form a hydrogen halide and a new halogenoalkane

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