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Organic Chemistry Flashcards

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1
Q

What is a saturated hydrocarbon?

A

A hydrocarbon that contains no carbon-carbon double bond and only contains single bonds

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2
Q

What is a hydrocarbon?

A

A molecule that contains only carbon and hydrogen

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3
Q

How and why does the boiling point of alkanes change as the chain length increases?

A
  • As chain length increases, the boiling point increases
  • Alkanes have induced dipole-dipoles between molecules
  • Strenght of attraction increases with increasing size of molecule and no. of electrons
  • The longer the chain, the bigger the molecule and the more electrons
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4
Q

Why does the boiling point of alkanes decrease with more branches?

A
  • There is more surface contact between unbranched molecules than branched molecules
  • Therefore stronger IDDs between unbranched molecules
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5
Q

What is fractional distillation?

A

Seperating a mixture of compounds based on boiling points

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6
Q

What is a fraction?

A

A group of hydrocarbons with similar boiling points

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7
Q

Explain the process of fractional distillation

A
  • Crude oil is heated up and vapourised as it enters column at the bottom
  • Hydrocarbons have different boiling points deoending on chain length and branches
  • Column is hotter at the bottom
  • The larger molecules condense first
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8
Q

What is the purpose of cracking?

A

To break longer, less useful hydricabons, into shorter, more useful hydrocarbons that are in higher demand

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9
Q

Descibe thermal cracking

A
  • Thermal cracking produces one alkane with all other molecules being alkenes
  • High pressure: (7000 kPa)
  • High temperature: (700-1200 K)
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10
Q

Describe catalytic cracking

A
  • Produces a high percentage of branched alkanes and cycloalkanes
  • Temperature: (720 K)
  • Slight pressure: (1000 kPa = 1ATM)
  • Catalyst: (Zeolite)
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11
Q

What is complete combustion?

A

Combustion of alkanes in a plentiful supply of oxygen to form carbon dioxide and water

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12
Q

What is incomplete combustion?

A

Combustion of alkanes in a limited supply of oxygen to produce carbon monoxide or solid carbon

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13
Q

Describe the polluting effects of the following chemicals produced during combustion: CO2, H2O, CO, C

A
  • CO2: Greenhouse gas (prevents heat escaping into space)
  • H2O: Greenhouse gas
  • CO: Poisonous (prevents haemoglobin from binding to oxygen)
  • C: Damages the lungs
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14
Q

Give the formula for the formation of Sulfur Dioxide

A

S(s) + O2(g) –> SO2(g)

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15
Q

Give the formula for the formation of Sulfuric acid/ acid rain

A

SO2(g) + 0.5O2(g) + H2O(l) –> H2SO4(l)

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16
Q

Give the formulas of Nitrogen reacting with Oxygen to form Nitric Oxide and Nitrogen Dioxide

A

N2(g) + O2(g) –> 2NO(g)
2NO(g) + O2 –> 2NO2(g)

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17
Q

Give the formula for the formation of Nitric Acid/ acid rain

A

4NO2(g) + 2H2O(l) + O2(g) –> 4HNO3(g)

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18
Q

Give the formula for flue gas desulphurisation using Calcium Oxide

A

CaO(s) + 2H2O(l) + SO2(g) + 0.5O2 –> CaSO4 2H2O(s)

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19
Q

Give the formula for desulphurisation using Calcium Carbonate

A

CaCO3 + 0.5O2(g) + SO2(g) –> CaSO4(S) + CO2(g)

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20
Q

Describe how a catalytic converter is made to increase the rate of reaction

A
  • The honeycomb structure increases the surface area, increasing the rate of reaction
  • Platinum and rhodium metals are used as catalysts
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21
Q

Give the formula for the removal of CO and NO in a catalytic converter

A

2NO(g) + 2CO(g) –> N2(g) + 2CO2(g)

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22
Q

Give the formula for the removal of unburned hydrocarbons and nitrogen monoxide

A

C8H18 + 25NO –> 8CO2 + 9H2O + 12.5N2

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23
Q

What is a free-radical?

A

A species with a single unpaired electron

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24
Q

What is the essential condition for free-radical substitution?

A

UV light

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25
Q

State the equation and description of Initiation of free-radical substitution

A
  • Cl2 –> 2Cl*
  • Homolytic fission by UV light forms the radical from the halogen molecule
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26
Q

Give the formula and description for Propogation 1 of free-radical substitution

A
  • CH4 + Cl* –> *CH3 + HCl
  • The free-radical produced during initiation takes a H from the alkane
  • This turns the alkane into a free-radical and also produces a hydrogen halide byproduct
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27
Q

Give the formula and description of Propogation 2 of free-radical substitution

A
  • CH3 + Cl2 –> CH3Cl + Cl
  • The alkyl radical in step 1 of propogation takes a halogen atom from a halogen molecule (since not all halogen molecules were split in initiation)
  • This forms a haloalkane and reproduces the halogen free-radical that started propogation 1
28
Q

Give the three possible equations for termination of free-radical substitution

A

1- 2Cl* –> Cl2
2- CH3 + Cl –> CH3Cl
3- 2*CH3 –> C2H6

29
Q

Write the overall equation for the reaction of fluorine with methane to form trichloromethane

(2 marks)

A

CH4 + 3F2 –> CHF3 +3HF

30
Q

Give the three equations to show how the trichlorofluoromethane CFC is involed in damaging the ozone layer

(3 marks)

A

1- Initiation: CCl3F –> Cl* + CCl2F
2- Propogation:
- 1) Cl + O3 –> ClO + O2
- 2) ClO* + O3 –> 2O2 + Cl*

31
Q

Explain why CFCs can cause the breakdown of the ozone layer using a single chlorine free-radical

A

Cl* is regenerated in the final propogation step and causes a chain reaction in the decomposition of ozone

32
Q

Define a nucleophile and an electrophile

A
  • A nucleophile is an electron pair donor
  • An electrophile is an electron pair acceptor
33
Q

Give the reagent, conditions and nucleophile for nucleophilic substitution by OH ions.

A

Reagent: NaOH
Conditions: aqueous
Nucleophile: OH- (hydroxide)

34
Q

Give the reagent, conditions and nucleophile for nucleophilic substitution by nitrile ions

A

Reagent: KCN
Conditions: Ethanol, aq
Nucelophile: -CN

35
Q

Give the reagent and nucleophile for nucleophilic substitution by NH3

A

Reagent: excess NH3
Nucleophile: NH3 (ammonia)

36
Q

Give the reagent, conditions and role of OH ion in elimination reaction

A

Reagent: NaOH
Conditions: Ethanolic solvent
Role of OH: Base (accepts H+)

37
Q

Explain the mechanism of Elimination

(3 marks)

A
  • Lone pair on OH- moves to H and forms bond
  • e pair in C-H moves to C-C (breaks C-H to form C=C)
  • e pair in C-Br moves to Br (breaks C-Br bond)
38
Q

Why is there no rotation around a C=C double bond?

A
  • The Pi bond is formed by overlap of P orbital
  • If there was any rotation the P orbitals would not overlap and the Pi bond would break
39
Q

What is the positive inductive effect?

A

When electron density can be donated between covalent bonds

40
Q

Why are tertiary carbocations more stable than primary carbocations?

A
  • Tertiary carbocations have more positive inductive effect (than secondary and primary carbocations)
  • Because there are more alkyl groups bonded to C+
41
Q

What is the test for oxidation of alcohols

A
  • Acidified K2Cr2O7
  • Turns orange to green
42
Q

Give the reagents and conditions for oxidation of Primary Alcohol to Aldehyde

A
  • Reagent: acidified potassium dichromate
  • Conditions: heat under distillation
43
Q

Give the reagents and conditions for the oxidation of Aldehyde to Carboxylic acid

A
  • Reagent: acidifies potassium dichromate
  • Conditions: heat under reflux
44
Q

Give the reagents and conditions for the oxidation of Primary alcohol to Carboxylic acid

A
  • Reagent: acidified potassium dichromate
  • Conditions: heat under reflux
45
Q

Give the reagents and conditions for the oxidation of secondary alcohols to ketones

A
  • Reagents: acidified potassium dichromate
  • Conditions: heat under distillation or reflux
46
Q

What type of alcohol cannot be oxidised and why?

A
  • Tertiary alcohols
  • Because there is no H atom on carbon in C-OH
47
Q

Name 2 test tube tests for aldehydes, and give their observations when aldehyde is present

A
  • Tollens reagent: Silver mirror forms
  • Fehlings solution: Brick-red precipitate
47
Q

Name 2 test tube tests for aldehydes, and give their observations when aldehyde is present

A
  • Tollens reagent: Silver mirror forms
  • Fehlings solution: Brick-red precipitate
48
Q

Give the reagent used to test for Carboxylic acids and give the observation for when it is present

A
  • Na2CO3: effervescence
49
Q

Describe what happens when a reaction mixture is refluxed and why it is necessary for the complete oxidation for ethanoic acid

(3 marks)

A
  • A mixture of liquids is heated to boiling point for a prolonged time
  • Vapour is formed which escapes from liquid mixture, is changed back into liquid then returned to liquid mixture
  • Any ethanal and ethanol that initially evaporates can then be oxidised
50
Q

Give the test-tube test for: alkenes, 1’ or 2’ alcohols, aldehydes and carboxylic acids

A
  • Alkenes: Shake with bromine water; orange to colourless
  • 1’ or 2’ alcohols: Add acidified K2Cr2O7 and warm; orange to green
  • Aldehydes: Warm with Fehlings OR Tollens; blue to brick red precipitate OR silver mirror forms
  • Carboxylic acid: Add Na2CO3; effervescence
51
Q

Give the test-tube reaction for Haloalkanes

A
  • Add NaOH and warm (white, cream or yellow ppt if Cl, Br or I)
  • Acidify with NHO3 and add AgNO3, then once a precipitate is formed, add dilute ammonia (any AgCl will dissolve)
  • Add conc. ammonia (AgBr ppt will dissolve, AgI ppt will remain)
52
Q

What is IR spectroscopy used to identify?

A

Functional groups

53
Q

How does IR spectroscopy work?

A
  • Infra-red energy is absorbed by bonds which makes them vibrate
  • Bonds vibrate at same frequency as IR spectroscopy
54
Q

What does a smooth broad peak indicate?

A

O-H bond in alcohols

55
Q

What does a bumpy broad peak indicate?

A

O-H bond in carboxylic acids

56
Q

What does a sharp peak at 1680-1750 indicate?

A

C=O bond

57
Q

What does a sharp peak at 1000-1300 indicate?

A

C-O bond

58
Q

What is the fingerprint region?

A
  • The area below 1500
  • That uniquely identifies a molecule and must be compared to a database
59
Q

Describe the molecular ion peaks in a mass spectra of a molecule

A
  • The peak with the largest Mz value is is called the molecular ion peak
  • The Mz ratio of the molcular ion peak is equal to the Mr of the molecule
60
Q

What is the purpose of high resolution mass spectrometry?

A

To identify ions with the same Mr to 1dp by measuring them to 5dp

61
Q

Why can’t a mass spectrometer which measures Mz ratios to 1dp tell the difference betgween C10H16O4 and C11H4O4?

A

Both molecules have the same Mr to 1dp

62
Q

Why can’t high resolution mass spectrometry tell the difference between propan-1-ol and propan-2-ol?

A

Both have same Mr to 5dp

63
Q

Why does C have a relative molecular mass of 12.00000?

A

By definition, C12 is the reference for atomic mass

64
Q

Explain how IR radiation relates to global warming?

A
  • When IR hits greenhouse gases in atmosphere:
  • O-H bonds in water, C=O in CO2 and C-H bonds in methane absorb IR radiation
  • The IR emitted by earth is not allowed to escape into the atmosphere

Chemistry (13 decks)

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