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Chemistry > Organic Chemistry > Flashcards

Organic Chemistry Flashcards

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
State the equation and description of **Initiation** of free-radical substitution
- Cl2 --> 2Cl* - Homolytic fission by UV light forms the radical from the halogen molecule
26
Give the formula and description for **Propogation 1** of free-radical substitution
- 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
27
Give the formula and description of **Propogation 2** of free-radical substitution
- *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
Give the three possible equations for **termination** of free-radical substitution
1- 2Cl* --> Cl2 2- *CH3 + Cl* --> CH3Cl 3- 2*CH3 --> C2H6
29
Write the overall equation for the reaction of fluorine with methane to form **tri**chloromethane | (2 marks)
CH4 + 3F2 --> CHF3 +3HF
30
Give the three equations to show how the trichlorofluoromethane CFC is involed in damaging the ozone layer | (3 marks)
1- Initiation: CCl3F --> Cl* + **CCl2F 2- Propogation: - 1) Cl* + O3 --> ClO* + O2 - 2) ClO* + O3 --> 2O2 + Cl*
31
Explain why CFCs can cause the breakdown of the ozone layer using a single chlorine free-radical
Cl* is **regenerated in the final propogation step** and causes a **chain reaction** in the decomposition of ozone
32
Define a nucleophile and an electrophile
- A nucleophile is an electron pair **donor** - An electrophile is an electron pair **acceptor**
33
Give the reagent, conditions and nucleophile for nucleophilic substitution by OH ions.
Reagent: NaOH Conditions: aqueous Nucleophile: OH- (hydroxide)
34
Give the reagent, conditions and nucleophile for nucleophilic substitution by nitrile ions
Reagent: KCN Conditions: Ethanol, aq Nucelophile: -CN
35
Give the reagent and nucleophile for nucleophilic substitution by NH3
Reagent: excess NH3 Nucleophile: NH3 (ammonia)
36
Give the reagent, conditions and role of OH ion in elimination reaction
Reagent: NaOH Conditions: Ethanolic solvent Role of OH: Base (accepts H+)
37
Explain the mechanism of Elimination | (3 marks)
- 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
Why is there no rotation around a C=C double bond?
- 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
What is the positive inductive effect?
When electron density can be donated between covalent bonds
40
Why are tertiary carbocations more stable than primary carbocations?
- Tertiary carbocations have more positive inductive effect (than secondary and primary carbocations) - Because there are more alkyl groups bonded to C+
41
What is the test for oxidation of alcohols
- Acidified K2Cr2O7 - Turns orange to green
42
Give the reagents and conditions for oxidation of Primary Alcohol to Aldehyde
- Reagent: acidified potassium dichromate - Conditions: heat under distillation
43
Give the reagents and conditions for the oxidation of Aldehyde to Carboxylic acid
- Reagent: acidifies potassium dichromate - Conditions: heat under reflux
44
Give the reagents and conditions for the oxidation of Primary alcohol to Carboxylic acid
- Reagent: acidified potassium dichromate - Conditions: heat under reflux
45
Give the reagents and conditions for the oxidation of secondary alcohols to ketones
- Reagents: acidified potassium dichromate - Conditions: heat under distillation or reflux
46
What type of alcohol cannot be oxidised and why?
- Tertiary alcohols - Because there is no H atom on carbon in C-OH
47
Name 2 test tube tests for aldehydes, and give their observations when aldehyde is present
- Tollens reagent: Silver mirror forms - Fehlings solution: Brick-red precipitate
47
Name 2 test tube tests for aldehydes, and give their observations when aldehyde is present
- Tollens reagent: Silver mirror forms - Fehlings solution: Brick-red precipitate
48
Give the reagent used to test for Carboxylic acids and give the observation for when it is present
- Na2CO3: effervescence
49
Describe what happens when a reaction mixture is refluxed and why it is necessary for the complete oxidation for ethanoic acid | (3 marks)
- 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
Give the test-tube test for: alkenes, 1' or 2' alcohols, aldehydes and carboxylic acids
- **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
Give the test-tube reaction for Haloalkanes
- 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
What is IR spectroscopy used to identify?
Functional groups
53
How does IR spectroscopy work?
- Infra-red energy is absorbed by bonds which makes them vibrate - Bonds vibrate at same frequency as IR spectroscopy
54
What does a smooth broad peak indicate?
O-H bond in alcohols
55
What does a bumpy broad peak indicate?
O-H bond in carboxylic acids
56
What does a sharp peak at 1680-1750 indicate?
C=O bond
57
What does a sharp peak at 1000-1300 indicate?
C-O bond
58
What is the fingerprint region?
- The area below 1500 - That uniquely identifies a molecule and must be compared to a database
59
Describe the molecular ion peaks in a mass spectra of a molecule
- 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
What is the purpose of high resolution mass spectrometry?
To identify ions with the same Mr to 1dp by measuring them to 5dp
61
Why can't a mass spectrometer which measures Mz ratios to 1dp tell the difference betgween C10H16O4 and C11H4O4?
Both molecules have the same Mr to 1dp
62
Why can't high resolution mass spectrometry tell the difference between propan-1-ol and propan-2-ol?
Both have same Mr to 5dp
63
Why does C have a relative molecular mass of 12.00000?
By definition, C12 is the reference for atomic mass
64
Explain how IR radiation relates to global warming?
- 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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