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Chemistry A- Level > CH6: Organic Chemistry I > Flashcards

CH6: Organic Chemistry I Flashcards

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1
Q

What are isomers? And the 2 types?

A

Molecules that have same molecular formula, but atoms arranged differently
2 types :
Structural
Stereoisomers

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2
Q

What is a structural isomer and the 3 types?

A

Molecular formula is same, but structural formula is different
1. CHAIN ISOMERS
Carbon skeletons is arranged differently (straight chain or branched) - so have similar chemical properties, but physical properties (BP /MP ETC) are different due to to different shape

  1. POSITIONAL ISOMERS
    Functional group attached to different carbon atom - physical/chemical properties are different
  2. FUNCTIONAL GROUP ISOMERS
    Same atoms can be arranged into different functional groups - physical/chemical properties are different
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3
Q

General forumula of alkanes ?

A

CnH2n+2
Saturated hydrocarbons - all C-C bond are single bonds

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4
Q

What is bond fission and the 2 types?

A

Breaking of a covalent bond

HETEROLYTIC FISSION - bond breaks unevenly , with one the bonded atoms receiving both electrons
- forms CATION and ANION (bc one gain electrons , the other loses it )

HOMOLYTIC FISSION - bond breaks evenly/each bonding atoms receives one electron
- forms 2 radicals (particles that have an unpaired electron)

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5
Q

How are halogenoalkanes formed from alkanes? What are the 3 stages?

A

Halogens react with alkanes in PHOTOCHEMICAL reactions - started by light
- hydrogen atom is substituted by chlorine/bromine - RADICAL SUBSTITUTION REACTION

3 stages to process :
Initiation
Propagation
Termination

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6
Q

What is the initiation stage ?

A

UV lights breaks the Cl-Cl or Br-Br bond
- produces 2 radicals in homolytic fission reaction

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7
Q

What is the propagation stage?

A

Radicals are used up/ created in a chain reaction
- free radicals will react with unreative alkanes to form an ALKYL RADICAL and hydrogen halide

  • this radical can attack another chlorine/bromine to from a halogenoalkane/regenerate chlorine/bromine free radicals

Cl. + CH4 —> CH3. + HCl
CH3 . + Cl2 —> CH3Cl + Cl.

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8
Q

What are termination reactions ?

A

2 radicals join together to make a stable molecule

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9
Q

What are the problems of free radical substitution?

A

Further substitution
Excess chlorine reacted with methane in the presence of UV light - causes further substitution and could produce CH2Cl2, CHCl3, CCl4
- nuisance because have to separate chloromethane from 3 unwanted products

Substitution of different carbon atoms - causes mixture of structural isomers

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10
Q

What is cracking?

A

Breaking lager hydrocarbons into smaller , more useful hydrocarbon fractions

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11
Q

What re the 2 types of cracking?

A

Thermal cracking - requires high temps(1000C)/pressure (70 atm) produces a lot of ALKENES

Catalytic cracking - lower temps(450 C)/pressure , but need catalyst (aluminium oxide/zeolite) to produce aromatic hydrocarbons

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12
Q

What is reforming and why do we need to do this?

A

Reforming : Converting straight chain alkanes into branched chain alkanes /cyclic hydrocarbons

Needed because : straight chan alkanes are more likely to explode , rather than combust , when compressed in engine —> CAUSE KNOCKING

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13
Q

How does complete/incomplete combustion of ALKANES cause pollution?

A

Complete combustion : forms CO2and H2O
Incomplete combustion: forms CO , Cand H20

Burning alkanes can also form :
- unburnt hydrocarbons - react with NO2 and SO2 to produce PAN in photochemical smog
- carbon particulates
- sulfur/nitrogen oxides

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14
Q

How s carbon monoxide harmful?

A

Toxic and odorless gas
- binds to haemorrhoid in blood before oxygen can
- so oxygen deprivation in body

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15
Q

How are oxides of sulfur/nitrogen harmful?

A

Fuels containing sulfur are burnt forming SULFUR DIOXIDE GAS —> converted into sulfuric acid

High pressure/temp in car engines cause NITROGEN OXIDES TO FORM —> converted into nitric acid

BOTH CAUSE ACID RAIN - destroys environment /plants/buildings
- makes rivers acidic - harmful to aquatic animals

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16
Q

How are particulates harmful ?

A

Carbon particles (particulates ) from incomplete combustion FORM SOOT

  • damage lungs /cause respiratory problems
  • damage buildings - corrode them
  • global dimming
17
Q

How are catalytic converters used to remove pollutants ?

A
  • use platinum catalyst to change into harmless/less harmful gases

Eg : 2NO + 2CO —> N2 + 2CO2
Nitrogen monoxide and carbon monoxide converted to nitrogen and carbon dioxide
NO is REDUCED
CO is OXIDISED

18
Q

What are biofuels and the 3 types?

A

Renewable fuels
BIODIESEL - made by refining renewable fats/oils
BIOETHANOL - made by fermentation
BIOGAS - made/released when organic waste breaks down

19
Q

Why are biofuels seen as carbon neutral ?

A
  • Bc CO2 produced from biofuels is absorbed by plants for growth
  • biodiesel/biogas can be made from waste that would go to landfill
  • biofuels can provide money for LEDCS , as they have space to grow crops needed , as less land needed for fuels
20
Q

Drawbacks of biofuels ?

A
  • cost of converting engines/machinery for biofuels instead of petrol/diesel
  • countries don’t have space to produce plants to make biofuels , bc needed for food production
21
Q

Fractional distillation of crude oil?

A
  1. Crude oil is vaporised to 350 degrees
  2. Enters column and gets cooler as you go up
  3. Larger alkanes , have larger BP so condense lower
    Smaller alkanes , have lower BP do condense higher up
  4. Largest hydrocarbons have to high BP so don’t condense —> residue at bottom
    Smallest hydrocarbons also don’t condense BP too low so drawn off as gases at top
22
Q

What are sigma bonds?

A
  • formed when 2 orbitals overlap , in straight line, in space between 2 atoms
  • gives highest possible electron density between positive nuclei
  • leads to strong electrostatic attractionbetween nuclei/shared pair of electrons
  • HAVE HIGH BOND ENTHALPY
23
Q

What is a pi bond?

A

Formed from sideways overlap of adjacent p orbitals
- electron density is spread out above/below the nuclei
- causes weaker electrostatic attraction between nuclei and shared pair of electrons , than sigma bond
- LOW BOND ENTHALPY

24
Q

What is a double bond made up of?

A

A sigma bond and pi bond

25
Q

What are stereoisomers?

A

Compounds that have same structural formula but different arrangement of atoms in space.

  • because of lack of rotation around double bond (due to way p orbitals overlap to form Pi bond), some alkenes have stereoisomers
26
Q

What is a E/Z isomer ?

A

E (trans) isomer have groups on opposite sides of double bond /carbon ring
Z (Cis) isomer have groups on same sideof double bond/carbon ring

27
Q

How to work out if isomer is E or Z if all carbons have different groups attached to them?

A

Using Cahn-Ingold-Prelog (CIP) priority rules
- look at atomic number of first atom attached to CARBON
- higher the atomic number, the higher the priority
- if high priority on same side - Z isomer
- if high priority on opposite sides - E isomer

28
Q

What’s an electrophilic addition ? What reactions are electrophilic addition?

A

The addition of an electrophile to a double bond
- double bond opens up / atoms added

The addition of :
Hydrogen
Steam
Hydrogen halide
Halogen

29
Q

What are electrophiles?

A

Electron pair acceptors - short of electrons ,sp attract to areas with many electrons
- positively charged ions /polar molecules

30
Q

Conditions and reaction of HYDROGEN + ALKENE?
How is this used in margarine manufacturing?

A
  • produce ALKANE

Conditions :
NICKEL catalyst
150 degrees

Margarine is made by hydrogenating unsaturated veg oils . By removing double bonds, you increase MP of oil so its solid at room temp

31
Q

HALOGEN + ALKENES - reaction?

A

Form dihalogenoalkanes
- halogens are added across the double bond

32
Q

Test for alkenes?

A

Add bromine water - solution will decolourise if alkene is present
- because bromine is added across double bondso goes colourless and forms dibromoalkane

33
Q

STEAM + ALKENE - reaction and conditions

A

Forms alcohol

Conditions : 300 degrees
60-70 atm
Phosphoric acid catalyst

34
Q

ALKENES + HYDROGEN HALIDES - reaction?

A

Form HALOGENOALKANES
- if halogen halide is added to unsymmetrical alkene- 2 products
- the amount of each product depends on how stable the carbocation is
- carbocations with more alkyl groups are more stable - they feed electrons towards + CHARGE
(Tertiary is most stable - so more of this made)

35
Q

Oxidation of alkenes using ACIDIFIED POTASSIUM MANGANATE (oxidising agent)

A

C2H4 + H2O + [O] —> C2H4(OH)2
- the purple solution turns colourless
Produced DIOL- alcohol with 2 -OH groups

  • this can be used to test for alkenes, as alkanes don’t have double bonds, so wont oxidise this way
36
Q

What is addition polymerisation? And what are polymers?

A

Where monomers (containing at least one C double bond) , form long chains of polymers
- double bond opens up

Polymers - long chain molecule made up of repeating units (monomers)

37
Q

Ways of disposing polymers?

A

RECYCLING : reduce amount of waste going to landfill sites - reduces use of finite resources
Some can be recycled by MELTING/REMOULDING
Some can be CRACKEDinto monomers/ used as ORGANIC FEEDSTOCK

BURNED : if can’t be recycled (due to chemical composition ) , can be burned to generate electricity
- needs to be controlled to reduce toxic gases
E.g PVC contain chlorines so forms HCl
- scrubbers can neutralise gases like HCl

38
Q

Principles for sustainable polymer manufacturing?

A
  • use safe/environmentally friendly reactants
  • use fewer chemicals/other materials
  • use renewable raw materials
  • use catalysts - keep energy use to minimum
  • limit waste products
  • produce polymers with long lifespan
39
Q

What are biodegradable/compostable polymers ? Ands what are the advantage of these?

A

Biodegradable- Polymers that naturally decompose
- products can be used for other applications
- can be made from renewable raw materials, so wont run out

BUT SORTING/COLLECTING MEANS ITS MORE EXPENSIVE THAN NON BIODEGRADABLE OPTIONS

Compostable - polymers that are plant based
- CO2 released in decomposition is same as CO2 absorbed by plant, so not adding to CO2 in air
- save energy compared to oil based plastics

Chemistry A- Level (20 decks)

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