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AS Chemistry > Developing Fuels: Alkenes > Flashcards

Developing Fuels: Alkenes Flashcards

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1
Q

How are covalent bonds formed

A

Overlap of orbitals

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2
Q

Describe electrophilic addition mechanism with Br2 and ethene ( 6 marks )

A
  1. Bromine molecule comes close to ethene molecule = dipole induced in bromine molecule
  2. A pair of electrons from 1 of the C-C bonds in ethene is attracted to (+ve delta ) bromine atom
  3. Bonding pair in of electrons in bromine molecule is repelled to (-ve delta) bromine atom = bond between 2 bromine atoms breaks

( free bromine atom receives both bonding electrons and becomes a bromide ion)

  1. Covalent bond forms between 1 of the carbon atoms and ( +ve delta ) bromine atom = ethene becomes +ve charge ion = carbocation
  2. the lone pair of electrons in the bromide ion is attracted to +ve charge on the carbocation
  3. Bromide ion moves towards the +ve charge carbon atom = covalent bond forms between them
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3
Q

What is the name of the intermediate formed in an addition reaction

A

Carbocation

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4
Q

What happens when you add sodium chloride to a solution of ethene and bromine water ???

A

Bromide (ion) / Br– attacks / bonds with carbocation
OR –
Bromide (ion) / Br attacks / bonds with intermediate A ✓
Chloride (ion) / Cl– attacks / bonds with carbocation OR Chloride (ion) / Cl– attacks / bonds with intermediate A ✓
Attack by Bromide (ion) / Br– gives CH2BrCH2Br
OR – Attack by Chloride (ion) / Cl gives CH2C/CH2Br ✓

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5
Q

Describe what a sigma bond is and how it is formed

A

head on overlap of orbitals forming a covalent bond

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6
Q

Describe what a pi bond is and how it is formed

A

sideways overlap of orbitals to form a covalent bond

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7
Q

What are 2 sayings of bonds simplified

A
  • sigma = single bond eg. Cl2

- pi = partner double bond ( sigma &pi ) eg. O2

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8
Q

What type of bond is formed from a s and s head on overlap

A

Sigma

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8
Q

What type of bond is formed from a s and p head on overlap

A

Sigma

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9
Q

What type of bond is formed from a p and p head on overlap

A

Sigma

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10
Q

What type of bond is formed from a p and p head on overlap

A

Pi

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11
Q

Explain how you could use a solution of bromine water to show that but-1,3-diene has a greater degree of unsaturation that but-1-ene (3)

A
  1. Same amount of bromine water, but-1,3-diene and but-1-ene
  2. But-1,3-diene would go colourless quicker
  3. But-1,3-diene has higher no. of saturated bonds
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12
Q

Definition of addition reaction

A

A reaction where 2 or more molecules react to form a single larger molecule

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13
Q

Definition of electrophile

A

+ve ion or a molecule with a partial +ve that is attracted to a
-ve charge region and reacts by accepting a lone pair of electrons to form a covalent bond

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14
Q

Definition of carbocation

A

An ion with a positively charged carbon atom

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15
Q

Definition of curly arrow

A

Represent the movement of a pair of electrons in chemical reactions

16
Q

Describe the ethene and bromine mechanism ( simple terms )

A

Bromine approaches close to the high electron density of an alkene double bond

Repulsion of the electrons in the Br2 molecule polarises the Br-Br bond so that it can then act as an electrophile

17
Q

Describe the mechanism of ethene and hydrogen bromide = bromoethane ( 5 marker )

A
  1. Pair of electrons is attracted out from the double bond towards the (delta +ve ) H atom.
  2. Pair of electrons in the HBr bond is attracted to the Br atom to form a -ve Br ion.
  3. A bond forms between C and H.
  4. The other C atom is left with a +ve charge = carbocation
  5. Lobe pair of electrons of the Br - ion is attracted to +ve charge carbocation to form a covalent bond
18
Q

Production of ethanol from ethene and water in INDUSTRY - write equation + identify the conditions needed

A

C2 H4 + H2O(steam) ->C2 H5 OH

  • high temp
  • high pressure
  • phosphoric acid on silica
19
Q

Production of ethanol from ethene and water in LAB

A

Concentrated sulphuric. Acid is added first followed by water

20
Q

Describe production of ethane from ethene and hydrogen ( hydrogenation ) in LAB write equation & conditions

A

C2 H4 + H2 ——> C2 H6

  • catalyst = Nickel (Ni ) powdered
  • 150°
  • 5 atm
21
Q

What catalyst is used in INDUSTRIAL production of ethane from ethene & hydrogen ( hydrogenation )

What is the reaction used to make

A

Platinum —> unsaturated fats into saturated fats

22
Q

Explain how experimental evidence supports the electrophilic addition mechanism,using the reaction between hex—1-ene and a mixture of bromine and chloride ions as an example ( 3 marker )

A
  1. 2 products are formed
  2. 1,2 dibromohexane and 1-bromine-2-chlorohexane
  3. However 1,2- dichlohexane is not formed as the electrophile must first attack to form a carbocation

AS Chemistry (43 decks)

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