Developing Fuels: Alkenes Flashcards
How are covalent bonds formed
Overlap of orbitals
Describe electrophilic addition mechanism with Br2 and ethene ( 6 marks )
- Bromine molecule comes close to ethene molecule = dipole induced in bromine molecule
- A pair of electrons from 1 of the C-C bonds in ethene is attracted to (+ve delta ) bromine atom
- 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)
- Covalent bond forms between 1 of the carbon atoms and ( +ve delta ) bromine atom = ethene becomes +ve charge ion = carbocation
- the lone pair of electrons in the bromide ion is attracted to +ve charge on the carbocation
- Bromide ion moves towards the +ve charge carbon atom = covalent bond forms between them
What is the name of the intermediate formed in an addition reaction
Carbocation
What happens when you add sodium chloride to a solution of ethene and bromine water ???
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 ✓
Describe what a sigma bond is and how it is formed
head on overlap of orbitals forming a covalent bond
Describe what a pi bond is and how it is formed
sideways overlap of orbitals to form a covalent bond
What are 2 sayings of bonds simplified
- sigma = single bond eg. Cl2
- pi = partner double bond ( sigma &pi ) eg. O2
What type of bond is formed from a s and s head on overlap
Sigma
What type of bond is formed from a s and p head on overlap
Sigma
What type of bond is formed from a p and p head on overlap
Sigma
What type of bond is formed from a p and p head on overlap
Pi
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)
- Same amount of bromine water, but-1,3-diene and but-1-ene
- But-1,3-diene would go colourless quicker
- But-1,3-diene has higher no. of saturated bonds
Definition of addition reaction
A reaction where 2 or more molecules react to form a single larger molecule
Definition of electrophile
+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
Definition of carbocation
An ion with a positively charged carbon atom
Definition of curly arrow
Represent the movement of a pair of electrons in chemical reactions
Describe the ethene and bromine mechanism ( simple terms )
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
Describe the mechanism of ethene and hydrogen bromide = bromoethane ( 5 marker )
- Pair of electrons is attracted out from the double bond towards the (delta +ve ) H atom.
- Pair of electrons in the HBr bond is attracted to the Br atom to form a -ve Br ion.
- A bond forms between C and H.
- The other C atom is left with a +ve charge = carbocation
- Lobe pair of electrons of the Br - ion is attracted to +ve charge carbocation to form a covalent bond
Production of ethanol from ethene and water in INDUSTRY - write equation + identify the conditions needed
C2 H4 + H2O(steam) ->C2 H5 OH
- high temp
- high pressure
- phosphoric acid on silica
Production of ethanol from ethene and water in LAB
Concentrated sulphuric. Acid is added first followed by water
Describe production of ethane from ethene and hydrogen ( hydrogenation ) in LAB write equation & conditions
C2 H4 + H2 ——> C2 H6
- catalyst = Nickel (Ni ) powdered
- 150°
- 5 atm
What catalyst is used in INDUSTRIAL production of ethane from ethene & hydrogen ( hydrogenation )
What is the reaction used to make
Platinum —> unsaturated fats into saturated fats
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 )
- 2 products are formed
- 1,2 dibromohexane and 1-bromine-2-chlorohexane
- However 1,2- dichlohexane is not formed as the electrophile must first attack to form a carbocation
