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A Level - Chemistry > 6C: Alkenes > Flashcards

6C: Alkenes Flashcards

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1
Q

What is the general formula of alkenes?

A

C(n)H(2n)

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2
Q

Why are alkenes unsaturated?

A

Not all bonds are with the max number of hydrogens

Double CC bond

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3
Q

How do covalent bonds form?

A

Atomic orbitals from different atoms overlap
Shares electrons
Bond forms from electrostatic attraction from atoms to the bonding electrons

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4
Q

What are single covalent bonds?

A

σ - sigma bonds
Overlap of two orbitals, high electron density
Strong electrostatic attraction, therefore strong bond

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5
Q

What is the double bond made of in hydrocarbons?

A

π - pi bond & σ - sigma bonds
π bond forms when two p orbitals overlap sideways
Electrons spread out, weaker electrostatic attraction
Therefore weaker bond

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6
Q

What is the effect on rotation by π bonds?

A

π electrons must overlap
Cannot rotate as easily
Leads to E-Z isomerism

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7
Q

What kind of isomerism is E/Z isomerism?

A

Geometric - rotation is prevented about a double bond

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8
Q

What is a cis isomer?

A

Same groups are on the same side of the CC double bond

Cis = Z-isomer

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9
Q

What is a trans isomer?

A

Same groups are on opposite sides of the CC double bond

Trans = E-isomer

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10
Q

What are the rules for E/Z isomerism?

A

The atom with the highest atomic number takes priority

If two atoms have the same atomic number and attached to same carbon, next bonded atom is taken into account

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11
Q

What 4 types of addition reactions do alkenes undergo?

A

Hydrogenation
Halogenation
Hydrogen halides
Addition polymerisation

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12
Q

What are the conditions for hydrogenation?

A

Nickle catalyst

150 C

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13
Q

What is the process of hydrogenation?

A

Alkene reacts with hydrogen gas to form alkane

Making margarine is an example

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14
Q

How does halogenation occur with alkenes?

A

Electrophilic addition

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15
Q

What occurs in electrophilic addition?

A

Heterolytic fission of halide molecule, electrons go to one atom and the other bonds to C atom
Causes positively charged carbocation
Bond forms between free halide ion and carbocation
Dihalogenoalkanes formed

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16
Q

How do alkenes react with bromine water?

A

Brown -> colourless if double CC bond

Forms a bromoalcohol and hydrogen bromide, e.g ethene forms 2-bromoethanol and hydrogen bromide

17
Q

What is steam hydration?

A

Alkenes hydrated by steam to form an alcohol

300 C & 60-70 atm with phosphoric (V) acid catalyst

18
Q

How do alkenes react with hydrogen halides?

A

Electrophillic addition

Forms halogenoalkane + hydrogen gas

19
Q

What is markovnikoff’s rule?

A

When a compound HX is added to an unsymmetrical alkene, the halogen binds to the carbon with the most hydrogens bonded to it

20
Q

What is a carbocation?

A

A positively charged carbon atom

21
Q

What is the stability of a carbocation determined by?

A

The more carbons it is bonded to, the more stable the carbocation is

22
Q

What is the process of the oxidation of alkenes?

A

Acidified potassium manganate (VII) added to alkene
Purple -> colourless
Produces alkene with two -OH alcohol groups (diol)

23
Q

What is the reaction between an alkene and sulphuric acid and water?

A

Forms HSO4 group on alkane

Then add water to form an alcohol group

24
Q

What is addition polymerisation?

A

Double bond in alkenes open up and join together to make polymers

25
Q

How do you convert monomers into polymers?

A

Change double CC bond to single bond

Add single bonds to each end of the carbon, which go through brackets

26
Q

How can waste plastic polymers be disposed?

A

Buried in landfill
Recycling - feedstock for cracking
Incineration- heat used for energy

27
Q

How can polymers be made to be sustainable?

A 
Use reactants that are as safe and environmentally friendly as possible
Few other materials should be used
Renewable raw materials should be used
Energy use should be kept to a minimum
Limit waste products
28
Q

How are toxic gases removed when plastics are burned?

A

PVC produces HCl which is toxic

They must be neutralised in order to remove toxic gas

29
Q

How do biodegradable polymers decompose?

A

Made of renewable raw materials
Produces CO2 and if plant- based it is carbon neutral
Naturally decompose

A Level - Chemistry (26 decks)

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