Alkanes and Alkenes (3.3.2 & 3.3.4- organic) Flashcards Preview

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Flashcards in Alkanes and Alkenes (3.3.2 & 3.3.4- organic) Deck (30)
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1
Q

Define saturated hydrocarbons

A

A molecule made only of carbon and hydrogen with only single bonds

2
Q

Define unsaturated hydrocarbons

A

A molecule made only of carbon and hydrogen that contains a double bond

3
Q

List the features of a homologous series

A
  • Similar chemical properties
    Because they have same functional group
    -Same general formula
    -Trend in physical properties
4
Q

How do you separate a mixture of alkanes? (e.g. crude oil)

A

Fractional distillation

5
Q

The larger the hydrcarbon…

A

The higher the boiling point and the less volatile

6
Q

Define volatile

A

Easily turned into a vapour, low bpt

7
Q

Pollutant: Carbon Dioxide

A

Source: complete combustion of fuel
Problem: Greenhouse gas—-> global warming
Solution: CCS- carbon capture and storage, used in extinguishers

8
Q

Pollutant: Carbon monoxide

A

Source: incomplete combustion of fuel
Problem: Toxic, replaces oxygen and binds to haemoglobin, less respiration
Solution: catalytic converters

9
Q

What is the equation used in catalytic converters?

A

CO + NO —–> CO₂ + 1/2 N₂

10
Q

What catalyst is used and why is it spread in a ‘honeycomb support’?

A

Paladium, to maximise SA

11
Q

Pollutant : Carbon

A

Source: incomplete combustion of fuel
Problem: medical particulates lead to lung cancer/ environmental global dimming
Solution: Filter, solids get trapped

12
Q

Pollutant : SO2

A

Source: Sulfur impurities in fuel burning
Problem: Acid rain, lowers pH of ocean, corrodes limestone
Solution: neutralise with lime/ slaked lime (CaO)

13
Q

Pollutant : NOx

A

Source: N from air, very high temp causes spark
Problem: Acid rain, lowers pH of ocean etc.
Solution: Catalytic converter

14
Q

What mechanism is involved with the reaction of alkanes?

A

Free radical substitution

15
Q

Stage 1 of free radical sub.

A

Initiation

Cl₂ ———–> [UV light] 2Cl•

16
Q

Define free radical

A

A highly reactive species with an unpaired electron

17
Q

Stage 2 of free radical sub.

A

Propagation

a) Cl• + CH₄ ———–>•CH₃ +HCl
b) •CH₃+ Cl₂ ———-> CH₃Cl + Cl•

18
Q

Stage 3 of free radical sub.

A

Cl • + •CH₃ ———–> CH₃Cl + Cl •

19
Q

Thermal cracking

A

-free radical sub.
Conditions: High temp, 400-900 deg.C and high pressure (70atm)
Equation: C₈H₁₈ ——-> C₆H₁₄ + C₂H₄
Products: High % of alkenes for polymers

20
Q

Catalytic cracking

A

-carbocation
Conditions : High temp- 450 deg.C, Low press- ~>1 atm, Catalyst zeolite
Products: Motor fuels, branched alkanes

21
Q

Why do we do cracking?

A
  • Supply and demand
  • high demand for small molecules
  • high supply of big molecules
  • crack to make smaller from bigger
22
Q

Smaller molecules are…

A
  • less volatile

- easier to ignite

23
Q

Alkenes test

A

Orange bromine water goes colourless

24
Q

Are alkenes reactive and why?

A

They are due to double bond that has a region of high electron density

25
Q

What type of reactions do alkenes do?

A

Electrophilic addition

26
Q

Where do the curly arrows go in alkene mechanisms?

A

From double bond to d+ atom, from single bond to Cl or Br

From lone pair on halogen to positive C

27
Q

Where is thte major product formed with unsymmetrical alkenes?

A

The more stable carbocation

28
Q

Order of stability and why?

A

Primary < Secondary < Tertiary

This is due to electron releasing effect of alkyl groups

29
Q

Alkenes + sulphuric acid, conditions?

A

Cold concentrated sulphuric acid
central S, H–O recieves pair of e- from double bond
(Sulphuric acid reformed at end so it acts as a catalyst)

30
Q

How do you draw H₂SO₄?

A

Central S, 2OH, and 2 =OS