ORGANIC CHEM - ALKANES + HALOGENOALKANES

Question 1

How is crude oil separated into fractions?

Answer 1

• crude oil vaporised
• crude oil rises up the column
• temp gradient in column (hotter at the bottom, cooler at the top)
• as the gas moves up the column, hydrocarbons condense at their boiling points
• boiling point depends on the size of the molecules (longer hydrocarbon chains have stronger van der waals forces so therefore higher boiling points)
• larger hydrocarbon chains condense at the bottom of the column while shorter hydrocarbon chains condense at the top

Question 2

What is a fraction?

Answer 2

a mixture of hydrocarbon chains with similar boiling points

Question 3

What is cracking?

Answer 3

breaking down longer hydrocarbon chains into smaller hydrocarbon chains as they are more useful

Question 4

What conditions are required for thermal cracking?

Answer 4

• temp - 900°C
• pressure - 70 atm
• steam
• no catalyst

Question 5

What are the products of thermal cracking?

Answer 5

alkenes

Question 6

What are the conditions required for catalytic cracking?

Answer 6

• temp - 450°C
• pressure - 1-2 atm
• catalyst - zeolites

Question 7

What are the products of catalytic cracking?

Answer 7

motor fuels (cyclic alkanes, branched alkanes, aromatics)

Question 8

What are the products of complete combustion of an alkane?

Answer 8

CO2 and H2O

Question 9

What are the products of incomplete combustion of an alkane?

Answer 9

CO/C (carbon particulates) and H2O

Question 10

How is CO2 formed?

Answer 10

complete combustion

Question 11

What problem(s) does CO2 cause?

Answer 11

global warming

Question 12

How can the problem caused by CO2 be reduced?

Answer 12

burn less fossil fuels

Question 13

How is CO formed?

Answer 13

incomplete combustion

Question 14

What problem(s) does CO cause?

Answer 14

death

Question 15

How can the problem caused by CO be reduced?

Answer 15

• burn substances in sufficient O2
• catalytic converters in cars

Question 16

How are carbon particulates (C) formed?

Answer 16

incomplete combustion

Question 17

What problem(s) do carbon particulates (C) cause?

Answer 17

• global dimming
• respiratory problems

Question 18

How can the problem caused by carbon particulates (C) be reduced?

Answer 18

burn substances in sufficient O2

Question 19

How is SO2 formed?

Answer 19

burning fuels

Question 20

What problem(s) does SO2 cause?

Answer 20

acid rain

Question 21

How can the problem caused by SO2 be reduced?

Answer 21

• can be removed from waste gases by flue gas desulfurization
• CaO + SO2 → CaSO3

Question 22

How are nitrogen oxides (NOx) formed?

Answer 22

at high temps (eg: in car engines) N reacts O2 to NOx

Question 23

What problem(s) do nitrogen oxides (NOx) cause?

Answer 23

• respiratory problems
• acid rain
• smog

Question 24

How can the problem caused by nitrogen oxides (NOx) be reduced?

Answer 24

• catalytic converters in cars remove NOx
• 2NO + 2CO → N2 + 2CO2

Question 26

What is free radical substitution?

Answer 26

a reaction mechanism where free radicals replace atoms in a molecule

Question 27

What are the 3 main stages of free radical substitution?

Answer 27

- initiation - propagation - termination

Question 28

What is the role of UV light in free radical substitution?

Answer 28

provides energy to break the bonds and generate free radicals

Question 29

Nucleophilic substitution with OH: - reagent? - conditions? - what happens?

Answer 29

- reagent: NaOH - conditions: aq, warm - what happens: halogen atom replaced by OH group

Question 30

Nucleophilic substitution with CN: - reagent? - conditions? - what happens?

Answer 30

- reagent: KCN - conditions: aq ethanol, warm - what happens: halogen atom replaced by CN group

Question 31

Nucleophilic substitution with NH3: - reagent? - conditions? - what happens?

Answer 31

- reagent: NH3 - conditions: excess concentrated NH3 dissolved in ethanol at pressure in sealed container - what happens: 1st molecule of NH3 replaces halogen, 2nd molecule of NH3 removes H^+ from added NH3

Question 32

Elimination of halogenoalkanes: - reagent? - conditions? - what happens?

Answer 32

- reagent: KOH - conditions: ethanolic (dissolved in ethanol), hot - what happens: halogen atom and 1 H atom from adjacent C atom is removed giving an alkene (mixture of alkenes can be formed depending on which of the adjacent C atoms the H is lost from)

Question 33

What are CFCs?

Answer 33

chlorofluorocarbons

Question 34

What were CFCs used as?

Answer 34

- coolant in refrigerators - propellent in aerosols - degreaser for circuit boards

Question 35

Whar is the ozone layer and what does it do?

Answer 35

- layer of O3 in the stratosphere - absorbs UV radiation

Question 36

What do CFCs do to the ozone layer?

Answer 36

- CFCs break down in the stratosphere to form Cl free radicals by the breaking of a C - Cl bond with energy from UV - the Cl free radicals catalyse the destruction of ozone in a free radical chain reaction - as CFCs went into large scale use, the conc of ozone in the ozone layer fell significantly