Alkanes

Question 1

Alkanes

Answer 1

Main component of natural gas, crude oil
Most stable organic compound
Cn H2n+2

Question 2

Uses

Answer 2

Domestic fuel, CH4
Petrol, C5H12
Kerosene, C10H22
Diesel, C12H26

Question 3

Alkanes bonding

Answer 3

Saturated hydrocarbon
Single covalent bond joined to 4 atoms,
Sigma bond results in the overlap of 2 orbitals
Each overlapping orbital has1 electron
4 sigma bonds per C

Question 4

Alkanes shape

Answer 4

4 electron pairs, 4 sigma bonds, axis where atoms rotate freely into different shapes
Tetrahedral, 109.5

Question 5

Boiling points of alkanes

Answer 5

Fractional distillation separates alkanes possible due to its boiling points
Chain length increases, boiling point increases
Chain length increases, surface area increases, more surface contact possible between molecules, more force needed to overcome London Forces

Question 6

Branching on boiling point

Answer 6

Branched isomers have lower boiling point
Fewer surface points of contact between molecules, fewer London forces
Branches get in the way, prevent branched molecules getting close as straight chain molecules, decrease intermolecular forces

Question 7

Reactivity of alkanes

Answer 7

Not reactive with most reagents
Strong sigma bonds
C-C, non polar bonds
Electronegativity of C, H are similar, not polar

Question 8

Combustion of alkanes, complete

Answer 8

Alkanes + Oxygen => Carbon dioxide +Water

Question 9

Incomplete combustion

Answer 9

Hydrogen in alkane oxidised to H2O

Result in CO and water/ Carbon and water

Question 10

Effects of carbon monoxide

Answer 10

Combines irreversibly with haemoglobin to form carboxyhaemoglobin

Question 11

Reactions of alkanes with halogens

Answer 11

UV radiation provides initial energy for reaction

Forms haloalkanes

Question 12

Radical substitution

Answer 12

Bromination of alkanes, show movement of electrons during reaction

Question 13

Initiation reaction

Answer 13

Covalent bond broken by homolytic fission

Very reactive radicals

Question 14

Propagation reaction

Answer 14

Chain reactions

Start and end with a radical

Question 15

Termination reactions

Answer 15

2 radicals collide, forms molecules, ends reactions

Question 16

Limitations of radical substitution in organic synthesis

Answer 16

Further substitution

Substitution at different positions in carbon chain

Question 17

Further substitution

Answer 17

Bromomethane collides with bromine radical, forms mixture of haloalkanes

Question 18

Substitution at different positions of carbon chain

Answer 18

Methane, 4 hydrogen atoms are bonded to the same carbon, only 1 monobromo compound formed
If chain is longer, mixture isomers formed