Ch12 Alkanes

Question 1

What are properties of alkanes?

Answer 1

• members of homologous series
• saturated hydrocarbons
• all C-C is single
• general formula - CnH2n+2
• non cyclic alkanes are bonded spaced tetrahedrally about the C atoms.

Question 2

Define structural formula:

Answer 2

Same molecular formula but different structural formula.

Question 3

Describe the hybridisation of orbitals in alkanes:

Answer 3

Question 4

Describe the structure of alkanes:

Answer 4

Question 5

Explain how crude oil can be separated by fractional distillation:

Answer 5

• hydrocarbons in crude oil are different sizes
• fractionating columns has a temperate gradient
• covalent bonds between Carbon and Hydrogen atoms within hydrocarbon are stronger than the intermolecular forces between hydrocarbon molecules
• during boiling intermolecular forces are broken
• intermolecular forces between large hydrocarbons are stronger than those between smaller hydrocarbon molecules
• hydrocarbons with large molecules have higher BP than those with smaller molecules
• hydrocarbons with higher BP condense near bottom of column (coolest) and are separated
• fractions containing mixtures of similar length hydrocarbons are obtained.

Question 6

Explain the physical properties of alkanes?

Answer 6

Question 7

How does branching affect the physical properties of alkanes?

Answer 7

Question 8

What are the physical properties of alkanes

Answer 8

• MP - general increase with molecular mass/ The trend i snot as regular as that for BP.
• Solubility - alkanes are non-polar so are immiscible with water they are soluble in most organic solvents.

Question 9

What are the chemical properties of alkanes?

Answer 9

• fairly unreactive
• have relatively strong, almost NON-POLAR, single covalent bonds
• they have no real sites will encourage substances to attack them

Question 10

Describe combustion in alkanes, complete + incomplete:

Answer 10

Question 11

What are the three stages of radical reactions?

Answer 11

• Initiation: produces 2 radicals in homolytic fission reaction
• Propogation: progression of substitution reaction in chain type reaction. Free radicals are very reactive, and attack unreactive alkanes. C-H bond breaks homolytically. An ALKYL free radical produced.
• Termination: chain reaction terminates due to 2 free radicals reacting together + forming single unreactive molecule.

Question 12

Why is the limitation of radical reactions?

Answer 12

Radial reactions are not suitble for preparing specific haloalkanes (mixture of substitutio products formed) not pure haloalkanes.
If enough Cl2/other halogens present, all Hydrogens in alkane will eventually get substituted.