12) Alkanes

Question 1

What is the general formula of an alkane?

Answer 1

CnH2n+2

Question 2

What is the 3D arrangement and bond angle of an alkane?

Answer 2

tetrahedral

109.5 degrees

Question 3

What is fractional distillation and how is it possible?

Answer 3

separation of crude oil into fractions

due to variation of boiling points

Question 4

Boiling points increase as chain length _ and as branching _, why?

Answer 4

increases - molecules have a larger surface area, increasing surface contact between molecules resulting in stronger induced dipole-dipole interactions and more energy to overcome
decreases - branching results in fewer surface points of contact

Question 5

Give two reasons for an alkane’s lack of reactivity

Answer 5

strong C-C and C-H sigma bonds

non-polar C-C and C-H bonds

Question 6

Describe the electronegativity of carbon and hydrogen atoms

Answer 6

very similar

Question 7

Alkanes undergo complete combustion to produce _ with a plentiful supply of _.

Answer 7

carbon dioxide and water

oxygen

Question 8

Name the toxic product of incomplete combustion

Answer 8

carbon monoxide

Question 9

Name the mechanism for bromination of alkanes and give its initiation, propagation (2) and termination (3) steps for methane.

Answer 9

radical substitution
initiation: Br2 -> Br. + .Br
propagation: CH4 + Br. -> .CH3 + HBr
.CH3 + Br2 -> CH3Br + Br.
termination: Br. + .Br -> Br2
.CH3 + .CH3 -> C2H6
.CH3 + .Br -> CH3Br

Question 10

Under what condition will an alkane react with halogens?

Answer 10

UV (sunlight)

Question 11

What can bromomethane from the second propagation step during the bromination of an alkane go onto do?

Answer 11

collide with another bromine radical and undergo further substitution

Question 12

What will substitution at different positions on a carbon chain result in?

Answer 12

a mixture of monosubstituted isomers