9.10-9.16 - Hydrocarbons

Question 1

List the first 4 alkanes

Answer 1

Methane
Ethane
Propane
Butane

(Monkeys Eat Peanut Butter)

Question 2

What is the formulae of molecules of the alkanes?

Answer 2

CnH2n+2

e.g. methane is CH₄

Question 3

Describe how you would draw the structure of the alkanes

Answer 3

A C covalently bonded to another C, each covalently bonded to Hs

e.g. for Ethane =

    H
     | H — C — H 
     | H — C — H
     |
     H

Question 4

Explain why the alkanes are saturated hydrocarbons

Answer 4

Because they are hydrocarbons (compounds made of hydrogen and carbon only) with only single bonds between the carbon atoms

Question 5

List the 1st 3 alkenes

Answer 5

Ethene
Propene
Butene

Question 6

What is the general formula for the alkenes?

Answer 6

CnH2n

e.g. ethene is C₂H₄

Question 7

Describe how you would draw the structure of the alkenes

Answer 7

A C double bonded to 1 other C (any other Cs are connected to the next by a single bond). A C on one end is bonded to 2 Hs. Except for in ethene, one C atom has only 1 H bond

e.g. for But-1-ene =

H — C — H
||
H — C
|
H — C — H
|
H — C — H
|
H

Question 8

Explain why the alkenes are unsaturated hydrocarbons

Answer 8

Their molecules contain the functional group C=C. An unsaturated molecule contains one or more double covalent bonds, as alkenes do.

Question 9

Describe the structural difference between But-1-ene and But-2-ene

Answer 9

But-1-ene and But-2-ene have the same molecular formula. However, their structure is difference as But-1-ene has the double bond between the first 2 Carbon atoms and in But-2-ene the double bond is between the 2nd and first carbon atom.

But-1-ene =

H — C — H
||
H — C
|
H — C — H
|
H — C — H
|
H

But-2-ene =

    H
     | H — C — H
     | H — C 
    || H — C 
     | H — C — H
     |
     H

Question 10

Describe the addition reaction of Ethene and bromine

Answer 10

Ethene + Bromine -> 1,2-dibromethane

CH2=CH2 + Br2 → CH2BrCH2Br

     H     H
     |      | H — C — C — H
     |      |
    Br    Br

This is an addition reaction because one molecule combines with another molecule forming one larger molecule and no other products.

This reaction works the same for any alkene or halogen.

Question 11

Explain how bromine water is used to distinguish between alkanes and alkenes

Answer 11

Alkenes react with bromine water, turning it from orange to colourless. Alkanes don’t react with bromine water.

Question 12

Describe the result of the combustion of hydrocarbons

Answer 12

The combustion of hydrocarbons releases energy. During combustion, the carbon and hydrogen in the fuels are oxidised to produce carbon dioxide and water.

alkane/alkene + oxygen –> carbon dioxide + water