4d. Alkenes

Question 1

4.23 What functional group do alkenes contain

Answer 1

C=C

Question 2

4.24 What is the general formula for alkenes

Answer 2

CnH2n

Question 3

4.25 Why are alkenes classified as unsaturated hydrocarbons

Answer 3

Because they have double carbon bonds (C=C)

Question 4

4.26 What is the empirical formula of ethene

Answer 4

CH2

Question 5

4.26 What is the empirical formula of Propene

Answer 5

CH3

Question 6

4.26 What is the empirical formula of but-1-ene

Answer 6

CH2

Question 7

4.26 What is the empirical formula of Pent-1-ene

Answer 7

CH2

Question 8

4.26 What is the molecular formula of ethene

Answer 8

C2H4

Question 9

4.26 What is the molecular formula of propene

Answer 9

C3H6

Question 10

4.26 What is the molecular formula of but-1-ene

Answer 10

C4H8

Question 11

4.26 What is the molecular formula of pent-1-ene

Answer 11

C5H10

Question 12

4.26 What is the structural formula of ethene

Answer 12

CH2 = CH3

Question 13

4.26 What is the structural formula of propene

Answer 13

CH2=CH-CH3

Question 14

4.26 What is the structural formula of but-1-ene

Answer 14

CH2=CH-CH2-CH3

Question 15

4.26 What is the structural formula of pent-1-ene

Answer 15

CH2=CH-CH2-CH2-CH3

Question 16

4.26 What is the displayed formula of ethene

Question 17

4.26 What is the displayed formula of Propene

Question 18

4.26 What is the displayed formula of but-1-ene

Question 19

4.26 What is the displayed formula of pent-1-ene

Question 20

4.27 What do alkenes form when they react with bromine

Answer 20

dibromoalkanes

Question 21

4.27 What kind of reaction occurs when alkenes are heated in an air of oxygen

Answer 21

Complete combustion

Question 22

4.27 Give the word equation of the addition reaction between ethene and bromine

Answer 22

Example: Bromine will react with ethene and the bromine molecule will react and add across the double bond of the ethene

ethene + bromine → dibromoethane

Question 23

4.27 Give the chemical formula for the addition reaction of ethene and bromine

Answer 23

C2H4 + Br2 → C2H4Br2

Question 24

4.28 How can bromine water be used to distinguish between an alkane and an alkene

Answer 24

Alkanes and alkenes have different molecular structures
All alkanes are saturated and alkenes are unsaturated
The presence of the C=C double bond allows alkenes to react in ways that alkanes cannot
Alkenes can be distinguished from alkanes using a simple chemical test called the bromine water test

Bromine water is an orange coloured solution
When bromine water is added to an alkane, it will remain as an orange solution as alkanes do not have double carbon bonds (C=C) so the bromine remains in solution

But when bromine water is added to an alkene:
The bromine atoms add across the C=C bond
The solution no longer contains free bromine so it loses its colour / decolourises