Unit 3: Section 3- Alkenes and Alcohols + RP5

Question 1

What is the general formula of alkenes?

Answer 1

CnH2n

Question 2

How can you use one word to describe alkenes?

Answer 2

unsaturated

Question 3

What shape is the arrangement of bonds around the C=C bond?

Answer 3

planar

Question 4

What is the bond angle in alkenes around the C=C bond?

Answer 4

120

Question 5

Explain why alkenes are vulnerable to attack by other species

Answer 5

Because the pi bonds are exposed which have high electron density.

Question 6

What does a C=C double covalent bond consist of?

Answer 6

one sigma bond
one pi bond

Question 7

What type of isomerism can alkenes exhibit?

Answer 7

E-Z stereoisomerism

Question 8

Define electrophile

Answer 8

an electron pair acceptor

Question 9

What is an addition reaction?

Answer 9

where two reactants form one product

Question 10

Describe each step in the electrophilic addition reaction between bromine and alkenes

Answer 10

1. the C=C bond repels the electrons in Br2, polarising Br-Br
2. the double bond then attracts the Br slightly +, and forms a bond with it. this repels electrons in the Br-Br bond further, until it breaks
3. you get a positively charged carbocation intermediate, the Br slightly - bonds to the C
4. one product is formed

Question 11

What is a carbocation?

Answer 11

a positively charged carbon atom

Question 12

What do alkenes form when they react with hydrogen halides?

Answer 12

halogenoalkanes

Question 13

Give three examples of electrophiles

Answer 13

H+
NO2+
Br slightly +

Question 14

Draw the mechanism for the electrophilic addition reaction between ethene and hydrogen bromide

Question 15

Why is HBr a polar molecule?

Answer 15

Br is more electronegative than H

Question 16

What happens if you add a hydrogen halide to an unsymmetrical alkene?

Answer 16

two isomeric products- 1 major product, 1 minor product

Question 17

What does the amount of product formed in electrophilic addition of alkenes and hydrogen halides depend upon?

Answer 17

how stable the carbocation intermediate is

Question 18

What is the order for stability of carbocations?

Answer 18

tertiary (most)
primary (least)

Question 19

Draw the mechanism for hydrogen bromide reacting with propene

Question 20

What is the chemical formula for sulphuric acid?

Answer 20

H2SO4

Question 21

What are the two changes in functional groups in electrophilic reactions with alkenes and H2SO4?

Answer 21

1. change in functional group from alkene to alkyl hydrogen sulphate
2. change in functional group from alkyl hydrogen sulphate to alcohol

Question 22

Describe the reaction between sulphuric acid and alkenes

Answer 22

1. cold concentrated sulphuric acid reacts with an alkene in an electrophilic addition reaction
2. if you then add cold water, and warm the product, it hydrolyses to form an alcohol
3. the sulphuric acid isn’t used up- it acts as a catalyst

Question 23

How can the bromine water test be used quantitively?

Answer 23

to show the presence of multiple bonds in compounds like polyunsaturated oils

Question 24

What is addition polymerisation?

Answer 24

when addition polymers are formed from alkenes

Question 25

What is a polymer?

Answer 25

lots of monomers joined together

Question 26

What is one word to describe polyalkene chains?

Answer 26

saturated

Question 27

What does saturated mean?

Answer 27

they only contain single carbon bonds in the carbon chain

Question 28

How does increasing length of polyalkenes effect Van der Waals forces?

Answer 28

the longer the polymer chains are, the closer together they can get, so the stronger the Van der Waals forces between the chains will be

Question 29

Describe the differences in physical properties of short chain and long chain polyalkenes

Answer 29

short, branched chains- weaker and more flexible long, straight chains- strong and rigid

Question 30

How can you make PVC more flexible?

Answer 30

adding a plasticiser

Question 31

What is rigid PVC used for?

Answer 31

drainpipes and window frames

Question 32

What can plasticised PVC be used for?

Answer 32

electric cable insulation, clothing, flooring tiles

Question 33

What is the general formula of alcohols?

Answer 33

CnH2n+1OH

Question 34

What is the H-C-H and C-C-O bond angle and the shape?

Answer 34

109.5 tetrahedral

Question 35

Explain the H-C-H and C-C-O bond angle

Answer 35

109.5 because there are 4 bonding pairs of electrons repelling to a position of minimum repulsion

Question 36

What is the H-O-C bond angle and the shape?

Answer 36

104.5 bent line shape

Question 37

Explain the H-O-C bond angle?

Answer 37

104.5 there are 2 bonding pairs of electrons and 2 lone pairs repelling to a position of minimum repulsion. Lone pairs repel more than bonding pairs so the bond angle is reduced.

Question 38

Explain the boiling points of alcohols

Answer 38

the alcohols have relatively high boiling points due to their ability to form hydrogen bond between alcohol molecules

Question 39

Describe what happens when smaller alcohols react in water

Answer 39

the can dissolve in water because they can form hydrogen bonds to water molecules

Question 40

Describe a primary alcohol

Answer 40

1 carbon is attached to the carbon adjoining the oxygen

Question 41

Describe a secondary alcohol

Answer 41

2 carbons are attached to the carbon adjoining the oxygen

Question 42

Describe a tertiary alcohol

Answer 42

3 carbon are attached to the carbon adjoining the oxygen

Question 43

What is potassium dichromate?

Answer 43

oxidising agent

Question 44

What reaction occurs when primary alcohols are partially oxized?

Answer 44

the primary alcohol forms an aldehyde and water

Question 45

What is an aldehyde?

Answer 45

contains the functional group with the structure R-CH=O

Question 46

What are the reagents in the partial oxidation of a primary alcohol?

Answer 46

potassium dichromate (VI) solution and dilute sulfuric acid

Question 47

Describe the conditions needed for the partial oxidation of primary alcohols

Answer 47

(use a limited amount of dichromate) warm gently and distil out the aldehyde

Question 48

Why should you use the approximate boiling point of the desired aldehyde and not higher when distilling?

Answer 48

in order to maximise the yield collected

Question 49

Where does the water go in and out in a condenser?

Answer 49

water goes in at the bottom to go against gravity, so prevents backflow

Question 50

Give a reason why some organic chemicals are heated with an electric heater

Answer 50

organic chemicals are normally highly flammable and could set on fire with a naked flame

Question 51

Describe the reaction of the full oxidation of primary alcohols

Answer 51

Reaction: primary alcohol -> carboxylic acid Reagent: potassium dichromate(VI) solution and dilute sulfuric acid Conditions: use an excess of dichromate, and heat under reflux: (distil off product after the reaction has finished) observation- the orange dichromate ion reduces to the green Cr3+ ion

Question 52

When is reflux used?

Answer 52

when heating organic reaction mixtures for long periods

Question 53

Why are anti-bumping granules used?

Answer 53

to prevent vigorous/ uneven boiling

Question 54

What is a ketone?

Answer 54

has two alkyl groups attached to the carbonyl carbon atom