MODULE 4

Question 1

4.1 what is a general formula?

Answer 1

A ratio of atoms in a molecule to calculate the size of a molecule e.g. an alkanes general formula is CnH2n+2

Question 2

4.1 give the general formula of alkenes

Answer 2

CnH2n

Question 3

4.1 define the term homologous series

Answer 3

A series of organic compounds having the same functional group, but with each successive member differing by CH2.

Question 4

4.1 define the term functional group

Answer 4

A group of atoms responsible for the characteristic reactions of a compound

Question 5

4.1 name the first 3 alkyl groups (R groups) and give their formula

Answer 5

Methyl- CH3
Ethyl- C2H5
Propyl- C3H7

Question 6

4.1 give an example of an aliphatic compound that is NOT alicyclic

Answer 6

Hexane

Anything that’s not cyclo-

Question 7

4.1 give an example of an aliphatic compound which IS alicyclic

Answer 7

Cyclohexane

Anything with cyclo-

Question 8

4.1 what is meant by an aromatic compound?

Answer 8

A compound that contains a benzene ring

Question 9

4.1 give the molecular formula for bromoalkanes

Answer 9

CnH2n+1Br

Question 10

4.1 define the term structural isomer

Answer 10

compounds that have the same molecular formula but different structural formulas

Question 11

4.1 Write an equation to explain the homolytic fission of a Br-Br bond

Answer 11

Search answer

Question 12

4.1 Write an equation to explain the heterocyclic fission of a F-F bond

Answer 12

Search answer

Question 13

4.1 define the term radical

Answer 13

Something with an unpaired electron (highly reactive)

Question 14

4.1 How would you represent a fluorine radical?

Answer 14

F. (F with a dot for an electron)

Question 15

4.1 what is shown by a curly arrow?

Answer 15

The movement of electrons

Question 16

4.1 draw a HBr molecule and label the relevant dipoles

Answer 16

H—Br
d+ d-

d(delta)

Question 17

4.1 what is meant by a saturated hydrocarbon?

Answer 17

A hydrocarbon where all carbon atoms make 4 single bonds

Question 18

4.1 what is the bond angle around each carbon in an alkane?

Answer 18

109.5

Question 19

4.1 state and explain the trend in boiling point as the alkanes increase in carbon chain length

Answer 19

An increased carbon chain length increases the boiling point because there are more points of contact between molecules therefore there are more London dispersion forces (induced dipole-dipole forces) requiring more energy to break them.

Question 20

4.1 explain the trend in boiling point between pentane, 2-methyl butane and 2,2-di methylpropane (increasing branches)

Answer 20

Branching weakens a molecules ability to tesselate which reduces their attraction and therefore they have less points of contact which means they have fewer London dispersion forces requiring less energy to break them apart, hence an increase in branching causes a decrease in the boiling point

Question 21

4.1 why are the alkanes generally unreactive?

Answer 21

The alkanes are generally unreactive because they are fully saturated meaning no addition reactions can take place

Question 22

4.1 explain the difference between incomplete and complete combustion (use equations with methane)

Answer 22

COMPLETE
Fully oxegenated reaction
CH4 + O2 -> CO2 + 2(H2O)

INCOMPLETE
Lacking oxygen
2(CH4) + 3(O2) -> 2(CO) + 4(H2O)
Forms carbon-monoxide (and carbon particles) which is toxic

Question 23

4.1 what is meant by an unsaturated hydrocarbon?

Answer 23

Unsaturated means that not all carbons atoms form four distinct covalent bonds with different atoms, for example the might form a double bond

Question 24

4.1 what is the bond angle around each carbon in an alkene?

Answer 24

120

Question 25

4.1 define the term stereoisomers

Answer 25

Molecules with the same structural formula but a different arrangement in space

Question 26

4.1 why can alkenes form stereoisomers while alkanes can’t?

Answer 26

Alkenes contain a pi bond which means that atoms a cant move about this bond whereas alkanes only contain sigma bonds, this means that the molecules can move around and therefore have no stereoisomers

Question 27

4.1 explain how you name a molecule using E/Z notation

Answer 27

Using CIP rules (cahn ingold prelog) you determine the highest priority atoms bonded to the carbons either side of the double bond. If they are both on the same side they are Z (zee zame zide) if they are on opposite sides they are E ``` Example of Z: bromine is highest priority and they are both on the same side so Z Br Br | | C = C | | H H ```

Question 28

4.1 explain how you name molecules using cis/trans notation

Answer 28

You determine which two atoms are the same on opposite sides of the C=C double bond and then label them cis if they are on the same side and label them trans if they are on opposite sides ``` Example of trans: the two bromine atoms (or hydrogen atoms) are the same but on opposite sides across the double bond, therefore they are trans H Br | | C = C | | Br H Trans-1,2-dibromoethene ```

Question 29

4.1 what are CIP rules?

Answer 29

Cahn Ingold Prelog rules are a set of rules used to determine the notation of E/Z isomers. You pick the highest priority atom (which is the atom with highest mass) either side of the CC double bond, then label them as Z if the two highest priority atoms are on the same side ``` E.g. Br Br | | C = C | | H H The Br atoms have a higher priority than the H atoms, both the Br atoms are on the same side, therefore it is a Z isomer ```

Question 30

4.1 why are alkenes more reactive than alkanes?

Answer 30

Alkenes are more reactive than alkanes because they are unsaturated, this means that addition reactions can take place easily at room temperature whereas alkanes are fully saturated which means that they are unreactive

Question 31

4.1 what is the catalyst used during the hydrogenation of alkenes?

Answer 31

Nickel

Question 32

4.1 prop-1-ene + hydrogen -> ?

Answer 32

Propane

Question 33

4.1 how do you test for a double bond?

Answer 33

Vapourise the sample then bubble it through bromine water, if the sample decolourises (turns clear from brown) the sample contained a double bond as the bromine has been added to the sample by breaking open the double bond (addition reaction). If the bromine water does not change colour the sample does not have a double bond

Question 34

4.1 what is an electrophile

Answer 34

An electron pair acceptor

Question 35

4.1 what type of fission takes place during the electrophilic addition of alkenes?

Answer 35

Heterolytic fission as two different products are made

Question 36

4.1 define the term monomer

Answer 36

The small molecules which join together to make a polymer e.g. ethene

Question 37

4.1 define the term polymer

Answer 37

Long chain molecules that are made from the same repeating unit (monomer) e.g. polyethene

Question 38

4.1 what is meant by sustainable?

Answer 38

Meeting the needs of the present without compromising the needs of future generations.

Question 39

4.1 what are the benefits of burning plastic waste?

Answer 39

- not filling the environment with plastic (landfills and ocean) - energy can be used to create electricity

Question 40

4.1 why is it important to treat the waste from incineration of halogenated plastics like PVC?

Answer 40

They can release harmful gases when burnt e.g. chlorine gas is produced when burning PVC

Question 41

4.1 what are the benefits to the environment from using biodegradable polymers?

Answer 41

- No harmful toxins produced - doesn’t take up space in landfills for very long - can’t enter ecosystems as it breaks down

Question 42

4.1 what are the problems associated with burning plastic waste?

Answer 42

- releases harmful gases - means more crude oil is needed to make new plastics - ugly to live near

Question 43

4.1 what are the three steps in a radical substitution reaction?

Answer 43

- initiation - propagation - termination

Question 44

4.1 what is the role of UV light in radical substitution?

Answer 44

Provides activation energy to form two radicals

Question 45

4.1 what is the main problem of using radical substitution of alkanes to form products? (E.g. chlorine and propane to make chloropropane)

Answer 45

There are other side products that are made to the reaction does not have a high percentage yield

Question 46

4.1 what is marikownikoffs rule?

Answer 46

When a compound HX is added to an unsymmetrical alkene the H will bond to the carbon with most H’s already bonded (this product is more abundant). This is because the X can bond to the carbon with a branch/ the rest of the chain which means the product is more stable.