Alkenes

Question 1

alkene general formula

Answer 1

Cn Hn2

Question 2

two types of bonds from orbital overlaps

Answer 2

sigma
pi

Question 3

sigma bond formation

Answer 3

overlaps from end to end across an axis

can be s - s , s - p, p - p

Question 4

where are the electrons found in a sigma bond

Answer 4

between the nuclei of the two atoms

the electrostatic attraction between the electrons and the nuclei bonds the atoms to each other

Question 5

what does hydrogen do reffering to bonds

Answer 5

hydrogen has just one s orbital

the s orbitals of the two hydrogen atoms will overlap to form a sigma bond

Question 6

pi bond formation

Answer 6

pi bonds are formed from a sideways overlap of adjacent p orbitals

the two “dumbell heads” of the orbitals lie below and above the x axis

Question 7

c=c bond structure in ethene

Answer 7

three of four e- are in sigma bonds:

two sigma bonds formed by the hydrogen atoms

one sigma bond formed with other carbon

Fourth electron occupies a p orbital on the other carbon atom to form a pi bond (overlapping sideways with other c atom):

c=c is double bond because it has one pi and one sigma bond

Question 8

why are pi bonds weaker than sigma bonds

Answer 8

less area of overlapping between orbitals causes weaker attraction between electrons and nuclei.

Question 9

What makes polymers ideal for many uses but also makes them difficult to biodegrade

Answer 9

Low reactivity

Question 10

Ways to encourage recycling

Answer 10

Recycling points at landfill sites

Question 11

How does the recycling of polymers reduce the use of finite resources

Answer 11

Lots of polymers are made from crude oil( non renewable fossil fuel)

Question 12

Disadvantage of recycling polymers

Answer 12

Time consuming as they have to be sorted into different categories

Question 13

Disadvantage of recycling polymers

Answer 13

Time consuming

Question 14

How does the recycling of polymers reduce the use of finite materials

Answer 14

Lots of polymers are made up of crude oil - a fossil fuel and non renewable

Question 15

Why can incineration of polymers occur

Answer 15

Large amount of energy stored within the polymer chains

Question 16

Advantage of incineration

Answer 16

Process can be used to boil water and use the water vapour to turn turbines inside a power station

Question 17

Process of recycling

Answer 17

Chopped, washed and dried then cast into pellets

Question 18

Problems in recycling

Answer 18

Large amounts of toxic chemicals can be released

Question 19

Why does incineration still cause pollution

Answer 19

Carbon in polymer is released as co2

Question 20

Why does incineration still cause pollution

Answer 20

Carbon in polymer is released as co2

Question 21

What is feedstock recycling

Answer 21

Wate polymers are broken down by chemical and thermal processes into monomers , gases and oils

These products can then be used as raw materials in the production of new polymers and other organic chemicals

Question 22

Major benefit of feedstock recycling

Answer 22

Works with unescorted and unwashed polymers

Question 23

What are chemists trying to do to make polymers better

Answer 23

Use chemicals that are safe and environmentally friendly

Reduce amount of chemicals used

Use renewable feedstock chemicals where possible

Reduce the energy requirements for the reaction

Improve atom economy

Consider the lifespan of the polymer

Question 24

Way to remove Hcl gas from an incinerator

Answer 24

Wasted gas is reacted with a base or carbonate
Base reacts with the Hcl gas neutralising it\

CaO (s) + 2HCl (aq)→ CaCl2 (aq) + H2O (l)

Question 25

Biodegradable polymers

Answer 25

Can be broken down over time by microorganisms

Question 26

Example of condensation polymers that are biodegradable

Answer 26

Polyester and polyamide can be broken down in hydrolysis reactions

When taken to landfill they can be broken down easily and their products used for other applications

Question 27

high electron density in double bond of alkenes

Answer 27

four electrons found on the bond

Question 28

electrophiles

Answer 28

electron loving species

Question 29

c=c are susceptable to …

Answer 29

electrophiles due to their high electron density

Question 30

what is electrophilic addition

Answer 30

addition of an electrophile to a double bond

Question 31

what does electrophilic addition include the addition of

Answer 31

C=c becomes c-c
hydrogen
steam (H2O)
hydrogen halide (HX)
Halogen

Question 32

hydrogenation electrophilic addition

Answer 32

c2h4 +H2 —> c2h6

Question 33

Steam electrophilic addition

Answer 33

c2h4 + H2O —> ethanol

Question 34

hydrogen halides electrophilic addition

Answer 34

propene + HBr —> bromopropane (room temp needed)

Question 35

halogens electrophilic addition

Answer 35

C2H4 + halogen (↓2) —> Halogenoalkane

Question 36

manufacture of margerine

Answer 36

hydrogenation
naturally occuring veg oils are unsaturated and contain c=c
bonds react with hydrogen to become c-c
process changes veg oil from liquid to solid

Question 37

oxidation of alkenes

Answer 37

by KMnO4 - oxidisng agent
when shaken , goes from purple to colourless (product is a diol)
means that the reaction can be used to distinguish alkanes from alkenes

Question 38

heterolytic fission

Answer 38

breaking covelant bonds in such a way that the more electronegative atom takes both electrons from the bond to form a negative atom and takes both the electrons from the bond to form a negative ion and leaving a positive ion behind

simply put a bond is split and one of the atoms takes both the electrons in the shared pair

Question 39

polarity of hydrogen halides

Answer 39

yes as hydrogen is positive and haliedes are negative

Question 40

why does bromine have a stronger pull on e- in H-Br bond

Answer 40

polarity of HBr
This means Br has a partiall negative and hydrogen has a partial postive

Question 41

electrophile in an addition reaction

Answer 41

H atom as it accepts a pair of electrons from the c-c bond in the alkene

H-Br breaks heteolytically forming a Br- ion

Question 42

The mechanics of an alkene electrophilic addition (Br - Br)

Answer 42

alkene is reacted with a halogen

the positive atom in the halogen moves towards the alkene

the positive atom draws the electron in the c=c bond of the alkene towards the other halogen atom which is now a negative ion (opposites attract)

this leaves a halogenalkane with a positive charge

this leftover positive charge attracts the negative half of the previous halogen

negative half of halogen also joins to alkane

resultibg in dihalogenalkane

Question 43

The mechanics of an alkene electrophilic addition (H - Br) or any halogen

Answer 43

alkene is reacted with H-Br

H has a slight positive charge while the Br has a slight negative charge

this means that the hydrogen attracts the electrons in the alkene

these electrons are passed to the bromine

if the hydrogen then bonds to the second carbon the 1 bromopropane will form

if hydrogen bonds to the first carbon then 2 bromopropane will form

thsis is after the propane is left with a positive charge which then attracts the neagtive bromine

Question 44

how to tell which alkane is more likely to form

Answer 44

more alkyl groups on the carbon with positive charge = more stable and more likely to form