Aqa A2 Chemistry Unit 4 Revision

Front 1

3 features of addition polymerisation?

Back 1

1) there is no bi product
2) they are formed from the same monomers
3) it involves breaking a c=c

Front 2

3 features of condensation polymerisation?

Back 2

1) there is a bi product, eg. 2nH20
2) they are formed from different monomers
3) the monomers have two functional groups (di)

Front 3

Examples of condensation polymerisation? What do the following form from?
1) polyester
2)polyamide (synthetic)
3)polypeptide (natural polyamide)

Back 3

1) diol and dicarboxylic acid
2) diamine and dicarboxylic acid
3) amino acid and amino acid
(amino acid have 2 functional groups an amine and a carboxylic acid)

Front 4

3 features of Nylon (synthetic polyamide)

Back 4

1) it is stress resistance
2) strong - due to H bonds
3) H bonds cause long single chains to twist into fibers.

Front 5

2 features of Kevlar (synthetic polyamide)

Back 5

1) it is resistant to high pressure
2) rigid due to benzene ring

Front 6

What is another method that Nylon can be formed by other than condensation polymerisation?
name: 1 Benefit, 1 problem

Back 6

It can be formed by using an di acyl chloride acid instead of a carboxylic acid.
The reaction is faster, however the bi product if hcl instead of h20

Front 7

Why cant addition polymers biodegrade?

Back 7

They have non-polar c-c and c-h bonds, hence they are very unreactive. They do not hydrogen bond with water.
They cant be broken down by hydrolysis.

Front 8

Why can condensation polymers biodegrade?
what are the conditions/ reagents for this breakdown process (x2)

Back 8

They can be broken down by hydrolysis into their monomers, but the reaction is slow.
Reagents: NaOH conditions: aqueous
OR
Reagents: add (2n)H20 conditions: hcl/h2so4 and heat

Front 9

Disposal of plastics:
name the benefits and problems of disposal by burying them (landfill sites)

Back 9

good: this is useful when its difficult to separate the plastics/recycle and it is a cheap and easy method.
bad: we are running out of landfill sites and some decomposed plastics/waste can release methane (ghg) which could contaminate water supplies

Front 10

Disposal of plastics:
name the benefits and problems of disposal by burning the plastics

Back 10

good: the heat energy generated can be used to make electricity
bad: it can release toxic gases such as hcl or waste gases such as co2 which contribute to global warming

Front 11

Disposal of plastics:
name the benefits and problems of disposal by recycling the plastics

Back 11

good: it conserves non-renewable resources such as oil.
The plastic can be cracked into its monomers or melted down and remoulded.

Front 12

How to distinguish between primary, secondary and tertiary alcohols?

Back 12

add potassium dichromate (vi) acidified with dilute h2s04
observation: orange ----> green

Front 13

How to distinguish between aldehydes and ketones?

Back 13

a) fehling's solution:
aldehyde: blue solution to brick red precipitate
b) tollen's reagent
aldehyde: colourless solution to silver mirror effect
(ketone does not change in either test)

Front 14

Explain the trend in boiling point of an alkane, carbonyl compound and an alcohol
(similar mr so that vdws im forces dont influence the boiling point)

Back 14

alkane<carbonyls<alcohol (--> bp increases)
carbonyls: they have polar c=o, hence they have permanent dd im forces which increases bp
- Alcohols can H bond between molecules, therefore they have a higher bp than both alkanes and carbonyls.

Front 15

1)Why are carbonyls solube in water?
2)Explain the trend insolubility with increasing chain length of a carbonyl compound

Back 15

1)They can form H bonds with water
2) As chain length increases, the im forces/ molecule becomes dominated by the hydrocarbon chain, hence the c=o group becomes a smaller portion of the molecule, hence it becomes less soluble in water.

Front 16

Why is the high mean bond enthalpy of c=o surprising?
What reactions are c=o groups prone to?

Back 16

Because high mean bond enthalpy suggests that it is unreactive, however c=o is polar hence it is reactive.
They are prone to NUCLEOPHLLIC ADDITIONS because the c=o is both polar and unsaturated.

Front 17

What is the mechanism name for the reduction of aldehyde/ketones to primary/secondary alcohols
What are the two options for this reaction ( reagents and conditions)?

Back 17

NUCLEOPHILLIC ADDITION
1) reduction with Hydrogen. Reagent= H2 gas, conditions: nickel catalyst, 60-150
2) reduction with NaBH4. Reagent: NaBH4 (provides hydride ions) conditions: aqueous. - MECHANISM REQUIRED

Front 18

Why is NaBH4 a selective reducing agent?

Back 18

NaBH4 will reduce c=o but not c=c, this is because the hydride ions provided by NaBH4 arent attracted to the region of high electron density around the c=c (like charges repel). However, the hydride ions are attracted to the delta +ve carbon on the c=o.

Front 19

Why can't you use HCN as a reagent for nucleophillic addition with a cyanide ion?

Back 19

HCN is a toxic gas that binds irreversibly with the haemoglobin in place of oxygen and hence prevents aerobic R/S. It is also a weak acid so only partially dissociates, hence doesn't provide enough H+

Front 20

What reagent and conditions do you use instead of HCN for nucleophillic addition?

Back 20

reagents: KCN OR NaCN
Conditions: dilute acid (hcl) to provide H+
- aqueous and alcoholic
MECHANISM REQUIRED.

Front 21

1)Why is nucleophillic addition with a cyanide ion useful?
2)What can it lead to the production of?

Back 21

1) It can lengthen the carbon chain
2) It can lead to the production of an optical isomer if there is a chiral carbon

Front 22

Why can an optical isomer be optically inactive?

Back 22

There is an equal probability of the nucleophille attacking from above or below the planar, polar c=o. Hence a racemic mixture forms - theres is equal amounts of both enantiomers present, which both rotate the plane of polarisation of light by equal amounts in opposite directions hence cancel out.

Front 23

What is the test for a carboxylic acid?

Back 23

Add sodium hydrogen carbonate
if there is a carboxylic acid present you will observe effervescence due to the production of Co2.

Front 24

What is the equation for esterification and what are the reagents and conditions for this reaction?

Back 24

alcohol + carboxylic acid -->(reversible) ester + h20
reagents: CONCENTRATED H2so4 or CONC HCl
conditions: warm, 50-60, conc h2s04/hcl acid catalyst

Front 25

What reactions have the temperatures:
1) 50-60
2) 60-150
3)150

Back 25

1) esterification
2) reduction with hydrogen
3) catalytic reduction with hydrogen

Front 26

Why does esterification have to have a warm temp of 50-60? (3 reasons)

Back 26

1) Increased rate: more successful collisions
2) increased yield: forward reaction is endothermic
3) Practical: Ester more likely to evaporate hence you can smell it easier.

Front 27

What is the problem of producing esters by esterification and what is the alternative method?

Back 27

The reaction is reversible hence doesnt go to completion thus meaning there is a low yield.
You can produce an ester via acylation

Front 28

What the the three uses of esters? (and why they are used for these things)

Back 28

1) solvents (have p d-d im forces hence since like dissolves like they dissolve other molecules with these permanent dipole dipole intermolecular forces)
2) plasticisers (added to plastics during polymerisation to make them more flexible/ reduce effects of im forces between chains)
3) food flavourings/perfumes - sweet smells

Front 29

What are the two options for hydrolysis? (reagents and conditions)

Back 29

1) Acid hydrolysis: reagent= dilute h2s04/hcl (aq)
conditions: warm, reflux
2) Base hydrolysis: reagent= NaOH
conditions: aqueous

Front 30

1)Why is base hydrolysis more favourable?
2)What is the one problem with it and how is it solved?

Back 30

1) the reaction goes to completion hence the yield is higher than the other which is a reversible reaction
2) it produces a carboxylate ion(+alcohol) instead of a carboxylic acid. Add excess h2s04 to turn carboxylate ion into carboxylic acid product

Front 31

What are esters that are:
1) liquid at room temp
2) solid at room temp
3) What do oils and fats contain?

Back 31

1) vegetable oils
2) animal fats
(Animals would beat vegetables in a fight because they are solid)
3)3 fatty acid chains = TRIGLYCERIDE

Front 32

What is the equation for hydrolysis of a triglyceride?

What can the mixture of carboxylate salts be used as?

Back 32

triglyceride + 3NaOH ---> (3x) carboxylate salt + glyerol

The mix of carboxylate salts can be used as soap

Front 33

Why are the mixture of carboxylate salts good soaps/ cleaning agents (due to features of the salt)

Back 33

They are ionic salts which dissociate to form Na+ and the -salt.
The hydrocarbon chain on salt has weak vdw's im forces which allow it to mix with vdws im forces in grease.
The coo-/ ionic/polar head mixes easily with water molecules. Therefore the whole salt allows water and grease to mix= good cleaning agent

Front 34

What are the properties of glycerol and what is it used for ?

Back 34

It has an -OH group so can hydrogen bond with water/is very soluble in water.
It is used in cosmetics/creams/ointments/makeup because it attracts water easily and prevents them from drying out. Also used in toothpaste.

Front 35

What is biodiesel and how is it formed?

NBB/ its good because you dont have to use up crude oil and the plant must be able to be grown readily in uk- problem is we dont have enough land for it.

Back 35

It is a renewable fuel
Extract natural ester (rape seed oil from plant)
triglyceride + 3CH3OH ---> glycerol + biodiesel
NBB/ THIS IS NOT HYDROLYSIS OR ESTERFICATION

Front 36

What are the benefits of Aclyation (an alternative method to esterfication) - 3 reasons

Back 36

1) High yield because the reaction goes to completion
2) extends the carbon chain
3) it can be used in the preparation of paracetamol and aspirin

Front 37

What is the mechanism name for acylation?

What are the two derivatives that can be used which both contain acyl groups?

Back 37

Nucleophillic addition-elimination

1) Acyl chloride 2) acid anhydride

Front 38

What are the products of the reaction of acyl chloride with:
1) h20 2)alcohol 3)ammonia 4) amine

Back 38

1) carboxylic acid + hcl
2) ester + hcl
3) amide + hcl
4) substituted amide + hcl
conditions: anhydrous

Front 39

What are the products of the reaction of acid anhydride with:
1) h20 2)alcohol 3)ammonia 4) amine

Back 39

1) carboxylic acid + carboxylic acid
2) ester + carboxylic acid
3) amide + carboxylic acid
4) N-substituted amide + carboxylic acid
conditions: anhydrous

Front 40

Why are acid anhydrides better to use than acyl chlorides for acylation? (4 reasons)
which reacts more readily with water?

Back 40

1) They are cheaper to produce 2) Their products are less corrosive 3) reacts less readily with water
4) safer bi-product = acyl chlorides produce HCl which is a toxic gas
- acyl chloride reacts vigorously with water

Front 41

What is the one reason acyl chloride is better to use than acid anhydride for acylation?

Back 41

Its products are easier to separate because HCl is a gas, where as acid anhydrides always product carboxylic acids which are more difficult to separate

Front 42

Why was Kekules Model replaced with the delocalised model for Benzene structure?

Back 42

Kekules model suggested that there was alternating c=c and c-c, hence you'd expected 3 bonds of each of the two lengths. However, x-rays showed that each of the six bonds were the same length with a length inbetween that of a c=c and a c-c.

Front 43

What is the delocalised model like?

Back 43

Each carbon donates one electron from its p orbital, and all the p orbitals overlap leading to two rings of delocalised electrons one above and one below the plane of the carbon. This is a region of high electron density. Each of the bonds are the same length with a length between that of c=c and c-c.

Front 44

What effect does the ring of delocalised electrons have on the stability of benzene?

Back 44

The delocalised ring of electrons gives benzene an unusual stability - hence it is very unreactive and reluctant to undergo addition reactions since this would destroy benzene ring and decrease stability. However it will undergo substitution and is prone to attack by electrophiles due the delocalised ring being a region of high electron density.

Front 45

What is the mechanism name for alkylation - reaction of aromatic compounds?

Back 45

ELECTROPHILIC SUBSTITUTION

Front 46

Give the reagents and conditions for nitration, the equation for the formation of the electrophile

Back 46

h2s04 + hn03 ---> +h2no3 + hs04-
+h2no3----> +no2 +h20 (no2=electrophile)
reagents: conc h2s04, conc hno3 conditions: t< 50 (for adding on nitro)

Front 47

Why would you nitrate? (2 reasons/uses)
b)Why would use friedel crafts acylation?

Back 47

1)Nitro compounds can be reduced to aromatic amines - used as dyes
2) Nitro compounds decompose violently when heated so can be used in explosives
b) Adds acyl group which can be further modified to produce useful products.

Front 48

Give reagents and conditions, as well as the formation of the electrophile for friedel-crafts acylation?

Back 48

ch3cocl + alcl3 ---> +ch3co + alcl4-
alcl4- + H+ ---> hcl + alcl3
reagents: acyl chloride conditions: heated under reflux, anhydrous, alcl3 catalyst