AQA A-level Chemistry paper 2

Relative atomic mass (Ar)

Average mass of an atom compared with one twelth of the mass of an atom of carbon 12

Electronegativity

Power of an atom to attract the pair of electrons in a covalent bond

Standard enthalpy of combustion

Enthalpy change when 1 mole of a substance burns completely in oxygen under standard conditions with all reactants and products being in their standard state

Standard enthalpy of formation

Enthalpy change when 1 mole of a compound is formed from it's elements under standard conditions in their standard states

Mean bond enthalpy

The average energy needed to break a certain type of bond over a range of compounds

Activation energy

Minimum energy required for colliding molecules to react

Maxwell-Boltzmann distribution x and y axes

x: Energy

y: fraction/number of molecules

What happens to the Maxwell-Boltzmann curve when temperature increases

Moves down and to the right

Rate of reaction

Rate at which product formed/reactant used up

Order of reaction

Power to which the concentration of a species is raised in the rate equation

rearrange k=Ae^-Ea/Rt

lnk=-Ea/Rt+lnA

Conditions for thermal cracking

High temperature and high pressure

Products of thermal cracking

High % of alkenes

Conditions for catalytic cracking

High temperature ,slight pressure and in the presence of a zeolite catalyst

Products of catalytic cracking

Motor fuels and aromatic hydrocarbons

Why do we crack alkanes?

Smaller alkanes/alkenes generally more useful than longer chain ones

Equation for complete combustion of alkanes

alkane + oxygen > carbon dioxide + water

Equations for incomplete combustion of alkanes

alkane + oxygen > carbon monoxide/carbon + water

Pollutants produced by combustion engines

NOx, CO, C and sunburned hydrocarbons

Reaction of methane with chlorine

I: Cl2 > 2Cl•

P: CH4 + Cl• > CH3• + Chi

CH3• + Cl2 > CH3Cl + Cl•

T: CH3• + Cl• > CH3Cl

2 equations showing decomposition of the ozone

Cl• + O3 > ClO• + O2

ClO• + O3 > 2O2 + Cl•

What types of mechanism do haloalkanes undergo?

-Nucleophilic substitution by aqueous hydroxide ions, cyanide ions or ammonia

-Elimination with ethanolic hydroxide ions

What type of mechanism do alkenes undergo?

Electrophilic addition by bromine, hydrogen bromide or sulphuric acid

Test for primary or secondary alcohols

Warm with acidified potassium dichromate (VI) and positive result is Solution turning green

Tests for aldehyde or ketone

-Warm with Fehlings Solution - brick red precipitate indicates aldehyde

-Warm with Tollens reagent (silver nitrate + sodium hydroxide + dilute ammonia) - aldehyde gives a silver mirror

Test for alkenes

Shake with bromine water- alkene goes from Orange to colourless

Test for carboxylic acids

Sodium carbonate and effervescence is positive

Relative stabilities of carbocations

tertiary>secondary>primary

What are addition polymers formed from?

Alkenes and substituted alkenes

Conditions for dehydration of alcohols to give alkenes and water

Heat with concentrated sulfuric acid

Conditions for production of ethanol by fermentation

Yeast, anaerobic, 30-40°C

Why are racemic mixtures optically inactive?+

There are equal concentrations of the (+) and (-) isomers

What are aldehydes oxidised to?

Carboxylic acids

What are aldehydes reduced to primary alcohols by and ketones reduced to secondary alcohols by?

NaBH4 in aqueous solution

Conditions for production of hydroxynitriles from caronyl compounds

KCN followed by dilute acid

Equations for formation of an ester (acid catalyst)

carboxylic acid + alcohol > ester + water

acyl chloride + alcohol > ester + HCl

Uses of esters

Solvents, plasticisers, perfumes and flavourings

Products of hydrolysis of vegetable oils/animal fats in alkaline conditions

salts of long chain carboxylic acids (soap) and glycerol

How is biodiesel produced?

Reacting vegetable oils with methanol with a catalyst

What type of mechanisms do acyl chlorides and acid anhydrides undergo with water, alcohols, ammonia and primary amines?

Nucleophilic addition-elimination

Reasons for making aspirin with ethanoic anhydride rather than ethanoyl chloride

-Cheaper

-Safer (less corrosive)

-Doesn't produce dangerous fumes of hydrogen chloride

Equation for generation of nitronium ion

HNO3 + 2H2SO4 > NO2+ + 2HSO4- + H3O+

Formation of electrophile in acylation

AlCl3 + ROCl > RO+ + AlCl4-

How can you prepare primary aliphatic amines?

-haloalkanes + ammonia

-reduction of nitriles

Relative base Strength of amines

2°>3°>1°>ammonia>aromatic amines

Condensation polymers formed by reactions between:

-dicarboxylic acids + diols

-dicarboxylic acids + diamines

-amines

Why can polyesters and polyamides be hydrolysed

C=O susceptible to Nucleophilic attack

What charge does an amino acid form in acidic solution?

Positive

What charge does an amino acid form in alkaline solution?

Negative

What is a stereospecific active site?

An active site that only one enantiomer can fit

Developing agents for a chromatogram

Ninhydrin or ultraviolet light

Method for Thin Layer Chromatography

1) Wearing gloves, draw pencil line 1 cm above bottom of plate

2) Add tiny drop of each solution using capillary tube and dry

3) Add solvent to chamber below pencil line

4) When solvent almost reaches top of plate take it out

5) Dry in fine cupboard then spray with ninhydrin and put in oven

6) Calculate Rf

Ho2 to calculate Rf

(Distance moved by amino acid) ÷ (Distance moved by solvent)

How does cisplatin prevent DNA replication?

Ligand substitution forms bond between Platinum and nitrogens from two guanines

Test for chloroalkane

Warm with silver nitrate gives white ppt of AgCl

Test for acyl chloride

Warm with silver nitrate gives steamy fumes of Hack and white ppt of AgCl

What will NaBH4 reduce?

C=O

What does hydrogen with a nickel catalyst reduce?

C=C

What does Sn/HCl reduce?

RNO2 to RNH2

What is a dehydrating agent for alcohols to alkenes?

heated aluminium oxide

What are samples dissolved in for 1H NMR?

CCl4

Why is TMS used as a standard?

-Chemical shift of 0 (signal far away from anything else)

-Inert

-Non toxic

-Easy to remove from sample (low bp)

Describe Thin-Layer Chromatography

A plate is coated with a solid and a solvent moves up the plate

Describe Column Chromatography

A column is packed with a solid and a solvent moves down the column

Describe Gas Chromatography

A column is packed with a solid or a solid coated by a liquid, and a gas is passed through the column under pressure at high temperature

What is the mobile phase?

Carries the soluble components of the mixture

What relationship between a sample and the mobile phase makes the sample move faster?

More soluble components/components with more affinity to the solvent move faster

What does the stationary phase do?

Holds back components of the mixture that are attracted to it

What is the relationship between a sample and the stationary phase and what type of bonding is usually involved?

More affinity for the stationary phase means that component moves slower, often attracted by hydrogen bonding

How are substances separated by chromatography?

If suitable stationary/mobile phases are chosen, the balance between affinity for the mobile phase and the stationary phase is different for each component of the mixture. Thus, they move at different rates and are separated over time

Why do different substances have different Rf values?

More polar bonds mranlobger retention time and smaller Rf value

What are the advantages of TLC over paper chromatography?

-Runs faster

-Smaller amounts of a mixture can be separated

-TLC plates are more robust than paper

What are the advantages of column chromatography?

-More than one solvent can be used which Leads to better separation

-Fairly large amounts can be separated

What is the main advantage of Gas Chromatography?

Very sensitive

What is chemical shift?

The resonant frequency of the nuclei compared with that of a 1H atom in TMS

What kind of environment Leads to a greater chemical shift?

A C atom next to a more electronegative atom has a greater chemical shift

Summarise what these mean for 13C NMR:

1)Number of signals

2)Chemical shift

3)Area under Peak

4)Splitting

1) One signal for each C environment

2) Greater chemical shift from atoms closer to electronegative atoms or C=C

3) No meaning

4) No splitting for 13C NMR

What leads to a lower chemical shift value for H NMR?

1H with more electrons around them/further away fromelectronegative atoms

What does the area under the peak represent for 1H NMR?

The area under the peak is proportional to the number of 1H atoms represented by the peak

What is the n+1 rule?

If there are n 1H atoms on the neighbouring carbon then the peak will split into n+1 peaks

Why do you try and keep the number of steps as low as possible? (organic synthesis)

Improve % yield of final product

What is the main oxidizing agent used in organic chemistry?

K2Cr2O7/H2SO4

What are primary alcohols oxidised to?

Aldehydes then carboxylic acids

What are secondaey alcohls oxidised to?

Ketones

What are the 3 main reducing agents and what dor they reduce?

-NaBH4 reduces C=O

-H2/Ni reduces C=C

-Sn/HCl reduces NO2 to NH2

What are the two main dehydrating agents?

-Al2O3 (vapours passed over it)

- Acid catalysed elimination by H3PO4

What does a compound being solid indicate?

Long C chain or ionic

What does a compound being liquid indicate?

Medium C chain or polar/hydrogen bonding

What does a compound being a gas indicate?

Short carbon chain or non-polar bonds

What does a smoky flame suggest?

High C:H ratio, possibly aromatic

In what form do amino acids exist as solids and what does this mean?

Zwitterions (ionic lattice) - high melting and boiling points

What conditions are needed for hydrolysis of proteins?

Conc HCl, reflux

What are two examples of secondary structure and how are they held together?

Alpha-helix or beta-pleatee sheets and held together by hydrogen bonds

How do enzymes increase rate of reaction?

Reacting molecules form temporary bonds with enzyme which weakens bonds and lowers Ea

Which monomers I terylene made from?

Benzene-1,4-dicarboxylic acid and ethane-1,2-diol

Which monomers is Nylon-6,6 made from?

1,6-diaminohexane and hexanedioic acid

Which monomers is Kevlar made from?

1,4-diaminobenzene and benzene-1,4-dicarboxylic acid

How do you name amines?

-amine or amino-

Is phenylamine soluble?

Not very because of non-polarity of benzene ring cannot form hydrogen bonds

How could you regenerate a soluble amine from the ammonium salt?

Add strong base such as NaOH