176 terms

Triple science Chemistry paper 2

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Activation energy
The minimum amount of kinetic energy particles need to react.
What does collision theory depend on?
-particles must collide the right way and with the activation energy
Maxwell boltzmann curve
peak represents
most likely energy of a single molecule
slightly to the right of peak represents
the mean/average energy of all the molecules
the area under a maxwell boltzmann curve represents
total number of molecules
Increase in temperature on curve
-more molecules have activation energy
-move faster so more collisions
Increase in concentration/pressure on curve
-molecules closer together so more collisions
-more molecules have activation energy
-graph gets taller
What is a homologous series?
-same functional group
-general formula
Structural isomer
-have the same molecular formula
-different structural formula
Stereoisomer
have the same structural formula but their atoms are arranged differently in space
Why does e/z isomerism occur?
restricted rotation about the planar carbon carbon double bond
Conditions for thermal cracking
high temp (1000'c)
high pressure (70 atm)
produces lots of alkenes to make polymers
Conditions for catalytic cracking
zeolite catalyst
slight pressure
high temp (500'c)
aromatic hydrocarbons/alkanes for motor fuels
How is NO produced when burning fuels?
high temp and pressure in engine cause oxygen and nitrogen in air to react
How is ground level ozone produced?
unburnt hydrocarbons and nitrogen oxides react in sunlight to produce O3
What are the risks of ground level ozone?
component of smog
aggravates respiratory problems
lung damage
Synthesis of chloromethane
electron should be oCH3
destruction of ozone
uses of CFC'S
-coolant gas
-propellant in aerosols
nucleophile
electron pair donor
Conditions for nucleophilic subn with OH-
warm aqueous OH-
what is made
alcohol
what is made
nitrile
Conditions for nucleophilic subn with CN-
warm with ethanolic potassium cyanide
Conditions for nucleophilic subn with NH3
warm with excess ethanolic ammonia in a sealed tube
nucleophilic
mechanism with ammonia
extra step another ammonia attacks H to form NH4+ and amine
Which halogenoalkane is the most reactive and why?
iodoalkanes as they have the lowest bond enthalpy
Conditions for elimination with OH- makes
OH- dissolved in ethanol
alkene and water
electrophile
electron pair acceptors
electrophilic addition of alkene (with sulfuric acid)
sulfuric acid is a catalyst
-add water to product get alcohol
Why are tertiary carbocations the most stable?
alkyl groups feed electrons to the positive charge
Why are addition polymers unreactive?
main carbon chain is mainly non polar
saturated chains
Why are longer chained polymers stronger than branched chained?
chains packed tighter together
stronger vdw
Why is pvc/ polychloroethene strong?
cl and c between chains form permanent dipole dipole
Dehydration of an alcohol
heated with a concentrated H2SO4 catalyst
Conditions for hydration of ethene
steam at 300'c
60atm
H3PO4
hydration of ethene
Conditions for fermentation to produce ethanol
glucose
yeast in anaerobic conditions
30-40'c
biofuel
a fuel that is made from biological material thats recently died
equations to show if ethanol is a carbon neutral biofuel
6CO2 + 6H2O ---> C6H12O6 + 6O2
C6H12O6 ---> 2C2H5OH + 2CO2
2C2H5OH + 6O2 ---> 4CO2 + 6H2O

-fossil fuels burnt in transportation
How does IR spec work?
IR radiation passed through sample
different bonds absorb different frequencies
What is the fingerprint region?
1000cm-1 to 1550cm-1
How does IR link with global warming
the earth admits IR
greenhouse gases absorb this IR
global warming occurs
What is a racemate?
Contains equal quantities of each enantiomer of an optically active compound.
rotate plane polarised light in opposite directions
attack from nucleophile is equally as likely
How to reduce aldehydes and ketones?
NaBH4
-nucleophilic addition reactions
How to produce hydroxynitriles
nucleophilic addition with CN-
followed by dilute acid
What are the hazards of KCN?
-toxic
-HCN can be released frm solution so perform in fume cupboard
-use a water bath or mantle to heat as organic compounds are flammable
What do carboxylic acids form when reacting with carbonates?
salt, carbon dioxide and water
What is an esterification reaction?
carboxylic acid + alcohol ---> ester + water

H+ catalyst
How to name an ester?
first part comes from alcohol methanol-methyl
second part comes from carboxylic acid ethanoic acid- ethanoate
Uses of esters?
-perfumes
-solvents/ glues/ inks
-plasticisers
Acid hydrolysis
-relfux ester with dilute acid and water
-splits into alcohol and carboxylic acid
Why must you use lots of water of water in acid hydrolysis?
The reaction is reversible, so lots of water gives a higher yield of product
Base hydrolysis
-reflux ester with dilute alkali
-get carboxylate ion and alcohol
What are animal fats and vegetable oils?
Esters of glycerol and fatty acids
Formula for glycerol
propane-1,2,3 triol
Whats the different between oils and fats?
Oils are unsaturated- weaker van der waals as they don't pack tight together
Fats are saturated- increased van der waals
What type of hydrolysis is used for fats and oils?
Base hydrolysis NaOH
Equation used in the hydrolysis of fats/oils
fat/oil + 3NaOH --->
glycerol + 3CH3(CH2)16COO-Na+
How to convert the soap into a long chain carboxylic acid?
add HCL

CH3(CH2)16COO-Na+ + H+ ---> CH3(CH2)16COOH + Na+
How to make biodiesel?
React with methanol and a strong alkali as a catalyst.
Equation to show formation of biodiesel
fat/oil + 3CH3OH ---> glycerol + 3 methyl ester
Acyl chlorides react via
Nucleophilic addition elimination
Acyl chlorides react with water
carboxylic acid + HCl
Acyl chlorides react with alcohols
ester + HCl
Acyl chlorides react with ammonia
amide + HCl
Acyl chlorides react with primary amides
N- substituted amide + HCl
How do the reactions of acid anhydrides differ?
get a carboxylic acid instead of HCl
How to make aspirin?
salicylic acid + ethanoic anhydride ---> aspirin + ethanoic acid
What does salicylic acid act as?
an alcohol
salicylic acid
Aspirin
Why is ethanoic anhydride used in manufacturing of aspirin rather than ethanoyl chloride?
-cheaper
-less corrosive
-reacts more slow with water
-doesn't produce toxic HCl fumes
structure and bonding of benzene
-planar cyclic structure
-covalent bonding between carbons and hydrogen
-ring of delocalised electrons
-bond lengths are the same
Why is benzene more stable than expected?
-the experimental enthalpy of hydrogenation is less exothermic
-electron density is shared over more atoms, which means the energy of the molecule is lowered
When benzene is not the main functional group?
-NH2 phenyl amine
-OH phenol
-COCH3 phenylethanoate
-CHCH2...phenylethene
Why does benzene not undergo electrophilic addition?
benzene ring is so stable
What are the two types of electrophilic substitution for benzene?
Nitration
Friedel Crafts Acylation
Nitration equation and catalyst
nitric acid + benzene ---> nitrobenzene + H2O

H2SO4 is catalyst
Equation to show the formation of the electrophile.
HNO3 + H2SO4 ---> HSO4- +NO2+ +H2O
How is the catalyst regenerated?
H+ +HSO4- ---> H2SO4
How to sure mononitration?
keep temperature below 55'c
What are the uses of nitration reactions?
-reduced to aromatic amines, used in dyes and pharmaceuticals
-also used in explosives
Conditions for acylation
-heat under reflux
-non aqueous solvent DRY ETHER
Equation for Friedel Crafts Acylation
acyl chloride + benzene ---> phenyl chloride + HCl
What is a halogen carrier?
A catalyst used to make a strong electrophile
Equation for generation of the electrophile and regeneration of catalyst
RCOCl + AlCl3 ---> ROC+ + AlCl4-
AlCl4- + H ---> AlCl3 + HCl
What is the functional group of an amine?
NH3
What is a surfactant?
A compound that is partly soluble and insoluble in water
Give an example of a cationic surfactant?
quaternary ammonium salt with a long hydrocarbon chain
How do cationic surfactants work?
-long chain insoluble in water to attaches to non polar grease
-polar head group will dissolve in water
What are cationic surfactants used for?
detergents, hair product etcs
What do amines act as and why?
Bases because the accept protons (BLB)
What does the strength of the amine base depend on?
how available the nitrogen's lone pair of electrons is

more available= more likely to accept proton
Why are primary aromatic amines weak bases?
benzene ring draws electrons towards itself
electron density on nitrogen decreases
lone pair less available
Why are primary aliphatic amines strong bases?
alkyl groups push electrons away from itself
lone pair more available
What is the functional group of an amide?
What is a N-substituted amide?
one of the hydrogens has been substituted with an alkyl group
N- ethylethanamide
Other than nucleophilic substitution, how else can an amine be formed?
Reduce Nitriles using LiAlH4 in dry ether and dilute acid
What is used instead in industry?
Nickel Catalyst/ H2
high temp and pressure
How to make an aromatic amine?
Nitrobenzene
Sn conc HCl
reflux
Add NaOH
phenylamine
Overall equation to produce phenylamine
nitrobenzene + 6[H] ---> phenylamine + 2H2O
Name the two types of condensation polymers
Polyesters
Polyamides /peptide bonds
How to make polyamides?
Condensation reaction
dicarboxylic acid
diamine
water is eliminated
Structure of Nylon 66
1,6 diaminohexane
hexanedioic acid
The uses of Nylon 66
strong and resistant to abrasion-clothing,carpet,rope,airbags, parachutes
Structure of Kevlar
benzene-1,4-dicarboxylic acid
1,4- diaminobenzene
The uses of Kevlar
light and strong- bulletproof vests, car tyres, sports equipment
How is a peptide formed?
When two amino acids react in condensation reactions.
How is a polyester formed?
dicarboxylic acid
diol
Structure of Terylene
benzene-1,4 dicarboxylic acid
ethane-1,2-diol
Uses of Terylene
stable at hot and cold temps
good containers for food
How to reverse a condensation polymer reaction?
Hydrolysis but too slow with water so acid/ alkali is used
Polyamides are hydrolysed more easily
in acidic conditions
Polyesters are hydrolysed more easily
in alkaline conditions
Why are condensation polymers stronger than addition polymers?
strong hydrogen bonding between chains
Why are polyalkenes chemically inert unlike condensation polymers?
bonds between repeating units are non polar
non susceptible to attack by nucleophiles
Structure of an amino acid
How to amino acids act as acids?
COOH ---> COO- + H+
donate a proton
How do amino acids act as bases
NH2 + H+ ---> NH3
How to name amino acids?
-longest carbon chain COOH
-NH2 have 'amino'
What is the isoelectric point?
pH where the overall charge is 0
What does the isoelectric point depend on?
The R group
Amino acids in acidic conditions
Amino acid is fully protonated
i.e. (-NH3+) and (-COOH)
Amino acids in basic conditions
Amino acid is fully deprotonated
i.e. (-COO(-)) and (-NH2)
What are proteins?
Sequences of amino acids joined by peptide links
What is the primary structure of an amino acid?
sequence of amino acids that make up the polypeptide chain
covalent bonds
What is the secondary structure of amino acids?
What is the tertiary structure of amino acids?
-coiled and folded
-extra bonds form
-3d shape
result of hydrogen bonds and disulfide bonds
Where and how does disulfide bonding occur?
in cytesine
S-S
What can affect the shape of proteins
temp and pH
How do inhibitors work?
Similar shape to substrate
block the active site
What are the three nucleotides that make up DNA?
Phosphate group
pentose sugar (2-deoxyribose)
Base
Structure of a nucleotide
What is a phosphodiester bond?
H2O is lost
condensation polymerisation
How is the structure of DNA formed?
2 hydrogen bonds adenine and thymine
3 hydrogen bonds guanine and cytosine
How does cisplatin work in a ligand replacement reaction?
Nitrogen on guanine replaces one of the chlorine ligands
Second guanine can replace other chlorine too
How to lessen the risks of cisplatin?
lower doses
target tumour specifically
What does NMR spectroscopy measure the difference in?
energy absorbed by nuclei in different environments relative to a standard substance
What is the standard for NMR? Why?
Tetramethylsilane
-single peak far to right
-inert
-non toxic
-volatile so easily removed
Carbons next to what type of atoms will have a higher chemical shift
electrochemical
In H NMR what type of deuterated solvent is used?
DC(Cl)3
What is the mobile phase?
Where the molecules can move. Liquid or gas.
What is the stationary phase?
Where the molecules cant move.
Must be a solid or a liquid on a solid support.
What does the separation depend on?
solubility in the mobile phase
retention by the stationary phase
What is the mobile phase in TLC?
liquid solvent- ethanol
What is the stationary phase in TLC?
thin layer of silica fixed onto a glass/metal plate
How to carry out TLC?
-draw baseline in pencil
-add drops of mixture to baseline
-allow spots to dry on the plate
-place plate in solvent and cover with watch glass
-solvent moves up plate and chemicals separate out
-remove plate and mark the solvent front
-place plate in fume cupboard to dry
Why is a watch glass used?
stops solvent from evaporating
Why must the solvent level be below the baseline?
so it doesn't dissolve samples away
What are the two ways to perform TLC if the chemicals are colourless?
-shine under uv lamp to view
-leave plate in a jar of iodine crystals, iodine will stick to chemicals and spots will appear purple
How to small Rf values arise?
not very soluble in mobile phase
strongly adsorbed in stationary phase
How to large Rf values arise?
Substance very soluble in mobile phase
weakly adsorbed in stationary phase
What is column chromatography used for?
purifying an organic product
How does column chromatography work?
Stationary phase- glass column packed with aluminium oxide coated with water
Mobile phase- solvent runs slowly and continuously through column
How can components of the mixture be identified using column chromatography?
Using the retention time.
What is Gas chromatography used for?
a mixture of volatile liquids
What is the stationary phase in gas chromatography?
solid or solid coated with oil (viscous liquid) packed into a long column
What is the mobile phase in gas chromatography?
Unreactive carrier gas such as nitrogen which is passed through at high temp and pressure
How to ensure accuracy of gas chromatography?
run a known sample through under same conditions for comparison
In a chromatogram what do the area under the peaks represent?
amount of each component present in the mixture
What is GC-MS?
sample separated using gas chromatography
fed into a mass spectrometer
mass spectrum produced
Why is GC-MS more useful?
components can be positively identified
impossible to do this just using GC as similar compounds have similar retention times
What method of purification should be used if product is insoluble in water?
separation
How does separation of organic product work?
-organic layer and aqueous layer containing soluble impurities separate out
-open tap and run off each layer into separate beakers
What is solvent extraction?
-used if your product and impurities are dissolved in a solution together
-shake impure product with immiscible solvent
What drying agent can be used to remove traces of water?
anhydrous MgSO4 or CaCl2
What method of purification should be used if there's liquids with different boiling points?
redistillation
How to perform distillation?
Heat impure product and when the liquid you want boils collect in a beaker
What method of purification should be used if product is a solid?
Recrystallisation
What are the steps for recrystallisation?
dissolve in minimum amount of hot solvent
leave to cool and crystals form
filter under reduced pressure using a buchner filter
Diagram of buchner filter
...
Steps to test purity of organic compound?
-pack small sample into capillary tube
-increase temperature until solid turns to a liquid
-measure melting point and compare with data tables
How to produce cyclohexene?
1.
-add H2SO4 and H3PO4 to a round bottom flask with cyclohexanol
-add anti bumping granules
-heat mixture to 83'c
-collect the liquid product

2.
-transfer to separating funnel and add water
-settle in layers and filter off

3.
-drain off impure cyclohexene
-add anhydrous CaCl2 and allow mixture to dry for 20 mins
-distill again
Shaking alkenes with bromine water
brown to colourless