Studied by 2 people
Alcohol general formula
CnH2n+1OH
Alcohol functional group
-OH
What can alcohols be classified as?
primary secondary or tertiary
primary alcohol
has the functional group attached to a carbon atom with no more than one alkyl group
secondary alcohol
has the functional group attached to a carbon atom with two alkyl groups
tertiary alcohol
has the functional group attached to a carbon atom with three alkyl groups
How does the boiling point of alcohols change as chain length increases?
increases
Why does the boiling point of alcohols increase as chain length increases?
more surface area contacts, so stronger induced dipole-dipole intermolecular forces, so more energy needed to overcome these forces
Are boiling points of alcohols higher or lower than the corresponding alkanes?
higher
Why are the boiling points of alcohols higher than the corresponding alkanes?
there are hydrogen bonds between the alcohol molecules
volatile
evaporates easily at room temperature and pressure
Are alcohols more or less volatile than the corresponding alkane?
less volatile
Why are alcohols less volatile than the corresponding alkane?
alcohols have hydrogen bonds
volatility increases as boiling point …
decreases
How does solubility change with an alcohol’s alkyl chain length?
as chain length increases, solubility of alcohol decreases
Why are alcohols soluble in water?
they form hydrogen molecules with the molecules
Reactions with alcohols (5)
combustion
oxidation
esterification
dehydration
halide substitution
Why are alcohols combusted to be used as fuels?
to transfer their stored chemical energy into a usable form (e.g. thermal energy)
What is the oxidising agent used to oxidise primary and secondary alcohols?
acidified potassium dichromate (VI)
What are the reaction conditions for oxidising a primary alcohol?
gentle heating, then stronger heating under reflux with excess potassium dichromate (VI)
Products of oxidising a primary alcohol
aldehyde then carboxylic acid (and water)
what is the colour change when you oxidise a primary or secondary alcohol?
orange to green
What are the reaction conditions for oxidising a secondary alcohol?
heat under reflux
Products of oxidising a secondary alcohol
ketone (and water)
General equation for the esterification of alcohols
alcohol + carboxylic acid → ester + water
Dehydration
a chemical reaction in which water molecules are eliminated from an organic compound
What type of reaction is dehydration?
elimination
elimination
an organic reaction in which one reactant forms two products and a small molecule like water is released
reaction conditions for dehydration
strong acid (e.g. sulfuric acid) and 170 degrees
products of the dehydration of an alcohol
alkene and water
halide substitution
halide ions react with alcohols and substitutes the alcohol group
General equation for halide substitution
ROH + HX → RX +H2O
Reagent and reaction conditions of halide substitution (3)
hydrogen halide
sulfuric acid catalyst
mixture warmed
haloalkanes
saturated organic compounds that contain carbon atoms and at least one halogen atoms
What makes the carbon halogen bond in haloalkanes polar?
large difference in electronegativities of carbon and halogens
nucleophiles
electron-pair donors
In a C-X bond, which atom has the slightly negative charge?
halogen
What are haloalkanes attacked by?
nucleophiles
What charge do nucleophiles often have?
negative
What factors affect the reactivity of a reaction with haloalkanes and nucleophiles?
strength and polarity of the C-X bond
How does mean bond enthalpy affect the reactivity of a halogen in a nucleophilic substitution reaction?
the higher the mean bond enthalpy the less likely the halogen will react in a nucleophilic substitution reaction
How does polarity of the C-X bond affect how likely a halogen is to react in a nucleophilic substitution reaction?
molecules with higher polarity are more likely to react
How does polarity change down the halogens?
polarity decreases going down the group
nucleophilic substitution
a chemical reaction in which an atom or group of atoms is replaced for a nucleophile
hydrolysis
a chemical reaction in which water is a reactant
When water is used as a reactant, what acts as nucleophiles?
hydroxide ions
In a hydrolysis reaction, what does the hydroxide ion nucleophile attack?
the electron deficient carbon in the haloalkane
What ion is produced in the hydrolysis of haloalkane?
halide ion
how do you measure the rate of a hydrolysis reaction when a haloalkane is reacted with silver nitrate?
time taken for the ppt to form
How does rate of hydrolysis change down the halogens?
increases
Why does an iodoalkane have a higher rate of hydrolysis than a chloroalkane?
it is the least polar, so least attractive, so the bond is weaker and easier to break
What is made when a haloalkane is heated under reflux with a aqueous solution containing hydroxide ions?
alcohol
CFCs
Chlorofluorocarbons
Why were CFCs used in the past
they are inert
What happens when CFCs disperse into the atmosphere?
they diffuse up the layers of the atmosphere and become exposed to UV radiation
What happens when CFCs are exposed to UV light?
they undergo homolytic fission
ozone layer
area of high concentration of ozone in the statosphere
ozone formula
O3
What can prolonged exposure to UV radiation lead to?
cell mutations that can cause skin cancer and cataracts
What do chlorine radicals from CFCs do to ozone?
catalyse the decomposition of ozone to make diatomic oxygen
What happened to the ozone layer because of using CFCs?
the ozone layer is shrinking
How long do CFCs remain in the atmophere?
more than 50 years
What (other than CFCs) can decompose ozone?
nitrogen monoxide
distillation
a technique used to separate miscible liquids or solutions
reflux
a technique used to stop reaction mixtures boiling away into the air
What do you do before connecting Quickfit apparatus?
grease the joints slightly with petroleum jelly
What equipment is required for distillation? (7)
round-bottomed flask
heating mantle
thermometer
thermometer holder
condenser
connector
collecting flask
What do you use to secure each piece of equipment as you build up your distillation apparatus?
clamp stands
Why do you need anti-bumping granules?
to ensure smooth boiling
What equipment do you need for reflux? (3)
pear-shaped flask
heating mantle
consenser
When do you use a separating funnel?
to separate an immiscible organic layer from an aqueous layer
Is the organic layer of aqueous layer less dense?
the organic layer is more dense
What do you use to separate immiscible liquids?
separating funnel
drying agents
inorganic salts that absorb water slowly to become hydrated and can be used to dry other chemicals
Examples of salts that are used as drying agents
MgSO4 and CaCl2
What do you do if the drying agent clumps together?
add more drying agent
When is the organic product dry?
when the drying agent remains free-moving
How do you collect the filtrate after using a drying agent?
use gravity filtration
redistillation
the purification of a liquid using multiple distillations
Test for unsaturated hydrocarbon
add bromine water
Test for haloalkane
add silver nitrate, ethanol and water
Tests for carbonyl (3)
acidified potassium dichromate
Fehling’s solution
Tollen’s reagent
Tests for carboxylic acid
universal indicator or pH probe
reactive metal
metal carbonate
Test for an alcohol
warm with an equal volume of carboxylic acid and a few drops of H2SO4
What are the observations for a positive test for an alcohol
sweet smell of an ester after a long time
What happens when molecules absorb infrared radiation?
it causes them to vibrate more
What does the amount of vibration of molecules depend on? (3)
bond strength
bond length
mass of each atom involved in the bond
What does each peak in an infrared spectrum represent?
the absorbance of energy from infrared radiation of a particular bond in the molecules under investigation
molecular ion, M+
the positive ion formed in mass spectrometry when a molecule loses and electron
What is caused when excess energy from the ionisation process is transferred to the molecular ion, making it vibrate?
the bonds weaken and the molecular ion splits into pieces by fragmentation
Note
Flashcard