alcohols Flashcards
what is the suffix of all alcohols ?
-ol
what is the general formula of alcohols ?
CnH2n + 1 OH
what is the functional group of alcohols ?
OH
what is the prefix/ name given to the functional group of alcohols if they are not the most important group in the molecule ?
hydroxy
what is it called when there are 2 alcohol functional groups in the molecule ?
diol
what is the additional subclass of all alcohols ?
primary alcohols
secondary alcohols
tertiary alcohols
how do you know if an alcohol is a primary , secondary or tertairy alcohol ?
you look at the carbon that is attached to the functional group and count how many carbons are attached to that specific carbon
what are the features of the bonds in alcohols ?
- dipole dipole bonding
oxygen is more electronegative than hydrogen - lone pair of electrons on oxygen
so hydrogen bonds can form between lone pair and electron deficient hydrogen in a neighbouring alcohol
what is the melting and boiling point of alcohols ?
hydrogen bonds between molecules means alcohols have a higher melting point than alkenes
what is meant by solubility ?
the ability to dissolve in water
describe the solubility of alcohols and explain why is that the case ?
alcohols are soluble in water
- because they form hydrogen bonds with water
-but the longer an alcohol gets, the less soluble it becomes
what is the bond angle between the hydrogen bond and the O-H bond ?
always 180 degrees
which point are alcohols considered to be insoluble ?
from octan-1-ol
there is a gradual change before that
what is considered to be he most important alcohol ?
ethanol
what are the 2 different ways of producing ethanol ?
- hydration of ethene
- fermentation
what are the benefits of producing ethanol from crude oil and ethene ?
- very fast method
- the products of hydration are already pure
- the method is a continuous process
what are the disadvantages of fermentation ?
-a very slow process
- products need to be distilled as it isn’t 100% pure
- batch process
state the overall equation for the hydration of ethene to produce ethanol ?
CH2 = CH2 + H2O —> C2H5OH
what reagent/ condition is essential for the hydration of ethene ?
a phosophuric acid catalyst must be added ( H3PO4)
show the hydration of ethene mechanism
picture is on your phone
how do you know that here was a catalyst present at the end of the hydration of ethene ?
because you are left with a H+ ion that was also there at the beginning
- this means it can be reused
state the overall equation for fermentation ?
C6H12O6 —->2 C2H5OH + 2 CO2
what are the reagents / conditions needed for fermentation ?
- yeast
- 35 degrees as a compromise because a high temp would speed up the reaction but also cause the enzymes to denature
- anaerobic conditions ( no oxygen )
- distillation of product to separate ethanol from the water as ethanol has a lower boiling point than water
what is happening in fermentation ?
it is the anaerobic respiration of the yeast
what would occur if oxygen was present during fermentation ?
ethanol would be oxidised and it would produce ethanoic acid
what is the boiling point of ethanol and what is the boiling point of water ?
ethanol = 78 degrees
water = 100 degrees
what does it mean if something is carbon neutral ?
carbon dioxide taken in during the process = the carbon dioxide released during a process
what is the process that takes in carbon dioxide needed for the process ?
photosynthesis
is the process y which carbon dioxide is released ?
fermentation + combustion of the alcohol produced
what is ethanol classified as ?
ethanol is a biofuel
in what reactions is ethanol most commonly used in ?
used in combustion reactions
what is the equation for the combustion of ethanol ?
C2H5OH + 6O2 —> 4CO2 + 6H2O
what happens to the CO2 in all of the 3 processes ?
CO2 in = CO2 out
why is the process of fermentation not completely carbon neutral even though it seems like it ?
because the processes involved in between the other processes such as transporting of the crops from one place to another releases co2 that is not considered in the equations
what are the 2 main alcohol reactions ?
- elimination reaction
- oxidation
what is meant by an elimination reaction ?
- a reaction where a small molecule leaves a parent molecule
what do alcohols always use in elimination reactions and other reactions ?
they always lose water (H2O)
the -OH is from the alcohol group
the -H is from the Carbon adjacent to the alcohol group
what are all elimination reactions with alcohols also known as ? and why ?
dehydration reactions
- as we lose water
what are the reagents and conditions for dehydration/ elimination reactions ?
- 600K
- Aluminium oxide catalyst (Al2O3)
what is the test to make sure that you made an alkene during elimination reactions ?
bromine water
goes from yellow / orange to colourless
what are the most common catalysts used in acid catalysed elimination ?
concentrated sulfuric acid (H2SO4)
concentrated phospohoric acid (H3PO4)
what does the dehydration / elimination of primary alcohols result in ?
1 alkene
what does the dehydration of a secondary alcohol result in ?
2+ alkenes
- due to isomeric products being made
wat does the dehydration of a tertiary alcohol produce ?
results usually in mixtures
what cannot happen to tertiary alcohols ?
they cannot be oxidised easily
what is meant by oxidation ?
oxidation is the
- gaining of oxygen
- loss of hydrogen
- loss of electrons
what does the oxidation of secondary alcohols result in ?
the oxidise to form ketones
what does the oxidation of primary alcohols result in ?
they oxidise to form aldehydes
- and then they can be oxidised further into carboxyllic acids
- or, under the right conditions, they can be directly oxidised to form carboxylic acids
what is added to the distillation flask and mixture ?
anti bumping granules
potassium dichromate
dilute sulfuric acid (H2SO4)
what is the function of anti bumping granules ?
ensures that the boiling is no too violent
what is the oxidizing agent in distillation ?
potassium dichromate
K2Cr2O7
why does distillation work to produce the aldehyde ?
the strongest attraction in aldehydes is dipole-dipole whilst the alcohols have hydrogen bonding which is the strongest intermolecular force
so alcohols have a higher boiling point
what are the conditions and reagents needed for the reflux reaction directly into a carboxylic acid ?
- conc H2SO4
- excess K2CR2O7
- reflux
what is the purpose of doing a reflux reaction ?
- it allows you to carry out a reaction at the boiling point of the chemicals without losing any reactants or products
what do you write instead of the formula for the oxidising agent in an oxidation equation ?
[O]
2 ways for testing for an aldehyde
- Warm , Fehling’s reagent
observation = red precipitate - warm Tollen’s
observation = silver mirror
testing for a carboxylic acid
-add Na2CO3 ( sodium carbonate) solution or powder
observation = effervescence (fizzing) due to CO2 being produced
testing for primary or secondary alcohols
- add (acidified )potassium dichromate (K2CR2O7) and H2SO4 and warm it
observation = orange to green colour change
test for ketones
add Fehling’s reagent or Tollen’s and warm it
observation = no visible change
to prove it is not an aldehyde
