Alcohols Flashcards
what are alcohols?
organic molecules containing an -OH functional group
what does the name of an alcohol tell us?
- the start of the name shows how many carbon atoms it has
- the end of the name is ‘-ol’ to show it is an alcohol
what is the chemical formula for methanol and how many carbons does it have?
CH3OH - one carbon
what is the formula for ethanol and how many carbons does it have?
C2H5OH - two
what is the formula for propanol and how many carbons does it have?
C3H7OH - three
what is the formula for butanol and how many carbons does it have?
C4H9OH - four
when the -OH group is attached to the middle of the carbon chain in a displayed formula what do we do to the name of the alcohol?
we include a number in the name to indicate where its attached
what are the three main categories of formula used to represent alcohols on paper?
- molecular formula
- displayed formula
- structural formula
what does the molecular formula show?
each element, once only - doesn’t show the structure of the molecule at all
what does the displayed formula show?
every atom and every bond, all drawn out - perfectly shows the structure of the molecule, but takes a while to draw
what does the structural formula show?
a balance between showing the structure of the molecule but not taking too long to draw
how many methods are there for the industrial ethanol manufacture?
two:
- hydration of ethene
- fermentation of glucose
method for hydration of ethene
in this method, ethene gas is mixed with steam under the following conditions:
- 300 degrees C
- 65 atm pressure
- phosphoric acid catalyst
raw material:
- crude oil provides the ethene
advantages of hydration of ethene method?
- makes pure ethanol
- can run continuously
disadvantages of hydration of ethene method
- conditions require lots of energy
- non-renewable raw material used
method for fermentation of glucose
in this method, glucose is fermented microbiologically under the following conditions:
- yeast (provides enzymes)
- 30 degrees celcius which is optimum temperature for enzymes
- anaerobic which prevents oxidisation
raw material:
- sugar cane provides the glucose
advantages of fermentation of glucose
- renewable raw material used
- conditions not energy intensive
disadvantages of fermentation of glucose
- makes impure ethanol
- must be done individual batches
what does the method depend on for ethanol manufacture?
the availability of crude oil or sugar cane in different parts of the world
what are the three ways ethanol can be oxidised?
- combustion
- microbial oxidation
- chemical oxidation
ethanol combustion method
- ethanol tends to combust completely because of the oxygen atom in the -OH group
- this results in a non-luminous, blue flame
ethanol microbial oxidation method
- many micro-organisms, such as bacteria and fungi, can use the oxygen in the air to oxidise ethanol into ethanoic acid
- this can only happen aerobically (the micro-organism is growing in the presence of air)
- we can represent the microbial use of oxygen in an equation using the [O] symbol
chemical oxidation method
- when we want to deliberately oxidise ethanol in the lab, we heat it with a mixture of: potassium dichromate(VI) and dilute sulfuric acid
- as with microbial oxidation, this forms ethanoic acid and we use the [O] symbol to write an equation for the reaction
- as this occurs, the orange dichromate(VI) are turned into green chromium(III) ions
- this means the reaction always has the colour change orange to green
