Organics 2 - 5th Flashcards
what are alcohols?
- organic molecules containing an -OH functional group
alcohol naming
each alcohol has a name, in which:
- 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
name of CH3OH
methanol
name of C2H5OH
ethanol
name of C3H7OH
propanol
name of C4H9OH
butanol
method for the hydration of ethene
in this method, ethene (C2H4) gas is mixed with steam (H2O) under the following conditions:
- 300 degrees celcius
- 65 atm pressure
- phosphoric acid catalyst
raw material of the hydration of ethene
- crude oil provides the ethene
advantages of the hydration of ethene.
- makes pure ethanol
- can run continuously
disadvantages of the hydration of ethene
- conditions require a lot of energy
- non-renewable raw material used
method for the fermentation of glucose
- yeast - provides enzymes
- 30 degrees celcius - enzymes optimum temperature
- anaerobic - prevents oxidation
raw material of the fermentation of glucose
- sugar cane provides the glucose
advantages of the fermentation of glucose
- renewable raw material used
- conditions not energy-intensive
disadvantages of the fermentation of glucose
- makes impure ethanol
- must be done in individual batches
how is it decided which method to use
- depends mostly on the availability of crude oil or sugar cane in different parts of the world
what are the three ways of oxidising ethanol
- combustion
- microbial oxidation
- chemical oxidation
describe the combustion of ethanol
- ethanol tends to combust completely because of the oxygen atom in the -OH group
- this results in a non-luminous, blue flame
- C2H5OH + 3O2 -> 2CO2 + 2H2O
describe microbial oxidation.
- 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 if anaerobically, ie if 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
- C2H5OH + 2 [O] -> CH3COOH + H2O
describe chemical oxidation
- when we want to deliberately oxidise ethanol in the lab, we heat it with a mixture of:
- potassium dichromate (VI) (K2Cr2O7)
- dilute sulfuric acid (H2SO4) - this forms ethanoic acid and we use the symbol [O] to write an equation for the reaction
- C2H5OH + 2[O] -> CH3COOH + H2O
- as this occurs, the orange dichromate ions are turned into green chromium ions
- this means the reaction is always accompanied by the same colour change
- CrO7 2- -> Cr 3+
- orange to green
what are carboxylic acids?
- organic molecules containing an -COOH functional group
how does each carboxylic acid get named?
- the start of the name shows how many carbon atoms it has
- the end of the name is ‘-oic’ acid to show its a carboxylic acid
name of HCOOH
methanoic acid
name of CH3COOH
ethanoic acid
name of C2H5COOH
propanoic acid
C3H7COOH
butanoic acid
what is vinegar?
- an aqueous solution of ethanoic acid
how does vinegar form?
- when the ethanol in wine undergoes microbial oxidation
- C2H5OH + 2[O] -> CH3COOH + H2O
- vinegar has a very sour, acrid taste because of the acidity of ethanoic acid
- red wine vinegar is the tastiest variety of vinegar
what is an acid?
- a H+ donor
- so like all other acids carboxylic acids can donate H+ to form a salt
how does a carboxylic acid become a salt?
- the carboxylic acid group (COOH) loses its H+ and becomes negatively charged
- the name changes from an ‘oic acid’ in the carboxylic acid to ‘-oate’ in the salt
how do carboxylic acids react with metals?
- acid + metal -> salt + hydrogen
what can you observe in an carboxylic acid and metal reaction?
- effervescence: due to the hydrogen (H2) gas being produced
- solid disappears: due to the metal being used up in the reaction
- methanoic acid + sodium -> sodium methanoate + hydrogen
how can carboxylic acids react with metal carbonates?
- acid + metal carbonate -> salt + water + carbon dioxide
what can you observe in a carboxylic acid and metal carbonate reaction?
- effervescence: due to the carbon dioxide gas being produced
- solid disappears: due to the metal carbonate being used up in the reaction
- methanoic acid + sodium carbonate -> sodium methanoate + water + carbon dioxide
what are esters?
- a family of organic molecules which form when a carboxylic acid and an alcohol join together by losing an H2O molecule
where does the ester functional group sit?
- between two carbon chains, joining them together
- it doesn’t matter what those other carbon chains look like, so they’re represented by question marks in the diagram
example of a carboxylic acid and alcohol reaction
- carboxylic acid + alcohol -> ester + water
- ethanoic acid + ethanol -> ethyl ethanoate
what is the reaction between carboxylic acid and alcohol reaction sometimes called?
- condensation because of the production of water vapour
- or esterification because it becomes an ester
method to make an ester
- mix the carboxylic acid and the alcohol together
- add a few drops of concentrated sulfuric acid (H2SO4) which acts as a catalyst for the reaction
- warm it for a while
- tip the mixture into sodium carbonate (Na2CO3) solution. this neutralises the sulfuric acid catalyst, which is otherwise really corrosive. this reaction produces CO2(g) so you wait until the fizzing has stopped
what are esters?
- they are volatile compounds with distinctive smells that make them suitable for use in food flavourings and perfumes
how do you choose the correct arboxylic acid and alcohol to make a particular ester?
- draw it out and split it down the middle where the oxygen atom is in line with the carbon chain
what is a polyester?
- a polyester is a polymer made of lots of molecules joined together in a chain by ester groups
what do you need to do to make a polyester?
- you need to mix two types of monomer
- a dicarboxylic acid (has -COOH at both ends)
- a diol (has -OH at both ends)
- lots of monomers can then join up into a very long, alternating chain
why is this type of polymerisation called condensation polymerisation?
- every time a monomer joins the end of the chain, an H2O molecule is lost
- the carbon chains between the -COOH and -OH groups in the monomers don’t change, so you can create almost any polyester you want by choosing the right dicarboxylic acid and diol
how should you work out the structure of the repeat unit?
- the best way to start is to highlight the OH in the -COOH groups and the H in the -OH groups, and then get rid of them and join what’s left together
what are bipolyesters?
- some polyesters are biodegradable, which means microbes such as bacteria and fungi can use enzymes to break down the polymer into its monomers and use them as an energy supply
- this is obviously a good thing, because it reduces our reliance on landfill and incineration to dispose of used polyesters
