3.5 Alcohols Flashcards
what are alcohols?
- a compound with an -OH group, with a general formula CnH2n+1OH
do alcohols have generally high or low boiling points?
- high, due to their ability to form hydrogen bonds between alcohol molecules
why can smaller alcohols dissolve in water?
- they can form hydrogen bonds to water molecules
what are the three types of alcohols?
- primary, secondary and tertiary
what is the oxidising agent used to oxidise alcohols?
- potassium dichromate
- K2Cr2O7
give the reagent, reaction and conditions for the partial oxidation of primary alcohols
reaction - primary alcohol into aldehyde
reagent - potassium dichromate solution and dilute sulfuric acid
conditions - warm gently and distil out the aldehyde as it forms
what is the observation for oxidation of primary alcohols?
- the orange dichromate ion reduces the green Cr3+ ion
when writing oxidation equations, how do we express the oxidising agent?
[ O ]
what is distillation?
- a technique used to seperate an organic product from its reacting mixture
how can we maximise the yield collected from distillation?
- collect the distillate at the approximate boiling point of the desired aldehyde and not higher
why are electrical heaters often used to heat organic chemicals?
- because organic chemicals are normally highly flammable and could set on fire with a naked flame
how can we help improve the yield of the distillate?
- collection flask can be cooled with ice
what are the main parts of the distillation equipment?
- thermometer
- liebig condenser
- water out then water in
- round bottomed flask
- collection flask
what are the reagents, conditions and reaction for the full oxidation of primary alcohols
reaction - primary alcohol to carboxylic acid
reagent - potassium dichromate solution and sulfuric acid
conditions - excess dichromate, heat under reflux
distill off product after reaction finished
what is the equation for full oxidation of primary alcohol
RCOH + 2[O] > RCOOH + H2O
when is reflux used?
- when heating organic reaction mixtures for long periods
how does the condenser work in reflux!
- prevents organic vapours from escaping by condensing them back to liquids
why should you never seal the end of the condenser
build up of gas pressure could cause the apparatus to explode
why are antibumping granules added to the flask?
- to prevent vigorous, uneven boiling by making small bubbles form instead of large bubbles
give the reaction, reagents and conditions for oxidation of secondary alcohols
reaction - secondary alcohol to ketone
reagent - potassium dichromate solution and dilute sulfuric acid
conditions - heat under reflux
why cant tertiary alcohols be oxidised?
- no hydrogen atom bonded to the carbon with the -OH group
how can i distinguish between aldehydes and ketones?
tollens’ reagent or fehling’s solution
how can tollens reagent be formed?
- mixing aqueous ammonia and silver nitrate
- the active substance is the complex ion of [Ag(NH3)2]+
give the reaction and observation for tollens reagent
- aldehydes only are oxidised by tollens reagent into a carboxylic acid
- silver ions recues to silver atoms
- a silver mirror forms inside test tube
give the reaction and observations for fehlings solution
- aldehydes only are oxidised by Fehling’s solution into a carboxylic acid
- copper ions reduced to copper oxide
- Blue copper ions change to red precipitate of Cu2O
how can the presence of a carboxylic acid be tested?
- addition of sodium carbonate
- it will fizz and produce CO2
what is meant by dehydration reaction?
- removal of a water molecule from a molecule
give the reaction, reagents conditions and role of reayent for the reaction of alcohols with dehydrating agents
reaction - acid catalysed elimination
reagent - concentrated sulfuric acid or phosphoric acid
conditions - warm (under reflux )
role of reagent - dehydrating agent
give the equation for alcohol to alkene in acid catalysed elimination
alcohol > alkene + water
draw on a sheet of paper the acid catalysed elimination mechanism
arrow from lone pair on O: to H+
positive O formed gaining a H
arrow from C-O bond to O+
arrow from C-H to C-C+
C=C forms
what are the two ways of producing ethanol
- fermentation and from ethene
give the conditions and type of reaction for production of ethene from fermentation
- yeast
- no air
- temperatures 30-40
fermentation
why is the optimum temp 38 for fermentation?
- lower temps reaction is too slow
- high temps the yeast dies and enzymes denature
why is fermentation done in an absence of air?
- presence of air can cause extra reactions to occur
- it oxidises the ethanol produced to ethanoic acid
what are the advantages of fermentation?
- sugar is a renewable resource
- production uses low level tech/ cheap equipment
what are the disadvantages of fermentation?
- batch processs which is slow and gives high production costs
- ethanol made is not pure and needs purifying
- depletes land for growing crops
give the reagent and type of reaction for production of ethene from industry
reagent - ethene - from cracking of fractions
reaction - hydration / addition
what are the essential conditions for production of ethene from industry
- high temperature at 300*
- high pressure 70atm
- strong acidic catalyst of conc H3PO4
what are the advantages of ethene from industry?
- faster reaction
- purer product
- continuous process
what are the disadvantages of production of ethene from industry
- high tech equipment needed
- expensive
- high enery costs for pumping to produce high pressures
- non renewable
