Alcohols, Aldehydes & Ketones Flashcards
What do alkanols belong to?
a larger family called the alcohols
What is the structure of alkanols based on?
the alkanes with the distinctive hydroxyl functional groups
What is the common alkanol ethanol made by?
fermentation
What is the word equation for fermentation?
sugar or starch ——– > ethanol + carbon dioxide
yeast
What is the enzyme found in the yeast?
zymase
What is the maximum concentration of ethanol that can be produced by fermentation?
12-15%
At higher concentrations of ethanol what happens to the cells in the yeast?
they are destroyed
To meet the high market demand, how is ethanol made?
by the catalytic hydration of ethene
What is the chemical equation for the catalytic hydration of ethene?
C2h4 +H20 —–> C2H5OH
What other kind of reaction is the catalytic hydration of ethene?
addition reaction
What can the hydration of some alkenes yield?
isometric alkanols
What is the general formula for the alkanols?
CnH2n+1OH
What does the type of intermolecular bonding influence?
the physical properties of molecular substances e.g. melting / boiling point, viscosity and solubility.
In terms of intermolecular bonding what type of bonds do alcohols have between their molecules?
hydrogen bonds
When compared to alkanes (non-polar) of similar mass, what do alcohols have?
a higher melting/boiling point higher viscosity water soluble (due to strong hydrogen bonds between the molecules)
What is a diol? (give an example)
an alcohol that has 2 hydroxyl groups e.g. ethan-1,2-diol
Why can the physical properties of ethan-1,2-diol (GFM 62g) be compared with the alkane butane (GFM 58g)?
because it has a similar mass
What is triol? (give an example)
an alcohol that has 3 hydroxyl groups e.g. propan-1,2,3-triol
Describe the relationship between the number of hydroxyl groups and the strength of hydrogen bonds?
The greater the number of hydroxyl groups the stronger the hydrogen bonds between the molecules
What effect does an alcohol with more hydroxyl groups have?
higher melting/boiling points
more viscous it will become
more soluble in water
Describe the combustion of alcohols?
burn in oxygen to produce carbon dioxide and water
Describe the dehydration of alkanols?
Alkanols can be converted to alkenes by dehydration
What alcohols be classed as?
primary
secondary
tertiary
How can you identify a primary alcohol? (give an example)
The carbon atom bonded to the hydroxyl group is bonded to one carbon atom e.g. ethanol
How can you identify a secondary alcohol? (give an example)
The carbon atom bonded to the hydroxyl group is bonded to two carbon atom e.g. butan-2-ol
How can you identify a tertiary alcohol? (give an example)
The carbon atom bonded to the hydroxyl group is bonded to three carbon atoms e.g. 2-methylpropan-2-ol
What is oxidation meant in terms of carbon compounds?
there is an increase in the oxygen to hydrogen ratio
Give example of oxidation and explain it?
CH3CH2OH > CH3CHO
Ethanol > Ethanal
Loss of these hydrogen atoms brings about an increase in the O:H ratio, therefore oxidation has taken place.
What is reduction meant in terms of carbon compounds?
There is a decrease in the oxygen to hydrogen ratio
Give example of reduction and explain it?
CH3CHO > CH3CH2OH
Ethanal > Ethanol
Gain of hydrogen atoms brings about a decrease in the O:H ratio, therefore reduction has taken place.
How can some alcohols be oxidised ?
by using a number of different oxidising agents
Give two examples of oxidising agents and the observation on oxidation from them?
Acidified potassium dichromate solution = changes from : orange > blue/green
Copper oxide = changes from black> red/brown
What are primary alcohols oxidised to?
alcohol> aldehyde> carboxylic acid
What are aldehydes?
carbon compounds that contain a carbonyl group, C=O, at the END of the chain of carbon atoms
What is the general formula for aldehydes?
CnH2nO
What are secondary alcohols oxidised to?
alcohols > ketones
What are ketones?
carbon compounds that contain a carbonyl group, C=O, on a MIDDLE carbon atom
What is the general formula for ketones?
CnH2nO
What are ketones based on?
an alkane structure and are referred to as alkanones
What are tertiary alcohols oxidised to?
They do not oxidise
How can unknown samples of aldehydes and ketones be distinguished?
They produce different results when mixed with oxidising agents
Describe how you can distinguish between unknown samples of aldehydes and ketones?
A sample of X and Y are mixed with the mild oxidising agent (acidified potassium dichromate) and placed in a warm water bath. The samples are observed for any signs of a chemical reaction. This procedure is repeated using other oxidising agents. The samples are not heated directly using a Bunsen Bruner because they are flammable
What is the colour change for acidified potassium dichromate?
orange > blue/green
What is the colour change for Benedict’s solution?
blue > orange/red
What is the colour change for Tollen’s reagent?
colourless > silver
What happens when food is exposed to the air?
many of the chemicals in the food react with oxygen and the food is spoiled.
What does oxygen which reacts with food do?
reacts with unsaturated edible oils to break them down
What does oxidation of food cause?
the deterioration of flavour (rancidity)
loss of colour
loss of nutritional value
a health risk from toxic oxidation products
What are antioxidants?
molecules which will prevent these oxidation reactions taking place
What do antioxidants do?
Antioxidants are easily oxidised by giving away electrons. They protect other compounds from oxidation as they themselves are more likely to be oxidised in the first instance.
Give 3 examples of antioxidants and state if they are natural and synthetic?
Vitamin C = Natural Vitamin E = Natural Butylated Hydroxyanisole (BHA) = synthetic
