Alcohols (lesson 7) Flashcards
What affects the activity of a functional group?
the position in the carbon chain
What is a primary carbon atom?
a carbon that is attached to the functional group and at least 2 hydrogen atoms
What is a secondary carbon atom?
a carbon that is attached to the functional group and to 1 hydrogen atom and 2 alkyl groups
What is a tertiary carbon atom?
a carbon that is attached to the functional group and to 3 alkyl groups (attached to no other hydrogen atoms)
Why do alcohols produce hydrogen bonding? Hence, describe MP and BP compared to hydrocarbons of similar molar mass.
they contain -OH groups which as a result gives them relatively high MP and BP compared to hydrocarbons of similar molar mass.
Describe Alcohol’s solubility?
alcohols will dissolve readily in water but as the carbon chain increases, solubility decreases.
What does the strength of hydrogen bonding depend on?
it depends on the extent to which the -OH group is exposed and available for bonding.
Why are the physical and chemical properties different for the types of alcohols? Give an example.
although all three classes have some common properties, the position of the -OH group varies. Primary alcohols have the most exposed -OH, whereas tertiary alcohols have the least exposed -OH. Primary alcohols have the highest boiling points compared to secondary and tertiary.
What reactions do alcohols undergo?
combustion, oxidation, dehydration, substitution, esterification
Compare the release of energy in a combustion reaction between a small alcohol and a larger alcohol.
during combustion, alcohols burn in oxygen to produce CO2, H2O and large amounts of energy. The release of energy per mole of alcohol increases as the alcohol’s carbon chain increases, due to the increase number of CO2 molecules being produced. Therefore, a larger alcohol will have a bigger difference in the ration between alcohol and the production of CO2. Hence, there will be an increase in the molar enthalpy of combustion.
What is the Molar Heat of Combustion?
it is the heat that is produced when 1 mole of the substance undergoes complete combustion with oxygen (burnt in excess oxygen) at 100kPa and 25oC with products being carbon dioxide gas and liquid water.
What is enthalpy or heat of a reaction?
The exchange of heat energy between the system and its surroundings under constant pressure. (ΔH)
What is the enthalpy of combustion of a fuel?
The enthalpy change that occurs when a specified amount of the fuel burns completely in oxygen.
What happens to energy during a combustion reaction?
Chemical energy is converted to thermal energy.
q=mcΔT
Where: q is the amount of heat energy in joules (J), m is the mass of the solution heated in grams (g), c is the specific heat capacity in Jg-1K-1 and ΔT is the temperature change in K.
ΔH=-q/n
Where: molar heat of combustion of fuel (alkanol), q is the heat content of the solution heated and n is the moles of fuel used in combustion
What happens during the oxidation of an alcohol?
The alcohol molecule reacts with an oxidising agent (usually acidified potassium dichromate: +[O],heat)
Which oxidises the carbon atom attached to the -OH group.
Oxidation of a primary alcohol.
They first form an aldehyde and then a carboxylic acid.
What happens when you need to collect an aldehyde and not the carboxylic acid (vice versa)?
To collect an aldehyde, you would carry out a distillation experiment, as aldehydes have lower BP. To collect a carboxylic acid, the aldehyde would be oxidised for longer and then you would complete a reflux reaction.
What colour is H+/Cr(VI) —> Cr(III)?
Orange —> green
Oxidation of a secondary alcohol.
They oxidise in one step and form a ketone.
Oxidation of a tertiary alcohol.
They do not produce a reaction or colour change and would need a lot more energy to break the carbon skeleton in order to oxidise.
What happens in a dehydration reaction of alcohols?
When undergoing dehydration, alcohols loose water and form an alkene, but only when heated with concentrated sulphuric acid.
