B3.4 - Alcohols
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What is the complete combustion of alcohols?
products: carbon dioxide and water exothermic reaction when balancing take one oxygen away before you work out how many O2 you need
Why do alcohols have a relatively low volatility compared to similarly sized alkanes?
harder for alcohol to turn into gas due to stronger intermolecular forces
Explain the solubility of alcohols in water.
as the hydrocarbon chain increases in size, the influence of the -OH group becomes relatively smaller therefore solubility in water decreases
Explain the polarity of alcohols.
alcohols have a polar O-H bond because of the electronegativity of the oxygen and hydrogen atoms therefore alcohol molecules are polar
What is the functional group for alcohols?
-OH
What is the suffix of alcohols?
-ol
What is the general formula for alcohols?
CnH2n+2O
What is the rule when naming alcohols involving vowels?
if the suffix starts with a vowel e.g. -ol then the alkane name is shortened e.g. butan is the suffix does not start with a vowel e.g. -diol then the alkane name is not shortened e.g. butane
What is the rule about the placement of the alcohol group when naming alcohols?
put alcohol group on lowest position carbon
Why do alcohols have a higher boiling point than alkanes?
alcohols can form hydrogen bonds hydrogen bonds are stronger than London forces therefore require more energy to overcome
Why does the difference in boiling point between alkanes and alcohols decrease?
as both alcohols and alkanes chain length increases, boiling point increases due to stronger London forces importance of hydrogen bonding in OH group decreases therefore difference in boiling point between alcohols and alkanes decrease
What is the strongest type of intermolecular force in alcohols?
hydrogen bonding
What is meant by the term volatility?
how easily a substance turns into a gas
Why are alcohols more soluble in water than alkanes of similar chain length?
they are polar molecules capable of forming hydrogen bonds with water alkanes are non-polar, therefore cannot form these bonds - insoluble
What is the oxidising mixture used to oxidise alcohols?
acidified potassium dichromate (VI) solution
What colour is acidified potassium dichromate (VI) solution?
orange due to the +6 oxidation state of the Cr in K2CrO7
What is acidified potassium dichromate (VI) solution a mixture of?
dilute sulphuric acid, H2SO4, and K2CrO7
What happens when acidified potassium dichromate (VI) oxidises something else
chromium itself is reduced and the solution turns green
Which types of alcohols can be oxidised?
primary and secondary NOT tertiary
REDOX reaction in term of oxygen
Oxidation - gain Reduction - loss
REDOX reaction in terms of hydrogen
Oxidation - loss Reduction - gain
What can primary alcohols do when oxidised?
form 2 products can control which product is made by controlling the reaction conditions
What are the names of the different products formed when primary alcohols are oxidised?
Aldehyde Carboxylic acid
What are the conditions required to form an aldehyde?
heat gently with acidified potassium dichromate (VI) distil product immediately