Chapter 14 (approved) Flashcards
Differences in physical properties between alcohols and alkanes with same number of carbon atoms (3)
Alcohols are less volatile
Alcohols have higher melting points
Alcohols are more soluble in water
As the length of the carbon chain increases, how do the differences between alcohols and alkanes change?
The differences become much smaller
Are alkanes polar/non-polar and why?
Non-polar as they only have C-C and C-H bonds, and C and H have very similar Electronegativity
What are the I.M. forces between non-polar molecules?
Very weak London forces
Are alcohols non-/polar and why?
Polar because of the electronegativity difference between O and H in the O-H bond
Why do alcohols have higher melting point and are less volatile than alkanes?
Alcohols have higher melting points and are less volatile as they have strong hydrogen bonds compared to the weak I.m. forces of alkanes so they require more energy to overcome
Why are alcohols soluble in water unlike alkanes?
Alcohols can form hydrogen bonds with the water molecules but alkanes can’t form hydrogen bonds
Why do longer chain alcohols become less soluble in water?
As the chain gets longer, the influence of the OH group becomes relatively smaller
How are alcohols classified?
As primary, secondary or tertiary based on how many carbons are attached to the carbon that is attached to the OH group
Combustion of alcohols
(3)
(In what situation do they burn and what does it form?
Endo/exothermic?
What affects the amount of heat released per mole?)
Alcohols burn completely in a plentiful supply of oxygen to make carbon dioxide and water
Exothermic
The longer the chain of the alcohol, the more heat released per mole
Conditions for primary alcohols to be oxidised to aldehydes
Gentle heating with acidified potassium dichromate, then the aldehyde is distilled out of the reaction mixture as it is formed to ensure that carboxylic acid isn’t prepared instead
Observation and by product when a primary alcohol is oxidised to an aldehyde
The dichromate ions, and therefore the solution changes colour from orange to green, and water is formed as well
Conditions for primary alcohols to be oxidised to carboxylic acids
The primary alcohol is heated strongly under reflux with excess acidified potassium dichromate, and a carboxylic acid is formed
Why are primary alcohols heated under reflux to form carboxylic acids?
To ensure that any aldehyde formed doesn’t escape before it is oxidised to a carboxylic acid
Why is excess K2Cr2O7 used when oxidising an alcohol to a carboxylic acid?
To ensure that all of the alcohol is oxidised
