C3- alcohols, carboxlic acids and esters Flashcards
What are alcohols?
The alcohols are a homologous series of organic compounds. They all contain the functional group –OH. This group is responsible for the properties of alcohols.
The names of alcohols end with ‘-ol’ – eg ethanol.
What are the first three alcohols in the homologous series?
The first three alcohols in the homologous series are methanol, ethanol and propanol.
What are the use of methanol, ethanol and propanol?
These alcohols are highly flammable, making them useful as fuels. They are also used as solvents in marker pens, medicines, and cosmetics (such as deodorants and perfumes). Ethanol is the alcohol found in alcoholic drinks such as wine and beer. Ethanol is usually mixed with petrol for use as a fuel
What is the structural formula of methanol?
CH3OH (small 3)
What is the structural formula of ethanol?
CH3CH2OH (small numbers)
What is the structural formula of propanol?
CH3CH2CH2OH (small numbers)
What are the properties of methanol, ethanol and propanol?
They are colourless liquids that dissolve in water to form a neutral solution (pH7).
They react with sodium to produce hydrogen and a salt. For example:
ethanol + sodium → hydrogen + sodium ethoxide
They burn in the air, releasing energy and producing carbon dioxide and water.
Why is the reaction of alcohol with sodium similar to the reaction of water with sodium?
This reaction is similar but less vigorous to the reaction of water with sodium. This is due to the similarity in structure between water and the –OH group in alcohols.
What are the carboxylic acids?
The carboxylic acids are a homologous series of organic compounds. They all contain the same functional group –COOH.
The names of carboxylic acids end in ‘-oic acid’ – eg ethanoic acid.
What is the structural formula of methanoic acid?
HCOOH
What is the structural formula of ethanoic acid?
CH3COOH (small 3)
What is the structural formula of propanoic acid?
CH3CH2COOH (small numbers)
What is vinegar?
Vinegar is an aqueous solution containing ethanoic acid.
How is ethanoic acid formed?
Ethanoic acid is formed from the mild oxidation of the ethanol (which is an alcohol). This can be achieved through:
The addition of chemical oxidising agents - such as acidified potassium dichromate. The action of microbes in aerobic conditions (in the presence of oxygen). This happens on a small scale when a bottle of wine is left open and exposed to air. On a commercial scale, it is achieved in a fermenter using acetic acid bacteria.
What are the properties of carboxlic acids?
They dissolve in water to produce acidic solutions (pH less than 7).
They react with carbonates to produce carbon dioxide and a salt and water. For example:
calcium carbonate + ethanoic acid → calcium ethanoate + water + carbon dioxide
They all react with alcohols, in the presence of an acid catalyst, to form esters. For example:
ethanol + ethanoic acid → ethyl ethanoate + water
What will strong acids do when dissolved in water?
Strong acid, such as hydrochloric acid, ionise fully in water:
HCl(aq) → H+(aq) + Cl–(aq)
Their aqueous solutions have a high concentration of hydrogen ions, H+. This gives them a low pH.
What will weak acids do when dissolved in water?
Carboxylic acids are weak acids. They do not completely ionise when they are dissolved in water. Instead only some of their molecules ionise to form H+ ions:
CH3COOH(aq) Equilibrium symbol CH3COO–(aq) + H+(aq)
This means that an aqueous solution of a weak acid will have a higher pH compared to the same concentration of an aqueous solution of a strong acid.
What are esters?
Esters are a group of organic compounds which all contain the functional group –COO–.
What properties do esters have in common?
they are volatile - they are liquids that become vapours easily
they have distinctive ‘fruity’ smells
What are the uses of esters?
very useful as food flavourings, and as perfumes in cosmetics. Some esters are obtained from natural sources, such as fruits. Others are manufactured.
How do you make Ethyl ethanoate?
Ethyl ethanoate is the ester made from ethanol and ethanoic acid. Sulfuric acid is added to act as a catalyst in the reaction.The distinctive smell of ethyl ethanoate (which is like modelling glue) can be detected as the reaction proceeds. Excess ethanoic acid in the reaction mixture is neutralised with sodium hydrogencarbonate, then a few drops of the mixture added to water so that the smell can be detected more effectively.
What is the equation for the reaction between ethanol and ethanoic acid?
ethanol + ethanoic acid (double arrow)ethyl ethanoate + water
CH3CH2OH(aq) + CH3COOH(aq) (double arrow) CH3CH2OOCCH3(aq) + H2O(l)
How do you name esters?
The first part of an ester’s name comes from the alcohol - it ends with the letters ‘yl’. The second part of its name comes from the carboxylic acid - it ends with the letters ‘oate’
