Carboxylic acids
No description yet. This curated deck is ready for daily study.
Card preview (24)
How would you name 3 carbons and a carboxyl group
Propanoic acid
How would you name 2 carbons with two carboxyl groups
EthanEdioic acid
Why are carboyxlic acids weak acids
They only slightly dissociate in aqueous conditions
Solubility in water
The smaller carboxylic (up to C4) acids dissolve in water in all proportions but after this the solubility rapidly reduces. They dissolve because they can hydrogen bond to the water molecules.
Strength of carboxylic acids
Increasing chain length pushes electron density on to the COO^- ion, making it more negative and less stable. This make the acid less strong. e.g. propanoic acid is acidic than ethanoic acid
Strength of carboxylic acids with halogens
Electronegative chlorine atoms withdraw electron density from the COOion, making it less negative and more stable. • This make the acid more strong. Chloroethanoic acid is more acidic than ethanoic acid
Salt formation reactions of carboxylic acids (Carboxylic acids can form salts with metals, alkalis and carbonates.)
Salt formation reactions of carboxylic acids This ones a metal 2CH3CO2H + 2Na –> 2CH3CO2 -Na+ + H2 acid + alkali (NaOH) salt + water CH3CO2H + NaOH–> CH3CO2 -Na+ + H2O acid + carbonate (Na2CO3) –> salt + water + CO2 2CH3CO2H + Na2CO3 –> 2CH3CO2 -Na+ + H2O + CO2
Oxidation of methanoic acid
Carboxylic acids cannot be oxidised by using oxidising agents, but methanoic acid is an exception as its structure has effectively an aldehyde group IIt forms carbonic acid (H2 CO3) which can decompose to give CO2
Esterification
Carboxylic acids react with alcohols, in the presence of a strong acid catalyst, to form esters and water. carboxylic acid + alcohol –(H+)–>ester + water
Naming for esters
Esters have two parts to their names, eg methyl propanoate. Propanoate comes from the carboxylic acid Methyl comes from the addition of the alcohol Extra: The bit ending in –yl comes fromthe alcohol that has formed it and is next to the single bonded oxygen. The bit ending in –anoate comes from the carboxylic acid and includes the C in the C=O bond.
Conditions for esterifcation
The reaction is quite slow and needs heating under reflux, The reaction is reversible.
What are esters
Esters are sweet smelling compounds that can be used in perfumes and flavourings.
Uses of esters
Esters can be used as solvents for polar organic substances. Ethyl ethanoate is used as a solvent in glues and printing inks Esters can be used as plasticisers for polymers.
How can esters be hydrolysed using the acid Including reagents + conditions
Esters can be hydrolysed and split up by either heating with acid or with sodium hydroxide i) with acid (This reaction is the reverse reaction of ester formation. When an ester is hydrolysed a carboxylic acid and an alcohol are formed.) reagents: dilute acid (HCl) conditions: heat under reflux
How can esters be hydrolysed Using the alkali Including reagents + conditions
ii) with sodium hydroxide reagents: dilute sodium hydroxide conditions: heat under reflux This reaction goes to completion. Using excess sodium hydroxide will ensure the ester is completely hydrolysed.
What happens if you add strong acid like HCl to the carboxylic acid salt
Convert the salt to the carboxylic acid form. CH3CH2CO2- Na+ + HCl –> CH3CH2CO2H + NaCl
Hydrolysis of ethyl benzoate
The liquid ethyl benzoate can be hydrolysed by sodium hydroxide by heating under reflux for 30 minutes. After the reaction is complete allow the mixture to cool to room temperature and add hydrochloric acid. A precipitate of benzoic acid will be produced that can be filtered off using suction filtration. C6H5COONa + HCl –> C6H5COOH + NaCl
Are both sodium benzoate and benzoic acid soluble
Sodium benzoate is soluble in water because it is ionic. Benzoic acid, however, is insoluble. This is because even though the polar COOH group can form hydrogen bonds, the benzene ring is non-polar.
What are fats and oils
Fats and oils are esters of glycerol and long chain carboxylic acids (fatty acids)
What are vegetable oils and animal fats hydrolysed into
soap, glycerol and long chain carboxylic (fatty) acids
Go to page 4 for how to see how something
https://chemrevise.org/wp content/uploads/2024/01/3.9-revision-guide-carboxylic-acids-and-derivatives-aqa.pdf
Use of glycerol and is it soluble
Glycerol (propane-1,2,3-triol) forms hydrogen bonds very easily and is readily soluble in water. It is used in cosmetics, food and in glues
What is biodiesel
A mixture of methyl esters of long chain carboxylic acids
How can biodiesel be made
Vegetable oils can be converted into biodiesel by reaction with methanol in the presence of a Potassium hydroxide