Carboxylic Acids Flashcards
What is the general formula for Carboxylic Acids?
CnH2nO2
Describe the process of naming Carboxylic Acids
- Select longest chain containing -COOH
- Change the ‘e’ suffix to ‘-oic acid’
- No number needed as it’s always at the end
- If substituent present then name C stretched to -COOH as C1
- For dicarboxylic Acids use suffix ‘-edioic acid
- For complex Carboxylic acids use suffix ‘carboxylic acid’
Describe the physical properties of Carboxylic acids
- Polar due to presence of O atoms
- low RMM = water soluble
- pungent, sharp, irritating odours
- in pure liquid state they are H-bonded dimers
- H bonding is stronger than in alcohols
- higher b.ps than alcohols
- more soluble than alcohols, aldehydes or ketones
When and Why do Carboxylic acids exist as H-bonded dimers
- In the pure liquid state in non-aqueous solvents
2. Due to polar OH group which allows H bonding between molecules
Why do Carboxylic acids have higher boiling points in comparison to alcohols?
Stronger intermolecular forces
What happens when water is the solvent for Carboxylic acids
- the dimers are broken up as the polar OH group allows for H-bonds with water molecules
- Each Carboxylic acids can form up to 3 H-bonds with water molecules
Why are Carboxylic acids more soluble than alcohols
Each Carboxylic acid molecule can form up to 3 H-bonds with water molecules
Draw the H-bonding in pure ethanoic acid
See pg 136
Draw the H-bonding in aqueous ethanoic acid
See page 136
Name the 3 ways to prepare Carboxylic acids
- Oxidation of primary alcohols or aldehydes
- Hydrolysis of esters
- Hydrolysis of Nitriles
Describe briefly how to prepare propanoic acid
Heat under reflux propan-1-ol or propanal with acidified potassium dichromate (VI) solution
Write the structural equations for the preparation of a Carboxylic acid using oxidation of propan-1-ol and pronanal
See page 136
What are the two types of hydrolysis of esters?
- Acid catalysed hydrolysis
2. Base catalysed hydrolysis
Describe how to prepare a Carboxylic acid via acid catalysed hydrolysis. Why is this a poor method
- Reflux ester with an excess of water and dilute HCl
2. Reversible and some ester left unhydolysed
Draw the equation for acid catalysed hydrolysis of an ester. What are the products
See notes
Products are Carboxylic acid and alcohol
Describe base catalysed hydrolysis (saponification). Why is it a good method for producing Carboxylic acid
- Reflux ester with NaOH(aq)
- Sodium salt of acid produced
- Acid liberated from salt via addition of strong acid
Good because irreversible
Draw the equations for base catalysed hydrolysis of ester. State the products
See notes for equation
Products = salt of acid and alcohol and NaCl
Describe acid based hydrolysis of nitriles
Heat under Reflux with strong acid (HCl)
Water
Write the equation for acid catalysed hydrolysis of nitriles and state the products
See notes
Products = Carboxylic acid ammonium salt
Describe alkaline catalysed hydrolysis of nitriles
- Reflux with strong alkali
- Produces salt and ammonium
- Acid liberated from salt by addition of strong acid
Write the method for carrying out test tube reactions of a Carboxylic acid with sodium carbonate, sodium hydroxide and aqueous ammonia and measure pH changes
- 1cm^3 Carboxylic acid in boiling tube
- Record pH (pH paper)
- Add spatula measure of sodium carbonate and record obs
- Record pH (pH paper)
- Repeat but with 1cm^3 sodium hydroxide
- Repeat using 1cm^3 aqueous ammonia
Write the general equation for Carboxylic acid with sodium carbonate. State the observations
Acid + Carbonate ➡️ salt + water + CO2
Obvs: bubbles of gas
Carbonate disappears to form colourless solution
Write the general equation of Carboxylic acid with sodium hydroxide. State the observations
- Acid + alkali ➡️ salt + water
2. Heat released, colourless solution
Write the product and observations when a Carboxylic acid is reacted with ammonia
- Ammonia salt formed
2. Heat released and all is colourless
