Salt formation
Carboxylic acids react with bases, carbonates and reactive metals to form carboxylate salts.
- Reagents
- alkali, carbonate or reactive metal
- Conditions
- room temperature
- Reaction class
- acid-base reaction
- Equation
- RCO2H + NaOH -> RCO2Na + H2O
Overview
Carboxylic acids react with bases, carbonates and reactive metals to form carboxylate salts.
Transformation
Carboxylic acids → Carboxylate salts
- Equation
- RCO2H + NaOH -> RCO2Na + H2O
- Reagents
- alkali, carbonate or reactive metal
- Environment
- room temperature
- Reaction class
- acid-base reaction
- Mechanism
- proton transfer
- Evidence level
- textbook core
Reference procedure
Ethanoic-acid neutralisation and assay
Ethanoic acid + sodium hydroxide → sodium ethanoate + water
Materials and quantities
- Diluted ethanoic-acid sample or vinegar
- Standardised sodium hydroxide
- Suitable indicator such as phenolphthalein
Apparatus
- Burette
- Volumetric pipette
- Conical flask
Procedure
- Titrate a known sample volume and obtain concordant readings.
- Calculate acid amount using the 1:1 mole ratio, then account for dilution.
Work-up and isolation
- The neutralised solution contains dissolved sodium ethanoate; this analysis does not isolate a pure dry salt.
Critical controls
- The indicator endpoint should lie within the sharp pH change for a weak-acid/strong-base titration.
- Other titratable acids in vinegar would contribute to the result; an acid-equivalent concentration is not unique molecular identification.
Practical techniques
Acid–base titration
Use a known concentration and measured reacting volumes to determine acid or base content.
Setup
- Rinse measuring apparatus appropriately, remove burette-tip bubbles and record initial and final readings.
- Approach the endpoint dropwise while mixing, then repeat to obtain concordant titres.
- Apply the balanced-equation mole ratio and any dilution factor.
Operating checks
- Choose an endpoint within the steep part of the relevant titration curve.
- Concordant readings show repeatability; they do not remove concentration, calibration or endpoint bias.
Scope and limitations
- Scope
- Carboxylic acids form carboxylate salts with bases; carbonates release carbon dioxide and reactive metals release hydrogen.
- Limitations
- The displayed equation uses sodium hydroxide as the representative reagent; carbonate and metal equations have different by-products.
Related reactions
- Oxidation: Alcohols → Carboxylic acids
Full oxidation of a primary alcohol gives a carboxylic acid.
- Complete oxidation: Primary alcohols → Carboxylic acids
Full oxidation of a primary alcohol gives a carboxylic acid.
- Reduction: Carboxylic acids → Primary alcohols
Reduction of a carboxylic acid gives a primary alcohol.
- Oxidation: Aldehydes → Carboxylic acids
Oxidation of an aldehyde gives a carboxylic acid.
- Hydrolysis: Nitriles → Carboxylic acids
Nitriles can be hydrolysed to carboxylic acids, splitting the old aggregate nitrile-to-amide route into a single functional-group conversion.
- Activation for amide formation: Carboxylic acids → Amide chemistry
Carboxylic acids or activated acid derivatives connect to amide-bond formation.
- Esterification: Carboxylic acids → Esters
Carboxylic acids react with alcohols to form esters.
- Hydrolysis: Esters → Carboxylic acids
Hydrolysis converts esters back into carboxylic acid products.
- Chlorination: Carboxylic acids → Acyl chlorides
PCl5 converts carboxylic acids into acyl chlorides.
- Chlorination with thionyl chloride: Carboxylic acids → Acyl chlorides
Thionyl chloride converts carboxylic acids into acyl chlorides with sulfur dioxide and hydrogen chloride as by-products.
- Hydrolysis: Acyl chlorides → Carboxylic acids
Water hydrolyses acyl chlorides to carboxylic acids, releasing hydrogen chloride.
- Carboxylation: Grignard reagents → Carboxylic acids
Grignard carboxylation gives carboxylic acids after acidic work-up.
- Grignard carboxylation co reactant: Carbon dioxide → Carboxylic acids
Carbon dioxide plus a Grignard reagent gives a carboxylic acid after acidic work-up.
- Anhydride hydrolysis: Acid anhydrides → Carboxylic acids
Water attacks an anhydride carbonyl, and collapse of the tetrahedral intermediate breaks the acyl-oxygen linkage. Proton transfer gives carboxylic-acid products; a mixed anhydride yields two different acids.
References
- Pearson Edexcel Level 3 Advanced GCE in Chemistry specificationPearson Education Limited · Pearson qualifications · 2024
Supports the textbook-core organic reaction routes used for displayed route and mechanism content.
- Practical science: learning to investigateRoyal Society of Chemistry · RSC Education
Ethanoic-acid concentration in vinegar using sodium hydroxide and phenolphthalein; extension to quantitative titration.
- Titration: practical videos for 16–18 studentsRoyal Society of Chemistry · RSC Education
Accurate volumetric measurement, endpoints and concentration calculations.