Berry Berry Easy would like to present you with the Part 6 of the SPM Form 5 Chemistry notes on Carbon Compound in the series. For those who missed out on the first 5 parts, the first 4 parts were on alkane and alkenes. Previously on part 5, was on the non-hydrocarbon alcohol. This part focuses on non-hydrocarbon carboxylic acids. SPM students typically ace through alcohols but have slight problems on carboxylic acids. So Form 5 SPM students would have to brace the difficulty of this subchapter.
SPM Form 5 – Terminology and Concepts: Carbon Compounds
Non-Hydrocarbon – Carboxylic Acids
1. General formula: CnH2n+1COOH
- Where n = 0, 1, 2, 3 … (n = number of carbon)
2. Carboxylic acids are non-hydrocarbons which contain carbon, hydrogen and oxygen atoms.
3. The functional group in alcohols is carboxyl group, – COOH.
|Name of carboxylic acids||Molecular formula of alcohol|
|Methanoic acid(Formic acid)||HCOOH|
|Ethanoic acid(Acetic acid)||CH3COOH|
4. Physical properties of carboxylic acid
|Name||Molecularformula||Boiling point (°C)|
|Methanoic acid(Formic acid)||HCOOH||101|
|Ethanoic acid(Acetic acid)||CH3COOH||118|
- Solubility in water – generally in carboxylic acid (the less than four carbon atoms) are very soluble in water and ionise partially to form weak .
- Density of carboxylic acid – density of carboxylic acid increases due to the increases in the number of carbon atoms in a molecule.
- Boiling points – all carboxylic acid in general have relatively high boiling points than the corresponding alkanes. This is due to the presence of carboxyl group in carboxylic acid.
- Smell – carboxylic acid (< 10 carbon) are colourless and pungent smell. Carboxylic acid (>10 carbons) are wax-like solids.
5. Preparation of carboxylic acid
- Oxidation of an alcohol
The oxidation of ethanol is used to prepare ethanoic acid.
C2H5OH + 2[O] –> CH3COOH + H2O
Carried out by refluxing* ethanol with an oxidising agent
[acidified potassium dichromate(VI) solution – orange colour turns to green /
acidified potassium manganate(VII) solution – purple colour turns to colourless]
* reflux = upright Liebig condense to prevent the loss of a volatile liquid by vaporisation.
6. Chemical properties of carboxylic acid
- Acid properties
Ethanoic acid is a weak monoprotic acid that ionises partially in water (produce a low concentration of hydrogen ions).
CH3COOH <–> CH3COO- + H+
Ethanoic acid turns moist blue litmus paper red.
- Reaction with metals
Ethanoic acid reacts with reactive metals (copper and metals below it in the reactivity series cannot react with ethanoic acid).
(K, Na, Mg, Al, Zn, Fe, Sn, Pb, Cu, Hg, Au)
2CH3COOH + Zn –> Zn(CH3COO)2 + H2
In this reaction, a colourless solution (zinc ethanoate) is formed.
2CH3COOH + Mg –> Mg(CH3COO)2 + H2
In this reaction, a colourless solution (magnesium ethanoate) is formed.
- Reaction with bases
acid neutralises alkalis (sodium hydroxide).
CH3COOH + NaOH –> CH3COONa + H2O
In this reaction, a salt (sodium ethanoate) and water are formed.
- Reaction with carbonates
Ethanoic acid reacts with metal carbonates (calcium carbonate, magnesium carbonate, zinc carbonate).
2CH3COOH + CaCO3 –> Ca(CH3COO)2 + CO2 + H2O
In this reaction, a salt (calcium ethanoate), carbon dioxide and water are formed.
- Reaction with alcohols (Esterification)
Ethanoic acid reacts with alcohol (ethanol, propanol, butanol)
CH3CO-OH + H-OC4H9 –> CH3COOC4H9 + H2O (Concentrated H2SO4 is a catalyst)
In this reaction, an ester (colourless sweet-smelling liquid) (butyl ethanoate) and water are formed.
7. Uses of Carboxylic Acid
- Carboxylic acid (methanoic acid and ethanoic acid) is used to coagulate latex.
- Vinegar (dilute 4% of ethanoic acid) is used as preservative and flavouring.
- Ethanoic acid is used to make polyvinvyl acetate which is used to make plastics and emulsion paints.
- Benzoic acid is used as food preservative.
- Butanoic acid is used to produce ester (artificial flavouring).
Stay tune for the next part in the carbon compound series. So for SPM Form5 Chemistry students, do remember to check out Berry Berry Easy for more notes.