Acids and bases review
Click on the links below to review Unit 2 information on acids and bases.
Some organic acids are carboxylic acid, phenol and ethanol. Each of these is able to donate a hydrogen - thus a Lowrey Bronsted acid by definition.
Most organic acids contain the carboxyl group- the donated H comes from this group. Most of the carboxylic acids are monoprotic (donates only one H to a base). These are weak acids.
These can react with bases to form a salt and water, or with carbonate bases to form salt, water and carbon dioxide gas.
Eg. Ethanoic acid and sodium bicarbonate:
CH3COOH + NaHCO3 → CH3COO−Na+ + CO2 + H2O
The most common organic bases contain amines (NH2). These groups will accept a H from acids. These are weak bases. Some typical examples are methylamine and ethylamine.
These can typically react with acids to form salts.
Eg, Ethylamine and hydrochloric acid form ethyl ammonium chloride.
C2H5NH2 + HCl ---> C2H5NH3Cl
Volumetric analysis of organic acids and bases.
Since organic acids and bases are weak, they need to be titrated against a strong acid or base. This will ensure a sharper endpoint.
When acids or bases are very weak a back titration can be used (no longer in the VCE chemistry)- see below.
Carboxylic group diagram by self made by Ben Mills at 20:04, 14 March 2006 (UTC).
Ethylamine diagram By Benjah-bmm27 (Own work) [Public domain], via Wikimedia Commons
Titration of a weak acid with a strong base.
Diagram courtesy of By Quantumkinetics - Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=14947161
Organic redox reactions
Titrations involving redox reactions can be used to determine amounts with organic compounds.
In these reactions hydrogenation and dehydrogenation occur - transfer of H2.
For example alcohols can be dehydrated (oxidised) to form aldehydes (see diagram).
Indicators used in these reactions must be highly colourled and must be a different colour in the oxidised and reduced form.
Potassium permanganate is often used in redox reactions as it changes from purple (KMnO4^-) to colourless (Mn^2+).
Alcohol oxidation By The original uploader was Hyper at English Wikibooks [Public domain], via Wikimedia Commons
Picture By Coloured-transition-metal-solutions.jpg: Benjah-bmm27 derivative work: Armando-Martin (Coloured-transition-metal-solutions.jpg) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons