Chem U4 AOS 2: Lab Analysis of Organic Compounds

End point

Colour change of chemical indicator during titration that acts as an estimate for the equivalence point

Equivalence point

Theoretical point at which the titrant and analyte are in their stoichiometric ratios

Wash standard (volumetric flask) with…

Deionised water only

Wash burette with…

Deionised water then solution

Wash pipette with…

Deionised water then solution

Wash conical (reaction) flask with…

Deionised water only

Give 2 examples of oxidising agents and their potential reducing agents

Oxidising agent: Potassium dichromate

Reducing agents: Iron (II) or potassium iodide

• Diphenylamine: Colour change green → violet

Oxidising agent: Potassium permanganate

Reducing agent: Iron (II)

• Self-indicating: Colour change purple → pale pink

Testing for C=C double bonds

• Bromine water test

• Potassium permanganate test

Bromine Water Test

Unsaturated - light brown/orange to colourless

Does not specify location or type of unsaturated bonds

Potassium Permanganate Test

Unsaturated - reduction of the purple KMnO4 solution to a colourless solution

Does not specify location or type of unsaturated bonds

Testing for hydroxyl groups

• Lucas test

• Acidified potassium dichromate test

• Acidified potassium dichromate followed by the Silver Mirror Test (Tollens’ test)

Lucas Test

Determine ANY alcohol present

Alcohol - when mixed with Lucas reagent (mixture of ZnCl(s) and HCl(aq)), will produce a cloudy liquid

Acidified potassium dichromate test

Partial oxidation occurs (determine primary alcohol to produce aldehyde)

Acidified potassium dichromate followed by the Silver Mirror Test (Tollens’ test)

1. If primary alcohol, partially oxidises into aldehyde with acidified potassium permanganate.

2. Aldehyde reduces with Tollens’ reagent.

3. Produces silver mirror-like substance is formed.

Tollens’ reagent (ammoniacal silver nitrate solution)

Distinguish between primary and secondary alcohols

Testing for carboxyl group

• Acid-base indicator test

• Reaction with metal carbonates or metal bicarbonates

• Esterification test

Acid-base indicator test

Adding an acid-base indicator (e.g. phenolphthalein) can identify the carboxyl group.

Carboxyl groups - Basic pink form to acidic colourless form

Reaction with Metal Carbonates or Metal Bicarbonates

Produce CO2(g) observed as bubbling

Type of neutralisation reaction where the carboxylic acid reacts with a base to form a salt, water and carbon dioxide.

Esterification test

Reacting with an alcohol and a strong acid (e.g. concentrated H2SO4) → ester

Sweet aromatic smell

How do impurities affect boiling point in substance?

Boiling point will be higher than known boiling temperature

• Impurities may have additional IMF

• Impurities decrease the vapour pressure of the compound - pressure exerted by the vapour in equilibrium with the liquid phase at a given temperature.