OBSERVATION: A pink colour will appear once the indicator has been added and when heated the pink colour will disappear.
EXPLANATION: This reaction is the hydrolysis of an ester; the pink colour disappears as the ester has completely reacted with NaOH and forms the salt of sodium.
HAZARDS: Phenolphthalein- 2^irritant^2. NaOH- 1^harmful^1 and 3^corrosive^3.
PHENOLS:
Phenol has the formula of C6H5OH, its structure consists of an OH group attached to a benzene ring.
APPARATUS: Unknown compound, ferric chloride (iron III chloride).
METHOD: Add 5 drops of ferric chloride to the unknown.
OBSERVATION: An intense violet-purple colour appears.
EXPLANATION: 2The iron (III) ions form strong coloured complexes with the phenol.2
HAZARDS: FeCl3- 1^harmful^1 and 3^corrosive^3. Phenol- 3^corrosive^3 and 4^toxic^4.
CARBOXYLIC ACIDS:
Carboxylic acids are products of the oxidation of a primary alcohol or an aldehyde. Their functional group is –COOH.
APPARATUS: Unknown compound, water, limewater, NaHCO3.
METHOD: 3Add water and NaHCO3 to the unknown compound.3
OBSERVATION: Effervescence occurs after NaHCO3 is added; test the gas with limewater and it will go cloudy.
EXPLANATION: Carboxylic acids although weak acids react like any other acid and undergo the same reactions. So CO2 is produced when reacted with NaHCO3.
HAZARDS: NaHCO3- 2^irritant^2.
CARBONYL COMPOUNDS:
Carbonyl compounds consist of the C=O bond, examples are aldehydes, ketones and esters. However the 2,4-DNPH test is only positive for aldehydes and ketones.
APPARATUS: Unknown compound, 2,4-DNPH.
METHOD: Add 5 drops of 2,4-DNPH to the unknown in a test tube.
OBSERVATION: A deep yellow/ orange precipitate appears.
EXPLANATION: 4See diagram below. 4
HAZARDS: 2,4-DNPH- 1^harmful^1, 5^highly flammable^5 and 7^explosive^7.
ALDEHYDES:
Aldehydes and ketones have a C=O bond and give a positive result for the above test, however in this test only aldehydes give a positive response.
APPARATUS: Unknown compound, Tollens’ reagent (aqueous solution of ammoniacal silver nitrate).
METHOD: Add Tollens reagent to the unknown in a test tube and heat.
OBSERVATION: Silver mirror will appear.
EXPLANATION: 5Silver mirror appears as the silver (I) ion is reduced to silver metal.5
HAZARDS: Tollens’ reagent- 1^harmful^1.
ALCOHOLS:
Alcohols contain the hydroxyl group, OH.
APPARATUS: Potassium dichromate, sulphuric acid, water bath.
METHOD: Add 2cm3 of K2Cr2O7 and H2SO4 to 2cm3 of the unknown and gently boil.
OBSERVATION: A colour change will occur from orange to green or will remain orange.
EXPLANATION: 6The colour change shows that the unknown is a primary alcohol which has now been oxidised. The orange dichromate (VI) ion, Cr2O72-, is reduced to green chromium (III), Cr3+. If the solution has remained orange it proves the presence of a tertiary alcohol as they cannot be oxidised.6
Another test can be carried out to confirm the presence of a tertiary alcohol, it is known as Lucas’ test.
APPARATUS: Lucas’ reagent: a solution of ZnCl2 in concn HCl.
METHOD: Add 2cm3 of Lucas’ reagent to 1cm3 of the unknown and shake.
OBSERVATION: A cloudy emulsion may be seen rapidly or no reaction may occur after 5 minutes.
EXPLANATION: 7The reagent dissolves the alcohol and removes the OH group leaving a carbocation. The cloudiness is caused as the carbocation reacts with Cl- forming a chloroalkane. Tertiary alcohol is present if the emulsion forms rapidly and a primary alcohol if no reaction occurs.7
HAZARDS: K2Cr2O7- 4^toxic^4 and 6^oxidising^6. H2SO4- 1^harmful^1 and 3^corrosive^3. Lucas’ reagent- 4^toxic^4 and 3^corrosive^3.
FLOWCHART:
APPENDIX
HAZARDS:
BIBLIOGRAPHY:
1. http://home.att.net/~cat6a/org_chem-X.htm
2. http://www.chemguide.co.uk/organicprops/phenol/other.html
3.http://www.wellesley.edu/Chemistry/chem211lab/Orgo_Lab_Manual/Appendix/ClassificationTests/carboxylic.html
4. Chemistry 2. Ratcliff and Eccles .Pg 25.
5. http://www.wpbschoolhouse.btinternet.co.uk/page13/ChemicalTests/ChemicalTests.htm
6. Chemistry 1. Ratcliff and Eccles. Pg.131.
7. http://en.wikipedia.org/wiki/Lucas_reagent
8. Hazards: http://ptcl.chem.ox.ac.uk/~hmc/hsci/chemicals/hsci_chemicals_list.html
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