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Dissociation equilibrium (with the Cobra3 Chem-Unit)

Product No: P3030940

Principle

Carboxylic acids are potential electrolytes which exist in a weakly dissociated condition in aqueous solutions. The location of the dissociation equilibrium is quantitativly described by the K_a or pK_a value which can be determined with potentiometric measurements.

Tasks

Measure the alteration of the pH value during a titration of approximately 0.1 molar aqueous solutions of formic acid, acetic acid, monochloroacetic acid, propionic acid, butyric acid and lactic acid with a 0.1 molar sodium hydroxide solution at constant temperature using Cobra3 system.
From the neutralisation curves read the pK_a values of the acids and compare them.

What you can learn about

True and potention electolytes
Strong and weak acids
Law of mass action
Henderson-Hasselbalch equation
Dissociation constant and pK_a value
Substituent effects
Potentionmetry

Materiallist (Excerpt)	Product	Amount
Set of Precision Balance Sartorius CPA 623S and measure software, 230 V	49224-88	1
Cobra3 Set automatic titration, 230 V	43040-88	1
Buffer solution, pH 4.62 1000 ml	30280-70	1
Buffer solution, pH 9 1000 ml	30289-70	1
Storage flask for pH electrodes,filled with 250 ml 3.0 M KCl solution	18481-20	1
Caustic soda sol.,0.1M 1000 ml	48328-70	1
Acetic acid 99...100%, pure 1 l	31301-70	1
Propionic acid, 500 ml	31753-50	1
N-butyric acid 100 ml	30047-10	1
Water, distilled 5 l	31246-81	1
Monochloroacetic acid 100 g	30060-10	1
Formic acid 98-100% 250 ml	30021-25	1
Lactic acid 100 ml	30264-10	1
Pipette dish	36589-00	1
Pipettor	36592-00	1
Pasteur pipettes, 250 pcs	36590-00	1
Volumetric flask 100 ml, IGJ12/21	36548-00	6
Rubber caps, 10 pcs	39275-03	1
Glass beaker DURAN®,tall, 150 ml	36003-00	1
Glass beaker DURAN®, tall, 50 ml	36001-00	2
Microspoon, steel	33393-00	1
Volumetric pipette, 5 ml	36577-00	6
Wash bottle, plastic, 500 ml	33931-00	1
Laboratory Experiments Physics, Chemistry, Biology andApplied Sciences, CD-ROM, incl. operating manuals	16502-42	1