Practicum 1: Quantitative Analysis Acid And Base Method

PRACTICUM O1 QUANTITATIVE ANALYSIS: ACID AND BASE METHOD Brief Theory Titration is a procedure for determining the concentration of a solution by reacting a measured volume of the solution with another solution whose concentration is known (standard solution) in stages. The most fundamental and practical concept in acid-base chemistry is undoubtedly the neutralization reaction. Neutralization can be defined as the reaction between protons and hydroxide ions to form water. Acid-base titration is an example of volumetric analysis. The titrant is added little by little until it reaches the equivalence point. This situation is called the equivalence point. To obtain accurate titration results, the end point of the titration is chosen as close to the equivalent point as possible. This can be done by choosing the right indicator and in accordance with the titration to be carried out. The situation where the titration is stopped by observing a change in the color of the indicator is called the end point of the titration. The end point of the titration is the state where the reaction has run perfectly which is usually marked by visual observation through changes in the color of the indicator. An indicator is a weak acid or base that changes color between its ionized form and its non-ionized form. The range of use of the indicator is 1 pH unit around its pKa value. For example, phenolphthalein (PP) has a pKa of 9.4 (color changes between pH 8.4 – 10.4). The Phenolphthalein structure will undergo rearrangement in this pH range because protons are removed from the Phenol structure of PP so that the pH increases as a result there will be a color change. Hydroxy benzoic acid is an organic compound that has an acidity level that is strong enough to be titrated using basic primary standards using the phenolphthalein indicator. For the hydroxyl group attached to the benzoic acid core group at positionorthocan increase the ionization of the carboxylic acid group more than 100 times compared to the ionization of the hydroxyl group in the benzoic acid core group. The degree of ionization of the hydroxy group at positionmetaAndparaalmost the same as benzoic acid. Substitution of the hydroxyl group at the alkyl or aryl position does not have an ionization effect on the acid group. So it can be concluded that the hydroxy benzoate acid derivative and its carboxyl group derivatives are not substituted, their levels can be determined using the acid base method with the phenolphthalein indicator. Tools and materials A. Tools - Test tubes and test tube racks - Stirring rod - Beaker - separation funnel - pH indicators - Erlenmeyer - Vortex - Burette - Statives and Claims. B. Material - Oxalic acid - Aquadest - Sodium Hydroxide (NaOH) 0.1 N - Phenolphthalein (PP) indicator - Ethanol - Ether - HCl - Salicylic acid ointment Work procedures Determination of Salicylic Acid Levels using the acid-base titration method 1. Standardization of NaOH Carefully weigh 65 mg of oxalic acid then put it in an Erlenmeyer then add distilled water until dissolved. Then add PP indicator then titrate with 0.1 N NaOH until indicated by a color change from colorless to pink. N NaOH = Oxalic Acid Weight/BE oxalic acid x V NaOH 2. Blank Titration Pipette 10 mL of ethanol into the Erlenmeyer then add the PP indicator then titrate with NaOH until the end point of the titration is indicated by a color change from colorless to pink. Record the volume of NaOH that reacts with ethanol (blank volume) 3. Determination of salicylic acid from ointment preparations Weigh the sample then put it in a test tube, then add ether then vortex until homogeneous. The solution is then put inseparating funnel then add NaOH then extract until the salicylic acid is extracted. The extracted water phase is put into a separating funnel and then added HCl until the pH is acidic. Then add ether and then extract until the analyte is extracted. The ether phase is evaporated and the residue formed is dissolved in ethanol then titrated with 0.1N NaOH and PP indicator. N salicylic acid =N NaOH x (V NaOH – V blank) V sample grams of salicylic acid = N as.salicylate x BE as.salicylate x V sample % salicylic acid =grams of salicylic acid x 100% grams of sample