475

8 Experiment 3. Influence of dilution on buffer capacity In a flask, prepare 15 ml of acetate buffer with pH 0 = 5 (mix 9.6 ml 0.1 mol/l CH 3 COONa and 5.4 ml 0.1 mol/l CH 3 COOH). 5 ml of the solution is transferred to another flask and add to this volume 5 ml of distilled water. Both solutions are gently titrated with 0.1 M NaOH in the presence of a methyl red indicator (3 drops) until the lemon-yellow color appears (pH = 6.2). Titration is repeated 2 times. The average alkali volume is taken for calculation. Calculate the buffer capacity of solutions in alkali (mmol/l) according to the formula: С NaOH  – normality of alkali solution, mol/l; V NaOH  – volume of alkali solution needed for titration, l; V buff  is the volume of the buffer solution, l; pH 0  and pH 1  – the pH value of the buffer, respectively, before and after the addition of alkali to it. Experience № 4. Determination of the buffer capacity of blood serum Pour 5 ml of blood serum (рH 0 = 7.36) in two flasks for titration. Then two drops of phenolphthalein indicator are added to one flask and titrated with 0.1 M NaOH until a weak pink staining (pH 1 = 9.1). Two drops of methyl orange are added to the other flask and titrated with 0.1 M HCl until orange-pink staining appears (pH 2 = 3.7). Calculate the buffer capacity of blood serum for alkali and acid by the formulas: Based on the results obtained, make a conclusion. LESSON 4. COLLATIVE PROPERTIES OF SOLUTIONS: LAWS OF RAUL AND VANT-GOFF Required base level. Molarity, molality, mole fraction. The boiling point and freezing point of water. Dissociation of acids, bases, salts. Questions for the preparation for the lesson. 1. Colligative properties of dilute solutions of nonelectrolytes: Raoult’s laws, Van’t Hoff’s law. NaOH NaOH 1 0 1000 (рН рН ) alk buff С V b V ⋅ ⋅ = − NaOH NaOH 1 0 1000 (рН рН ) alk buff С V b V ⋅ ⋅ = − HCl HCl 0 2 1000 ; (рН рН ) acid б С V b V ⋅ ⋅ = −