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7 will the pH value change when the solution is diluted two-fold? Is it possible to prepare acetate buffer with pH = 6.5 if K a (CH 3 COOH) = 1.75×10 –5 ? 4. What volumes of solutions of ammonium hydroxide (C = 0.05 mol/l) and ammonium chloride (C = 0.05 mol/l) should be taken to prepare 1 liter of 0.05 M ammonia buffer pH 8.54? pK b = 4.76. 5. The solution of HCl (1.5 ml of a 0.02 mol/l) was added to 1.5 ml of blood. The pH value was changed from 7.4 to 7.2. What is the buffer capacity of blood for acid? Questions for self-study. Gas solubility: Henry’s law, Dalton’s law, Sechenov’s law. Laboratory work: Experience number 1. Preparation of acetate buffer systems In three tubes, prepare 5 ml of acetate buffer solution, mixing the solutions of 0.1 M acetic acid and 0.1 M sodium acetate according to the table: No. of mixture 1 2 3 V (0.1 mol/l СН 3 СООН), ml V (0.1 mol/l СН 3 СООNa), ml 0,5 4,5 1,5 3,5 4,5 0,5 Methyl red pH Solutions of acid and salt are taken from burettes. Add 3 drops of the indica- tor – methyl red in each tube and observethe color in the table. Calculate the pH of each of the three buffer solutions using the Henderson- Hasselbach equation: рН р lg solt solt а acid acid С V К С V ⋅ = + ⋅ , where pK a (CH 3 COOH) = 4.76. The results of calculations are entered in the table. Experiment 2. The effect of acid, alkali and dilution on the pH of the buffer solution In four tubes, prepare 2 ml of acetate buffer solution: mix 1 ml of 0.1 M acetic acid and 1 ml of 0.1 M sodium acetate (pour from the respective burettes).). Then add 5 drops of 0.1 M HCl to the first of the tubes, add 5 drops of 0.1 M NaOH tothe second tube, and add 5 drops of distilled water to thethird tube, and leave the fourth tube for comparison. In each tube add 2 drops of the indicator – methyl red. Compare the color of solutions in four test tubes. Make a conclusion.