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5 6. Titration curves. A jump of titration and its importance for selecting an indicator. Input test-control on the topics «Concentration of solutions and acid-base titration». Homework exercises. 1. 10.8 ml of a 0.108 M solution of NaOH was used for titrating 10 ml of gastric juice. Calculate the normality of hydrochloric acid in gastric juice and its pHvalue. Answer : 0.117 mol/l; 0.93. 2. Titration of 5 ml of sodium hydroxide solution consumed 4.76 ml of 0.106 M hydrochloric acid. Calculate the normality and titer of the sodium hydroxide solution. Answer : 0.101 mol/l; 0.00404 g/ml. 3. TheKOHsamplewith amass of 1.2046g is dissolved in a 250ml volumetric flask. For titration of 20 ml of the resulting solution was used 14.82 ml of a 0.105M hydrochloric acid solution. Determine the content (in%) of KOH in the sample. Answer: 90.5%. 4. Titration of 45 ml of phosphoric acid required 28.3 ml of a 0.1 M solution of KOH. Write the equation of the reaction, calculate the pH value of the phosphoric acid’s solution, if degree of dissociation (α) is 0.035. Answer : 2.65. 5. A 10% solution of ammonium hydroxide, called ammonia, is used in medicine to excite the respiratory center. Titration of 10 ml of ammonia consumed 27.4 ml of 1 mol/l hydrochloric acid. Determine the pH value of 10% ammonia solution. ( K b (NH 4 OH) = 1.75×10 –5 ). Answer : 11.84. Laboratory work: Determination of the titer and molar concentration of the equivalent solution of soda by neutralization. Way of work: the exact concentration of (Na 2 CO 3 ) soda in the solution is determined by the titrimetric method. The titrant is a solution of nitric acid. For 10 ml of the analyzed solution, the measuring cylinder is transferred to four flasks for titration. Each solution is titrated from the burette with a solution of nitric acid in the presence of methylorange. Example of calculation: Test titration  V tr. = 13.0 ml Precise titration  V 1 = 12.2 ml V 2 = 12.1 ml Titration is considered accurate if the difference between the volumes is not more than 0.2 ml. 1 2 av. 3 (HNO ) 2 V V V + =