Chapter 15 Acid-Base Titration 1. A student dissolves 1.5013 grams of acetic acid (pK-4.74) in enough water to make 250.0 mL solution. 25.0 ml aliquot of the solution is then titrated against 0.100M NaOH solution. a) Find the initial pH of solution. b) Find the pH after the addition of 1.00 mL of the base. c) Find the volume of the 0.100 M NaOH needed to reach the equivalence point. d) Find the pH at the equivalence point. e) Find the pH after the addition of 20.00 mL of the base. f) Complete following table: pH (pH Units) Volume of base added (mL) 0.00 Half-equivalence Equivalence 30.00 g) Sketch a rough titration curve for the titration of the 25.0 ml of solution (S) with 0.100 M NaOH. Show on the on the curve the initial pH, the pH at halfway to the equivalence point, the pH at the equivalence point and the pH after the addition of 30.0 mL of the base. 12- 10- 8 PH 6 4 2 2 10 20 Volume of NaOH Added (ml.) 30 h) How would you select a proper indicator for this titration? i) Which of the following indicators is the best for the above titration? Justify your answer. Indicator pH Range рка Acid Form Base Form Methyl Orange 3.1-4.4 4.2 Red Yellow Bromocresol Green 3.8-5.4 4.7 Yellow Blue Methyl Red 4.2-6.2 5.0 Red Yellow Phenol Red 6.4-8.0 7.4 Yellow Red Phenolphthalein 8.0-9.8 9.7 Colorless Red 2. A 0.1276-g sample of an unknown weak monoprotic acid was dissolved in 250.0 mL of water and titrated with a 0.0633 M NaOH solution. The volume of the base required to bring the solution to the equivalent point was 18.4 ml. a) Calculate the molar mass of the acid. b) After 10.0-mL of base had been added during the titration, the pH was determined to be 5.87. What is the K, of the unknown acid? c) Calculate the pH of a 0.60 M solution of the unknown monoprotic acid.