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A 25.0 mL sample of an unknown acid in water is titrated with 0.1 M NaOH (aq) and resulted in the following data. Note: phenolphthalein indicator and a pH probe were used to monitor pH. Volume (ml) 0.1 M NaOH pH Observed colour 0 3.54 2.5 3.89 5 4.19 7.5 4.55 10 4.64 12.5 5.23 15.0 5.56 17.5 6 20.0 10.8 22.5 12.09 25.0 12.37 27.5 12.61 30.0 12.81 Based on the data above, answer the following questions. 1. What is your estimate of the pka of the unknown acid based on this data? Report your answer to 2 decimal places (i.e., 1.23)

2. Identify the unknown acid. A table of pka values can be found here Submit Answer Tries 0/13 3. What is the % error in your estimated pka as compared to the literature value? Report your answer to 1 decimal place (i.e., 1.2) Submit Answer Tries 0/13 4. Assign the letter to the correct label on the graph for your identified acid. 14 12 10 8 폼 G A 4 2 0 0 10 25 30 35 15 20 Volume (mu B с endpoint Өрка @ half-titration point Submit Answer Tries 0/13

Acid Name Acid formula pka oxalic acid HOOCCOOH 1.23 chloroacetic acid CIH2CCOOH 2.87 nitrous acid HNO2 3.37 lactic acid C2H5OCOOH 3.86 benzoic acid C6H5COOH 4.2 acetic acid CH3COOH 4.75 propanoic acid C2H5COOH 4.87 potassium hydrogen phthalate (KHP) KC8H504 5.4 carbonic acid HOCOOH 6.37

5. a)Which of the following statements are TRUE for a buffer solution. Select all that are True. When a strong acid is added to a buffer, it reacts with the conjugate base which slightly increases the pH of the solution. A buffer can be prepared by combining a weak acid and its conjugate base." A buffer resists changes in pH. Submit Answer Tries 0/13 b) The extent that a buffer can resist changes in pH when acid or base is added is called the Submit Answer Tries 0/13 6. When the following solutions are combined, is a buffer created? H2CO3 (aq) + NaHCO3(aq) CH3COOH (aq) + NaCH3COO (aq) H3PO4 (aq) + HPO42- (aq) Submit Answer Tries 0/13 7. Given the following data set: Indicate where the buffer capacity has been exceeded. Solution Грн Change in pH Acetic acid (25 mL) 2.88 Sodium acetate 7.46 Mixture (50 mL) 4.70 After 5 ml NaOH 4.90 0.20 After 10 ml NaOH 5.13 0.23 After 15 ml NaOH 5.42 0.29 After 20 ml NaOH 5.95 0.53 After 25 mL NAOH 11.17 5.22 The buffer capacity was exceeded when @ mL of NaOH was added. Submit Answer Tries 0/13