Answer Happy

Include all units Trial 3 0.10 Standardizing a Sodium Hydroxide Solution Trial 1 Trial 2 Mass of KHP 0.693 0.699 Volume of NaOH(aq) 36.5 mL 31.06 31L Molarity of NaOH(aq) 0.0929 Average Molarity Include all units Part 1: Molar Mass Determination of the Unknown Acid Using the Indicator Phenolphthalein Include all units Sample Number #70729 Sample size determination: Mass of HA 0.1019 Volume of NaOH 5.5ml Sample size Trial 1 Trial 2 Trial 3 Mass of HA 0.642 0.642 0.644 Volume of NaOH(aq) 34.2 34.4 32.7 Molar Mass of HA Average Molar Mass of HA as determined by the Phenolphthalein Titration data Part 2: Molar Mass and pk. Determination of the Unknown Acid Using Titration Curve Trial 1 include all units Mass of HA 0.643 0.643 Volume of NaOH(aq) at Equivalent Point Molar Mass of HA Average Molar Mass of HA as determined by the Titration Curve True value of Molar Mass provided by grader Trial 1 Trial 2 Volume of NaOH at Half-equivalence Point pH at Half-equivalence Point Trial 2 PK Average pK, for HA True value of pK provided by grader post-lab questions on other side Lab 8. Determining the Ka and Molar Mass of an Unknown Acid
Post-Lab Questions Submit your answers in the spaces provided below. Do not submit any calculations. Mass of unknown acid: 32.00 ml Molar Mass: 1. A student found that the molar mass calculated from the phenolphthalein data was very different from the molar mass found using the titration curve. A summary of the data follows: Concentration of NaOH: 0.101 M Phenolphthalein Titration Data 0.7458 Volume of NaOH at endpoint: 231 g/mol Titration Curve Data Mass of unknown acid: 0.732 g Volume of NaOH at endpoint: 37.00 ml. pH at Equivalence Point 9.39 Molar Mass: 196 g/mol 1. Assuming that all calculations were correct and that no experimental mistakes were made, which of these molar masses is closer to the true molar mass? Explain. Hint In your explanation include a discussion on how phenolphthalein changing color around pH 8 would affect the results. b. Other indicators also exist that have endpoints at different pHs. Use the internet and find an Indicator that would be appropriate for this student's sample. Fill in the following information about this indicator name of indicator transition pH range color before endpoint color after endpoint 2. Hydrogen cyanide, HCN, is a very weak acid (K 6.2 x 10-6). If a 500 ml sample of 0.100 M HCN is titrated with 0.100 M NaOH. determine the pH of the resulting solution... a. after 8.00 ml. of 0.100 M NaOH has been added. b. at the half-equivalence point of the titration, c. at the cquivalence point b. 21. report all pH values to no decimal places Lab 8: Determining the Ka and Molar Mass of an unknown Acid