This homework assignment is composed of questions on the first 3 problem sets. The exam will ask questions at a variety of levels of Blooms Taxonomy, i.e., some questions will require lower levels of understanding, while other questions will require you to evaluate a method or response. The length of this assignment will be about half of that of the midterms, however, this should take more than half the time (due to the difficulty of the material). If this is the first time your team is attempting to work on this assignment, I would not be surprised if you spent more than 2 hours on this assignment. Please don’t be discouraged. During an exam, students tend to go as fast as they can through the material. During homework, however, students tend to discuss and debate. This process takes more time. If you have been working on the problem sets, I would expect your group solution would take less than an hour to compose. Lastly, keep in mind that this assignment will be graded like an exam—you will receive partial credit throughout. Earning 80% will grant you full credit on the assignment, so please do not be discouraged if you miss a few points.
Letters in front of points correlate to level of Bloom’s Taxonomy
Acids base titration (25 points)
- We will titrate a benzoic acid solution with sodium hydroxide. The Ka of benzoic acid is 1.6 × 10−4. If you have 200. mL of 0.5 M acid solution and 15 M NaOH solution:
1.1.What is the initial pH before inputting any base? (U.6 points)
1.2.What volume of base is the equivalence point at? (U.3 points)
1.3.After you add 3.3 mL of NaOH, what are the major substituents in the solution? (Ap.4 points)
1.4.What is the pH of the resulting solution? (U.6 points)
1.5.Is the solution in 1.3 a buffer? Explain using 20 words or less. (U.6 points)
Producing gas from carbonates (20 points)
- You want to calculate how much CaCO3 is held inside of a tums tablet. The manufacturer says there is 1000 mg of active ingredient. To answer this question, you turned a tablet into powder then placed the compound into a graduated cylinder filled with acid. The carbonate would react with the acid producing carbon dioxide at a one to one ratio. The resulting balloon had a volume of 230 mL. Assume you performed this experiment at room temperatures. Answer the following questions:
2.1.What was the chemical equation for the reaction that took place? (R.3 points) (Note: label phases of matter)
- What is the law of mass action for the expression above? (U.3 points)
2.3. Do you expect the equilibrium constant to be greater than or less than 1? Explain your answer in 15 words or less. (U.4 points)
- Did the manufacturer create a product up to their specifications? Explain your reasoning in 30 words or less. (E.5 points)
2.5. What would the pH be if all the calcium carbonate reacted with HCl and bubbled out of solution? How do you know this? Explain your answer with 20 words or less. (An.5 points)
Intermolecular interactions (15 points)
- When calcium cations dissolve in water, there are generally 6 water molecules around it.
Bush, M.F., Saykally, R.J. and Williams, E.R. (2007), Hydration of the Calcium Dication: Direct Evidence for Second Shell Formation from Infrared Spectroscopy. ChemPhysChem, 8: 2245-2253.
- Draw the resulting structure in water. What are the dominating intermolecular interactions between the complexes? (U.5 points)
- Draw HF dissolved in water. What type of interactions dominate these solutions? (U.5 points)
- On your last midterm, many students wrote that NaCl dissolved in water destroying all bonding interactions. However, this is not so. What kind of interactions are still occurring? Are they strong or weak? Explain using relative strengths. Explain with 30 words or less. (U.5 points)