Chemistry 2720 Practice Problems

Some of these problems may require data from the textbook or other sources for their solution.

1. Phosphoenolpyruvate (PEP) is an alternative energy storage compound formed from pyruvate in many living cells by reaction with phosphate:

   

   (All data in this question is given at 298K.) The physiological concentration of phosphate is approximately 3mmol/kg. The ratio of ATP to ADP in typical cells is about 10. What is the maximum ratio of PEP to pyruvate which can be maintained if the phosphate group is provided by ATP hydrolysis?

   

2. 1. Using the data at the end of this paper, predict the normal boiling point of water.
   2. What are the possible reasons that your answer might differ from the accepted value of C?
3. Derive the differential of H. Use it to relate to a state variable.
4. 1. The molar entropy of water at is and the specific heat capacity is . Derive an expression for the molar entropy at an arbitrary temperature T.
   2. Assume that is small and derive a polynomial approximation for the entropy. Keep all terms up to those in .
   3. Calculate the entropy using the exact equation and your polynomial approximation at a few different temperatures. How large can be if we want the error in the approximation to be no more than 1%?
5. HF is not ionic but forms strong hydrogen bonds to itself. What can you say about its activity coefficient in a polar solvent (such as water)?
6. Solutes always behave ideally when they are in sufficiently dilute solution. Estimate the ionic strength below which, at 298K, the Debye-Hückel corrections make little difference.
7. The solubility product of calcium oxalate ( ) is at 298K. Use Debye-Hückel theory to estimate the solubility of calcium oxalate in water. Report your answer in g/L. Is Debye-Hückel theory expected to be accurate for this problem?
8. In industry, water is often used as a coolant by running uninsulated pipes through the factory (where the water picks up heat) and then outside (where the water can release heat to the cooler air). The plant engineer comes to your office and tells you that he has been having trouble with the cooling pipes freezing in the winter. By his reckoning, the temperature in the pipes should never drop below C, provided you can keep the water moving. The cooling system contains 18t (1 tonne is 1000kg) of water. What mass of sodium chloride would you have to add to the cooling system to keep the pipes from freezing? The freezing point depression constant for water is .
9. Your highly varied career then takes you to the police forensic lab. One night (a dark and stormy one, no doubt), a police officer brings in a sample of a substance which she believes to be 3,4-methylenedioxyamphetamine (MDA, one of the many varieties of the street drug ``ecstasy''). The molecular formula of MDA is . Your supervisor just bought you a shiny new osmometer which you are itching to try out so you decide to determine the molecular weight of the unknown substance as a first step toward working out its structure. You dissolve 2.841mg of the sample in 100mL of water. The osmotic pressure of this solution at is 394Pa. Compute the molar mass of the unknown. Is it likely to be MDA?
10. Starch is a glucose polymer, i.e. a very large molecule made by stringing many glucose molecules together. The osmotic pressure of a starch solution is measured over a period of weeks. Between measurements, the solution is kept in a sealed container so that little evaporation takes place. It is observed that the osmotic pressure rises over time. Give a chemical interpretation of this phenomenon.

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