A suppose that you wanted to determine the standard

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(a) Suppose that you wanted to determine the standard enthalpy of formation of this compound. Describe an experimental method you could use for this purpose. Explain what you would measure and how you would calculate the enthalpy of formation. Show any necessary equations. State clearly what additional data you would need. [11 marks] (b) For the dissociation of the first proton, the apparent (i.e., not considering nonideal effects) K a in aqueous solution is 1 1 . 26 × 10 - 8 at 25 C and an ionic strength of 0.002 mol/L. What is the value of the thermodynamic equilibrium constant? Assume that the undissociated acid behaves ideally. [7 marks] (c) At an ionic strength of 2.00 mol/L, the apparent K a is 2 . 75 × 10 - 8 . What is the mean ionic activity coefficient at this ionic strength? [2 marks] 2 Answer all questions in this section. Value of this section: 52 All questions in this section relate to work done in the laboratory of Hans-J¨urgen Hinz, whose group in M¨unster has been studying the formation of DNA double strands using short (12-base) complementary single-stranded sequences. 1. In one set of experiments, they studied the binding equilibrium for the following com- plementary sequences: 2 5’-TAG GTC AAT ACT-3’ 3’-ATC CAG TTA TGA-5’ 1 M. E. Krahl, J. Phys. Chem. 44 , 449 (1940). 2 E. Carrillo-Nava et al., J. Phys. Chem. B , 114 , 16087 (2010). 2
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The following data were obtained: T/ C 10 15 20 25 K/ 10 8 3.19 2.82 2.25 1.10 Calculate the standard enthalpy, entropy, and free energy of reaction. [11 marks] 2. Explain the meaning of the sign of the standard entropy of reaction. Is this sign in agreement with your expectations? Explain briefly. [2 marks] 3. Calculate the equilibrium concentrations of single and double strands at 25 C in an experiment starting with 4 μ mol / L of each single strand. [9 marks] 4. In another set of experiments, they studied the kinetics of double-strand formation by stopped-flow kinetics for the following complementary pair: 3 5’-ATC CTC AAT ACT-3’ 3’-TAG GAG TTA TGA-5’ Briefly explain how a stopped-flow apparatus would be used to study this reaction.
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  • Fall '07
  • Roussel
  • Chemistry, J. Phys, vitamin C., Barbital

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