ANSWERS TO PROBLEMS

A1

Chapter 1

1. The hydrogen-bond donors are the NH and NH₂ groups. The hydrogen-bond acceptors are the carbonyl oxygen atoms and those ring nitrogen atoms that are not bonded to hydrogen or to deoxyribose.

2. Interchange the positions of the single and double bonds in the six-membered ring.

3. (a) Ionic interactions; (b) van der Waals interactions.

4. Processes a and b.

5. ΔS_system = −661 J mol⁻¹ K⁻¹(−158 kcal mol⁻¹K⁻¹)

ΔS_surroundings = +842 J mol⁻¹K⁻¹(+201 cal mol⁻¹K⁻¹)

6. (a) 1.0; (b) 13.0; (c) 1.3; (d) 12.7

7. 2.88

8. 1.96

9. 55.5 M

10. 11.83

11. 447; 0.00050

12. 0.00066 M

13. 6.0

14. 5.53

15. 6.48

16. 7.8

17. 100

18. (a) 1.6; (b) 0.51; (c) 0.16.

19.

20. 0.1 M sodium acetate solution: 6.34; 6.03; 5.70; 4.75. 0.01 M sodium acetate solution: 5.90; 4.75; 3.38; 1.40.

21. 90 mM acetic acid; 160 mM sodium acetate, 0.18 moles acetic acid; 0.32 moles sodium acetate; 10.81 g acetic acid; 26.25 g sodium acetate.

22. 0.50 moles of acetic acid; 0.32 moles of NaOH; 30.03 g of acetic acid; 12.80 g of NaOH.

23. 250 mM; yes; no, it will also contain 90 mM NaCl.

24. 8.63 g Na₂HPO₄; 4.71 g NaH₂PO₄

25. 7.0; this buffer will not be very useful, because the pH value is far from the pK_a value.

26. +1.45 kJ mol⁻¹ (+0.35 kcal mol⁻¹); +57.9 kJ mol⁻¹ (+13.8 kcal mol⁻¹)

27. There will be approximately 15 million differences.

28. (20!)/(10!*10!) = 184,756

29. 7.9%