CHEM 1474 Test 3 Summer 1997

SHORT ANSWER: 2 points each. Fill in the blank with the most correct answer.

1. ___________________ is the name for the process of water molecules spontaneously separating into ions.

2. A(n) _____________ solution is one for which [H⁺] > [OH^-].

3. A(n) ________________________ acid is considered to be a proton donor.

4. A(n) ___________________ acid/base pair is a set of two chemical species for which the structure of the species vary by only the presence/absence of one hydrogen ion.

5. _________ is defined as the negative of the base ten logarithm of the concentration of the hydronium ion.

6. A(n) _____________ acid is one for which we assume complete dissociation of the proton from the anion.

7. For the pair of substances in (4) , we can say that K_a * K_b = ________________.

8. From a microscopic viewpoint, the ________________ (stronger/weaker) the acid, the weaker the bond between the hydrogen and the rest of the molecule.

9. The _________________ (smaller/larger) a metal ion is, the more likely a solution of that ion will be acidic.

10. The _________________________ effect is a subset of LeChatlier's Principle that applies to equilibria that contain ions.

11. The pH at the equivalence point for the titration of a strong acid with a strong base will = ___.

12. A(n) _________________ is a mixture that is resistant to a change in pH, and maintains a constant pH upon dilution. It is most commonly made up of a mixture containing both species discussed in (4).

13. The _________________________ constant (abbreviated K_sp) is simply an equilibrium constant that involves the dissociation of 'insoluble' ionic compounds.

14. The __________________________ of a slightly soluble salt is the moles of that salt that will dissolve to form a solution of exactly 1 liter.

15. If G is positive, we know that the equilibrium constant for the system is _____________ (greater than / equal to / less than) 1.PROBLEMS (Point totals are shown in parenthesis) Show your work and circle you answers where appropriate for full credit.

16. (15) Calculate the pH of the following solutions:

a) 0.025 M HClO₄

b) 0.025 M Na₂O

c) 0.025 M HCN

d) 0.025 M NaCN

e) 0.025 M NaClO₄

17. (15) Calculate the pH of the following solutions:

a) 75.0 mL 0.025 M benzoic acid mixed with 25.0 mL of 0.025 M sodium benzoate.

b) 75.0 mL 0.025 M benzoic acid reacted with 25.0 mL of 0.025 M sodium hydroxide.

c) 50.0 mL of 0.10 M HCl reacted with 50.0 mL of 0.10 M hydrazine (H₂NNH₂).

18. (10) Sketch the shape of the titration curve for the following titrations, labeling both axes and the equivalence point. If there is a single equivalence point, determine if this point is acidic, basic, or neutral. If there is more than one equivalence point be sure to label all equivalence points.

a) HC₂H₃O₂ titrated with NaOH b) NaCO₃ titrated with HCl

19. (15) Calculate the molar solubility of the following salts under the specified conditions:

a) CdS in water (K_sp = 8.0 x 10^-27)

b) AuCl₃ in water (K_sp = 3.2 x 10^-25)

c) Pb(OH)₂ in a buffer of pH = 10.00 (K_sp = 1.2 x 10^-15)

20. (15) The formation constant for the reaction Cu²⁺ + 4NH₃ [Cu(NH₃)₄]²⁺ is 5 x 10¹².

a) Calculate G for this reaction.

b) What is G for this reaction at equilibrium?

c) Calculate G for this reaction if [Cu²⁺] = 0.00050; [NH₃] = 0.050; and [Cu(NH₃)₄]²⁺ = 1.5 M

EXTRA CREDIT (10) What is the lowest concentration of sodium ion we could have in 100.0 mL of solution?