[sam12103]

43. A buffer is composed of 0.250 mol H2PO4- and 0.250 mol HPO42- diluted with water to a volume of 1.00 L. The pH of the buffer is 7.208. How many moles of HCl must be added to reduce the pH to 6.208?
a) 0.0455 mol    b) 0.063 mol    c) 0.125 mol    d) 0.187 mol    e) 0.205 mol

answer e

45. A volume of 25.0 mL of 0.100 M CH3CO2H is titrated with 0.100 M NaOH. What is the pH after the addition of 12.5 mL of NaOH? (Ka for CH3CO2H = 1.8 10-5)
a) 1.34    b) 2.87    c) 4.74    d) 5.12    e) 5.87

answer c



47. At what pH will a solution 0.150 M Cu2+ begin to precipitate as Cu(OH)2? The Ksp for
Cu(OH)2 is 1.6 10-19.
a) 1.80    b) 5.01    c) 7.23    d) 8.99    e) 13.18

answer: b


48. A solution contains 0.10 M Cl- and 0.10 M Br-. If Ag+ is added until AgCl just begins to precipitate, what are the concentrations of Ag+ and Br-?                                                                (Ksp for AgCl = 1.8 10-10, Ksp for AgBr = 3.3 10-13)
a) [Ag+] = 1.8 10-9 M, [Br-] = 3.3 10-12 M
b) [Ag+] = 1.8 10-9 M, [Br-] = 1.8 10-4 M
c) [Ag+] = 3.3 10-12 M, [Br-] = 1.0 10-1 M
d) [Ag+] = 3.3 10-12 M, [Br-] = 1.8 10-4 M
e) [Ag+] = 1.8. 10-9 M, [Br-] = 1.8 10-3 M


answer: b


Thank you guys very much, I really appreciate your help, and you please explain to me how to do these problems.

Thank you

[hobobot]

instead of making 3 threads and copy/pasting your quiz/test online . . . you should pick the problem you think is the hardest and tell us what you've tried so far. Then tell us why it's hard for you. I love helping, but my goal is to make sure you understand the concepts, not to give away answers.