Chemistry Department / Analytical Chemistry / Student Number:
3rd Hr Exam
Dec, 2015
Answer The Following Questions:
1. Indicate whether each of the following statements is true (T) or false (F)
1. / ( ) / In Mohr method for chloride determination, the medium should be acidic.2. / ( ) / Performing a back titration is a good choice to overcome the problem of slow reactions.
3. / ( ) / The concentration of the indicator in Volhard's method should be much smaller than theoretically predicted.
4. / ( ) / EDTA metal chelates usually have higher stability than complexes with multiple monodentate ligands.
5. / ( ) / Phenolphthalein is an acid base indicator that can be used in the pH range from 0-14.
2. Calculate the pH of a 0.1 M NaHC2O4 solution (Ka1 = 6.5*10-2, Ka2 = 6.1*10-5, kw = 1*10-14).
3. Find the pH of the solution resulting from mixing 20 mL of 0.1 M NaOH and 80 mL 0f 0.1 M Na3PO4 ((Ka1 = 1.1*10-2, Ka2 = 7.5*10-8, Ka3 = 4.8*10-13)
4. A 20 mL of 0.1 M diprotic acid (H2A) was titrated NaOH, requiring 15 and 30 mL of the base to reach the first and second end points. Addition of 7.5 mL and 22.5 mL of the base to 20 mL of the acid solution resulted in pH values of 1.9 and 4.6, respectively. Find the equilibrium constants of the diprotic acid.
H2A D HA- + H+
HA- + H2O D A2- + H+
5. Find the concentration of Mg2+ in a 20 mL of 0.1 M MgCl2 solution adjusted to pH 10 after addition of 20 and 30 mL of 0.1 M EDTA. Kf = 5*108, a4 at pH 10 = 0.35.
Mg2+ + Y4- D MgY2-
6. Find the pI in a 20 mL solution of a 0.1 M NaI after addition of 20 mL of 0.1 M AgNO3 (ksp (AgI) = 1*10-16)
AgI(s) D Ag+ + I-
7. Find the concentration of copper ion in a solution containing 0.1 M Cu2+ and 1.2 M NH3 (kf1 = 2.5*104, kf2 = 4*103, kf3 = 6.6*102, kf4 = 1.1*102).
Cu2+ + 4NH3 D Cu(NH3)42+
8. A 0.342 g feed sample was digested using concentrated sulfuric acid. The solution was treated with excess NaOH and the generated ammonia was collected in dilute boric acid. The borate required 25 mL of 0.1 M HCl to reach the end point, calculate the percentage protein in the sample (mg protein = mg N * 6.25, and AW N = 14.0).
9. Find the pH of the solution resulting from mixing 50 mL of 0.1 M H2CO3 (ka1 = 4.3*10-7 and ka2 = 4.8*10-11) with 100 mL of 0.1 M NaOH.
10. Calculate the solubility of PbS (ksp = 3*10-28, Ka1 = 1*10-7, Ka2 = 1*10-14) in a solution adjusted at pH 4.
PbS(s) D Pb2+ + S2-
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