Analytical Chemistry

Analytical Chemistry

Part I Multiple Choice Questions (2 points each)
1.- Which of the following pairs of compounds and ions could be used to form a buffer solution? (a) 0.10 M HCl and 0.10 M NaCl (b) 0.10 M NH4Cl and 0.10 M NH3 (c) 0.10 M HNO2 and 1.0 x 10-4 M NaNO2
2.- Sulfurous acid (H2SO3) has pKa1 = 1.91 and pKa2 = 7.18. At what pH does [HSO3-] = [SO32-]? (a) 1.91 (b) 4.54 (c) 7.18
3.- In the following reaction, identify the conjugate acid and conjugate base: NO2- + H2O ↔ HNO2 + OH-. (a) HNO2, OH- (b) NO2-, H2O (c) NO2-, HNO2
4.- The predominant for dissolved CO2 in water at pH 13.25 is: (a) CO2 (b) H2CO3 (c) HCO3- (d) CO32-
5.- 4. Sulfurous acid (H2SO3) has pKa1 = 1.91 and pKa2 = 7.18. At what pH does [HSO3-] = [SO32-]?
(a) 1.91 (b) 4.54 (c) 7.18
6.- Calculate the hydrogen ion concentration of a 0.100 molar solution of chloroacetic acid. Ka for chloroacetic acid = 1.36 x 10-3. (a) 0.0117 molar (b) 0.0369 molar (c) 7.39 x 10-12 molar
7.- Which is the strongest base? (a) HCl (b) CH3NH2 (c) RbOH
8.- The equivalence point of a titration is defined as (a) the point of the titration where the indicator changes. (b) the actual measured volume of titrant required to complete a titration. (c) the volume associated with actual stoichiometric quantity of titrant required to complete a titration.
9.- Iron in the +2 oxidation state reacts with potassium dichromate to produce Fe3+ and Cr3+ according to the equation 6Fe2+ + Cr2O72- + 14H+ → 6Fe3+ + 2Cr3+ + 7H2O. How many milliliters of 0.1658 M K2Cr2O7 are required to titrate 200.0 mL of 0.2500 M Fe2+ solution? (a) 50.26 mL (b) 301.6 mL (c) 8.290 mL
10.- A solution of sodium sulfate was found to have a pNa+ of 5.83. What is the sulfate concentration of the solution? (a) 7.40 x 10-7 molar (b) 1.48 x 10-6 molar (c) 7.66 x 10-1 molar
11.- Which statement concerning titrations is incorrect? (a) The titration error can be accounted for by running a blank titration. (b) The titrant is a primary standard after standardization. (c) The endpoint and equivalence point are not the same.
12.- An activity coefficient (a) measures the deviation of behavior of ions from ideality. (b) is obtained by multiplying the concentration of a solution times the ionic strength. (c) replaces the concentration term in chemical calculations. It corrects for the ionic strength of the solution.
13.- Given the chemical equilibrium HC2H3O2 + H2O ↔ C2H3O2- + H3O+, which of the following best represents the mathematical expression of this equilibrium. (a) [H3O+][C2H3O2-]/HC2H3O2 = Ka (b) [H3O+]γH3O+ [C2H3O2-]γC2H3O2-/HC2H3O2 γHC2H3O2 = Ka (c) [H3O+][C2H3O2-]/HC2H3O2 = Ka γa
14.- A solution contains a 0.100 M Al(NO3)3 and 0.100 M MgCl2.
Which of the following represents the correct charge balance equation for this system? (a) 3[Al3+] + 2[Mg2+] = [NO3-] + [Cl-] (b) [Al3+] + [Mg2+] + [H+] = 3[NO3-] + 2[Cl-] + [OH-] (c) 3[Al3+] + 2[Mg2+] + [H+] = [NO3-] + [Cl-] + [OH-]
15.- The amino acid glycine (H2NCH2COOH) has two equilibrium constants, one for the -COOH group, and one for the -NH3 group. pKa for -COOH = 2.350 and pKa for -NH3 = 9.778.
At pH 6.06, which compounds or ions predominate in solution? (a) A mixture of H3NCH2COOH and H3NCH2COO- (b) A mixture of H3NCH2COO- and H2NCH2COO2- (c) H3NCH2COO- only
Part 2 SHORT PROBLEMS (10 points each, show work for full credit)
16.- Calculate the ratio of ethyl amine (CH3CH2NH2) to the ethyl ammonium ion (CH3CH2NH3+) in a solution with a pH of 11.0. pKa for CH3CH2NH3+ = 10.636. (a) 2.31 (b) 10.81 (c) 0.432
17.- How many grams of NaH2PO4 would be added to 5.60 grams of Na3PO4 to produce 500.0 mL of a buffer at pH = 7.3? For H3PO4 pKa1 = 2.148, pKa2 = 7.199, and pKa3 = 12.15. (a) 7.36 g NaH2PO4. (b) 1.63 g NaH2PO4. (c) 5.73 g NaH2PO4.
PART III EXCERSICES (20 points each)
18.- The chloride content of blood serum, cerebrospinal fluid or urine can be measured by titration of the chloride with mercuric ion: Hg2+ + 2Cl- → HgCl2(aq). When the reaction is complete, excess Hg2+ reacts with the indicator, diphenylcarbazone, which forms a violet-blue color.
(a) Mercuric nitrate was standardized by titrating a solution containing 147.6 mg of NaCl, which required 28.06 mL of Hg(NO3)2 solution.
Find the molarity of the Hg(NO3)2.
(b) When this same Hg(NO3)2 solution was used to titrate 2.000 mL of urine, 22.83 mL was required.
Find the concentration of Cl- (mg/mL) in the urine.
19.- What is the pH of water containing 0.0333 M Ca(NO3)2. (remember ionic strength changes the activity coefficients!)

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