CHEM 10123/10125, Exam 2

Transcription

1 CHEM 10123/10125, Exam 2 March 7, 2012 (50 minutes) Name (please print) Please box your answers, and remember that significant figures, phases (for chemical equations), and units do count! 1. (13 points) SHOW ALL WORK. Ascorbic acid, H 2 A, has K a1 = 8.0 x 10 5 and K a2 = 1.6 x Determine the following values for a 2.5 M solution of this acid. Briefly show your work in the space below. (Reactions need not be shown here) a. [HA ] b. ph c. [A 2 ] 2. (16 points) Briefly define the following terms: Lewis base Indicator Arrhenius base Buffer range 1

2 3. (8 points) For the amphoteric molecule HCO 3, write one equation showing it acting as an acid, and another equation showing it acting as a base (label which is which). 4. (5 points) Among the following, circle the weakest Bronsted-Lowry acid. HClO HClO 2 HClO 3 HBrO HBrO 2 HBrO 3 5. (5 points) Among the following, circle the strongest Bronsted-Lowry base. HS HO HSe Br F Cl 6. (15 points) Arrange the following M solutions in order of increasing ph: NH 3, HNO 3, NaNO 2, HC 2 H 3 O 2, NaOH, NH 4 C 2 H 3 O 2, NH 4 ClO 4 7. (13 points) For each reaction, identify the Lewis acid and Lewis base, then predict the reaction product. Draw the complete and correct Lewis structure of the product for reaction (a) only. a) OH (aq) + CO 2(aq) b) Cr 3+ (aq) + 6 H 2 O (l) c) Al(OH) 3(aq) + OH (aq) 2

3 8. SHOW ALL WORK. A ml sample of M HF is titrated with M NaOH. The initial ph is [We used the K a of HOCl here, since HF was not on the table.] Calculate the ph when the neutralization is a) (12 points) 25% complete b) (5 points) 50% complete c) (20 points) 100% complete 3

4 9. (12 points) Fill in the blanks. [H + ] [OH ] ph poh 4.5 x 10 5 M (6 points) Coal can be used to generate hydrogen gas ( a potential fuel) by the endothermic reaction: C (s) + H 2 O (g) CO (g) + H 2(g) If this reaction is at equilibrium, predict whether each disturbance will result in the formation of additional hydrogen gas, the formation of less hydrogen gas, or have no effect on the quantity of hydrogen gas. a.) adding more C to the reaction b.) adding more H 2 O to the reaction c.) raising the temperature of the reaction d.) increasing the volume of the reaction e.) adding a catalyst to the reaction f.) adding an inert gas to the reaction 11. (20 points) A solution is formed by mixing ml of M KOH with ml of a solution that is both M in CH 3 COOH and M in HI. Identify in the final solution a) all the solute species present b) the two most abundant solute species, and c) the two least abundant solute species. 4

5 CHEM 10123/10125, Exam 2 March 7, 2012 (50 minutes) Name (please print) Please box your answers, and remember that significant figures, phases (for chemical equations), and units do count! 1. (13 points) SHOW ALL WORK. Carbonic acid, H 2 A, has K a1 = 4.4 x 10 7 and K a2 = 4.7 x Determine the following values for a 2.5 M solution of this acid. Briefly show your work in the space below. (Reactions need not be shown here) a. [HA ] b. ph c. [C 6 H 6 O 6 2 ] 2. (16 points) Briefly define the following terms: Bronsted acid Equivalence point Buffer capacity Lewis acid 5

6 3. (8 points) For the amphoteric molecule HS, write one equation showing it acting as an acid, and another equation showing it acting as a base (label which is which). 4. (5 points) Among the following, circle the strongest Bronsted-Lowry base. ClO 3 ClO 4 ClO 2 - BrO 2 BrO 4 BrO 3 5. (5 points) Among the following, circle the weakest Bronsted-Lowry acid. CH 4 H 2 S SiH 4 PH 3 H 2 O NH 3 6. (15 points) Arrange the following M solutions in order of decreasing ph: NH 3, HNO 3, NaNO 2, HC 2 H 3 O 2, NaOH, NH 4 C 2 H 3 O 2, NH 4 ClO 4 7. (13 points) For each reaction, identify the Lewis acid and Lewis base, then predict the reaction product. Draw the complete and correct Lewis structure of the product for reaction (a) only. a) SO 2(aq) + OH (aq) ) b) B(OH) 3(aq) + OH (aq) c) Al 3+ (aq) + 6 H 2 O (l) 6

7 8. SHOW ALL WORK. A ml sample of M propanoic acid is titrated with M KOH. The initial ph is Calculate the ph when the neutralization is a) (12 points) 25% complete b) (5 points) 50% complete c) (20 points) 100% complete 7

8 9. (12 points) Fill in the blanks. [H + ] [OH ] ph poh 6.7 x (6 points) Coal can be used to generate hydrogen gas ( a potential fuel) by the endothermic reaction: C (s) + H 2 O (g) CO (g) + H 2(g) If this reaction is at equilibrium, predict whether each disturbance will result in the formation of additional hydrogen gas, the formation of less hydrogen gas, or have no effect on the quantity of hydrogen gas. a.) raising the temperature of the reaction b.) removing some H 2 O from the reaction c.) removing some of the C from the reaction d.) adding an inert gas to the reaction e.) adding a catalyst to the reaction f.) decreasing the volume of the reaction 11. (20 points) A solution is formed by mixing ml of M KOH with ml of a solution that is both M in CH 3 COOH and M in HI. Identify in the final solution a) all the solute species present b) the two most abundant solute species, and c) the two least abundant solute species. 8

9 Selected K a Values for Weak Monoprotic Acids at 25 C. Name of Acid Formula K a Chloroacetic acid HCl 3 C 2 O x 10 3 Iodic Acid HIO x 10 1 Acetic Acid HC 2 H 3 O x 10 5 Nitrous Acid HNO x 10 4 Lactic Acid HC 3 H 5 O x 10 4 Hydrocyanic acid HCN 4.9 x Hydrazoic acid HN x 10 5 Hypochlorous acid HOCl 3.0 x 10 8 Propanoic acid HC 3 H 5 O x 10 5 Selected K b Values for Weak Molecular Bases at 25 C Name of Base Formula K b Butylamine C 4 H 9 NH x 10 4 Methylamine CH 3 NH x 10 4 Ammonia NH x 10 5 Hydrazine N 2 H x 10 6 Strychnine C 21 H 22 N 2 O x 10 6 IA Periodic Table of the Elements VIIIA (1) (18) H IIA IIIA IVA VA VIA VIIA He (2) (13) (14) (15) (16) (17) Li Be B C N O F Ne Na Mg IIIB IVB VB VIB VIIB VIIIB IB IIB Al Si P S Cl Ar (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn Fr Ra Ac Rf Db Sg Bh Hs Mt Ds Uuu Uub Uug (261) (262) (266) (264) (270) (268) (281) Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr