Chemistry 17 (Third Long Exam) I. Modified True or False: Read the following statements carefully, and then write TRUE if the statement is true. Otherwise, change the underlined word to make the statement true. 1. Zn can be substituted by Mg as an oxidizing agent in Experiment # 14 (Selected Redox Reactions). R eactions). 2. A certain voltage is applied in an electrolytic cell to make a non-spontaneous reaction spontaneous. 3. A yellow precipitate, Zn3[Fe(CN)2], is produced if K 4Fe(CN)6 is added to a Zn2+ solution. 4. The charge of Co in the complex [CoCl(NO2)(NH3)4]+ is +4. 5. The cell reaction of a primary battery can be reversed by passing electricity through the battery. 6. Cr3+ interferes with the formation of the red lake in the prescence of NH 4OAc and aluminon reagent. 7. The coordination number of Pt(en) 2I2C2O4 is 4. 8. Electrons flow from anode to cathode in an electrolytic cell. 9. NH4+ is the only cation that did not form a precipitate with 3.0 M NaOH. 10. Only NO 2-, NO3- and CrO42- give positive result in the test for strong reducing anions. II. Multiple Choice: Choose the letter of the best answer. 1. What is the cell reaction for a charging lead battery? A. PbO2(s) + Pb(s) + 2H+(aq) + 2HSO4-(aq) → 2PbSO4(s) + 2H2O(l) B. PbO2(s) + 4H+(aq) + 2HSO4-(aq) + 4e- → PbSO4(s) + H2(g) + 2H2O(l) + SO42-(aq) C. 2PbSO4(s) + 2H2O(l) → PbO2(s) + Pb(s) + 2H+(aq) + 2HSO4-(aq) D. PbSO4(s) + H2(g) + 2H2O(l) + SO42-(aq) → PbO2(s) + 4H+(aq) + 2HSO4-(aq) + 4e2. The following anions interfere with the formation of a brown ring in the confirmatory test of Nitrate: A. Chloride, Thiocyanate, Nitrite C. Iodide, Thiocyanate, Oxalate B. Thiocyanate, Nitrite, Bromide D. Bromide, Nitrite, Sulfate 3. Which of the following complexes are diamagnetic? A. [CoF6]3B. [Fe(CN)6]3-
C. [Co(H2O)6]2+
4. Calculate the equilibrium equilibrium constant at 25 ˚C for the the reaction: Pb2+(aq) + Sn(s) → Pb(s) + Sn2+(aq) (E0Pb2+/Pb = -0.126 V, E 0Sn2+/Sn = -0.14 V) A. 0.34 B. 9.7 x 10 8 C.2.97 5. Which of the following is not a characteristic of the complex [Fe(CN) 6]3-? A. Pairing energy is greater than splitting energy B. Low spin complex C. Produces large crystal field splitting. D. Strong-field complex
D. [Co(NH3)6]3+
D. 1.0 x 10 -9
III. Qualitative Analysis. A. Determine Cations A to E and compounds F and G.
Cations A, B, C, D and E 6.0 M HCl Cations B, C, D and E
White ppt F from Cation A
6.0 M NH3 White ppt from Cation B and C
NVR for Cation D and E 3.0 M NaOH
X’s NH3
White ppt of B dissolves
White ppt of C undissolved
White ppt due to Cation D
Pungent colorless gas G due to Cation E
Test Yellow-green Flame B. Determine anions H-L and compounds M-R. Cations H, I, J, K and L FeCl3 K 3Fe CN 6
Blue ppt M due to Anion H and I
Anions J, K and L
Acidified AgNO3 NVR due to H 6M H2SO4 1M FeSO4 Brown solution due to Fe(NO)2+
Yellow ppt N due to anion I
Acidified AgNO3 NVR due to K and L
White ppt O due to anion J
AgNO3
X’s NH3
Colorless solution
White ppt due to K
6M H2SO4 Effervescence Q
NVR due to L 6M H2SO4 Acid R that has a vinegar smell
IV. Problem Solving 1. a. Determine the standard reduction potential of Cr 3+(aq) + 3e- → Cr(s) given the E˚ red of E˚Cr2+/Cr = -0.91V and E˚Cr3+/Cr2+ = -0.41V. b. Using Cr3+(aq) + 3e- → Cr(s) as the anode with [Cr 3+] = 1M, determine whether the reaction is spontaneous or not, and if Pb (s) can be plated out from the following cathodes: i. PbSO4(s) + 2e- → Pb(s) + SO42-(aq) E˚red = -0.356 ii. Pb2+ (aq) + 2e- → Pb(s) E˚red = -0.126 Note: The concentrations of all aqueous species are 1M. c. Solve for the equilibrium constant for the reactions in (b) which is/are spontaneous. 2. Consider the frost diagram for Vanadium in acidic medium.
Frost Diagram, Vanadium, pH = 0 0
V
VO2+ ) -1 V ( 0
d e r
E N
V2+
-2
VO2+ V3+
-3 0
1
2
3
4
5
Oxidation Number (N)
a. Which vanadium series is the most stable? b. Which species is the strongest oxidizing agent? c. Which species is the strongest reducing agent? d. Will V 3+ disproportionate to V 2+ and VO2+? e. Will VO2+ and V 3+ comproportionate comproportionate to VO2+? 3. a. Determine which complex is high-spin and which is low-spin between [Ni(H 2O)6]2+ and [Ni(CN)4]2-. b. What is the charge of Ni in the low-spin complex? Write its electronic configuration. configuration. Draw the orbital diagram of the complex if it is diamagnetic. c. Name the high spin complex in (a). d. Write the water dissociation reaction of the high spin complex in (a). e. From the reaction in (d), name the conjugate of the high-spin complex.
