Page 1 of 10 CHEMISTRY 151
Midterm Exam #2
#1: Multiple choice __________/ 21
#2: Equilibrium __________/ 12
#3: More equilibrium __________/ 13
#4: Inorganic nomenclature __________/ 12
#5: Le Chatlier’s Principle __________/ 06
#6: Crystal field theory __________/ 16
Group-work extra credit: __________/ 04
TOTAL: __________/80
Information that might be useful (and periodic table) can be found on the last page of the exam. You may remove this page for convenience.
Instructions:
1. Only non-graphing calculators are allowed; cell phones must be put away. 2. Once we begin each section of the exam, you cannot leave and return.
3. Anyone caught cheating in any fashion will receive an automatic F for the entire course, as indicated in the syllabus.
4. Section I of the exam: You will have 1 hr 45 min to complete this exam individually. Following this “traditional” exam time, you will be permitted a 5-min break.
5. Section II of the exam: You will have 1 hr to re-work another copy of the exam. This time you must work together in groups, talking & consulting with one another. Each group will submit one exam.
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Page 3 of 10 Part #1: Multiple Choice (3 points each)
1. Which of the following has an effect on the magnitude of the equilibrium constant? A) removing products as they are formed
B) adding more of a reactant C) adding a catalyst
D) increasing the pressure, in a gas-phase reaction E) change in temperature
Ans: E Difficulty: E
2. Which of the following transition elements can have an oxidation number of +7? A) V B) Cr C) Mn D) Fe E) Co
Ans: C Difficulty: M
3. Carbon monoxide and chlorine combine in an equilibrium reaction to produce the highly toxic product, phosgene (COCl2)
CO(g) + Cl2(g) COCl2(g)
If the equilibrium constant for this reaction is Kc = 248, predict, if possible, what will happen when the reactants and product are combined with the concentrations shown. [CO] = [Cl2] = 0.010 M; [COCl2] = 0.070 M
A) The reaction will proceed to the right. B) The reaction will proceed to the left.
C) The reaction is at equilibrium, and no change in concentrations will occur. D) The container volume needs to be specified before a prediction can be made. E) The temperature needs to be specified before a prediction can be made. Ans: B Difficulty: M
4. Which of the following ions is least likely to form colored compounds? A) Mn2+ B) Cr5+ C) Sc3+ D) Fe3+ E) Co2+
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5. The equilibrium constant for the reaction of bromine with chlorine to form bromine monochloride is 58.0 at a certain temperature.
Br2(g) + Cl2(g) 2BrCl(g)
What is the equilibrium constant for the following reaction? BrCl(g) 1
2Br2(g) + 12Cl2(g)
A) 2.97 10–4 B) 1.72 10–2 C) 3.45 10–2 D) 1.31 10–1 E) > 1.00 Ans: D Difficulty: M
6. Which of the following atoms has the biggest radius? A) Ti B) Cr C) Fe D) Ni E) Zn
Ans: A Difficulty: M
7. In the presence of a strong octahedral ligand field, the number of unpaired electrons in Co(III)will be
Page 5 of 10 Read the questions carefully. Please write legibly and show all work in order to receive full credit. Report numerical answers with appropriate significant figures and units.
2. (12 points) The equilibrium constant, Kp ,for the gas-phase reaction between hydrogen and iodine to form hydrogen iodide is 55.2 at 425°C. A rigid cylinder at that temperature contains 0.134 atm of hydrogen, 0.134 atm of iodine, and 1.055 atm of hydrogen iodide.
a.) (4 points) Is the reaction at equilibrium? Justify your answer.
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3. (13 pts) Answer the following questions regarding equilibrium: N2(g) + O2(g) 2NO(g) Kc = 4.8 x 10-31
2NOBr(g) 2NO(g) + Br2(g) Kc = 0.50
a. (5 pts) Write the overall equation for the complete decomposition of NOBr and calculate Kc.
b. (4 points) In which direction would the equilibrium shift given the following changes? Explain your reasoning.
(i) The pressure is increased by decreasing the volume of the container.
(ii)Bromine gas is removed by condensing to a liquid.
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4. (12 pts) Inorganic nomenclature. Write formulas or names for the following coordination complexes or compounds. Spelling counts.
a. calcium tetrachloronickelate _____________________________________________________
b. diamminedichloroethylenediaminecobalt(III) bromide _________________________________
c. pentaamminechloroiron (III) aquatrichlorocobaltate(II)________________________________
d. [CoH2O(en)2Cl]PO3 ____________________________________________________________
e. [Cr(CO)3(NH3)3]3+_____________________________________________________________
f. K3[Fe(CN)6] _________________________________________________________________
5. (6 points) Ammonia (NH3) is a weak base and when it reacts with water, it exists in equilibrium
with hydroxide and ammonium ion.
Indicate the shift you would see if the following stresses are placed on the system and explain your reasoning.
A) Silver nitrate is added to the solution. (Note that the Kc for the formation of diamminesilver
ion from silver ion and ammonia is 1.7 x 107)
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6. (16 pts) Consider the three complexes [Co(H2O)6]3+, [Co(NH3)6]3+, [CoF6]3-. The colors of the
complexes are yellow-orange, green, and blue; two of them are diamagnetic.
a. (4 points) State the following:
(i) The charge of cobalt is _______.
(ii) The number of 3d electrons is ______.
(iii)The geometry of the complexes is __________________.
(iv)The orbital hybridization in the complexes is __________ or __________.
b. (6 pts) Predict and explain the color and magnetism of each complex. Use energy-level diagrams for each substance as support.
Page 9 of 10 Information that might be useful
(You may remove this page for convenience)
c = 2.998 × 108 m/s h = 6.626 × 10–34 J s R = 0.0821 L atm/K mol
Kp = Kc(RT)ng
CO > CN– > NO2– > en > NH3 > SCN– > H2O > C2O42– > OH– > F– > Cl– > Br– > I–
a ac b
b x
2 4 2
