DOUSKEY Chemistry 1A, Spring 2003
Name__________________ TA ____________________
DOUSKEY Chemistry 1A, Spring 2003 Final Exam-KEY May 19, 2003 (270 min., closed book) Name:
TA:
SID:
Section:
Please read this first: Write your name and that of your TA on all 17 pages of the exam
Test-taking Strategy This test consists of two parts: multiple choice (answers to be entered in the boxes provided) and short answer. In order to maximize your score on the exam: • Do the questions you know how to do first. • Go back and spend more time on the questions you find more challenging. • Budget your time carefully -- don't spend too much time on one problem. • Show all work for which you want credit and don't forget to include units.
Question
Page
Points
Multiple Choice
4-12
160
A- Kinetics
13
24
B- Electrochemistry
14
36
C- Structure and Reactivity
15
18
D- Acid Base Equilibria
16
26
E- Light and Molecular Structure
17
16
Total
280
Score
Name__________________ TA ____________________
E=hν
R = 8.314 J / (mol K)
λν = c
A = εlC
λdeBroglie = h / p = h / mv
Pa = XaPtot
T star = 2.898 mm· K/λmax
P = F/A
Ekin(e-) = hν - Φ = hν - hνo
∆E = q + w
Ekin = ½mv2
∆G° = ∆H° - T∆S°
Ekin = 3RT/2
∆G = ∆G° + RT ln Q
vrms =
∆G° = -RT ln K
(3RT / M )
q = mCs∆T
En = -R∞(Z2/n2) ∆E = -R∞(Z2/nf2 - Z2/ni2) R∞ = 2.18 × 10-18 J -23
kB = 1.381 × 10
J/K
me- = 9.11 × 10-31 kg h = 6.626 × 10
-34
w = -Pext∆V ∆H° = Σ∆H°f (products) - Σ∆H°f (reactants) NA = 6.022 × 1023 1 cal = 4.18 J 101.3 J = 1 L atm
Js
KaKb = Kw
c = 3.0 × 108 m/s
Kw = 10-14
1 nm = 10-9 m
pX = -log X pKa + pKb = pKw
1 kJ = 1000 J
[ A- ] pH = pKa + log [ HA]
1 Torr = 1 mmHg 1 atm = 760 mmHg J = (kg m2)/s2
Ecell = Ecathode − Eanode -19
1 eV = 1.602 × 10
J
PV = nRT MM = mRT / (PV) T(K) = T(C) + 273.15 R = 0.0821 L·atm / (mol·K)
∆G = −nFEcell F = 96,485C/mol e-
Name__________________ TA ____________________ Table of Standard Reduction Potentials
2 H+(aq) + 2 e-
→ H2 (g)
0
Name__________________ TA ____________________ Multiple Choice. (4 points each, 160 points total) Determine the best answer to the questions below and write your answer in the box provided. 1.) Which neutral atom could have the configuration 1s22s22p63s23p54s1? A) K
B) Cl
C) Na
D) Ar
E) S
2.) A mixture of oxygen atoms was allowed to react to form O2 molecules. Based on the mass spectrum below, which statements are true?
32 A) B) C) D)
34
36
32
O, 34O, and 36O isotopes are present in the sample there is only one isotope of oxygen present in the sample carbon dioxide was formed in the reaction there are two isotopes of oxygen in a 25:75 mixture
3.) A molecular picture for the reaction of H2 and NO is shown below. 2H2
+
2NO
Legend:
→
H=
N2 + N=
2H2O O=
+ Which of the diagrams below best represents the molecules after the reaction has taken place? (Circle one)
Name__________________ TA ____________________ 4.) Which of the following is a valid set of quantum numbers for an electron in a 2p orbital? A)
n=2, =2, m =0
B)
n=1, =3, m =3
C)
n=2, =1, m =1
D)
n=3, =1, m = -1
E)
n=1, =2, m =3
5.) A photon of wavelength 270 nm has the minimum energy needed to eject an electron from chromium metal. What effect will a photon of 540 nm have on chromium? A) B) C) D) E)
twice as many electrons will be ejected half as many electrons will be ejected no effect, no electron will be ejected the electron will be ejected but remain at rest the electron will be ejected with some kinetic energy
6.) What is the maximum number of electrons with the same spin quantum number (ms) for the principle quantum number 2? A) 1
B) 2
C) 3
D) 4
E) 8
7.) 2.00 liters of an ideal gas was heated in a balloon from 25°C to 50°C. What is the final volume of the balloon? A) 0.46 L
B) 1.00 L
C) 2.16 L
D) 4.00 L
8.) Under identical conditions, which gas will have the highest root mean square velocity? A) O2
B) He
C) Cl2
D) Ar
E) N2
Name__________________ TA ____________________
Name__________________ TA ____________________ 9.) For the energy levels shown below, which diagram best represents the absorption spectrum generated as electrons are excited? (Circle your answer.)
E
→ν 10.)
A) B) C) D) E)
B) Si
C) Ge
D) Sn
E) Pb
B) K+
C) Ar
D) S2-
E) Cl–
B) Si
C) Ge
D) Sn
E) Pb
Which species has the highest effective nuclear charge felt by the outermost electron? A) B
14.)
→ν
Which species has the highest ionization energy? A) C
13.)
→ν
Which species has the largest radius? A) Ca2+
12.)
→ν
Which element has the largest radius? A) C
11.)
→ν
B) Al
C) Ga
D) In
Which of the following substances is most ionic? H2S NO PH3 Na2S SO2
E) Tl
Name__________________ TA ____________________ 15.)
In the titration of 0.1173 g of base (MW=121.14 g/mol) it takes 11.43 mL of acid to reach the endpoint. What is the concentration of the acid in mol/L?
A) B) C) D) E)
16.)
0.08472 8.472 × 10-5 0.085 1.243 11.80
If butyric acid (shown right) smells sour, which one of the following compounds is also likely to smell sour? (circle one) butyric acid
17.)
What is the hybridization of oxygen in acetic acid (shown right)? A) sp
B) sp
2
C) sp
3
D) bent
O
Bad question: accept all answers! C
H
18.) Which molecular orbital has the highest energy? (circle one)
O
H
Name__________________ TA ____________________ 19.)
Consider the following reactions at equilibrium and determine which of the indicated changes will cause the reaction to proceed to the right. 1) CO(g) + 3 H2(g)
CH4(g) + H2O(g)
(remove H2O)
2) N2(g) + 3 H2(g)
2 NH3(g)
(add NH3)
3) BaO(s) + SO3(g) A) B) C) D) E)
BaSO4(s)
(add BaO)
1 2 3 1 and 3 1, 2 and 3
20.) What is the molarity of F- in a saturated solution of InF3? (Ksp = 7.9 x 10-10) InF3(s) A) B) C) D) E)
In3+(aq) + 3F-(aq)
2.3 x 10-3 3.8 x 10-3 5.8 x 10-4 2.8 x 10-5 7.0 x 10-3
21.) The following reaction is endothermic. What is true about the relative strengths of the bonds? Cl + CH4 → HCl + CH3 A) B) C) D) E)
breaking bonds takes energy making bonds releases energy a C-H bond is stronger than a H-Cl bond a C-H bond is weaker than a H-Cl bond the reaction absorbs heat
22.) A solution of an indicator is blue. When a lot of acid is added, the indicator turns yellow. Which statement is true when the solution is green? Ind- + H3O+ A) B) C) D) E)
HInd + H2O
The water produced dilutes the blue color and makes it appear green. Both Ind- and HInd are present in solution. The H3O+ is the green species. All the reactants have formed products. The endpoint was missed in the titration.
Name__________________ TA ____________________ 23.) In an atom of any element, the 2s orbital is: A) B) C) D)
always at the same energy as the 2p orbital always at lower energy than the 2p orbital only at the same energy as the 2p orbital for atoms with more than one electron only at lower energy than the 2p orbital for atoms with more than one electron
24.) For a gaseous atom of any element, X, an electron can be removed according to the following equation: X (g) → X+ (g) + eThis process A) requires energy for all elements, because the initial state is less stable than the final state B) requires energy for all elements, because the initial state is more stable than the final state C) does not require energy for any element, because the initial state is the same energy as the final state D) requires energy for some elements, because sometimes the initial state is more stable than the final state
25.) Consider the reaction of the weak base NH3 with the strong acid HCl: NH3(aq) + HCl(aq) NH4Cl(aq) Which of the following statements is true at the equivalence point for this general acid-base reaction? A) The pH is equal to 7 since salt and water are the main products B) The pH is equal to 7 because the acid is neutralized C) The pH is less than 7 because NH4+ is a weak acid D) The pH is greater than 7 because Cl- is a weak base 26.) You have a 1.00 M solution of acetic acid (CH3COOH) and a 1.00 M solution of iodic acid (HIO3). The Ka for acetic acid is 1.8 × 10-5 and the Ka for iodic acid is 1.7 × 10-1. Which + solution has the highest concentration of H3O and why? A) CH3COOH: It is a stronger acid than iodic acid and fully hydrolyzes to give more + H3O in solution. +
B) HIO3: It is a stronger acid than acetic acid, and hydrolyzes to give more H3O in solution. + C) Same concentration of H3O : Both solutions have a concentration of 1.00 M + H3O . + D) Same concentration of H3O : The concentration of CH3COOH is equal to the concentration of HIO3.
Name__________________ TA ____________________ 27.) You have two solutions: 0.100 M NaOH and 0.100 M NH3. To each, you add an equal volume of 0.100 M HCl to reach the equivalence point. After the addition of acid, which relationship is true for the resulting two solutions? (A) [NH4+] = [Na+]
(B) [NH4+] < [Na+]
(C) [NH4+] > [Na+]
28.) Heat is given off when hydrogen burns in air according to the equation 2 H2 + O2 → 2 H2O Which of the following is responsible for the heat? A) breaking H-H and O-O bonds B) breaking O-H bonds C) forming H-H and O-O bonds D) forming O-H bonds
29.) Given the following Ka values, determine which species is the strongest base.
A) B) C) D) E)
CO32H2SO4 SO42H2CO3 HPO42-
HSO4H2PO4HCO3-
1.2 × 10-2 6.3 × 10-8 4.7 × 10-11
30.) What is the pH of a 0.100M solution of acetic acid? Ka = 1.8 × 10-5 A) B) C) D) E)
1.00 2.87 4.74 7.00 10.63
31.) Which of the following species will oxidize Au(s)? A) B) C) D)
F2(g) O2 (g) Br2 (l) Ag+ (aq)
Name__________________ TA ____________________ 32.) Which of the following species will reduce Cl2(g) ? A) B) C) D)
Ag+ (aq) O2 (g) Au3+(aq) H2O
33.) What is the greatest producer of NOx pollutants? A) B) C) D)
utilities (burning of fossil fuels) non-industrial combustion (burning of biomass like wood) manufacturing transportation (high temperature combustion and burning of fossil fuels)
34.) What is the greatest producer of SOx pollutants? A) B) C) D)
utilities (burning of fossil fuels) non-industrial combustion (burning of biomass like wood) manufacturing transportation (high temperature combustion and burning of fossil fuels)
35.) Atmospheric carbon dioxide has an affect on the pH of rain. What is the normal pH of rain? A) B) C) D) E)
2.5 5.5 7.0 9.5 11.0
36.) Greenhouse gases are able to absorb and emit which type of light? A) B) C) D) E)
microwaves x-rays infrared visible ultraviolet
37.) Which of the following gases are greenhouse gases? A) B) C) D) E)
H2O CO2 NO2 SO3 all of the above
Name__________________ TA ____________________ 38.) The use of sodium azide decomposition for automobile airbag inflation is dangerous because: A) B) C) D) E)
sodium azide is toxic sodium metal is generated by the reaction the gas produced is toxic both A and B none of the above
Given the emission spectra for two different stars, answer the following questions. Star #1
Star #2
120
200 100
150 Intensity
Intensity
80 60 40
100
50
20 0
0 350
400
450
500
550
600
Wavelength (nm)
650
700
350
400
450
500
550
600
Wavelength (nm)
39.) Circle the spectrum corresponding to the star that is at the higher temperature. 40.) At 486 nm, there is a pronounced dip in the spectrum for Star # 2. To which energy transition in hydrogen atoms does the dip in the spectrum correspond? A) B) C) D)
n=2 to n=3 n=3 to n=2 n=4 to n=2 not enough information
650
700
Name__________________ TA ____________________
A. Kinetics (24 points total) In an analogy to the gas-phase chlorine catalytic cycle, NO also contributes to gas-phase ozone destruction. Step Reaction Ea (kJ/mol) A (cm3 molecule-1 s-1)_ 2.0 x 10-12 1 NO(g) + O3(g) → NO2(g) + O2(g) 11.6 ± 1.7 6.5 x 10-12 2 -1 ± 1 NO2(g) + O(g) → NO(g) + O2(g) What is the overall reaction corresponding to this two step process? O(g) + O3(g) → 2 O2(g) Which molecule is the intermediate in the two step reaction?______ NO2________ Which molecule is the catalyst in the two step reaction?_____ NO ________ Which step of the reaction is likely to be the slowest?_____1________ Four reaction coordinate diagrams are shown below. Energy is plotted versus the progress of the reaction. Use the diagrams to answer the questions below.
C B A D Which diagram represents the reaction(s) with the highest activation energy? ____D_____ Which diagram represents the reaction(s) with the lowest activation energy? ___C______ Which diagram represents a two step reaction? ____B_____ Which diagram represents that of reaction D in the presence of a catalyst? ____C_____ Which diagram represents the most greatly exothermic reaction? _____A____ Which two reactions absorb heat from the surroundings? ___C, D______
Name__________________ TA ____________________ B. Electrochemistry (36 points total) Balance the following oxidation/reduction reaction in acidic solution. -
MnO4 → Mn
MnO4- + Cl- → Mn2+ + Cl2
2+
Cl- →
Cl2
MnO4- → Mn2+
2Cl- →
Cl2
8H+ + MnO4- → Mn2+ + 4H2O
2Cl- →
Cl2
5e- + 8H+ + MnO4- → Mn2+ + 4H2O
2Cl- →
Cl2 + 2e-
10e- + 16H+ + 2MnO4- → 2Mn2+ + 8H2O (cathode: reduction ½ reaction)
10Cl- → 5Cl2 + 10e(anode: oxidation ½ reaction)
Full reaction: 16H+ + 2MnO4- + 10Cl- → 2Mn2+ + 8H2O + 5Cl2 This reaction can be used to do work. Write the cell notation for the galvanic cell.
׀
Cl- (aq) Cl2 (g)
׀׀H (aq), MnO (aq), Mn +
4
-
2+
(aq)
Aluminum metal will react with bromine gas to produce aluminum bromide salt. Assign the oxidation numbers for each element and place them in the boxes provided.
2Al(s) + 3Br2(l) 0
0
→ 2AlBr3(s) +3
-1
Calculate the free energy in kJ for the reaction. (use formulas and data from page 2 and 3)
Ecell = Ecathode − Eanode ∆G = −nFE cell
EBr2/Br - EAl/Al3+ = 1.08 –(-1.66) = 2.74 V = 2.74J/C
∆G = - (6e-)(96485C/mol e-) (2.74J/C) = 1586213 J = 1586 kJ
Name__________________ TA ____________________ C. Structure and Reactivity (18 points total) Consider the decomposition of 1 mole of N2O4 and answer the questions below. N2O4 (g) O
O N O
2 NO2 (g)
2
N
at 298K, K = 4.0 × 10-2
O
∆S = 175.73 J/K
N
O
O
What is the free energy for this reaction in kJ?
∆G° = -RT ln K = - (8.314 J/mol K) (298K) ln 4.0 × 10-2 = 7.98 × 103 J = 7.98 kJ Based on the data for this reaction, what is the bond enthalpy (in kJ) of a mole of nitrogennitrogen single bonds? Since the only thing happening in the reaction is the breaking of a N-N bond, the bond enthalpy will be equal to ∆H° for the reaction.
∆G° = ∆H° - T∆S°
∆H° = ∆G° + T∆S°
= 7.98 × 103 J + (298K) (175.73J/K) = 6.03 × 104 J = 60.3 kJ A flask is filled with 5 atm of N2O4, what will be the partial pressure of NO2 (in atm) when the system reaches equilibrium? 2 NO2 (g) N2O4 (g) initial 5 0 change -x +2x equilibrium 5-x 2x P2
(2 x) 2 K= = = 4.0 × 10 − 2 PN 2O 4 (5 − x) x is negligible in the 5–x expression because K is small relative to the 5atm of initial material. 0.020 = 4x2 x = 0.234 PNO2 = 2x = 0.447 atm NO 2
Name__________________ TA ____________________ D. Acid-Base Equilibria (26 points total) NO2 gas can dissolve in water and react to make acids. NO2(g) + H2O(l)
HNO3(aq) nitric acid
+
HNO2(aq) nitrous acid
Write the chemical reaction for the reaction of nitric acid in water. Circle the conjugate base. HNO3(aq)
H3O+(aq) +
+ H2O(l)
NO3-(aq)
Write the chemical reaction for the reaction of nitrous acid in water. Circle the conjugate base. HNO2(aq)
H3O+(aq) +
+ H2O(l)
NO2-(aq)
Based on the relative stabilities of the conjugate bases produced, which acid is stronger? Circle one and explain your reasoning. nitric acid nitrous acid NO3- is more stable than NO2- because it has more oxygens. Oxygen is electronegative and will stabilize the extra e- in the ion. Also, NO3- has 3 resonance structures while NO2 has only two. Resonance allows the electron density to be spread over the entire molecule further lowering the energy of the ion.
What is the pH of a solution of a 1.00L solution that is 0.100M HNO2 and 0.150M NaNO2? pKa = -log Ka pKa = 3.37 (Ka = 4.3 × 10-4)
[ A- ] pH = pKa + log [ HA]
pH = 3.37 + log (0.150NO2-/0.100HNO2) = 3.55
If you add 20.00 mL of 1.00M NaOH to the solution, what is the resulting pH? moles OH- = 1.00 M × 0.0200 L = 0.0200 moles initial change equilibrium
HNO2(aq) 0.100 -0.0200 0.080
+ OH0.0200 -0.0200 0
NO2-/ 0.150 +0.0200 0.170
pH = 3.37 + log (0.170NO2-/0.080HNO2) = 3.70
H2O
Name__________________ TA ____________________ E. Light and Molecules (16 points total) Molecules with conjugation (a series of alternating single and double bonds) are often colorful. Beta carotene is the molecule in carrots that makes them appear orange. The structure and absorbance spectrum of beta carotene are shown below.
A bs orbanc e
Absorbance Spectrum of Beta Carotene
250.00
350.00
450.00
550.00
650.00
750.00
Wavelength (nm)
Using the data in the absorbance spectrum, explain why beta carotene appears orange? Beta carotene absorbs from 400-500 nm in the visible range. This corresponds to absorbing green, blue, indigo and violet light. The light that is transmitted is a combination of red, orange, and yellow which we perceive as orange.
Household bleach is a strong oxidizing agent. When bleach reacts with beta carotene, the product is this beta-apo-14’-carotenal which absorbs light only in the UV region. beta-apo-14’-carotenal
O
Explain why a strong oxidizing agent like bleach would cause the color of the molecule to change from orange to colorless. An oxidizing agent takes electrons from other molecules. When electrons are taken from the beta carotene, the molecular structure breaks and a new structure is formed. Light is absorbed by a molecule when the photon has the same energy as that of an electronic excitation for the molecule. The new structure absorbs light differently because its electrons are configured differently. Specifically, for molecules with conjugated bonds, the electrons are promoted from a π to a π* level. In beta carotene, there is a large amount of bond conjugation than in the oxidized form beta-apo-14’-carotenal. Using particle in a box theory, electrons confined to smaller spaces have higher energy. In the beta-apo-14’-carotenal, the reduced conjugation will lead to high energy photons being required to excite the electrons so the molecule no longer absorbs lower energy visible light, but rather only the higher energy UV light.
DOUSKEY Chemistry 1A, Spring 2003 Final Exam-KEY May 19, 2003 (270 min., closed book) Name:
TA:
SID:
Section:
Please read this first: Write your name and that of your TA on all 17 pages of the exam
Test-taking Strategy This test consists of two parts: multiple choice (answers to be entered in the boxes provided) and short answer. In order to maximize your score on the exam: • Do the questions you know how to do first. • Go back and spend more time on the questions you find more challenging. • Budget your time carefully -- don't spend too much time on one problem. • Show all work for which you want credit and don't forget to include units.
Question
Page
Points
Multiple Choice
4-12
160
A- Kinetics
13
24
B- Electrochemistry
14
36
C- Structure and Reactivity
15
18
D- Acid Base Equilibria
16
26
E- Light and Molecular Structure
17
16
Total
280
Score
Name__________________ TA ____________________
E=hν
R = 8.314 J / (mol K)
λν = c
A = εlC
λdeBroglie = h / p = h / mv
Pa = XaPtot
T star = 2.898 mm· K/λmax
P = F/A
Ekin(e-) = hν - Φ = hν - hνo
∆E = q + w
Ekin = ½mv2
∆G° = ∆H° - T∆S°
Ekin = 3RT/2
∆G = ∆G° + RT ln Q
vrms =
∆G° = -RT ln K
(3RT / M )
q = mCs∆T
En = -R∞(Z2/n2) ∆E = -R∞(Z2/nf2 - Z2/ni2) R∞ = 2.18 × 10-18 J -23
kB = 1.381 × 10
J/K
me- = 9.11 × 10-31 kg h = 6.626 × 10
-34
w = -Pext∆V ∆H° = Σ∆H°f (products) - Σ∆H°f (reactants) NA = 6.022 × 1023 1 cal = 4.18 J 101.3 J = 1 L atm
Js
KaKb = Kw
c = 3.0 × 108 m/s
Kw = 10-14
1 nm = 10-9 m
pX = -log X pKa + pKb = pKw
1 kJ = 1000 J
[ A- ] pH = pKa + log [ HA]
1 Torr = 1 mmHg 1 atm = 760 mmHg J = (kg m2)/s2
Ecell = Ecathode − Eanode -19
1 eV = 1.602 × 10
J
PV = nRT MM = mRT / (PV) T(K) = T(C) + 273.15 R = 0.0821 L·atm / (mol·K)
∆G = −nFEcell F = 96,485C/mol e-
Name__________________ TA ____________________ Table of Standard Reduction Potentials
2 H+(aq) + 2 e-
→ H2 (g)
0
Name__________________ TA ____________________ Multiple Choice. (4 points each, 160 points total) Determine the best answer to the questions below and write your answer in the box provided. 1.) Which neutral atom could have the configuration 1s22s22p63s23p54s1? A) K
B) Cl
C) Na
D) Ar
E) S
2.) A mixture of oxygen atoms was allowed to react to form O2 molecules. Based on the mass spectrum below, which statements are true?
32 A) B) C) D)
34
36
32
O, 34O, and 36O isotopes are present in the sample there is only one isotope of oxygen present in the sample carbon dioxide was formed in the reaction there are two isotopes of oxygen in a 25:75 mixture
3.) A molecular picture for the reaction of H2 and NO is shown below. 2H2
+
2NO
Legend:
→
H=
N2 + N=
2H2O O=
+ Which of the diagrams below best represents the molecules after the reaction has taken place? (Circle one)
Name__________________ TA ____________________ 4.) Which of the following is a valid set of quantum numbers for an electron in a 2p orbital? A)
n=2, =2, m =0
B)
n=1, =3, m =3
C)
n=2, =1, m =1
D)
n=3, =1, m = -1
E)
n=1, =2, m =3
5.) A photon of wavelength 270 nm has the minimum energy needed to eject an electron from chromium metal. What effect will a photon of 540 nm have on chromium? A) B) C) D) E)
twice as many electrons will be ejected half as many electrons will be ejected no effect, no electron will be ejected the electron will be ejected but remain at rest the electron will be ejected with some kinetic energy
6.) What is the maximum number of electrons with the same spin quantum number (ms) for the principle quantum number 2? A) 1
B) 2
C) 3
D) 4
E) 8
7.) 2.00 liters of an ideal gas was heated in a balloon from 25°C to 50°C. What is the final volume of the balloon? A) 0.46 L
B) 1.00 L
C) 2.16 L
D) 4.00 L
8.) Under identical conditions, which gas will have the highest root mean square velocity? A) O2
B) He
C) Cl2
D) Ar
E) N2
Name__________________ TA ____________________
Name__________________ TA ____________________ 9.) For the energy levels shown below, which diagram best represents the absorption spectrum generated as electrons are excited? (Circle your answer.)
E
→ν 10.)
A) B) C) D) E)
B) Si
C) Ge
D) Sn
E) Pb
B) K+
C) Ar
D) S2-
E) Cl–
B) Si
C) Ge
D) Sn
E) Pb
Which species has the highest effective nuclear charge felt by the outermost electron? A) B
14.)
→ν
Which species has the highest ionization energy? A) C
13.)
→ν
Which species has the largest radius? A) Ca2+
12.)
→ν
Which element has the largest radius? A) C
11.)
→ν
B) Al
C) Ga
D) In
Which of the following substances is most ionic? H2S NO PH3 Na2S SO2
E) Tl
Name__________________ TA ____________________ 15.)
In the titration of 0.1173 g of base (MW=121.14 g/mol) it takes 11.43 mL of acid to reach the endpoint. What is the concentration of the acid in mol/L?
A) B) C) D) E)
16.)
0.08472 8.472 × 10-5 0.085 1.243 11.80
If butyric acid (shown right) smells sour, which one of the following compounds is also likely to smell sour? (circle one) butyric acid
17.)
What is the hybridization of oxygen in acetic acid (shown right)? A) sp
B) sp
2
C) sp
3
D) bent
O
Bad question: accept all answers! C
H
18.) Which molecular orbital has the highest energy? (circle one)
O
H
Name__________________ TA ____________________ 19.)
Consider the following reactions at equilibrium and determine which of the indicated changes will cause the reaction to proceed to the right. 1) CO(g) + 3 H2(g)
CH4(g) + H2O(g)
(remove H2O)
2) N2(g) + 3 H2(g)
2 NH3(g)
(add NH3)
3) BaO(s) + SO3(g) A) B) C) D) E)
BaSO4(s)
(add BaO)
1 2 3 1 and 3 1, 2 and 3
20.) What is the molarity of F- in a saturated solution of InF3? (Ksp = 7.9 x 10-10) InF3(s) A) B) C) D) E)
In3+(aq) + 3F-(aq)
2.3 x 10-3 3.8 x 10-3 5.8 x 10-4 2.8 x 10-5 7.0 x 10-3
21.) The following reaction is endothermic. What is true about the relative strengths of the bonds? Cl + CH4 → HCl + CH3 A) B) C) D) E)
breaking bonds takes energy making bonds releases energy a C-H bond is stronger than a H-Cl bond a C-H bond is weaker than a H-Cl bond the reaction absorbs heat
22.) A solution of an indicator is blue. When a lot of acid is added, the indicator turns yellow. Which statement is true when the solution is green? Ind- + H3O+ A) B) C) D) E)
HInd + H2O
The water produced dilutes the blue color and makes it appear green. Both Ind- and HInd are present in solution. The H3O+ is the green species. All the reactants have formed products. The endpoint was missed in the titration.
Name__________________ TA ____________________ 23.) In an atom of any element, the 2s orbital is: A) B) C) D)
always at the same energy as the 2p orbital always at lower energy than the 2p orbital only at the same energy as the 2p orbital for atoms with more than one electron only at lower energy than the 2p orbital for atoms with more than one electron
24.) For a gaseous atom of any element, X, an electron can be removed according to the following equation: X (g) → X+ (g) + eThis process A) requires energy for all elements, because the initial state is less stable than the final state B) requires energy for all elements, because the initial state is more stable than the final state C) does not require energy for any element, because the initial state is the same energy as the final state D) requires energy for some elements, because sometimes the initial state is more stable than the final state
25.) Consider the reaction of the weak base NH3 with the strong acid HCl: NH3(aq) + HCl(aq) NH4Cl(aq) Which of the following statements is true at the equivalence point for this general acid-base reaction? A) The pH is equal to 7 since salt and water are the main products B) The pH is equal to 7 because the acid is neutralized C) The pH is less than 7 because NH4+ is a weak acid D) The pH is greater than 7 because Cl- is a weak base 26.) You have a 1.00 M solution of acetic acid (CH3COOH) and a 1.00 M solution of iodic acid (HIO3). The Ka for acetic acid is 1.8 × 10-5 and the Ka for iodic acid is 1.7 × 10-1. Which + solution has the highest concentration of H3O and why? A) CH3COOH: It is a stronger acid than iodic acid and fully hydrolyzes to give more + H3O in solution. +
B) HIO3: It is a stronger acid than acetic acid, and hydrolyzes to give more H3O in solution. + C) Same concentration of H3O : Both solutions have a concentration of 1.00 M + H3O . + D) Same concentration of H3O : The concentration of CH3COOH is equal to the concentration of HIO3.
Name__________________ TA ____________________ 27.) You have two solutions: 0.100 M NaOH and 0.100 M NH3. To each, you add an equal volume of 0.100 M HCl to reach the equivalence point. After the addition of acid, which relationship is true for the resulting two solutions? (A) [NH4+] = [Na+]
(B) [NH4+] < [Na+]
(C) [NH4+] > [Na+]
28.) Heat is given off when hydrogen burns in air according to the equation 2 H2 + O2 → 2 H2O Which of the following is responsible for the heat? A) breaking H-H and O-O bonds B) breaking O-H bonds C) forming H-H and O-O bonds D) forming O-H bonds
29.) Given the following Ka values, determine which species is the strongest base.
A) B) C) D) E)
CO32H2SO4 SO42H2CO3 HPO42-
HSO4H2PO4HCO3-
1.2 × 10-2 6.3 × 10-8 4.7 × 10-11
30.) What is the pH of a 0.100M solution of acetic acid? Ka = 1.8 × 10-5 A) B) C) D) E)
1.00 2.87 4.74 7.00 10.63
31.) Which of the following species will oxidize Au(s)? A) B) C) D)
F2(g) O2 (g) Br2 (l) Ag+ (aq)
Name__________________ TA ____________________ 32.) Which of the following species will reduce Cl2(g) ? A) B) C) D)
Ag+ (aq) O2 (g) Au3+(aq) H2O
33.) What is the greatest producer of NOx pollutants? A) B) C) D)
utilities (burning of fossil fuels) non-industrial combustion (burning of biomass like wood) manufacturing transportation (high temperature combustion and burning of fossil fuels)
34.) What is the greatest producer of SOx pollutants? A) B) C) D)
utilities (burning of fossil fuels) non-industrial combustion (burning of biomass like wood) manufacturing transportation (high temperature combustion and burning of fossil fuels)
35.) Atmospheric carbon dioxide has an affect on the pH of rain. What is the normal pH of rain? A) B) C) D) E)
2.5 5.5 7.0 9.5 11.0
36.) Greenhouse gases are able to absorb and emit which type of light? A) B) C) D) E)
microwaves x-rays infrared visible ultraviolet
37.) Which of the following gases are greenhouse gases? A) B) C) D) E)
H2O CO2 NO2 SO3 all of the above
Name__________________ TA ____________________ 38.) The use of sodium azide decomposition for automobile airbag inflation is dangerous because: A) B) C) D) E)
sodium azide is toxic sodium metal is generated by the reaction the gas produced is toxic both A and B none of the above
Given the emission spectra for two different stars, answer the following questions. Star #1
Star #2
120
200 100
150 Intensity
Intensity
80 60 40
100
50
20 0
0 350
400
450
500
550
600
Wavelength (nm)
650
700
350
400
450
500
550
600
Wavelength (nm)
39.) Circle the spectrum corresponding to the star that is at the higher temperature. 40.) At 486 nm, there is a pronounced dip in the spectrum for Star # 2. To which energy transition in hydrogen atoms does the dip in the spectrum correspond? A) B) C) D)
n=2 to n=3 n=3 to n=2 n=4 to n=2 not enough information
650
700
Name__________________ TA ____________________
A. Kinetics (24 points total) In an analogy to the gas-phase chlorine catalytic cycle, NO also contributes to gas-phase ozone destruction. Step Reaction Ea (kJ/mol) A (cm3 molecule-1 s-1)_ 2.0 x 10-12 1 NO(g) + O3(g) → NO2(g) + O2(g) 11.6 ± 1.7 6.5 x 10-12 2 -1 ± 1 NO2(g) + O(g) → NO(g) + O2(g) What is the overall reaction corresponding to this two step process? O(g) + O3(g) → 2 O2(g) Which molecule is the intermediate in the two step reaction?______ NO2________ Which molecule is the catalyst in the two step reaction?_____ NO ________ Which step of the reaction is likely to be the slowest?_____1________ Four reaction coordinate diagrams are shown below. Energy is plotted versus the progress of the reaction. Use the diagrams to answer the questions below.
C B A D Which diagram represents the reaction(s) with the highest activation energy? ____D_____ Which diagram represents the reaction(s) with the lowest activation energy? ___C______ Which diagram represents a two step reaction? ____B_____ Which diagram represents that of reaction D in the presence of a catalyst? ____C_____ Which diagram represents the most greatly exothermic reaction? _____A____ Which two reactions absorb heat from the surroundings? ___C, D______
Name__________________ TA ____________________ B. Electrochemistry (36 points total) Balance the following oxidation/reduction reaction in acidic solution. -
MnO4 → Mn
MnO4- + Cl- → Mn2+ + Cl2
2+
Cl- →
Cl2
MnO4- → Mn2+
2Cl- →
Cl2
8H+ + MnO4- → Mn2+ + 4H2O
2Cl- →
Cl2
5e- + 8H+ + MnO4- → Mn2+ + 4H2O
2Cl- →
Cl2 + 2e-
10e- + 16H+ + 2MnO4- → 2Mn2+ + 8H2O (cathode: reduction ½ reaction)
10Cl- → 5Cl2 + 10e(anode: oxidation ½ reaction)
Full reaction: 16H+ + 2MnO4- + 10Cl- → 2Mn2+ + 8H2O + 5Cl2 This reaction can be used to do work. Write the cell notation for the galvanic cell.
׀
Cl- (aq) Cl2 (g)
׀׀H (aq), MnO (aq), Mn +
4
-
2+
(aq)
Aluminum metal will react with bromine gas to produce aluminum bromide salt. Assign the oxidation numbers for each element and place them in the boxes provided.
2Al(s) + 3Br2(l) 0
0
→ 2AlBr3(s) +3
-1
Calculate the free energy in kJ for the reaction. (use formulas and data from page 2 and 3)
Ecell = Ecathode − Eanode ∆G = −nFE cell
EBr2/Br - EAl/Al3+ = 1.08 –(-1.66) = 2.74 V = 2.74J/C
∆G = - (6e-)(96485C/mol e-) (2.74J/C) = 1586213 J = 1586 kJ
Name__________________ TA ____________________ C. Structure and Reactivity (18 points total) Consider the decomposition of 1 mole of N2O4 and answer the questions below. N2O4 (g) O
O N O
2 NO2 (g)
2
N
at 298K, K = 4.0 × 10-2
O
∆S = 175.73 J/K
N
O
O
What is the free energy for this reaction in kJ?
∆G° = -RT ln K = - (8.314 J/mol K) (298K) ln 4.0 × 10-2 = 7.98 × 103 J = 7.98 kJ Based on the data for this reaction, what is the bond enthalpy (in kJ) of a mole of nitrogennitrogen single bonds? Since the only thing happening in the reaction is the breaking of a N-N bond, the bond enthalpy will be equal to ∆H° for the reaction.
∆G° = ∆H° - T∆S°
∆H° = ∆G° + T∆S°
= 7.98 × 103 J + (298K) (175.73J/K) = 6.03 × 104 J = 60.3 kJ A flask is filled with 5 atm of N2O4, what will be the partial pressure of NO2 (in atm) when the system reaches equilibrium? 2 NO2 (g) N2O4 (g) initial 5 0 change -x +2x equilibrium 5-x 2x P2
(2 x) 2 K= = = 4.0 × 10 − 2 PN 2O 4 (5 − x) x is negligible in the 5–x expression because K is small relative to the 5atm of initial material. 0.020 = 4x2 x = 0.234 PNO2 = 2x = 0.447 atm NO 2
Name__________________ TA ____________________ D. Acid-Base Equilibria (26 points total) NO2 gas can dissolve in water and react to make acids. NO2(g) + H2O(l)
HNO3(aq) nitric acid
+
HNO2(aq) nitrous acid
Write the chemical reaction for the reaction of nitric acid in water. Circle the conjugate base. HNO3(aq)
H3O+(aq) +
+ H2O(l)
NO3-(aq)
Write the chemical reaction for the reaction of nitrous acid in water. Circle the conjugate base. HNO2(aq)
H3O+(aq) +
+ H2O(l)
NO2-(aq)
Based on the relative stabilities of the conjugate bases produced, which acid is stronger? Circle one and explain your reasoning. nitric acid nitrous acid NO3- is more stable than NO2- because it has more oxygens. Oxygen is electronegative and will stabilize the extra e- in the ion. Also, NO3- has 3 resonance structures while NO2 has only two. Resonance allows the electron density to be spread over the entire molecule further lowering the energy of the ion.
What is the pH of a solution of a 1.00L solution that is 0.100M HNO2 and 0.150M NaNO2? pKa = -log Ka pKa = 3.37 (Ka = 4.3 × 10-4)
[ A- ] pH = pKa + log [ HA]
pH = 3.37 + log (0.150NO2-/0.100HNO2) = 3.55
If you add 20.00 mL of 1.00M NaOH to the solution, what is the resulting pH? moles OH- = 1.00 M × 0.0200 L = 0.0200 moles initial change equilibrium
HNO2(aq) 0.100 -0.0200 0.080
+ OH0.0200 -0.0200 0
NO2-/ 0.150 +0.0200 0.170
pH = 3.37 + log (0.170NO2-/0.080HNO2) = 3.70
H2O
Name__________________ TA ____________________ E. Light and Molecules (16 points total) Molecules with conjugation (a series of alternating single and double bonds) are often colorful. Beta carotene is the molecule in carrots that makes them appear orange. The structure and absorbance spectrum of beta carotene are shown below.
A bs orbanc e
Absorbance Spectrum of Beta Carotene
250.00
350.00
450.00
550.00
650.00
750.00
Wavelength (nm)
Using the data in the absorbance spectrum, explain why beta carotene appears orange? Beta carotene absorbs from 400-500 nm in the visible range. This corresponds to absorbing green, blue, indigo and violet light. The light that is transmitted is a combination of red, orange, and yellow which we perceive as orange.
Household bleach is a strong oxidizing agent. When bleach reacts with beta carotene, the product is this beta-apo-14’-carotenal which absorbs light only in the UV region. beta-apo-14’-carotenal
O
Explain why a strong oxidizing agent like bleach would cause the color of the molecule to change from orange to colorless. An oxidizing agent takes electrons from other molecules. When electrons are taken from the beta carotene, the molecular structure breaks and a new structure is formed. Light is absorbed by a molecule when the photon has the same energy as that of an electronic excitation for the molecule. The new structure absorbs light differently because its electrons are configured differently. Specifically, for molecules with conjugated bonds, the electrons are promoted from a π to a π* level. In beta carotene, there is a large amount of bond conjugation than in the oxidized form beta-apo-14’-carotenal. Using particle in a box theory, electrons confined to smaller spaces have higher energy. In the beta-apo-14’-carotenal, the reduced conjugation will lead to high energy photons being required to excite the electrons so the molecule no longer absorbs lower energy visible light, but rather only the higher energy UV light.
