AP® Chemistry 2006 Free-Response Questions

392 Pages·2015·8.29 MB·English

AP® Chemistry
2006 Free-Response Questions

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INFORMATION IN THE TABLE BELOW AND IN THE TABLES ON PAGES 3-5 MAY BE USEFUL IN ANSWERING
THE QUESTIONS IN THIS SECTION OF THE EXAMINATION.

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STANDARD REDUCTION POTENTIALS IN AQUEOUS SOLUTION AT 25°C

Half-reaction E°(V)
F (g) + 2e- Æ 2F- 2.87
2
Co3+ + e- Æ Co2+ 1.82
Au3+ + 3e- Æ Au(s) 1.50
Cl (g)+ 2e- Æ 2Cl- 1.36
2
O (g)+ 4H+ + 4e- Æ 2H O(l) 1.23
2 2
Br (l)+ 2e- Æ 2Br- 1.07
2
2Hg2+ + 2e - Æ Hg 2+ 0.92
2
Hg2+ + 2e- Æ Hg(l) 0.85
Ag+ + e- Æ Ag(s) 0.80
Hg 2+ + 2e- Æ 2Hg(l) 0.79
2
Fe3+ + e- Æ Fe2+ 0.77
I (s)+ 2e- Æ 2I- 0.53
2
Cu+ + e- Æ Cu(s) 0.52
Cu2+ + 2e- Æ Cu(s) 0.34
Cu2+ + e- Æ Cu+ 0.15
Sn4+ + 2e- Æ Sn2+ 0.15
S(s)+ 2H+ + 2e- Æ H S(g) 0.14
2
2H+ + 2e- Æ H (g) 0.00
2
Pb2+ + 2e- Æ Pb(s) –0.13
Sn2+ + 2e- Æ Sn(s) –0.14
Ni2+ + 2e- Æ Ni(s) –0.25
Co2+ + 2e- Æ Co(s) –0.28
Cd2+ + 2e- Æ Cd(s) –0.40
Cr3+ + e- Æ Cr2+ –0.41
Fe2+ + 2e- Æ Fe(s) –0.44
Cr3+ + 3e- Æ Cr(s) –0.74
Zn2+ + 2e- Æ Zn(s) –0.76
2H O(l)+ 2e- Æ H (g) + 2OH- –0.83
2 2
Mn2+ + 2e- Æ Mn(s) –1.18
Al3+ + 3e- Æ Al(s) –1.66
Be2+ + 2e- Æ Be(s) –1.70
Mg2+ + 2e- Æ Mg(s) –2.37
Na+ + e- Æ Na(s) –2.71
Ca2+ + 2e- Æ Ca(s) –2.87
Sr2+ + 2e- Æ Sr(s) –2.89
Ba2+ + 2e- Æ Ba(s) –2.90
Rb+ +e- Æ Rb(s) –2.92
K+ +e- Æ K(s) –2.92
Cs+ +e- Æ Cs(s) –2.92
Li+ +e- Æ Li(s) –3.05

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ADVANCED PLACEMENT CHEMISTRY EQUATIONS AND CONSTANTS

ATOMIC STRUCTURE E = energy u = velocity
v = frequency n = principal quantum number
E = hv c = lv
h l = wavelength m = mass
l = p = mu
mu p = momentum
-2.178 ¥ 10-18
E = joule
n n2 Speed of light, c = 3.0 ¥ 108m s-1
EQUILIBRIUM Planck’s constant, h = 6.63 ¥ 10-34 J s
+ −
[H ][A ]
Ka = [HA] Boltzmann’s constant, k = 1.38 ¥ 10-23 J K-1

K = [OH−][HB+] Avogadro’s number = 6.022 ¥1023 mol-1
b [B]
K = [OH−][H+] = 1.0 × 10−14 @ 25(cid:68)C Electron charge, e = -1.602 ¥ 10-19 coulomb
w
= K × K 1 electron volt per atom = 96.5 kJmol-1
a b
pH = − log [H+], pOH = − log[OH−]

14 = pH + pOH Equilibrium Constants
− K (weak acid)
pH = pK + log [A ] a
a [HA] K (weak base)
b
pOH = pK + log [HB+] Kw (water)
b [B] K (gas pressure)
p
pK = − log K , pK = − log K
a a b b K (molar concentrations)
c
K = K (RT)Dn,
p c S(cid:68) = standard entropy
where Dn = moles product gas − moles reactant gas
H(cid:68) = standard enthalpy
THERMOCHEMISTRY/KINETICS G(cid:68) = standard free energy

DS(cid:68) = Â S(cid:68) products -Â S(cid:68) reactants E(cid:68) = standard reduction potential
DH(cid:68) = Â DH(cid:68) products -Â DH(cid:68) reactants T = temperature
f f
n = moles
DG(cid:68) = Â DG(cid:68) products -Â DG(cid:68) reactants
f f m = mass
DG(cid:68) = DH(cid:68) - TDS(cid:68) q = heat
c = specific heat capacity
= -RT ln K = -2.303RT log K
C = molar heat capacity at constant pressure
p
= -n(cid:1) E(cid:68)
E = activation energy
a
DG = DG(cid:68) + RT lnQ = DG(cid:68) + 2.303RT logQ k = rate constant
A = frequency factor
q = mcDT

DH
C = Faraday's constant,(cid:1) = 96,500 coulombs per mole
p DT
of electrons
ln A - ln A = -kt
t 0 Gas constant, R = 8.31 J mol-1 K-1
1 1
A - A = kt = 0.0821 L atm mol-1 K-1
t 0
= 8.31 volt coulomb mol-1 K-1
-E e1j
ln k = a + ln A
R T

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GASES, LIQUIDS, AND SOLUTIONS

PV = nRT P = pressure
V = volume
Ê n2a ˆ
ÁË P + V2 ˜¯ (V - nb) = nRT T = temperature
n = number of moles
moles A
PA = Ptotal ¥ XA,where XA = D = density
total moles
P = P + P + P + ... m = mass
total A B C
m u = velocity
n =
M

K = (cid:68)C + 273
u = root-mean-square speed
rms
PV PV
1 1 = 2 2 KE = kinetic energy
T T
1 2 r = rate of effusion
m
D = M = molar mass
V
p = osmotic pressure
3kT 3RT
urms = m = M i = van't Hoff factor
K = molal freezing-point depression constant
KE per molecule = 1mu2 f
2 K = molal boiling-point elevation constant
b
3 A = absorbance
KE per mole = RT
2 a = molar absorptivity
r M
1 = 2 b = path length
r M
2 1 c = concentration
molarity, M = moles solute per liter solution Q = reaction quotient

molality = moles solute per kilogram solvent I = current (amperes)
DTf = iKf ¥ molality q = charge (coulombs)
DTb = iKb ¥ molality t = time (seconds)
p = iMRT E(cid:68) = standard reduction potential
A = abc
K = equilibrium constant

OXIDATION-REDUCTION; ELECTROCHEMISTRY Gas constant, R = 8.31 J mol-1 K-1
= 0.0821 L atm mol-1 K-1

= 8.31 volt coulomb mol-1 K-1
c d
[C] [D]
Q = a b , where a A + b B Æ c C + d D Boltzmann's constant, k = 1.38 ¥ 10-23 J K-1
[A] [B]
K for H O = 1.86 K kg mol-1
q f 2
I =
t K for H O = 0.512 K kg mol-1
b 2
RT 0.0592 1 atm = 760 mm Hg
E = E(cid:68) - ln Q = E(cid:68) - logQ @ 25(cid:68)C
cell cell n(cid:1) cell n = 760 torr
nE(cid:68) STP = 0.000(cid:68)C and 1.000 atm
log K =
0.0592 Faraday's constant,(cid:1) = 96,500 coulombs per mole

of electrons

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2006 AP® CHEMISTRY FREE-RESPONSE QUESTIONS

CHEMISTRY
Section II
(Total time—90 minutes)

Part A
Time—40 minutes
YOU MAY USE YOUR CALCULATOR FOR PART A.

CLEARLY SHOW THE METHOD USED AND THE STEPS INVOLVED IN ARRIVING AT YOUR ANSWERS.
It is to your advantage to do this, since you may obtain partial credit if you do and you will receive little or no credit if
you do not. Attention should be paid to significant figures.

Be sure to write all your answers to the questions on the lined pages following each question in the booklet with the
pink cover. Do NOT write your answers on the green insert.

Answer Question 1 below. The Section II score weighting for this question is 20 percent.

1. Answer the following questions that relate to solubility of salts of lead and barium.
(a) A saturated solution is prepared by adding excess PbI (s) to distilled water to form 1.0 L of solution at
2
25°C. The concentration of Pb2+(aq) in the saturated solution is found to be 1.3 × 10−3 M. The chemical
equation for the dissolution of PbI (s) in water is shown below.
2
PbI (s) ←→ Pb2+(aq) + 2 I−(aq)
2
(i) Write the equilibrium-constant expression for the equation.
−
(ii) Calculate the molar concentration of I (aq) in the solution.
(iii) Calculate the value of the equilibrium constant, K .
sp
(b) A saturated solution is prepared by adding PbI (s) to distilled water to form 2.0 L of solution at 25°C. What
2
are the molar concentrations of Pb2+(aq) and I−(aq) in the solution? Justify your answer.
(c) Solid NaI is added to a saturated solution of PbI at 25°C. Assuming that the volume of the solution does
2
not change, does the molar concentration of Pb2+(aq) in the solution increase, decrease, or remain the
same? Justify your answer.
(d) The value of K for the salt BaCrO is 1.2 × 10−10. When a 500. mL sample of 8.2 × 10−6 M Ba(NO )
sp 4 3 2
is added to 500. mL of 8.2 × 10−6 M Na CrO , no precipitate is observed.
2 4
(i) Assuming that volumes are additive, calculate the molar concentrations of Ba2+(aq) and CrO 2−(aq)
4
in the 1.00 L of solution.
(ii) Use the molar concentrations of Ba2+(aq) ions and CrO 2−(aq) ions as determined above to show
4
why a precipitate does not form. You must include a calculation as part of your answer.
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2006 AP® CHEMISTRY FREE-RESPONSE QUESTIONS

Answer EITHER Question 2 below OR Question 3 printed on page 8. Only one of these two questions will be
graded. If you start both questions, be sure to cross out the question you do not want graded. The Section II score
weighting for the question you choose is 20 percent.

1
CO(g) + O (g) → CO (g)
2 2 2
2. The combustion of carbon monoxide is represented by the equation above.
(cid:68)
(a) Determine the value of the standard enthalpy change, DH , for the combustion of CO(g) at 298 K using
rxn
the following information.
C(s) + 1O (g) → CO(g) DH(cid:68) = −110.5 kJ mol−1
2 2 298
C(s) + O (g) → CO (g) DH(cid:68) = −393.5 kJ mol−1
2 2 298
(cid:68)
(b) Determine the value of the standard entropy change, DS , for the combustion of CO(g) at 298 K using
rxn
the information in the following table.

S(cid:68)
298
Substance
(J mol−1 K−1)
CO(g) 197.7
CO2(g) 213.7
O (g) 205.1
2
(cid:68)
(c) Determine the standard free energy change, DG , for the reaction at 298 K. Include units with
rxn
your answer.
(d) Is the reaction spontaneous under standard conditions at 298 K ? Justify your answer.
(e) Calculate the value of the equilibrium constant, K , for the reaction at 298 K.
eq

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2006 AP® CHEMISTRY FREE-RESPONSE QUESTIONS

3. Answer the following questions that relate to the analysis of chemical compounds.

(a) A compound containing the elements C, H, N, and O is analyzed. When a 1.2359 g sample is burned
in excess oxygen, 2.241 g of CO (g) is formed. The combustion analysis also showed that the sample
2
contained 0.0648 g of H.
(i) Determine the mass, in grams, of C in the 1.2359 g sample of the compound.
(ii) When the compound is analyzed for N content only, the mass percent of N is found
to be 28.84 percent. Determine the mass, in grams, of N in the original 1.2359 g sample of
the compound.
(iii) Determine the mass, in grams, of O in the original 1.2359 g sample of the compound.
(iv) Determine the empirical formula of the compound.

(b) A different compound, which has the empirical formula CH Br, has a vapor density of 6.00 g L−1 at 375 K
2
and 0.983 atm. Using these data, determine the following.
(i) The molar mass of the compound
(ii) The molecular formula of the compound

STOP
If you finish before time is called, you may check your work on this part only.
Do not turn to the other part of the test until you are told to do so.

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2006 AP® CHEMISTRY FREE-RESPONSE QUESTIONS

CHEMISTRY
Part B
Time—50 minutes
NO CALCULATORS MAY BE USED FOR PART B.

Answer Question 4 below. The Section II score weighting for this question is 15 percent.

4. Write the formulas to show the reactants and the products for any FIVE of the laboratory situations described
below. No more than five choices will be graded. In all cases, a reaction occurs. Assume that solutions are
aqueous unless otherwise indicated. Represent substances in solution as ions if the substances are extensively
ionized. Omit formulas for any ions or molecules that are unchanged by the reaction. You need not balance the
equations.

Example: A strip of magnesium is added to a solution of silver nitrate.

(a) Solid potassium chlorate is strongly heated.
(b) Solid silver chloride is added to a solution of concentrated hydrochloric acid.
(c) A solution of ethanoic (acetic) acid is added to a solution of barium hydroxide.
(d) Ammonia gas is bubbled into a solution of hydrofluoric acid.
(e) Zinc metal is placed in a solution of copper(II) sulfate.
(f) Hydrogen phosphide (phosphine) gas is added to boron trichloride gas.
(g) A solution of nickel(II) bromide is added to a solution of potassium hydroxide.
(h) Hexane is combusted in air.

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