ACS Scholarship Exam
North Central College
May 24, 2008
Problem Solving. Show your work on these problems as partial credit is awarded for partially correct answers. You have 75 minutes.
INFORMATION THAT MAY BE OF USE TO YOU IN THE EXAM
NA = 6.022 x 1023 /mol
Order
R = 8.31447J/(mol.K) or 0.08206 L atm/(mol K)
Integrated Rate Law
Half-Life
other kinetics equations
0
[A]t = -kt + [A]0
[A]o/2k
k = Ae
1
ln[A]t = -kt + ln[A]0
0.693/k
lnk = lnA - Ea/RT
2
1/[A]t = kt + 1/[[A]0
1/k[A]o
ln
Ea / RT
k 2 Ea 1 1
=
k 1 R T1 T2
Enthalpy Changes Involving H2O
Per Mole
ΔHfus (at 0˚C)
ΔHvap (at 100˚C)
Molar heat cap. (s)
Molar heat cap. (l)
Molar heat cap. (g)
6.02 kJ/mol
40.7 kJ/mol
37.6 J/mol˚C
75.4 J/mol˚C
33.1 J/mol˚C
Per Gram
ΔHfus (at 0˚C)
334 J/g
ΔHvap (at 1000˚C)
2260 J/g
Specific heat (s)
2.09 J/g˚C
Specific heat (l)
4.18 J/g˚C
Specific heat (g)
1.84 J/g˚C
Periodic Table
Page 1 of 5
ACS Scholarship Exam
North Central College
May 24, 2008
Name
School
1) The Ksp of the mineral fluorite – Illinois’ state mineral, CaF2, is known to be 2 x 10-10. Estimate the solubility, in mol/L of this
mineral.
2) In the laboratory synthesis of hydrogen gas, zinc was reacted with hydrochloric acid. Hydrogen gas was evolved and collected
over water at 25˚C; it had a volume of 355 cm3 at a total pressure of 750 mm Hg. The vapor pressure of water at 25˚C is known
to be about 24 mm Hg.
a.
What was the partial pressure of hydrogen in the sample?
b.
How many moles of hydrogen were collected?
3) An ice cube weighing 30.0 g melts in water originally at 20.0˚C.
a.
How much heat is absorbed from the water when the ice cube melts?
b.
How many grams of water can be cooled to 0˚C by the melting of the ice cube?
Page 2 of 5
ACS Scholarship Exam
North Central College
May 24, 2008
4) A solution prepared by dissolving 30.0 g of ethyl alcohol, C2H5OH, in 50.0 g of carbon tetrachloride, CCl4, has a density of 1.28
g/mL. Calculate
a.
the weight per cent (%) of ethyl alcohol.
b.
the mole fraction of ethyl alcohol.
c.
the molality (m = mol/kg solvent) of ethyl alcohol.
d.
the molarity (M = mol/L soln) of ethyl alcohol.
5) For the reaction
A(g) + 2B(g) + C(g)  D(g)
the following data were obtained at constant temperature:
Experiment
a)
b)
c)
d)
Initial [A]
Initial [B]
(mol/L)
(mol/L)
1
0.0500
0.0500
2
0.1000
0.0500
3
0.1000
0.1000
4
0.0500
0.0500
What is the order with respect to each reactant?
Write the rate law.
What is the overall order?
Calculate k.
Initial [C]
(mol/L)
0.0100
0.0100
0.0100
0.0200
Initial Rate
(mol/L.s)
6.25 x 10-3
1.25 x 10-2
5.00 x 10-2
6.25 x 10-3
Page 3 of 5
ACS Scholarship Exam
North Central College
May 24, 2008
THESE LAST THREE QUESTIONS WILL BE USED TO DETERMINE TIEBREAKERS
6) In the analysis of organic compounds containing C, H, and O, the sample is burned in excess oxygen; this converts all of the
carbon to CO2 and all of the hydrogen to H2O. These products then are separated and weighed. Analysis of a 2.00 mg vitamin C
sample gives 3.00 mg and 0.816 mg of CO2 and H2O, respectively. What are the percentages of C, H, and O in vitamin C and
determine its empirical formula. If the molar mass is determined to be ~180 g/mol, determine the molecular formula.
7) If you are asked to make 20 g of the compound [Co(NH 3)5SCN]Cl2 from [Co(NH3)5Cl]Cl2 via the reaction
[Co(NH3)5Cl]Cl2 + KSCN  KCl + [Co(NH3)5SCN]Cl2
but you know that you can only expect a 55% yield and this is done using a 60% excess of KSCN. How much (in g) of each
reagent should you use?
Page 4 of 5
ACS Scholarship Exam
North Central College
May 24, 2008
8) Determine the pH of a 0.0025 M sodium carbonate solution if the pKa1 and pKa2 of H2CO3 are 6.37 and 10.25, respectively.
Finally, determine the molar concentrations of all species in solution.
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