Test 3A
Test 3A
Test 3A
Department of Chemistry
Memorial University of Newfoundland
Chemistry 1051 Term Test 3A
March 23rd, 2006
Instructor: Dr. T. D. Fridgen
Name:
Student Number:
Signature:
Time Allowed: 50 minutes
Aids Allowed: Electronic Calculator
Answer all questions in the spaces provided. Marks will be deducted for incorrect use of significant
figures.
Question
Value
A1 - A5
10 marks
B1 - B8
8 marks
C1
7 marks
C2
5 marks
C3
9 marks
C4
6 marks
Total
45 marks
1
Mark
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PART A. Short Answer
A1.
Complete and balance the following chemical equations. (4 marks)
a) MnO2
+
H2
→
b) Na(s)
+
H 2O(l)
→
c) Mg(s)
+
H 2O(l)
→
d) Which of b) or c) do you think is the most vigorous?
A2.
Fe2+, Fe3+, MnO2, and MnO4! are species involved in a redox reaction. Write an unbalanced
redox reaction involving these species. (ie. One species gets oxidized and one reduced) (1
mark).
A3.
Write the formulas of the ionic compounds that calcium forms between CO32- and PO43-.(1 mark)
A4.
The molar solubility of PbI2 is 1.5x10-3 M. Calculate the value of Ksp for PbI2. (2 marks)
A5.
Give an example of a sparingly soluble salt that (2 marks)
a) would be more soluble at lower pH.
b) would be mostly unaffected by a pH change.
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Part B. Multiple Choice (Each question is worth 1 = 8 marks)
B1.
The electron configuration, [Kr]4d5 is the electron configuration of (refer to periodic table
below).
A)
B)
C)
D)
E)
B2.
Which of the following pairs of elements do you think represents the largest increase in atomic
size? (refer to periodic table above)
A.
B.
C.
D.
E.
B3.
Tc
Mo+
Tc2+
Both 1 and 2
Both 2 and 3
Sc to V
Pd to Ru
Ag to Au
Cu to Ag
Ta to V
Which of the following hydroxides would have the lowest pH? (You do not need a calculator!!!)
A.
B.
C.
D.
E.
KOH
Pb(OH)2 Ksp = 1.4×10-20
Be(OH)2 Ksp = 6.9×10-22
Sc(OH)3 Ksp = 4.2×10-18
Y(OH)3 Ksp = 1.0×10-22
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B4.
B5.
A.
2H 2O(l) → 2H 2 + O2 (g)
B.
NaCl(s) → Na(s) +
C.
NH 3 (g) + HCl(g) → NH 4Cl(s)
D.
Fe 2O3 (s) + 3H 2 (g)
E.
C6 H12O6 (s) + 6O 2 (g) → 6CO2 (g) + 6H 2O(g)
Cl 2 (g)
2Fe(s) + 3H 2O(g)
If Q<K the reaction is spontaneous in the direction of the products
If Q=K, ΔG = 0.
If K >>> 1 the reaction will essentially go to completion.
If Q>K then ΔG< 0.
For a spontaneous process, if ΔSsys is negative then ΔSsurr must be positive.
In which case must a reaction be spontaneous at all temperatures?
ΔH is positive, ΔS is positive
ΔH=0, ΔS is negative
ΔS=0, ΔH is positive
ΔH is negative, ΔS is positive
none of these
If ΔGo = 0 for a reaction which of the following statements must always be true.
A.
B.
C.
D.
E.
B8.
→
1
2
Which of the following statements is incorrect?
A.
B.
C.
D.
E.
B7.
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For which of the following processes would ΔSo be expected to be most positive?
A.
B.
C.
D.
E.
B6.
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ΔΗo = 0 kJ
ΔSo = 0 J K-1
Keq = 0
Keq = 1
Keq < 1
The Ksp for lead (II) phosphate, Pb3(PO4)2 is 1×10-54 298 K. Which of the following statements is
incorrect?
Pb3 (PO 4 ) 2 (s) → 3Pb 2+ (aq)
A.
B.
C.
D.
E.
+ 2PO 34− (aq)
Pb3(PO4)2 is only slightly soluble.
ΔGo is positive for the dissolution of Pb3(PO4)2.
The entropy change for the dissolution of Pb3(PO4)2 is positive.
For a saturated solution, ΔG = 0.
For a saturated solution ΔGo = 0.
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Part C. Long Answer Questions
C1.
a) What is the pH of a buffer solution made by mixing 140.0 mL of a 0.300 M formic acid
solution (HCOOH) and 75.0 mL of a 0.450 M sodium formate (NaOOCH)? (For HCOOH Ka =
1.9×10-4).
(3 marks)
b) What is the pH of the buffer solution in a) after the addition of 10.0 mL of 0.150 M NaOH
solution? (3 marks)
c) If the initial concentrations of the acid and base in the buffer were halved, briefly explain
how the pH change would be different from part b) after the addition of base. (1 mark)
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C2.
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A solution is saturated with CrPO4 (Ksp = 2.4×10-23). A second solution, of equal volume, is
saturated with Ca(IO3)2 (Ksp = 7.1×10-7). If the two solutions are mixed (no solids from either
solution) will Ca3(PO4)2 (Ksp = 1.3×10-32) precipitate? A picture may help to understand what the
question is asking. (5 marks)
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C3.
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Iron rusts according to the following chemical equation.
2Fe(s)
+
3
O 2 (g)
2
→
Fe 2O3 (s)
a) Given the standard enthalpies of formation and standard entropies below, determine the
standard free energy for the rusting of iron, at 298 K, according to the above equation. (3 marks)
Fe(s)
O2(g)
Fe2O3(s)
ΔfHo / kJ mol-1
0
0
-826
So / J K-1 mol-1
27
205
90
b) The partial pressure of O2 in the atmosphere is about 0.20 atm. Show that this reaction is
spontaneous even on a cold Labrador day at -45 oC. (R=8.314 J K-1) (3 marks)
c) At what temperature does the conversion of rust to pure iron and oxygen (reverse of the above
reaction) become spontaneous? (R=8.314 J K-1) (3 marks)
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C4.
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The normal boiling point for mercury is 630 K. What is the vapor pressure of mercury at room
temperature, 298 K? (R=8.314 J K-1) (6 marks)
Hg(l) → Hg(g)
Δ vap H D = 59.3 kJ
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