CHM110H5 Final: CHM110H5 2015 Exam Practice

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10 Apr 2016
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CHM110H5F
1. a. Hydrogen peroxide can be prepared by the reaction of an alkaline earth metal peroxide and an
acid, for example
Ba O2
(
s
)
+2HC l(aq)H2O2
(
aq
)
+BaC l2
(
aq
)
. When 1.30 g of BaO2 are
mixed with 25.0 mL of HCl solution which contains 0.0272 g of HCl per mL, how many g
of hydrogen peroxide can be produced?
b. An aqueous antifreeze solution of 40.0% w/w ethylene glycol, C2H6O2, and has a density of
1.05 g/mL. Calculate the molarity, the molality and the mole fraction of ethylene glycol in the
solution.
2. a. Manganese is a transition metal which can exhibit a number of different oxidation states in
different compounds. A 2.747 g sample of manganese metal was reacted with excess HCl to
produce 3.22 L of H2 gas at 373 K and 0.951 atm. The other product was MnClx(aq). What is
the molecular formula of the manganese chloride compound produced in the reaction? Show
all calculations. Assume ideal gas behaviour for the gaseous product.
b. In the van der Waal’s equation,
(
P+n2
V2a
)
(
Vnb
)
=nRT
, why is a term added to the
measured pressure and why is a term subtracted from the container volume to correct for non-
ideal gas behaviour?
3. At 275°C, the equilibrium constant for the endothermic reaction
N H 4Cl
(
s
)
N H3(g)+HC l(aq)
is 1.04E-02 atm2.
a. If solid NH4Cl was mixed with 0.800 atm HCl and 0.500 atm NH3 in a 1.00 L flask, in what
direction will spontaneous reaction occur? Briefly explain.
b. Calculate the partial pressures of HCl and NH3 that will exist when equilibrium is established.
4. a. What is the solubility of AgOH (in g/L) in a 0.10 M aqueous solution of AgNO3? You may use
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any method that you wish to do this, but you should explain any simplifying assumptions
made in the calculations.
Ksp for AgOH = 2.0E-08
b. Explain how you would expect the solubility of AgOH to depend on the pH of the solution.
c. Why does the solubility of AgOH increase when NH3 is added to the solution?
5. Use the simultaneous equations method taught in class to solve the following problem.
Explain any simplifying assumptions made in the derivation or calculation.
How many moles of solid NaOH must be added to 1.0 L of 1.5 M weak acid, HNO2, in order to
produce a buffer solution whose pH is 3.0? (assume that adding the solid causes no volume change).
KA for HNO2 = 4.0E-04
6. a. For hydrofluoric acid, HF, KA = 6.78E-04 M at room temperature. An aqueous solution of HF
has a pH = 3.00. What is the original acid concentration, CA? You may use any method to do
these calculations, but you should note and justify any simplifying assumptions made in the
calculations.
b. Consider the following data for each of the three acid/conjugate base pairs.
Acid pKAConjugate Base pKB
H2S 7.05 HS6.95
H2CO36.35 HCO37.65
CH3COOH 4.74 CH3COO9.26
What one equation fits the data for each of the acid/conjugate base pairs?
Show a derivation of that equation.
7. In one half-cell of a galvanic cell, a piece of platinum metal, Pt, dipe into a solution
containing 0.850 M Fe3+ and 0.010 M Fe2+. In the other half-cell, Cd, dips into a 0.500 M
solution of Cd2+.
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ε0=+0.771V
for
2+¿
¿F e¿
3+¿+e¿
F e¿
ε0=0.403V
for
a. Draw a diagram of this galvanic cell, labelling its parts.
b. Write the shorthand notation for the cell.
c. Write the equation for the cell reaction
d. Calculate the standard cell potential.
e. Calculate the equilibrium constant for the cell reaction.
f. Calculate the cell potential.
8. Consider the reaction
S O3
(
g
)
+SC l2(aq)SOC l2
(
l
)
+S O2
(
g
)
for which
∆ G0=75.2 kJ /mol
. Using the data below to answer each of the following questions by
doing a quantitative calculation of the appropriate thermodynamic functions AND giving a
very brief explanation of each.
Species ΔH°f (kJ/mol) ΔS° (J/mol K)
S O3
(
g
)
-396.0 256.7
SC l2(aq)
-50.0 184
SOC l2
(
l
)
-245.6 121
S O2
(
g
)
-296.8 248.1
a. What is the equilibrium constant for the reaction?
b. Are the product more or less ordered than the reactants?
c. Do the reactants absorb or release heat?
d. To increase the yield of products would the temperature need to be increased or
decreased?
e. At what temperature would the reaction become non-spontaneous?
9. Answer Part a. OR Part b.
a. (1) Define what is meant by the Boyle Temperature for a gas.
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