課程名稱︰普通化學甲下
課程性質︰
課程教師︰彭旭明
開課學院：理學院
開課系所︰化學系
考試日期（年月日）︰2010/04/16
考試時限（分鐘）：120min
是否需發放獎勵金：是
（如未明確表示，則不予發放）
試題 :
1.Colligative properties can be sources of insight into not only the
properties of solutions, but also the properties of the solute. For
example, acetic acid, CH3COOH, behaves different solvents. (8 points)
(a) The freezing point of a 5.00% by mass aqueous acetic acid solution is
-1.72℃. What is the molar mass of the solute? Explain any discrepancy
between the experimental and the expected molar mass.
(b) The freezing-point depression associated with a 5.00% by mass solution
of acetic acid in benzene is 2.32℃. What is the experimental molar
mass of the solute in benzene? What can you conclude about the nature
of acetic acid in benzene?
Solvent Freezing Kf(K‧kg Boiling Kb(K‧kg
point(℃) ‧mol^-1) point(℃) ‧mol^-1)
--------------------------------------------------------------
Benzene 5.5 5.12 80.1 2.53
Water 0 1.86 100.0 0.51
2.Calculate the equilibrium constant at 25℃ for each of the following
reactions. (12 points)
(a) The synthesis of carbon disulfide from natural gas (methane):
2CH4(g)+S8(s)→2CS2(l)+4H2S(g)
(b) The production of acetylene from calcium carbide:
CaC2(s)+2H2O(l)→Ca(OH)2(s)+C2H2(g)
(c) The oxidation of ammonia, the first step in the production of nitric
acid:
4NH3(g)+5O2(g)→4NO(g)+6H2O(l)
(d) The industrial synthesis of urea, a common fertilizer:
CO2(g)+2NH3(g)→CO(NH2)2(s)+H20(l)
3.Let α be the fraction of PCl5 molecules that have decomposed to PCl3 and
Cl2 in the reaction PCl5(g)→PCl3(g)+Cl2(g) in a constant-volume container;
then the amount of PCl5 at equilibrium is n(1-α), where n is the amout
present initially. (6 points)
(a) Derive an equation for K in terms of α and the total pressure P, and
solve it for α in terms of P.
(b) Calculate the fraction decomposed at 556 K, at which temperature K=4,96,
and the total pressure is 0.5 bar, and 1.00 bar, respectively.
4.A chemist needs to prepare the compound PH3BCl3 by using the reaction PH3(g)
+BCl3(g)→PH3BCl3(s) for which K=19.2 at 60℃. (12 points)
(a) Write the expression for K.
(b) What is the value of Kc for this reaction?
(c) Some solid PH3BCl3 was added to a closed 500mL vessel at 60℃ that
already contains 0.0128 mol PH3. What is the equilibrium concentration
of PH3.?
(d) At 70℃, K=26.2. Is the reaction endothermic or exothermic? Explain
your reasoning.
(e) What is the new value of Kc?
(f) Can the reactants in the preceding reacion be classified as acids or
bases? Explain your answer.
5.A combustion analysis of 1.200 g of an anhydrous sodium salt gave 0.942g of
CO2, 0.0964 g of H2O, and 0.246g of Na. The molar mass of the salt is 112.02
g‧mol^-1.[The acid: Ka1=5.9*10^-2; Ka2=6.5*10^-5] (9 points)
(a) What is the chemical formula of the salt?
(b) The salt contains carboxylate group (-CO2^-), and the carbon atoms are
bonded together. Draw the Lewis structure of the anion.
(c) Next, 1.50 g of this sodium salt was dissolved in water and diluted to
50.0 mL. Identify the dissolved substance: Is it an acid, a base, or is
it amphiprotic? Calculate the pH of the solution.
6.Although many chemical reactions take place in water, it is often necessary
to use solvents; liquid ammonia (normal boiling point,-33℃) has been used
extensively. Many of the reactions that take place in water have analogous
reactions in liquid ammonia. (10 points)
(a) Write the chemical equation for the autoprotolysis of NH3.
(b) What are the formulas of the acid and base species that result from the
autoprotolysis of liquid ammonia?
(c) The autoprotolysis constant, Kam, of liquid ammonia has the value 1*10^
-33 at -35℃. What is the value of pKam at that temperature?
(d) What is the molarity of NH4+ ions in liquid ammonia?
(e) Evalute pNH4 and pNH2, which are the analogs of pH and pOH, in liquid
ammonia at -35℃.
(f) Determine the realtion between pNH4, pNH2, and pKam.
7.Suppose that 15.0 mL of 0.15 M NH3(aq) is titrated with 0.10 M HCl(aq).[NH3:
Kb=1.8*10^-5] (12 points)
(a) What is the initial pH of the 0.15 M NH3(aq)?
(b) What is the pH after the addition of 15.0 mL of 0.10 M HCl(aq)?
(c) What volume of 0.10 M HCl(aq) is required to reach halfway to the
stoichiometric point?
(d) Calculate the pH at the halfway point.
(e) What volume of 0.10 M HCl(aq) is required to reach the stoichiometric
point?
(f) Calculate the pH at the stoichiometric point.
(g) Use the following table to select an indicator for the titration.
Indicator pH range of pKIn Indicator pH range of pKIn
color change color change
---------------------------------------------------------------------------
Thymol blue 1.2-2.8 1.7 Phenol ree 6.6-8.0 7.9
Methyl orange 3.2-4.4 3.4 Thymol blue 8.0-9.6 8.9
Bromophenol blue 3.0-4.6 3.9 Phenolphthalein 8.2-10.0 9.4
Bromocresol green 3.8-5.4 4.7 Alizarin yellow R 10.1-12.0 11.2
Methyl red 4.8-6.0 5.0 Alizarin 11.0-12.4 11.7
8.Consider the two equilibria: (9 points)
CaF2(s)→Ca2+(aq)+2F-(aq) Ksp=4.0*10^-11
F-(aq)+H20(l)→HF(aq)+OH-(aq) Kb(F-)=2.9*10^-11
(a) Write the chemical equation for the overall equilibrium and determine
the corresponding equilibrium constant.
(b) Determine the solubilitu of CaF2 at pH=7.0, and pH=3.0, respectively.
9.In attempt to determine the amount of sulfur dioxide in the air near a power
plant, two students set up a bubbler that passes air through 50.0 mL of 1.0*
10^-4 M NaOH(aq). The temperature is 22℃, and the atmospheric pressure 753
Torr. The air is pumped for 2.5 h at a flow rate of 3.0 L‧h^-1. The
students then returned to the laboratory and titrated the solution with 1.5*
10^-4 M HCl(aq) with phenolphthalein indicator to see how much NaOH was left
unreacted. They found that 30.2 mL of HCl(aq) was required to reach the
stoichiometric point. [molar mass: S=32; air=78% N2+ 22% O2] (9 points)
(a) Write the balanced chemical equation for the reaction of SO2 and NaOH
(aq).
(b) What amount of NaOH (in mol) had reacted with the SO2?
(c) What was the concentration of sulfur dioxide in the air, in parts per
million?
10.A seris of solutions known to contain one or more of the folowing was
analyzed:Na2CO3, NaHCO3, and NaOH. 100-ml aliquots of the solution were
titrated with 0.100 N HCl. Given below are the volumes case. Calculate
the concentrations of each constituent in each solution. (15 points)
(a) 27.3 and 30.7
(b) 0.0 and 18.1
(c) 4.60 and 12.2
(d) 27.1 and 27.1
(e) 15.1 and 30.2
11.The compound P4S3 is oxidized by nitrate ions in acid solution to give
phosphoric acid, sulfate ions, and nitric oxide, NO. Write the balanced
equation for each half-reaction and the overall equaion for the reaction.
(6 points)
12.Determine the emf of each of the following cells: (8 points)
(a) Pt(s)│H2(g,1.0 bar)│HCl(aq,0.075 M)║HCl(aq,1.0 mol‧L^-1)│H2(g,1.0
bar)│Pt(s)
(b) Zn(s)│Zn2+(aq,0.37 mol‧L^-1)║Ni2+(aq,0.059 mol‧L^-1)│Ni(s)
(c) Pt(s) │Cl2(g,250 torr)│HCl(aq,1.0M)║HCl(aq,0.85M)│H2(g,125 torr)│
Pt(s)
(d) Sn(s)│Sn2+(aq,0.277mol‧L^-1)║Sn4+(aq,0.867mol‧L^-1),Sn2+(aq,0.55mol
‧L^-1)│Pt(s)
13.The reduction of ClO4- can be conducted in either basic or acidic solutions
. The two half- reactions are: (6 points)
(1,acidic) ClO4-(aq)+2H+(aq)+2e-→ClO3-(aq)+H2O(l) E°=+1.23V
(2,basic) ClO4-(aq)+H2O(l)+2e-→ClO3-(aq)+2OH-(aq) E°=+0.36V
(a)Show how these processes are related by deriving an expression that
gives the pH dependence of the emf for each half-reaction.
(b)What is the potential of each reaction in neutral solution?
***Total 122 points; Examination time 2hrs***
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