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CHEM 10054
Fall 2002
Exam #3
Name______________________
V=nRT, Kw = [H+][OH-] = 1.0 x 10-14, pH = log [H+], [H+] = 10-pH,
mol
mass sol ute
[A  ]
pH = pKa + log
, G = H – TS, M =
, (w/w)% =
x 100%,
l i ter
mass sol uti on
[HA ]
M1V1 = M2V2
Formula’s:
Multiple Choice (3 pts. each)
____ 1) What is the molarity of a solution prepared by dissolving 0.175 mol of AgNO 3
in enough water to make 755 ml of solution?
a) 0.00431 M
b) 0.132 M
c) 0.232 M
d) 4.31 M
____ 2) How many grams of NaOH are in 172 ml of a 3.5 M solution of NaOH?
a) 0.602 g
b) 24 g
c) 0.041 g
d) 1.66 g
____ 3) If H is positive (+) and S is positive (+) for a chemical reaction then which
of the following is true?
a)
b)
c)
d)
The reaction is spontaneous at high temperature.
The reaction is spontaneous at low temperature.
The reaction is never spontaneous.
The reaction is always spontaneous.
____ 4) What is the molarity of a solution that has an osmotic pressure of 1,330 torr
at 25C.
a) 0.853 M
b) 54.4 M
c) 14.0 M
d) 0.0715 M
c) C2H6
d) C6H12O6
____ 5) Which of the following is an electrolyte?
a) H2O
b) MgCl2
____ 6) A substance with a pOH of 8.20 has an [H+] =
a) 6.31 x 10-9 M
b) 1.58 x 10-6 M
c) 8.20 x 10-10 M
d) 12.5 x 10-14 M
____ 7) Solutions that have the same osmotic pressure are:
a) isotonic
b) hypertonic
c) hypotonic
d) hypnotic
____ 8) The products formed when carbonates (MCO3) react with acids are:
a) water + salt + carbon dioxide
c) salt + carbon dioxide
b) salt + water
d) water + carbon dioxide
____ 9) A rapid chemical reaction must always have a:
a) high reaction enthalpy
c) high activation energy
b) low reaction enthalpy
d) low activation energy
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____ 10) Pure water is separated by a semi-permeable membrane from a solution
containing 2 %NaCl(aq). Which event will take place?
a) water flows into the salt solution.
c) water flows out of the salt solution.
b) nothing happens.
d) NaCl flows into the water.
____ 11) How many grams of glucose (C6H12O6) are required to make 500 ml of
0.344 M solution?
a) 172 g
b) 0.0321 g
c) 31.0 g
d) 0.172 g
____ 12) Which of the following processes involves an increase in entropy?
a) freezing
b) crystallization
c) boiling
d) condensation
____ 13) A chemical reaction that releases heat to the surroundings is said to be
___________ and has a _________ value of H.
a) endothermic, positive
c) exothermic, negative
b) endothermic, negative
d) exothermic, positive
____ 14) Which of the following would be combined with nitrous acid (HNO2) to make
a buffer solution?
a) KNO3
b) HNO2
c) NaOH
d) KNO2
____ 15) Which of the following is not a colligative property of solutions?
a) melting point
b) boiling point
c) density
d) vapor pressure
____ 16) If 30 g of benzene is added, to 120 g of toluene, the mass percent of
benzene in the solution is:
a) 40%
b) 30%
c) 25%
d) 20%
c) 7
d) 9
____ 17) A solution of which pH is most acidic:
a) 3
b) 5
____ 18) Which of the following contains the most energy:
a) ice
b) water
c) steam
d) all are equal
____ 19) Liquids that are mutually soluble in all proportions are:
a) saturated
b) immiscible
c) unsaturated
d) miscible
____ 20) What is the conjugate base of ammonia, NH3?
a) NH4+
c) NH2
b) NH3
d) none of these
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Solve the following problems showing all work. Answer essay questions using
complete sentences. Remember to use proper units, significant figures and
rounding.
1.
Sulfur dioxide reacts with oxygen gas to give sulfur trioxide according to the
following unbalanced equation: (18 pts.)
SO3(g) 
 SO2(g) + O2(g) H =56 kJ
a) Balance this equation and write the equilibrium constant (K eq) expression for this
reaction.
b) Given the following equilibrium concentrations, calculate the value of K eq:
[SO2] = 0.350 mol/L, [O2] = 0.0450 mol/L, [SO3] = 0.274 mol/L
c) Are the reactants or products favored at equilibrium? Explain.
d) Is the reaction endothermic or exothermic? Explain.
e) Is the reaction endergonic or exergonic? Explain.
f) Explain the effects of the following on the equilibrium:
1) Increasing the concentration of SO2.
2) Decreasing the temperature.
3) Increasing the pressure by decreasing the volume.
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2) What is the hydronium ion concentration of a solution that contains 0.700 M acid
and 0.440 M conjugate base if Ka = 3.59 x 10-8. (6 pts.)
3) a) Describe how to prepare a buffer solution and explain how pH is regulated when
acid (H+) or base (OH-) is added to a buffer solution. Use the equation shown
below to assist with your answer (6 pts).
 H+ + HSO H2SO3 
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4) Calculate the number of grams of hydrogen gas produced when 125 ml of 2.75 M
HCl is reacted with magnesium according to the following unbalanced equation:
(10 pts.)
HCl + Mg  H2 + MgCl2
b) What was the percentage yield for this reaction if 0.285 g of H 2 was actually
collected?
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Bonus: Draw a heating curve for H2O. Label: each axis, Hf, Hv, solid phase, liquid
phase and gaseous phase. Define Hf and Hv. (6 pts.)