Use the following information to answer questions
44-45.METAL IONIONIC RADIUS
(pm) (CUBIC
ENVIRONMENT)MELTING
POINT OF
OXIDE (°C)
Sodium Na+ 132 1275
(sublimes)
Cadmium Cd^2 + 124 1500
Lanthanum La^3 + 130 2256- Each of the ions in the table form stable oxides
(Na 2 O, CdO, and La 2 O 3 ). Lanthanum oxide,
La 2 O 3 , has a melting point significantly higher
than that of the other oxides. Which of the fol-
lowing is the best explanation of why this is true?
(A) Lanthanum is a lanthanide element and the
melting points of these elements are always
high.
(B) There is more oxygen in the formula La 2 O 3
than in the other formulas.
(C) Lanthanum had the highest charge; there-
fore, it has the highest lattice energy.
(D) Alkali metals like sodium and transition metals
like cadmium tend to have low melting points. - The lithium ion, Li+, is smaller than the sodium
ion. How does the melting point of lithium
oxide, Li 2 O, compare to that of sodium oxide?
(A) It is higher because smaller ions have a
higher lattice energy.
(B) It is the same because the charges are the same.
(C) It is lower because smaller ions have a
smaller lattice energy.
(D) It is impossible to predict because there is
insufficient information in the problem.
46. During the investigation of a chemical reaction
by a chemistry student, she was able to determine
that the reaction was nonspontaneous at 1 atm
and 298 K. However, she learned that cooling
the system with dry ice (- 78 °C) caused the reac-
tion to become spontaneous. Which of the fol-
lowing combinations must apply to this reaction?
(A) ΔH < 0, ΔS < 0, and ΔG = 0
(B) ΔH > 0, ΔS < 0, and ΔG > 0
(C) ΔH < 0, ΔS < 0, and ΔG > 0
(D) ΔH > 0, ΔS > 0, and ΔG > 0
47. What is the ionization constant, Ka, for a weak
monoprotic acid if a 0.060 molar solution has a
pH of 2.0?
(A) 2.0 × 10 -^3
(B) 2.0 × 10 -^1
(C) 1.7 × 10 -^1
(D) 5.0 × 10 -^3
HHH
CC C
HHH- Cyclopropane, pictured above, is a relatively unsta-
ble compound. As seen in the diagram, the carbon
atoms form the corners of an equilateral triangle
and each carbon atom has two hydrogen atoms
attached to complete an octet of electrons around
the carbon atoms. Based upon this structure, why
is cyclopropane a relatively unstable compound?
(A) Hydrocarbon compounds are relatively
unstable in general.
(B) Compounds that have identical atoms
bonded to each other are relatively unstable.
(C) The bonds do not match the angles.
(D) There is no resonance to stabilize the
compound.
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