5 Steps to a 5 AP Chemistry 2019

AP Chemistry Practice Exam 2 ❮ 351

Use the following information on the bases in the

following table to answer questions 43–44.

A large number of compounds adopt the sodium

chloride structure. The following table contains

some examples of the compounds in this group

with their respective melting points and the sum

of the cation-anion radii.

COMPOUND FORMULA

MELTING

POINT

(çC)

SUM OF

IONIC

RADII

(PM)

Sodium chloride NaCl 801 283

Sodium fluoride NaF 996 235

Calcium oxide CaO 2898 240

Strontium oxide SrO 2531 258

Barium oxide BaO 1972 275

43. Why are the melting points of the alkaline earth
    oxides (CaO, SrO, and BaO) so much higher
    than those of the other two compounds in the
    table?
    (A) Smaller ions have lower lattice energy.
    (B) Smaller ionic charges lead to higher lattice
    energy.
    (C) Larger ions have higher lattice energy.
    (D) Higher ionic charges lead to higher lattice
    energy.


44. Why do the melting points of the alkaline metal
    oxides decrease in the order CaO > SrO > BaO?
    (A) Larger ions have higher lattice energies,
    which leads to lower melting points.
    (B) Smaller ions have lower lattice energies,
    which leads to higher melting points.
    (C) Larger ions have lower lattice energies,
    which leads to lower melting points.
    (D) Smaller ions have a greater affinity for
    oxygen, which leads to a higher melting
    point.
    45. Joseph Priestly discovered oxygen gas by the decom-
    position of solid mercury(II) oxide, HgO, to oxygen
    gas, O 2 , and liquid mercury metal, Hg. How many
    moles of oxygen gas will form when 4.32 g of solid
    mercury(II) oxide decomposes? The formula mass
    of mercury(II) oxide is 216 g mol-^1.
    (A) 0.100 mol
    (B) 0.0100 mol
    (C) 0.0200 mol
    (D) 0.0150 mol

COMPOUND

FOR-

MULA

MOLAR

MASS

(g mol−1)

MELTING

POINT

(çC)

Carbon tetrafluoride CF 4 88 - 184

Carbon tetrachloride CCl 4 154 - 23

Carbon tetrabromide CBr 4 332 92

Carbon tetraiodide CI 4 520 171

46. According to the data in the table above, which of
    the following best explains the trend in increasing
    melting points?
    (A) All the molecules are nonpolar and, for such
    molecules, intermolecular forces increase
    with increasing molar mass.
    (B) All the molecules are polar and, for such
    molecules, intermolecular forces increase
    with increasing molar mass.
    (C) The molecules with the lower melting
    points are nonpolar and the molecules with
    the higher molar masses are polar.
    (D) The sequence is a coincidence since all the
    molecules have the same intermolecular forces.


47. Determine the H+(aq) concentration in 1.0 M
    phenol, C 6 H 5 OH, solution. (The Ka for phenol is
    1 × 10 -^10 .)
    (A) 1 × 10 -^10 M
    (B) 1 × 10 -^9 M
    (C) 1 × 10 -^3 M
    (D) 1 × 10 -^5 M

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21-Moore_PE02_p341-370.indd 351 31/05/18 1:54 pm