5 Steps to a 5 AP Chemistry 2019

320 ❯ STEP 5. Build Your Test-Taking Confidence

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The average distribution of bromine isotopes on

Earth is in the following table:

ISOTOPE PERCENT ABUNDANCE

(^79) Br 50.7%
(^81) Br 49.3%
The highest mass peaks in the mass spectrum
of methyl bromide, CH 3 Br, are at 94 and 96
atomic mass units (there are smaller peaks cor-
responding to the small quantities of the less
common isotopes of carbon and hydrogen). The
spectrum plot shown is of this region.
94
Intensit
y
Mass (atomic mass units)
96
The mass spectrum for methylene bromide,
CH 2 Br 2 , is more complicated in that there are
three main peaks in the highest mass region
(again ignoring minor contributions from other
carbon and hydrogen isotopes). Methylene bro-
mide has a mass of about 174 atomic mass units.

51. Which of the following is the best representa-
    tion of the mass spectrum of CH 2 Br 2 in the 174
    region?
    (A) (B)

172

Intensit

y

Mass (atomic mass units)

174 176 172

Intensit

y

Mass (atomic mass units)

174 176

(C) (D)

172

Intensit

y

Mass (atomic mass units)

174 176 172

Intensit

y

Mass (atomic mass units)

174 176

52. There are three steps in the formation of a
    solution. It is necessary to overcome the inter-
    molecular forces present within the solute. It is
    also necessary to overcome the intermolecular
    forces present within the solvent. Both of these
    steps require energy related to the strength of
    the intermolecular forces. The final step in the
    formation of a solution involves the creation of
    new intermolecular forces between the solute
    and solvent. This energy release is related to the
    strength of the intermolecular forces created.
    Which of the following illustrates a situation
    most likely to require the least amount of energy
    to overcome the intermolecular forces?
    (A) CaO(s) + H 2 O(l)

+ –

–++––++––++–

+–+–+––++–+–

(B) CH 3 OH(l) + H 2 O(l)

(C) CCl 4 (l) + Cl 2 (g)

(D) CCl 4 (l) + CH 3 OH(l)

20-Moore_PE01_p307-340.indd 320 31/05/18 1:58 pm