AP Chemistry Practice Exam 1 ❮ 339Question 6(a)Br Br
H C CHYou get 1 point for the correct Lewis structure.
(b)Br BrBr BrH C CHYou get 1 point for the correct Lewis structure.
(c) The order is C 2 H 2 > C 2 H 2 Br 2 > C 2 H 2 Br 4.
The structure of acetylene shown in the problem indicates a linear molecule with a HCC bond angle
of 180°. The correct Lewis electron-dot diagram for C 2 H 2 Br 2 indicates a trigonal planar arrangement
about each carbon atom with a HCC bond angle of 120°. The correct Lewis electron-dot diagram for
C 2 H 2 Br 4 indicates a tetrahedral arrangement about each carbon atom with a HCC bond angle of 109°.
You get 1 point if you list the compounds in the correct order, and you get 1 point for a correct
explanation including the bond angles.
Total your points for the problem. There is a maximum of 4 possible points.Question 7(a) Ptotal = 626 mm Hg
Poxygen = 626 - 25 = 601 mm Hg
P = 601 mm Hg/760 mm Hg = 0.791 atm (The 760 mm Hg = 1 atm is in the exam booklet and
in the back of this book.)
V = 500.0 mL = 0.5000 L
T = 26°C = 299 K
R = 0.0821 L atm mol–1 K–1 (given in the exam booklet and in the back of this book)
n = PV/RT (Rearranged from PV = nRT, which is in exam booklet and in the back of this book.)
= (0.791 atm × 0.5000 L)/(0.0821 L atm mol–1 K–1 × 299 K)
= 0.0161 mol O 2 (32.0 g O 2 /mol O 2 ) = 0.516 g O 2 (3 significant figures)
Give yourself 1 point for the correct answer (no deduction for rounding differently). You must include
ALL parts of the calculation (including “=”). There is no deduction for combining steps. You cannot
get this point if you did not subtract the vapor pressure of water from the total pressure.20-Moore_PE01_p307-340.indd 339 31/05/18 1:58 pm