Physics 5A, Fall Semester 2007
Cuesta College, San Luis Obispo, CA
Cf. Giambattista/Richardson/Richardson, Physics, 1/e, Conceptual Question 13.11
Students were asked the following clicker question (Classroom Performance System, einstruction.com) at the beginning of their learning cycle:
[0.6 participation points.] The mass of a single aluminum atom is 27.0 u. What is the mass of one mole of aluminum atoms?
(A) (27.0/N_A) g = 4.48*10^-23 g.
(B) 27.0 g.
(C) 27.0 kg.
(D) (N_A/27.0) g = 2.23*10^22 g.
(E) (27.0*N_A) g = 1.63*10^25 g.
(F) (I'm lost, and don't know how to answer this.)
Sections 0906, 0907
(A) : 11 students
(B) : 5 students
(C) : 2 students
(D) : 4 students
(E) : 9 students
(F) : 2 students
Correct answer: (B)
The unified atomic mass unit, "u" is defined to be exactly 1/12th the mass of one mole of carbon-12 atoms (as opposed to the defunct "amu" atomic mass unit, which is either defined to be exactly 1/16th the mass of one mole of oxygen-16 atoms, or 1/16th the mass of one mole of all isotopes of oxygen as found in their naturally occurring proportions). Thus the mass of any particle, in unified atomic mass units, is exactly the mass of one mole of these particles.
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