Each atom in a sample of lithium (Z = 3, atomic mass 6.941 u) has all of its electrons removed. If a charge of magnitude 1.0 mC was collected in this way, what is the mass of the lithium sample?
A) 0.010 µg
B) 0.024 µg
C) 0.031 µg
D) 0.072 µg

Question

Quizplus · Accepted Answer

Each lithium atom has 3 protons, so removing all the electrons from it results in a charge of +3.0e, where e is the elementary charge. Therefore, the number of lithium atoms in the sample is:
(1.0 × 10^-3 C) / (3.0 × 1.602 × 10^-19 C/atom) = 20833.3 atoms
The mass of one lithium atom is 6.941 u / Avogadro's number = 1.15 × 10^-22 g/atom. Therefore, the mass of the lithium sample is:
(20833.3 atoms) × (1.15 × 10^-22 g/atom) = 0.024 µg.

Each Atom in a Sample of Lithium (Z = 3