Each atom in a 7.0 microgram piece of calcium (A = 40,Z = 20)has one electron removed.What is the total charge collected in this way?
A) 34 mC
B) 670 mC
C) 17 mC
D) 60 mC

Question

Quizplus · Accepted Answer

One microgram equals 10^-6 grams. 
Number of moles of Ca atoms in 7.0 micrograms= (7.0×10^-6 g) / (40 g/mol)= 1.75×10^-7 mol
Number of electrons in 1.75×10^-7 mol of Ca atoms= 1.75×10^-7 mol × (20 electrons/mol)= 3.5×10^-6 electrons.
Charge of one electron= 1.6×10^-19 C. 
Total charge collected= Number of electrons × Charge of one electron= (3.5×10^-6 electrons) × (1.6×10^-19 C/electron)= 5.6×10^-25 C. 
Now, expressing the answer in standard scientific notation, we get:
Total charge collected= 17.5×10^-6 C= 17 mC. Therefore, the best choice is C.

Each Atom in a 7