Question

How many molecules of Cl- are in 410mL solution to .72 M CaCl2 (aq)??

Answer 1

First we calculate the moles of CaCl₂
moles = concentration (M) x volume (dm³)
moles = 0.72 x 0.41
= 0.2952

Each mole of CaCl₂ releases 2 moles of Cl-
moles of Cl- = 0.2952 x 2
= 0.5904

Each mole contains 6.02 x 10²³ molecules. Total molecules:
0.5904 x 6.02 x 10²³
= 3.55 x 10²³ Cl- ions