Question

How do you determine the number of ions per formula unit?

Answer 1

one formula unit is equal to one mol of a substance. So one formula unit of carbon dioxide would have the formula CO2.

Now, in every formula unit there are 6.022 X 10^23 ions (avogadro's number). In the case of CO2, there are 3 ions in each formula unt. So for carbon dioxide, you add up the total number of ions present (3--1 carbon plus 2 oxygen) and multiply 3 by 6.022 x 10^23 to find out the number of ions in a formula unit.

CO2 = 1.8 X 10^23 ions
H3PO4 = 4.8 X 10^24 ions
AL(OH)3 = 4.2 X 10^24 ions
KNO2 = 2.4 X 10^24 ions
Al(OH)CL2 = 3.01 X 10^24 ions