Question

How many moles of cei3 are in 9.42 × 1021 formula units of cei3 (cerium(iii) iodide; a bright, water, soluble solid). answer in units of mol?

Answer 1

1 mol of any substance is made of 6.022 x 10²³ units.
When its 1 mol of a formula, its made of 6.022 x 10²³ formula units
Therefore if 6.022 x 10²³ formula units of CeI₃ make up 1 mol of CeI₃
Then 9.42 x 10²¹ formula units make up - 1/(6.022 x 10²³) x (9.42 x 10²¹) = 0.0156 mol of CeI₃
Therefore number of moles of CeI₃ - 0.0156 mol