To calculate the number of formula units in 0.671 moles of iron III sulfate, we need to use Avogadro's number, which is 6.022 x 10^23 particles per mole.

The formula for iron III sulfate is Fe2(SO4)3, which means that each formula unit contains 2 iron ions and 3 sulfate ions.

So, the number of formula units in 0.671 moles of iron III sulfate is:

0.671 moles Fe2(SO4)3 x (2 Fe ions + 3 SO4 ions) / 1 mole Fe2(SO4)3 = 4.03 x 10^23 formula units

Therefore, there are 4.03 x 10^23 formula units in 0.671 moles of iron III sulfate.