Answer:
1.23 x 10²⁴ formula units K₂S
Step-by-step explanation:
To find the amount of formula units in potassium sulfide, you need to (1) convert grams to moles (via the molar mass) and then (2) convert moles to formula units (via Avogadro's number). The conversions/ratios need to be arranged in a particular way that allows for the cancellation of units. Units are cancelled when then are located both in the numerator and denominator somewhere in the math. The final answer should have 3 sig figs because the given value (225 grams) has 3 sig figs.
Avogadro's number:
6.02 x 10²³ formula units = 1 mole
Molar Mass of K₂S:
110.26 g/mol
225 g K₂S 1 mole 6.02 x 10²³ units
---------------- x ----------------- x ---------------------------- = 1.23 x 10²⁴ formula units
110.26 g 1 mole