7. how many formula units are equal to a 0.25 g sample of chromium (iii) sulfate,
cr2(so4)3?
a

38.541 × 10¹⁹ formula units

Explanation:

Given data:

Mass of chromium sulfate = 0.25 g

Formula units in 0.25 g = ?

Solution:

The given problem will solve by using Avogadro number.

It is the number of atoms , ions and molecules in one gram atom of element, one gram molecules of compound and one gram ions of a substance.

The number 6.022 × 10²³ is called Avogadro number.

For example,

18 g of water = 1 mole = 6.022 × 10²³ formula units of water

Number of moles of chromium sulfate =  Mass / molar mass

Number of moles of chromium sulfate = 0.25 g/ 392.16 g/ mol

Number of moles of chromium sulfate = 6.4 × 10⁻⁴ moles

Number of formula units:

1 mole = 6.022 × 10²³ formula units

6.4 × 10⁻⁴ moles × 6.022 × 10²³ formula units / 1 mol

38.541 × 10¹⁹ formula units