Question

7. How many formula units are equal to a 0.25 g sample of Chromium (III) sulfate,

Cr2(SO4)3?
A

Answer 1

To determine the number of formula units in a sample of Chromium (III) sulfate, divide the mass of the sample by the molar mass of the compound.

Step-by-step explanation:

To determine the number of formula units in a sample of Chromium (III) sulfate, we need to use the molar mass of the compound. The molar mass of Cr2(SO4)3 can be calculated by adding up the atomic masses of all the atoms in the compound.

The atomic masses are: Cr = 52 g/mol, S = 32 g/mol, and O = 16 g/mol.

So the molar mass of Cr2(SO4)3 = (2 x 52 g/mol) + (3 x (32 g/mol + 4 x 16 g/mol)) = 392 g/mol.

To find the number of formula units, we can now use the following equation:

Number of formula units = (Mass of sample)/(Molar mass)

Plugging in the values, we get Number of formula units = 0.25 g/392 g/mol = 0.000637 formula units.

Answer 2

38.541 × 10¹⁹ formula units

Step-by-step 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