Question

1- Calculate the following: A- Number of moles in 10 gram of Cr(OH)s. B- Number of Atoms in 2.5 gram of Cr(OH)s.

Answer 1

Q1. (A) mass Cr(OH)₅ = 10 g

moles Cr(OH)₅ = (mass Cr(OH)₅) / (molar mass Cr(OH)₅)

moles Cr(OH)₅ = (10 g) / (137.0 g/mol)

moles Cr(OH)₅ = 0.073 mol

(B) mass Cr(OH)₅ = 2.5 g

moles Cr(OH)₅ = (mass Cr(OH)₅) / (molar mass Cr(OH)₅)

moles Cr(OH)₅ = (2.5 g) / (137.0 g/mol)

moles Cr(OH)₅ = 0.0182 mol

molecules Cr(OH)₅ = (moles Cr(OH)₅) * (Avogadro's number)

molecules Cr(OH)₅ = (0.0182 mol) * (6.022 x 10²³ molecules/mol)

molecules Cr(OH)₅ = 1.1 x 10²² molecules

there are 11 atoms in one molecule of Cr(OH)₃

atoms Cr(OH)₅ = (molecules Cr(OH)₅) * (11 atoms/molecule)

atoms Cr(OH)₅ = (1.1 x 10²² molecules) * (11 atoms/molecule)

atoms Cr(OH)₅ = 1.2 x 10²³ atoms