Step-by-step explanation:
We have a 63.9 g sample of calcium hydroxide. First we have to convert those grams into moles. To do that we have to use the molar mass of calcium hydroxide.
Calcium hydroxide = Ca(OH)₂
molar mass of Ca = 40.08 g/mol
molar mass of O = 16.00 g/mol
molar mass of H = 1.01 g/mol
molar mass of Ca(OH)₂ = 1 * 40.08 g/mol + 2 * 16.00 g/mol + 2 * 1.01 g/mol
molar mass of Ca(OH)₂ = 74.10 g/mol
mass of Ca(OH)₂ = 63.9 g
moles of Ca(OH)₂ = 63.9 g /(74.10 g/mol)
moles of Ca(OH)₂ = 0.862 moles
In 1 molecule of Ca we have 2 atoms of O. So in 1 mol of Ca(OH)₂ we will have 2 moles of O atoms.
1 mol of Ca(OH)₂ = 2 moles of O atoms
moles of O atoms = 0.862 moles of Ca(OH)₂ * 2 moles of O /1 mol of Ca(OH)₂
moles of O atoms = 1.724 moles
One mol is similar to a dozen. When we say that we need a dozen eggs we know that we need 12 eggs. If we want a mol of eggs, we want 6.022*10^23 eggs. So one mol of something is 6.022 * 10^23 of that.
1 mol of O atoms = 6.022 * 10^23 atoms
n° of O atoms = 1.724 moles * 6.022 * 10^23 atoms/1 mol
n° of O atoms = 1.04 * 10^24 atoms
Answer: In a 63.9 g sample of Ca(OH)₂ we have 1.04 *10^24 atoms of oxygen.