Part B: Calculate the number of moles of magnesium, chlorine, and oxygen atoms in 4.20 moles of magnesium perchlorate Mg(CIO₄)₂.
In one molecule of Mg(CIO₄)₂ we have 1 atom of Mg, 2 atoms of Cl and 8 atoms of O. One mol of Mg(CIO₄)₂ molecules has 1 mol of Mg atoms, 2 moles of Cl atoms and 8 moles of O atoms.
We will use those relationships to find the number of moles of each element.
1 mol of Mg(CIO₄)₂ = 1 mol of Mg atoms = 2 moles of Cl atoms = 8 moles of O atoms
moles of Mg = 4.20 moles of Mg(CIO₄)₂ * 1 mol of Mg/(1 mol of Mg(CIO₄)₂)
moles of Mg = 4.20 moles
moles of Cl = 4.20 moles of Mg(CIO₄)₂ * 2 moles of Cl/(1 mol of Mg(CIO₄)₂)
moles of Cl = 8.40 moles
moles of O = 4.20 moles of Mg(CIO₄)₂ * 8 moles of O/(1 mol of Mg(CIO₄)₂)
moles of O = 33.6 moles
Answer: 4.20 , 8.40 , 33.6
Part c: a sample of propane, C₃H₈, contains 10.7 moles of carbon atoms. How many total moles of atoms does the sample contain?
One molecule of C₃H₈ contains 3 atoms of C and 8 atoms of H. Then, 1 mol of C₃H₈ molecules has 3 moles of C atoms and 8 moles of H atoms.
1 mol of C₃H₈ molecules = 3 moles of C atoms = 8 moles of H atoms
We have 10.7 moles of C, we can use the ratio between C and H to find the number of moles of H. The ratio between them is 3 to 8.
moles of C = 10.7 moles
moles of H = 10.7 moles of C * 8 moles of H/(3 moles of C)
moles of H = 28.5 moles
And now we can add them to find the total moles of atoms.
total moles of atoms = moles of C atoms + moles of H atoms
total moles of atoms = 10.7 moles + 28.5 moles
total moles of atoms = 39.2 moles
Answer: the sample contains 39.2 moles of atoms in total.