Moles and Avogadro's Numbers

One mole KMnO₄ contains four moles oxygen atoms. Thus only 0.25 mol KMnO₄ contains one mole oxygen atoms.

One mole Pb(NO₃)₂ forms one mole PbO. Molar mass PbO = 207 + 16 = 223 g.

Atomic mass = mass of one atom × Avogadro's number = 2.66 × 10⁻²³ × 6.022 × 10²³ ≈ 16 u.

One mole of CCl₄ contains 4 moles of Cl atoms. Thus 0.5 mol contains 2 mol Cl atoms.

From the ratio, 2 mol H₂S produce 3 mol S. Therefore, 1 mol H₂S produces 1.5 mol S. Mass = 1.5 × 32 = 48 g.

Urea contains two nitrogen atoms per molecule. Thus 0.5 mol nitrogen atoms correspond to 0.25 mol urea. Mass = 0.25 × 60 = 15 g.

10 g CaCO₃ = 0.1 mol. One mole CaCO₃ gives one mole CO₂. Therefore volume = 0.1 × 22.4 = 2.24 dm³.

The balanced equation shows equal coefficients for K and KOH, giving a simplified ratio of 1:1.

Benzene contains six carbon atoms in each molecule, so one mole contains six moles of carbon atoms.

Multiplication by Avogadro's number gives approximately 56 g mol⁻¹, the atomic mass of iron.

16 g CH₄ = 1 mol. One mole methane requires two moles oxygen. Mass = 2 × 32 = 64 g.

Iron provides only 0.5 mole while sulfur provides 0.625 mole. Iron is present in the smaller stoichiometric amount.

Twelve moles of water react with one mole Al₄C₃. Mass = 12 × 18 = 216 g.

Each mole KMnO₄ contains four moles oxygen atoms. Therefore, 0.25 mole contains one mole oxygen atoms.

One mole Pb(NO₃)₂ forms one mole PbO whose molar mass is 223 g.

1.6 g oxygen equals 0.05 mole. Therefore, the number of molecules equals 0.05 × Avogadro's number.

Twenty-five grams equal 0.25 mole CaCO₃. The same amount of CO₂ occupies 5.6 dm³ at STP.

Moles of CS₂ = 19/76 = 0.25 mol. According to the equation, 1 mol CS₂ produces 2 mol SO₂. Therefore, 0.25 mol CS₂ forms 0.5 mol SO₂. Mass = 0.5 × 64 = 32 g.

One formula unit produces 5 ions (2 Al³⁺ + 3 SO₄²⁻). Therefore, 0.1 mol gives 0.5 mol ions = 3.011 × 10²³ ions.