Properties, magnetism and catalysts of the first series
Answers are for parents and teachers.
1
Find the mass of 12.0 cm³ of a nickel-like metal of density 8.9 g/cm³.
m = ρ × V = 8.9 × 12.0 = 106.8 g.
2
Use M = 65 g/mol and ρ = 7.1 g/cm³ for zinc to find the volume of one mole. Compare it with 7.1 cm³/mol for iron and say what it tells you about zinc’s density.
V = 65 ÷ 7.1 = 9.2 cm³/mol. A mole of zinc takes more room than a mole of iron (9.2 against 7.1) and is not much heavier, so zinc’s density is lower.
3
Rank Co²⁺, Mn²⁺, Cu⁺ and V²⁺ from the smallest to the largest magnetic moment. (Atoms: Co [Ar] 3d⁷ 4s², Mn [Ar] 3d⁵ 4s², Cu [Ar] 3d¹⁰ 4s¹, V [Ar] 3d³ 4s².)
Cu⁺ 3d¹⁰ (0) < Co²⁺ 3d⁷ (3) = V²⁺ 3d³ (3) < Mn²⁺ 3d⁵ (5).
4
A task: 68 g of hydrogen peroxide H₂O₂ (H = 1, O = 16) decomposes with MnO₂ as 2H₂O₂ → 2H₂O + O₂. Find the mass of oxygen and its volume at STP (22.4 L/mol).
n(H₂O₂) = 68 ÷ 34 = 2 mol, so n(O₂) = 1 mol. m = 1 × 32 = 32 g and V = 22.4 L.
5
In 2SO₂ + O₂ ⇌ 2SO₃ with V₂O₅ (S = 32, O = 16), what is the largest mass of SO₃ from 32 g of SO₂, and what mass of oxygen is needed?
n(SO₂) = 32 ÷ 64 = 0.5 mol. At most 0.5 mol of SO₃ = 0.5 × 80 = 40 g, using 0.25 mol of O₂ = 8 g.