Chapter 2: The Mole MCQ 2

Avogadro's Law

• Equal volumes of gases, under the same conditions of temperature and pressure, contain equal numbers of molecules.
• 1 mole of a gas at standard temperature and pressure (s.t.p) occupies a volume of 22.4L or 22,400cm³.

Moles and Molar Mass

• Moles: a mole of a substance is the amount of that substance that contains as many particles (atoms, molecules, or ions) as there are atoms of ¹²C in 12g of ¹²C.
• Molar Mass (Mr): the mass of 1 mole of a substance, usually expressed in units of g/mol.
• Formula: Moles x Mr = Mass (in grams)

Conversions

• Moles to Mass: Moles x Mr = Mass (in grams)
• Moles to Volume: Moles x 22.4 = Volume (in liters) at s.t.p
• Mass to Moles: Mass ÷ Mr = Moles
• Volume to Moles: Volume ÷ 22.4 = Moles at s.t.p

Standard Temperature and Pressure (s.t.p)

• Standard Temperature: 273K
• Standard Pressure: 101325 Pa

The Mole (mol)

• A mole is the unit for the amount of a substance, defined as the amount of a substance that contains as many particles (atoms, molecules, or ions) as there are atoms of ¹²C in 12g of ¹²C.
• Avogadro's Number (L) is 6 × 10²³ atoms, which is the number of atoms in 12g of ¹²C.

Moles and Particles

• 1 mole = 6 × 10²³ atoms or molecules or ions
• Moles are represented in chemical formulas, e.g., H₂ + Br₂ → 2HBr (2 moles, 1 mole, 1 mole)

Converting Moles to Grams

• Moles × Mᵣ (relative molecular mass) = Mass (in grams)
• Example: Calculate the mass of 0.33 moles of calcium chloride (CaCl₂) → Mᵣ = 111, Mass = 0.33 × 111 = 37g

Molar Volume of Gases

• Avogadro's Law: Equal volumes of gases, under the same conditions of temperature and pressure, contain equal numbers of molecules.
• At standard temperature and pressure (s.t.p.), 1 mole = 22.4L = 22,400cm³
• Example: Calculate the number of moles in 560 cm³ of N₂ at s.t.p. → 0.025 moles

Calculations Involving Moles

• (a) Moles → atoms/molecules: 0.75 moles of Na = 4.5 × 10²³ atoms
• (b) Grams → atoms/molecules: 950g carbon dioxide balloon → 21.59 moles → 1.295 × 10²⁵ molecules
• (c) Atoms/molecules → moles: 4.5 × 10²² atoms of Copper → 0.075 moles
• (d) Atoms/molecules → moles: 6× 10²² molecules of ethane → 0.1 moles → 2.8g
• (e) Volumes → atoms/molecules: 500 cm³ of SO₂ at s.t.p. → 0.02232 moles → 4.017 × 10²² atoms