Mole Concept

The Mole Concept Study Notes

Objectives

  • Define mole and molar mass.

  • Perform calculations involving the mole.

  • State Avogadro’s Law.

  • Write balanced equations.

  • Apply the mole concept to equations, both ionic and molecular.

  • Define the term standard solution.

Recap of Key Concepts

Relative Atomic Mass (Ar)

  • Definition: The average mass of one atom of an element compared to one-twelfth the mass of an atom of carbon-12.

  • Example: The relative atomic mass of sodium (Na) is 23.

Relative Molecular Mass (Mr)

  • Definition: The average mass of one molecule of an element or compound compared to one-twelfth the mass of an atom of carbon-12.

  • Example: For nitrogen (N₂), relative molecular mass = (2 × 14) = 28.

Relative Formula Mass

  • Definition: The average mass of one formula unit of a compound compared to one-twelfth the mass of an atom of carbon-12.

  • Example: For magnesium carbonate (MgCO₃):

    • It consists of:

    • 1 atom of Mg

    • 1 atom of C

    • 3 atoms of O

    • Calculation: Relative formula mass of MgCO₃ = (1 × 24) + (1 × 12) + (3 × 16) = 84.

Question Set 1

  1. Determine the relative molecular mass of the following substances:

    • a. Nitrogen dioxide, NO₂

    • b. Chlorine gas, Cl₂

  2. Determine the relative formula mass of the following:

    • a. Calcium oxide, CaO

    • b. Ammonium sulphate, (NH₄)₂SO₄

Introduction to Moles

  • Click on the video to get an overview of what a mole is.

Definition of a Mole

  • Mole Definition: In chemistry, a mole is the amount of substance that contains 6.0 imes 10^{23} particles, known as Avogadro’s constant.

Moles and Number of Particles

  • A mole of a substance always contains 6.0 imes 10^{23} particles.

  • Calculation of Number of Particles:

    • Formula: ext{moles} = rac{ ext{number of particles}}{ ext{Avogadro's constant} ext{(6.0 } x 10^{23})}

Counting Particles

  • Click on the video for an explanation on how to calculate the number of particles.

Converting Between Moles, Atoms, and Molecules

  • Click on the video for further explanation.

Question Set 2

  1. Calculate the number of eggs in 2.5 dozens.

  2. Calculate the number of dozens in 456 loaves of bread.

  3. Calculate the number of particles in 0.5 mol of copper (Cu).

  4. Calculate the number of moles of carbon dioxide (CO₂) that contain 2.0 imes 10^{23} carbon dioxide molecules.

Moles and Mass

  • Molar Mass provides the relationship between mass and the number of moles of an element or compound.

  • This relationship allows for the determination of the number of moles or the mass of a compound or element.

  • Formula: ext{moles} = rac{ ext{mass}}{ ext{molar mass}}

Molar Mass (M)

  • Definition: The mass in grams of one mole of a substance.

  • Unit: g/mol

Molar Mass Example

  • Example: What is the molar mass of magnesium carbonate (MgCO₃)?

    • It consists of:

    • 1 atom of Mg

    • 1 atom of C

    • 3 atoms of O

    • Calculation: Molar mass of MgCO₃ = (1 × 24) + (1 × 12) + (3 × 16) = 84 g/mol.

    • Interpretation: 1 mol of MgCO₃ has a mass of 84 g.

Question Set 3

  1. Calculate the mass of 0.2 mol of sulfuric acid (H₂SO₄).

  2. Determine the mass of 0.4 mol of zinc hydroxide (Zn(OH)₂).

  3. Calculate the number of moles in 10 g of calcium carbonate (CaCO₃).

  4. How many moles are in 8.28 g of potassium carbonate (K₂CO₃)?