The Mole

Module 9: The Mole

10.1 Main Idea

  • Chemists use the mole to count atoms, molecules, ions, and formula units.

10.1 Objectives

  • Explain how a mole is used to indirectly count the number of particles of matter.

  • Relate the mole to a common everyday counting unit.

  • Convert between moles and number of representative particles.

Review Vocabulary

  • Molecule: A group of atoms bonded together.

  • Ion: An atom or molecule with a net electric charge due to the loss or gain of one or more electrons.

  • Atom: The smallest unit of a chemical element.

  • Formula Unit: The lowest whole number ratio of ions in an ionic compound.

  • Matter: Anything that has mass and takes up space.

  • Dozen: A counting unit equal to twelve.

  • Significant Digits: The digits in a number that carry meaningful information about its precision.

New Vocabulary

  • Mole: The mole is a quantity used to count particles in chemistry, represented by Avogadro's number (6.022 x 10^23).

  • Avogadro's Number: A constant (6.022 x 10^23) that defines the number of particles in one mole of a substance.

Counting Particles

  • Everyday counting involves:

    • Pair (2 items)

    • Dozen (12 items)

    • Mole (6.02 x 10^23 items)

  • Avogadro's number is a pivotal unit in counting atoms and molecules.

Mass of Common Elements

  • Examples of the mass of 1 mole of various elements:

    • 65.4 g Zn

    • 12.0 g C

    • 24.3 g Mg

    • 63.5 g Cu

    • 32.1 g S

    • 28.1 g Si

    • 207 g Pb

    • 118.7 g Sn

Understanding the Mole

  • 1 mole equals 6.022 x 10^23 items (Avogadro's number).

  • Perspective: 1 mole of M&M's would require an immense amount of space (3.83x10^8 km^3).

    • This volume is comparable to California's area.

Unit Analysis Example

  • Calculation:

    • 1 mole M&M's = 6.022 x 10^23 M&M's

    • Volume for 1 M&M = 0.636 cm³

    • Total volume for 1 mole of M&M's approximates to 3.83 x 10^8 km³.

Conversions and Counting Examples

  • Examples of conversions using moles:

    1. How many eggs in 1 mol of eggs?

    2. 3.00 moles of water = 3.00 mol H2O × 6.022 x 10^23 molecules/mol = 1.81 x 10^24 molecules of H2O.

Cookies Example

  • Recipe yield for cookies:

    • Ingredients needed for 5 dozen:

      • 2 1/4 cups all-purpose flour

      • 1 cup butter

    • If one egg yields 30 cookies, then determine yields based on number of eggs.

    • Adjust ingredients accordingly if needing to make 100 cookies.

Practice Problems

  • Determine the number of Zn atoms in 2.50 mol Zn = 1.51 x 10^24 atoms.

  • 1.5 mol of water = 6.92 x 10^24 molecules.

  • Silver nitrate's formula units in 3.25 mol = 1.96 x 10^24 units, where AgNO3 is the formula.

Challenge Examples

  • How many molecules are in 5.0 mol of oxygen gas? = 6.02 x 10^24 atoms.

  • How many atoms in 0.250 moles of water? = 4.51 x 10^24 atoms.

  • Optional assignment: Calculate moles and molecules in cookies or describe chemical reactions.

9.2 MAIN IDEA: Mass and the Mole

  • A mole always contains the same number of particles, but different substances have different masses.

Objectives 9.2

  • Relate the mass of an atom to the mass of a mole of atoms.

  • Convert between the number of moles and the mass of an element.

  • Convert between the number of moles and number of atoms of an element.

Vocabulary 9.2

  • Conversion factor: A ratio used to convert from one unit to another.

  • Dimensional analysis: A method to convert units using multiplication by conversion factors.

  • Atomic number and mass: Correspond to the number of protons in an atom and the atomic weight respectively.

9.2 Molar Mass

  • The mass of one mole of an element is equal to its atomic mass expressed in grams.

    • Examples:

      • Egg: 64 g, Jelly bean: 24 g, Copper: 63.546 g, Water: 18 g

Molar Calculations Example

  • Mass of 0.25 mol Cu?

  • How many moles in 10.0 g Mn?

Moles in Compounds 9.3

  • Molar mass of compounds calculated from chemical formulas and using to convert from mass to moles.

Practice and Examples 9.3

  • Molar mass of HCl, HNO3, and moles in compounds like CCl2F2 and NH3 were calculated.

Percent Composition 9.4

  • Percent by mass of elements determined from mass percent and empirical formulas.

  • Example: Determine % composition of NaHCO3 and PH3.

Hydrates 9.5

  • Definition: Solid ionic compounds with trapped water.

  • Naming hydrates involves indicating the number of water molecules (e.g., CaCl2·2H2O).

Practice Problems 9.5

  • Analyze the hydrates' formulas from their mass data.

Summary of Learning Objectives

  • Understand moles in relation to counting particles,

  • Relate molar mass to compounds,

  • Calculate empirical formulas and analyze hydrates.