1.2: The Mole Concept

Understandings:

• The mole is a fixed number of particles and refers to the amount (n) of a substance.
  
• The empirical and molecular formula of a compound give the simples ratio and the actual number of atoms present in a molecule respectively.
  

Applications:

• Calculation of the molar masses of atoms, ions, molecules, and formula units.
  
• Solution of problems involving the relationships between the number of particles, the amount of substances in moles, and the mass in grams.
  
• Interconversion of the percentage composition by mass and the empirical formula.
  
• Determination of the molecular formula by a compound from its empirical formula and molar mass.
  
• Obtaining and using experimental data for deriving empirical formulas from reactions involving mass changes.
  

Mission 1: The Mole
Mission Objectives.  You should be able to...
1.  Calculate the molar masses of atoms, ions, molecules and formula units.
2.  Solve problems involving the relationship between number of particles, the amount of substance in moles and mass in grams.
3.  Calculate percent composition using mass and the empirical formula of a compound.
4.  Identify the molecular formula of a compound using its empirical formula and molar mass.
5.  Use experimental data to derive empirical formulas using mass changes.

"Particles" is a generic term for atoms, formula units, and molecules.  Avogadro's number of atoms clearly references an element, Avogadro's number of formula units references an ionic compound, and Avogadro's number of molecules references a covalent compound.

The molar mass of a substance is either the element's atomic mass on the periodic table, or the sum of the atomic masses of a formula unit or a compound.

Below are two PowerPoints that discuss in detail the mole concept.  Download the reading guide and answer the questions embedded within the ppt.

The Mole, part 1
The Mole, part 2
The Mole Reading Guide

Below are some stoichiometry word problems.  You have to utilize the periodic table, molar mass and mole ratios to solve these problems.

Practice Problems I
Practice Problems II
Practice Problems III

Percent Composition Practice
Empirical and Molecular Formula Practice

In any chemical reaction, the limiting reactant (or reagent) is the reactant that determines how much product is made.  Typically, the limiting reactant (LR) is the most expensive.  The LR is completely consumed in the reaction; all other reactants are considered to be in excess (ER).  Below are the steps for solving LR problems.

Limiting Reactant Practice
Theoretical & Percent Yield Practice