Converting Between Grams and Moles

Introduction

• Moles: A method to convert atomic mass units to grams, allowing discussion of macroscopic samples in numerical quantities of molecules.
• This conversion is crucial for understanding reactions and stoichiometry.

Conversion of Grams to Moles

Example 1: Potassium

• Given: 4.7 grams of potassium.
• Objective: Calculate the number of moles.
• Importance: Necessary to know how many moles of another substance are required to react with potassium.
• Method: Use dimensional analysis and the molar mass of the element.

Calculation

• Atomic Mass of Potassium: 39.1 atomic mass units
• Molar Mass: 39.1 grams per mole (from periodic table)

• Conversion Factor: Multiply grams by the factor to cancel out grams:

  [ 4.7 \text{ grams} \times \left( \frac{1 \text{ mole}}{39.1 \text{ grams}} \right) = 0.12 \text{ moles} ]

Conversion of Moles to Grams

Example 2: Argon

• Given: 9.2 x 10⁻⁴ moles of argon
• Objective: Find the mass in grams.

Calculation

• Atomic Mass of Argon: 39.95 atomic mass units
• Molar Mass: 39.95 grams per mole

• Conversion Factor: Multiply moles by the factor to convert to grams:

  [ 9.2 \times 10^{-4} \text{ moles} \times \left( \frac{39.95 \text{ grams}}{1 \text{ mole}} \right) = 0.037 \text{ grams} ]

Summary

• By using the molar mass of an element from the periodic table, one can easily convert between grams and moles using dimensional analysis.
• This technique is applicable to any pure element, facilitating the calculation of reactants and products in chemical reactions.