Lecture Notes: Mass-Mole Stoichiometry

Introduction

• Stoichiometry: Quantitative relationship between reactants and products in a chemical reaction.
• Mass-Mole Stoichiometry: Focuses on conversions between mass and moles using stoichiometric principles.

Key Concepts

• Mole Ratio: Derived from the coefficients of a balanced chemical equation, essential for converting between moles of different substances.
• Molar Mass: Used to convert between mass and moles. The molar mass is the mass of one mole of a substance, taken from the periodic table.

Mass to Moles Problems

• Involves converting the mass of a given substance to moles of another substance.
• Steps:
  1. Convert given substance's mass to moles using its molar mass.
  2. Use the mole ratio to determine moles of the unknown substance.
• Example 1: Tin (Sn) and hydrogen fluoride (HF) reaction to form SnF2 and H2.
  • Known: 75.0 g Sn, molar mass of Sn = 118.69 g/mol, 1 mol Sn = 2 mol HF
  • Unknown: Moles of HF required
  • Solution:
    • Calculate moles of Sn and then use mole ratio to find moles of HF.
    • Calculation: (75.0 \text{g Sn} \times \frac{1 \text{ mol Sn}}{118.69 \text{ g Sn}} \times \frac{2 \text{ mol HF}}{1 \text{ mol Sn}} = 1.26 \text{ mol HF})

Moles to Mass Problems

• Involves converting the moles of a given substance to the mass of another substance.
• Steps:
  1. Use mole ratio to find moles of the unknown substance.
  2. Convert moles of unknown to mass using its molar mass.
• Example 2: Reaction of hydrogen sulfide (H2S) with oxygen (O2) to produce SO2 and H2O.
  • Known: 4.60 mol SO2, 2 mol SO2 = 3 mol O2, molar mass of O2 = 32.00 g/mol
  • Unknown: Mass of O2 consumed
  • Solution:
    • Use mole ratio to find mol O2 and convert to grams.
    • Calculation: (4.60 \text{ mol SO2} \times \frac{3 \text{ mol O2}}{2 \text{ mol SO2}} \times \frac{32.00 \text{ g O2}}{1 \text{ mol O2}} = 221 \text{ g O2})

Summary

• Importance of conversions between mass and moles in stoichiometry.
• Utilization of mole ratios and molar masses to solve stoichiometry problems.

Review Questions

1. What happens if grams of Sn are multiplied by 118.69 g/mol Sn?
2. Why is a balanced equation necessary in stoichiometry calculations?
3. Does the physical state of a substance affect these calculations?

These notes provide a concise overview of mass-mole stoichiometry, covering essential principles and example problems to illustrate the conversion process.