Stoichiometry and Solutions Lecture Notes

Overview

• Revisit of stoichiometry, focusing on concentration and solutions.
• Central concept: Moles and the mole ratio.

Stoichiometric Map

• Central feature: Moles.
• Pathways to reach moles:
  • Mass
  • Volume of gas (at standard temperature and pressure)
  • Representative particles
• Molarity: Molarity = moles/liter.
• With known concentration and volume, calculate moles of solute.

Example Problem: Ammonium Nitrate Production

• Given: 55.0 mL of 3.2 M ammonium carbonate solution + 100 mL of excess copper(II) nitrate.
• Goal: Find grams of ammonium nitrate produced.
  1. Balanced Chemical Equation:
     • Ammonium carbonate + Copper(II) nitrate → Ammonium nitrate + Copper carbonate (precipitate).
  2. Information Setup:
     • Known: 55 mL of 3.2 M solution.
     • Unknown: Grams of ammonium nitrate.
  3. Molar Mass Calculation:
     • Ammonium nitrate: 80.06 g/mol.
  4. Stoichiometric Calculations:
     • Convert volume to moles using concentration:
       • 3.2 moles of ammonium carbonate per 1 L of solution.
     • Use mole ratio from the balanced equation (1 mole of ammonium carbonate to 2 moles of ammonium nitrate).
     • Convert moles of ammonium nitrate to grams using molar mass.
  5. Final Calculation:
     • Result: 28 grams of ammonium nitrate.

Bonus Question: Concentration of Ammonium Nitrate in Final Solution

• Steps:
  1. Calculate moles of ammonium nitrate from grams using molar mass.
  2. Determine volume of final solution (mixing 55 mL + 100 mL = 155 mL = 0.155 L).
  3. Calculate concentration:
     • Moles of ammonium nitrate / Volume of solution.
  4. Result: Approximately 2.3 M ammonium nitrate.

Identifying Limiting Reagent Problem

• Task: Solve for the limiting reactant using a balanced equation:
  • 2 moles of silver nitrate + 1 mole of magnesium chloride → 2 moles of silver chloride + 1 mole of magnesium nitrate.
• Process:
  1. Calculate Moles:
     • Use molarity to convert concentrations to moles for both silver nitrate and magnesium chloride.
  2. Mole Ratio Calculations:
     • From silver nitrate to magnesium chloride. If more magnesium chloride is available than needed, then silver nitrate is limiting.
  3. Result: Silver nitrate is the limiting reagent.

Summary

• Understanding of stoichiometric problems with solutions is essential.
• Skills in balancing equations, calculating concentrations, and identifying limiting reactants are crucial in stoichiometry.