Stoichiometry

• Definition

  • Study of quantitative relationships in chemical reactions

  • Involves calculations based on balanced chemical equations

• Mole Concept

  • Avogadro's number: 6.022 x 10^23

  • Molar mass: mass of one mole of a substance

• Balanced Chemical Equations

  • Coefficients represent mole ratios

  • Used to determine mole ratios in reactions

• Calculations

  • Molar Ratio

    • Convert moles of known substance to moles of unknown substance

      • Definition: Ratio of moles of one substance to another in a chemical reaction

      • Importance: Determines the stoichiometry of a reaction

      • Calculation: Obtain from coefficients in balanced chemical equation

      • Example: 2H₂ + O₂ → 2H₂O has a molar ratio of 2:1 (H₂:O₂)

  • Mass-Mole Conversions

    • Convert mass of a substance to moles and vice versa

  • Volume-Volume Conversions

    • Convert volume of a gas to moles and vice versa

• Limiting Reactant

  • Reactant that limits the amount of product formed

  • Determined by comparing actual and theoretical yields

• Percent Yield

  • Ratio of actual yield to theoretical yield

  • Indicates efficiency of a reaction

• Applications

  • Determining reactant quantities

  • Predicting product yields

Practice Problems

• Mole to Mole Conversions

  • Example: 1 mol of A reacts with 2 mol of B according to the balanced chemical equation:A + 2B ⟶ C

    • If 3 mol of A are used, 6 mol of B will be needed for the reaction.

• Mass to Mole Conversions

  • Example: Convert 24 grams of carbon dioxide to moles. First, find the molar mass of CO2 (12 g/mol + 16 g/mol + 16 g/mol = 44 g/mol). Then, divide the given mass by the molar mass to get the answer in moles (24 g / 44 g/mol ≈ 0.545 moles).

• Moles to Mass Conversions

  • Example:Calculate the mass of 2 moles of carbon dioxide (CO2).1 mole of CO2 = 44.01 g2 moles of CO2 = 44.01 g/mol * 2 mol = 88.02 g

• Mass to Mass Conversions

  • Example: How many grams of aluminum are nedded to produce 11.0 grams of aluminum chloride given the chemical equation 2 Al + 3 Cl2 →2 AlCl3?

    • 2.23 g

• Limiting Reactants

  • Example: A recipe calls for 2 cups of flour and 1 cup of sugar to make cookies. If there are only 1 cup of flour and 1 cup of sugar available, what is the limiting reactant?

    • flour is the limiting reactant.

Molarity

• Definition:

  • Molarity is a measure of the concentration of a solute in a solution.

  • It is defined as the number of moles of solute per liter of solution.

• Formula:

  • Molarity (M) = moles of solute / liters of solution

• Units:

  • Molarity is expressed in moles per liter (mol/L) or Molar (M).

• Calculations:

  • Calculate moles of solute if mass and molar mass are given.

  • Calculate volume of solution if molarity and moles of solute are given.

• Importance:

  • Essential in chemistry for preparing solutions of known concentrations.

  • Used in stoichiometry calculations to determine reactant quantities.

• Dilution:

  • Dilution is the process of reducing the concentration of a solution by adding more solvent.

  • Formula for dilution: M1V1 = M2V2 (initial molarity and volume = final molarity and volume).

• Example:

  • If 0.5 moles of NaCl are dissolved in 2 liters of water, the molarity is 0.25 M (0.5 moles / 2 L).

• Applications:

  • Used in various industries like pharmaceuticals, food and beverage, and environmental testing.

  • Important in biological sciences for preparing buffers and solutions for experiments.

Making a Solution in a Lab

• Central Idea: Making a Solution in a Lab

  • Main Branches:

    • Types of Solutions

      • Homogeneous

      • Heterogeneous

    • Components of a Solution

      • Solvent

      • Solute

    • Steps to Make a Solution

      • Weighing the Solute

      • Mixing the Solute and Solvent

      • Stirring or Shaking

      • Filtering (if necessary)

      • Adjusting Concentration (if needed)