Amount of Substance - AQA Chemistry Revision

Jun 10, 2024

Amount of Substance - Revision for AQA Chemistry Exam

Introduction

  • Overview of amount of substance concepts for AQA.
  • PowerPoint slides can be purchased via the link in the description.

The Mole and Avogadro's Number

  • A mole measures the amount of substance (abbreviated as mole).
  • One mole contains 6.02 x 10^23 atoms or molecules (Avogadro's number).
  • Calculation: Number of particles = Avogadro's number x Number of moles.

Mass and Mr (Relative Molecular Mass)

  • Equation: Number of moles = mass (g) / Mr (or Ar for elements).
  • Example: Calculating moles of 23g of gold (Ar of gold = 197).
  • Rearrangement of the formula for various purposes.

Solutions

  • Moles in a solution: Number of moles = concentration (mol/dm^3) x volume (dm^3).
  • Important: Volume must be in dm^3.
  • Conversion: cm^3 to dm^3 (divide by 1000 or multiply by 10^-3).
  • Example: Calculating moles for 200 cm^3 of 0.35 mol/dm^3 HCl.

Gases and Ideal Gas Equation

  • Ideal Gas Equation: PV = nRT.
  • Definitions: P = pressure (Pascals), V = volume (m^3), n = number of moles, R = gas constant (8.31 J/mol·K), T = temperature (Kelvin).
  • Must convert pressure to Pascals and volume to m^3.
  • Example: Calculating volume for 0.36 moles of gas at 100 kPa and 298K.

Conversion of Units

  • Converting between meters, decimeters, and centimeters for areas and volumes.
  • Example conversions:
    • m^3 to dm^3: multiply by 1000
    • m^3 to cm^3: multiply by 1,000,000

Ionic Equations

  • Ionic equations show ions in solution and ions that react.
  • Process: Split ionic compounds into their ions and cancel out spectator ions.
  • Example: Reaction of H2SO4 with KOH forming K2SO4 and H2O.

Using Equations to Calculate Masses

  • Calculate the theoretical mass from a balanced equation.
    • Example: Ca + O2 → CaO and related calculations.
  • Find moles, use ratios, and perform division and multiplication to find desired masses.

Using Equations to Calculate Volumes of Gases

  • Example: Volume of H2 from 12g of potassium reacting with water using Ideal Gas Law.

Titration

  • Used to determine concentration of an acid or alkali.
  • Setup: Buret with known concentration, conical flask with unknown concentration and a known volume.
  • Process: Add indicator, titrate until endpoint is reached, read meniscus at eye level.

Titration Calculations

  • Example calculations for determining concentration and volume using titration data.
  • Important steps: write balanced equation, calculate moles, use ratios, and final calculations.

Empirical and Molecular Formulas

  • Calculate percentage composition, divide by relative atomic mass to find moles, then determine simplest ratio.
  • Example: A compound containing Mg, S, and O.

Percentage Yield

  • Formula: (Actual yield / Theoretical yield) x 100.
  • Example: Calculating yield from a reaction involving calcium oxide.

Atom Economy

  • Formula: (Molecular mass of desired product / Sum of molecular masses of reactants) x 100.
  • Importance: High atom economy means efficient use of raw materials, less waste, and cost savings.
  • Example: Extraction of iron from Fe2O3.

Conclusion

  • For more detailed revision, purchase the PowerPoint presentation via the provided link. Goodbye!