Amount of Substance

Cards (31)

  • The mole is a way of measuring the amount of substance in chemistry
  • Mole
    One mole of any substance contains 6.02 * 10^23 atoms or molecules
  • Avogadro's number
    6.02 * 10^23
  • Calculating number of particles
    Avogadro's number * number of moles
  • Mass and Mr/Ar
    Number of moles = mass (in grams) / Mr (molecular mass) or Ar (atomic mass)
  • Look for two of the components (moles, mass, Mr/Ar) in the question to use the formula
  • Moles in solutions
    Number of moles = concentration (mol/dm^3) * volume (dm^3)
  • Convert volume from cm^3 to dm^3 by dividing by 1000 or multiplying by 0.001
  • If in doubt, work out the moles as this allows you to calculate other quantities
  • Ideal gas equation
    PV = nRT (P = pressure in Pa, V = volume in m^3, n = moles, R = gas constant 8.31 J/mol·K, T = temperature in K)
  • Converting units
    1. Meters to decimeters: multiply by 100
    2. Decimeters to centimeters: multiply by 100
    3. Meters to centimeters: multiply by 100 (10 x 10)
  • For each dimension added, multiply by 100 (e.g. m^2 to dm^2: multiply by 100, m^2 to cm^2: multiply by 10,000)
  • Converting units
    1. Multiply by 100 to go from meters to decimeters
    2. Multiply by 100 to go from decimeters to centimeters
    3. Multiply by 100 to go from meters to centimeters
    4. Multiply by 100 to go from square meters to square decimeters
    5. Multiply by 100 to go from square decimeters to square centimeters
    6. Multiply by 1000 to go from cubic meters to cubic decimeters
    7. Multiply by 1000 to go from cubic decimeters to cubic centimeters
  • General rule for converting units
    For every dimension added, multiply by 100
  • Ionic equation

    Shows the ions formed in solution and the particles reacting
  • Ionic equations show the important ions involved in the reaction, with spectator ions cancelled out
  • State symbols
    S for solid, L for liquid, G for gas, Aq for aqueous
  • Calculating theoretical mass from a balanced equation
    1. Write balanced equation
    2. Calculate molar masses
    3. Divide mass of reactant by molar mass to find moles
    4. Use mole ratio to find moles of product
    5. Multiply moles of product by molar mass to find theoretical mass
  • Calculating volume of gas from a balanced equation
    1. Write balanced equation
    2. Calculate moles of reactant
    3. Use mole ratio to find moles of gas product
    4. Use PV=nRT to calculate volume of gas
  • Titration
    Used to determine the concentration of an acid or alkali by neutralization reaction
  • Titration procedure
    • Add titrant to analyte until indicator changes colour (end point)
    • Read volume from burette meniscus at eye level
    • Repeat until two concordant results within 0.1 cm3
  • Indicators
    • Phenolphthalein is colourless in acid, pink in alkali
    • Methyl orange is yellow in acid, red in alkali
  • Calculating concentration from titration data
    1. Calculate moles of titrant from volume and concentration
    2. Use mole ratio from balanced equation to find moles of analyte
    3. Divide moles of analyte by volume to find concentration
  • Reaction between HCl and potassium hydroxide
    1. Write balanced equation
    2. Calculate moles of HCl using concentration and volume
    3. Moles of potassium hydroxide is same as moles of HCl
    4. Calculate concentration of potassium hydroxide using moles and volume
  • Calculating volume of sodium hydroxide being neutralized
    1. Write balanced equation
    2. Calculate moles of sulfuric acid using concentration and volume
    3. Use 1:2 mole ratio to calculate moles of sodium hydroxide
    4. Calculate volume of sodium hydroxide using moles and concentration
  • Empirical formula
    Simplest whole number ratio of elements in a compound
  • Determining empirical formula from composition data
    1. Write elements and their percentages
    2. Convert percentages to moles using relative atomic masses
    3. Divide moles by smallest to get whole number ratio
  • Molecular formula
    Actual formula of a compound, may be a multiple of the empirical formula
  • Percentage yield

    Actual yield divided by theoretical yield, times 100
  • Atom economy
    Molecular mass of desired product divided by sum of molecular masses of all reactants, times 100
  • Importance of atom economy
    • Indicates efficiency of reaction
    • Promotes sustainability by minimizing waste
    • Reduces time and cost of separating byproducts