C3 Stoichiometry

C3 Stoichiometry Keywords

C3.1 Formulas

• Formulas of Elements and Compounds

  • State the formulas for elements and compounds presented in the subject content.

• Molecular Formula Definition

  • Define the molecular formula as the number and type of atoms in a single molecule.

• Deduction of Formula

  • From a model or diagram, deduce the formula of a simple molecular compound based on the number of atoms present.

• Word Equations

  • Construct word equations to represent how reactants form products.

• Balancing Symbol Equations

  • Balance and interpret simple symbol equations, including state symbols.

• Ionic Compound Formula

  • Deduce the formula of an ionic compound from the relative quantities of ions based on a model or diagram, or ion charges.

• Symbol Equations with State Symbols

  • Construct symbol equations with state symbols, including ionic equations.

• Deduction of Symbol Equations

  • Given relevant information, deduce the symbol equations with state symbols for a chemical reaction.

C3.2 Relative Masses of Atoms and Molecules

• Relative Atomic Mass (Ar)

  • Describe relative atomic mass as the average mass of isotopes of an element compared to 1/12 of the mass of an atom of carbon-12.

• Relative Molecular Mass (Mr)

  • Define relative molecular mass as the sum of the relative atomic masses; use 'relative formula mass' (M) for ionic compounds.

• Calculating Reacting Masses

  • Calculate reacting masses in simple proportions; calculations will omit the mole concept.

C3.3 The Mole and the Avogadro Constant

• Concentration Measurement

  • State that concentration can be measured in g/dm³.

• Definition of Mole

  • Define the mole (mol) as the unit of amount of substance; one mole contains 6.02 x 10²³ particles (Avogadro’s number).

• Calculating with Mole Relationships

  • Use the relationship: amount of substance (mol) = mass (g) / molar mass (g/mol) to calculate:

    • a) Amount of substance

    • b) Mass

    • c) Molar mass

    • d) Relative atomic mass or relative molecular/formula mass.

• Molar Gas Volume

  • Use the molar gas volume (24 dm³ at room temperature and pressure) in gas-related calculations.

• Stoichiometric Calculations

  • Calculate reactant masses, limiting reactants, and gas volumes at room temperature and pressure, including conversions between cm³ and dm³.

Balancing Chemical Equations

• Combining Fixed Ratios

  • Atoms combine in fixed ratios as indicated by chemical formulas.

• Example of Balance

  • Given Reaction: CH4 + 1.5O2 → CO2 + 2H2O

  • Balanced: CH4 + 2O2 → CO2 + 2H2O.

Exercises and Examples

• Example Reaction

  • Sodium burns in oxygen to produce sodium oxide. Balance the equation.

    • Possible solutions include:

      • A) 4Na + O2 → 2Na2O

      • B) 4Na + O2 → 2NaO

      • C) 2Na + O2 → 2NaO

• Balancing Practice

  • Practice with layout for balancing carbon dioxide and water:

    • Example: CO2 + H2O → C2H2 + O2

      • Ensure both sides are balanced.

Reaction Calculations

• Volume Calculations

  • 1 mole of gas occupies 24 dm³ at r.t.p.; use to calculate the volume of given masses.

• Example Calculation

  • For 352g of CO2:

    • Mr (CO2) = 44, calculate moles (m = mass/M):

      • moles CO2 = 352/44 = 8

        • Volume = 8 x 24 = 192 dm³.

Additional Topics

• Radicals in Compounds

  • Identify common ions and their formulas, e.g., sulfate (SO4²⁻), nitrate (NO3⁻).

• Determining Ionic Formulas

  • Use charge balance to derive formulas for ionic compounds, such as ammonium sulfate [(NH4)2SO4].

• Applications

  • Understand relationships between moles, gas volumes, and concentrations in real-world scenarios, such as in titrations.