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Flashcards · 5070 · Topic 3
Stoichiometry flashcards
18 cards on Topic 3, subtopics 3.1 to 3.3. Pick a subtopic or study them all.
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3.1 Formulae
- Molecular formula
- The number and type of each atom in one molecule.
- State symbols
- (s) solid, (l) liquid, (g) gas, (aq) aqueous — dissolved in water.
- Formulae of the sulfate, nitrate, carbonate, hydroxide and ammonium ions
- SO₄²⁻, NO₃⁻, CO₃²⁻, OH⁻, NH₄⁺
- Empirical formula
- The simplest whole-number ratio of the different atoms in a compound.
- Use the ion charges to write the formula of aluminium oxide (Al³⁺, O²⁻)
- Al₂O₃. The lowest common multiple of 3 and 2 is 6, so 2 Al³⁺ balance 3 O²⁻.
- Formula of calcium nitrate (Ca²⁺, NO₃⁻)
- Ca(NO₃)₂ — brackets because two nitrate ions are needed.
- Ionic equation for the neutralisation of an acid by an alkali
- H⁺(aq) + OH⁻(aq) → H₂O(l)
3.2 Relative masses of atoms and molecules
- Relative atomic mass, Ar
- The average mass of the isotopes of an element compared with 1/12 of the mass of an atom of carbon-12.
- Relative molecular mass, Mr
- The sum of the relative atomic masses of all the atoms in a molecule. (For an ionic compound: relative formula mass.)
- Mr of carbon dioxide, CO₂ (Ar: C = 12, O = 16)
- 12 + 2 × 16 = 44
- Mr of calcium carbonate, CaCO₃ (Ar: Ca = 40, C = 12, O = 16)
- 40 + 12 + 3 × 16 = 100
3.3 The mole and the Avogadro constant
- Two units for the concentration of a solution
- g/dm³ and mol/dm³
- The mole
- The amount of substance that contains 6.02 × 10²³ particles (the Avogadro constant).
- Equation linking moles, mass and molar mass
- moles = mass (g) ÷ molar mass (g/mol)
- Molar gas volume at room temperature and pressure (rtp)
- 24 dm³ (24 000 cm³) per mole of any gas.
- Equation linking moles, concentration and volume
- moles = concentration (mol/dm³) × volume (dm³). Convert cm³ to dm³ by dividing by 1000.
- Percentage yield
- actual yield ÷ theoretical yield × 100. It can never be more than 100%.
- Mass of 0.25 mol of CaCO₃ (Mr = 100)
- 0.25 × 100 = 25 g