(EL) - Formulae, Equations and Amount of Substance

• Structure of the atom:

  • Nucleus contains protons and neutrons
  • Electrons orbit the nucleus
  • Charges: protons have a relative charge of +1, neutrons are neutral, electrons have a relative charge of -1
  • Relative mass of electrons is 1/2000
  • Mass number in the periodic table indicates the number of protons and neutrons
  • Atomic number in the periodic table indicates the number of protons, which is equal to the number of electrons
• Ions and isotopes:

  • Ions have different numbers of electrons and protons
  • Isotopes have the same number of protons but different numbers of neutrons
• Definitions:

  • Relative atomic mass (AR): weighted mean mass of an atom compared to 1/12 of the mass of carbon-12
  • Relative isotopic mass: mass of an isotope compared to 1/12 of the mass of carbon-12
  • Relative molecular mass or formula mass: mean mass of a molecule compared to 1/12 of the mass of carbon-12
• Mole concept:

  • One mole of any substance contains 6.02 x 10^23 atoms or molecules (Avogadro's number)
  • Number of particles = Avogadro's number x number of moles
• Calculating moles from mass and AR:

  • Number of moles = mass in grams / AR
• Mole of solutions:

  • Number of moles in a solution = concentration (mol/dm^3) x volume (dm^3)
  • Convert volume from cm^3 to dm^3 by dividing by 1000
• Ionic equations:

  • Show ions formed in solution
  • Cancel out spectator ions
  • Charges must balance
• State symbols:

  • S: solids
  • L: liquids
  • G: gases
  • Aq: aqueous (dissolved in water)
• Balanced equations:

  • Used to calculate theoretical mass
  • Calculate theoretical mass by balancing the equation and finding the molar masses of the species involved
• Empirical formula is the simplest whole number ratio of elements in a compound
• Calculate moles by dividing masses by relative atomic masses.
• Water of crystallization is the amount of water attached to a compound
• Percentage yield is actual yield divided by theoretical yield times 100
• Making a standard solution involves precise weighing, dissolving, and diluting
• Weigh out solid, transfer to beaker, dissolve in deionized water
• Transfer to volumetric flask, rinse all equipment, fill to graduation line with deionized water
• Mix thoroughly, calculate concentration using mass and volume
• To calculate the number of moles of a solution, use the formula: number of moles = concentration x volume
• To calculate the mass, use the formula: mass = number of moles x relative formula mass
• The volume of a more concentrated solution needed to make a standard solution is: volume to use = final concentration / initial concentration x required volume
• Final concentration is the concentration of the final solution needed
• Initial concentration is the concentration of the solution being diluted
• Titrations can be used to determine the concentration of an acid or alkali
• In a titration, an indicator is added to show the endpoint when the color changes
• Results should be recorded to two decimal places and repeated for concordant results
• Indicators like phenolphthalein and methyl orange are commonly used
• Titration calculations involve balancing equations and calculating moles and concentrations
• Titration can also be used to find the volume of an acid or alkali needed