Amount of substance

• The symbol for amount of substance is 'n'
• The unit used to measure amount of substance is 'Mole'
• The Avogadro constant represents the number of atoms per mole of the carbon-12 isotope
• To calculate the mass of 1 mole of an element: Mass of 1 mole = relative atomic mass in grams
• To calculate moles when mass and molar mass are given: Moles (mol) = mass (g) / molar mass (g mol -1)
• Avogadro’s law states that under the same temperature and pressure, one mole of any gas would occupy the same volume
• At room temperature and pressure, a gas occupies 24 dm3 or 24000 cm3
• Molar gas volume is defined as the volume per mole of gas molecules
• Different gas particles occupy the same volume because the gas particles are very spread out, hence individual differences have no effect
• To calculate moles when gas volume is given: Moles (mol) = volume (dm3) / 24 or Moles (mol) = volume (cm3) / 24000
• Ideal gas behavior includes:

  • Continuous motion
  • No intermolecular forces experienced
  • Exert pressure when they collide with each other or container
  • No kinetic energy is lost in the collisions
  • When temperature increases, kinetic energy of gases also increases
• The ideal gas equation is: pV = nRT, where Pressure (Pa) x volume (m3) = number of moles (mol) x gas constant (8.314 J mol-1) x temperature (K)
• 1 atmospheric pressure is equal to 101325 Pascal (Pa)
• 0℃ is equal to 273 Kelvin (K)
• The concentration of a solution is the amount of solute dissolved in 1 dm3 of solvent
• Concentration of a solution:

  • Amount of solute dissolved in 1 dm3 of solvent
• In single-celled organisms, substances can easily enter the cell due to a short distance, while in multicellular organisms, the distance is larger due to a higher surface area to volume ratio
• To calculate moles when concentration and volume are given:

  Moles (mol) = concentration (mol dm-3) x volume (dm3)
• A standard solution is:

  A solution of known concentration
• Steps to prepare a standard solution:

  1. Weigh the solute using the weigh by difference method

  2. Dissolve the solute in a beaker using the solvent

  3. Pour the solution into a volumetric flask

  4. Rinse the beaker with the solution and add it to the flask

  5. Add solvent carefully to the flask until it reaches the graduation line

  6. Thoroughly mix the solution to ensure complete mixing
• Concentrated means a large amount of solute per dm3 of solvent, while dilute means a small amount of solute per dm3 of solvent
• A species in a chemical reaction is:

  Any particle that takes part in a reaction
• Four common state symbols:

  1. Solid (s)

  2. Liquid (l)

  3. Gaseous (g)

  4. Aqueous (aq)
• Percentage yield:

  The efficiency of reactants converted into products
• Reasons for not obtaining 100% yield:

  • Reaction may be at equilibrium
  • The reactants may be impure
  • Side reactions could happen
  • Reactants or products may be left behind during transfer
  • Loss of products during separation and purification
• Percentage yield calculation:

  Percentage yield = (actual amount of product (mol) / theoretical amount of product (mol)) x 100
• Atom economy tells us about:

  The proportion of desired products compared with all the products formed in the reaction
• Atom economy calculation:

  Atom economy = (molecular mass of desired product / sum of the molecular masses of all products) x 100
• 100% yield does not mean 100% atom economy because even if all reactants are converted into products, not all products will be the required products
• Type of reaction with 100% atom economy:

  Addition reactions where two or more reactants are combined to form a product