CONCENTRATION OF SOLUTIONS

• Percentage composition


  The proportion of a certain substance relative to the entirety of the system being considered
• Ways of expressing percentage composition

  • Per weight basis (% w/w)
  • Per volume basis (% v/v)
  • Weight per volume basis (% w/v)
• Percentage composition is used to express concentrations, as it is easier to understand, especially for individuals with no background in chemistry
• Parts per million (ppm)


  Used to express very minute concentrations
• Parts per billion (ppb)


  Used to express very minute concentrations
• Molarity (M)


  The number of moles of solute present in a liter of a solution
• Molality (m)


  The number of moles of solute present per kilogram of solvent
• Normality (N)


  The ratio of gram equivalent of solute and the volume of the solution in liters
• Calculating normality


  1. Divide mass of solute by equivalent weight

  2. Divide result by volume of solution in liters
• For acids, the number of equivalents equals the number of protons that the acid can donate
• For basic solutions, the number of equivalents equals the number of hydroxide ions (─OH) that can ionize in the solution
• Solving for molarity


  1. Convert mass of solute to moles using molar mass

  2. Convert volume of solution from mL to L
• Solving for normality


  1. Divide mass of solute by equivalent weight

  2. Divide result by volume of solution in liters
• Solving for molality


  Divide moles of solute by mass of solvent in kg