Concentration of Aqueous Solutions


6.5  Concentration of Aqueous Solutions
  • Concentration and molarity are measurements of the amount of solute that dissolves in a solvent.
  • The concentration can be measured in two terms, \(\text{mol dm}^{-3}\) or \(\text{g dm}^{-3}\)


The formula for concentration in \(\textbf{g dm}^{-3}\)
\(\text{Concentration } \text{(g dm}^{-3}) = \dfrac{\text{Mass of solute dissolved (g)}}{\text{Volume of solution (dm}^3)}\)


The formula for concentration in \(\textbf{mol dm}^{-3}\)
\(\text{Concentration } \text{(mol dm}^{-3}) = \dfrac{\text{Number of moles of solute (mol)}}{\text{Volume of solution (dm}^3)}\)


Relationship between pH values and molarities of acids or alkalis.

  • pH value of an acidic or an alkali depends on two factors; 
    • Degree of dissociation
    • Molarity or concentration
  • Even at the same concentration, the pH value still depends on the degree of dissociation:
    • Higher the degree of dissociation of an acid, the lower the pH value.
    • Higher the degree of dissociation of an alkali, the higher the pH value.
  • Both acid and alkali depend on their pH value for molarity.
    • High molarity of acid, lower the pH value. 
    • Higher molarity of alkali, higher the pH value.