4) The pH scale and neutralisation

Cards (4)

  • When substances dissolve in water, they dissociate into their individual ions:
    • Hydroxide ions, OH-(aq), make solutions alkaline.
    Hydrogen ions, H+(aq), make solutions acidic.
  • The pH scale is a measure of the acidity or alkalinity of an aqueous solution:
    • A solution with a pH of 7 is neutral.
    • Aqueous solutions with a pH less than 7 are acidic.
    • The closer to a pH of zero, the stronger the acid.
    • Aqueous solutions with a pH of more than 7 are alkaline.
    • The closer to a pH of 14, the stronger the alkali.
  • The pH of a solution can be measured using a pH probe or universal indicator.
  •  Indicators are dyes that change colour depending on whether they are in acidic or alkaline solutions:
    • Litmus changes colour from red to blue or vice versa.
    • Universal indicator is a mixture of dyes that shows a range of colours to indicate how acidic or alkaline a substance is.