key words

• indicator

  • substance that can be used to test whether a solution is acidic or alkaline
  • some indicators can be used to measure pH
• litmus

  • an example of an indicator
  • comes in red, blue or purple varieties
  • red with acid
  • blue with alkali
• phenolphthalein

  • another indicator
  • is pink in alkaline solution
  • colourless in acids
• methyl orange

  • another indicator
  • red in acid
  • yellow in alkali
• pH scale

  • a scale that is used to measure the acidity or alkalinity of a solution
  • low pH e.g. pH 1 is strongly acidic
  • high pH e.g. pH 14 is strongly alkaline
  • pH is neutral
• universal indicator

  • an indicator that changes colour depending on pH
  • red at pH 1 through orange + yellow
  • green at pH
  • dark blue at pH 14
• digital pH meter

  • an electronic device that can be used to directly measure the pH of a solution
  • more accurate than using universal indicator
• hydrogen ion

  • hydrogen ions (H+) are the particles that make acids acidic
  • all acidic solutions contain them
• hydroxide ion

  • Hydroxide ions (OH-) are the particles that make alkalis alkaline
  • all alkaline solutions contain them
• hydroxide ion

  • Hydroxide ions (OH-) are the particles that make alkalis alkaline
  • all alkaline solutions contain them
• neutralisation

  • when equal amounts of (moles) of acid + alkali react together, they create a neutral solution
  • the ionic equation for this reaction is H+ + OH- = H2O
• solubility

  • solubility is a measure of the mass of solid that will dissolve in 100g of a solvent
  • substances that do not dissolve are said to be insoluble