investigating pH

• What is the aim of the investigation described?

  Investigate pH change with calcium compounds
• What equipment is needed for the pH investigation?

  • 25 cm​3 measuring cylinder or volumetric pipette
  • Beaker
  • Glass rod
  • Universal indicator or pH probe
  • Spatula
• What chemicals are required for the experiment?

  • Hydrochloric acid
  • Powdered calcium hydroxide or calcium oxide
• Why is a volumetric pipette preferred over a measuring cylinder?

  It offers greater accuracy in measurements
• What should be done before taking a pH reading?

  Stir the solution to ensure consistency
• What is the first step in the method?

  Add 25 cm​3 of dilute hydrochloric acid
• What is the purpose of adding universal indicator?

  To compare and record the initial pH
• How should calcium hydroxide or calcium oxide be added?

  One level spatula at a time, stirring
• When should you stop adding calcium hydroxide or calcium oxide?

  When the pH remains constant
• What are the equations for the reactions with hydrochloric acid?

  1. CaO + 2HCl → CaCl​2​ + H​2​O
  2. Ca(OH)​2​ + 2HCl → CaCl​2​ + 2H​2​O
• What safety equipment must be worn during the experiment?

  Safety glasses must be worn
• Why should hands be washed immediately after contact with hydrochloric acid?

  It is corrosive in high concentrations
• What should be done in case of spillages?

  Clear up immediately
• What are the key points to remember about the experiment?

  • Use a volumetric pipette for accuracy
  • Stir before measuring pH for consistency
  • pH probe offers greater accuracy than indicators
• How can the effect of adding calcium compounds be investigated?

  By recording starting and final pH values