Investigating solubility (including practical)

• How can you measure solubility?

  By evaporating all the water in a solution
• What is the procedure to investigate how temperature affects solubility of ammonium chloride?

  1. Make a saturated solution with excess ammonium chloride in 10 cm³ of water.
  2. Stir and place in a water bath at 25 °C.
  3. Check for excess solid and temperature.
  4. Weigh an empty evaporating basin and pour in the solution.
  5. Re-weigh and heat to remove water.
  6. Re-weigh to find pure ammonium chloride.
  7. Repeat at different temperatures (e.g., 35 °C, 45 °C).
• What indicates that ammonium chloride is in excess during the experiment?

  It starts to sink to the bottom of the tube
• What should you do after stirring the solution in the boiling tube?

  Place it in a water bath set to 25 °C
• Why is it important to check that all excess solid has sunk to the bottom?

  To ensure accurate measurement of solubility
• What should you use to check that the solution has reached 25 °C?

  A thermometer
• What is the first step after weighing the empty evaporating basin?

  Pour some of the solution into the basin
• What must you avoid pouring into the evaporating basin?

  Any undissolved solid
• What happens if you heat the basin too strongly?

  Some ammonium chloride may turn into gas
• What is the consequence of ammonium chloride escaping as gas?

  Your solubility value will be lower
• What do you do after all the water has evaporated?

  Re-weigh the evaporating basin and contents
• What is the formula for calculating solubility?

  • Solubility (g per 100 g of solvent) =
  • (mass of solid (g) / mass of water removed (g)) × 100
• What should you do after completing the first trial at 25 °C?

  Repeat steps at different temperatures
• What are the other temperatures you can use for the experiment?

  35 °C and 45 °C