example experiment

• Titration


  A technique used to determine the concentration of an unknown solution
• Titration process

  1. Use a pipette to measure the volume of alkali into a conical flask

  2. Add a few drops of indicator (thymol or methyl orange)

  3. Use a burette filled with a known concentration of acid

  4. When almost neutralised, slowly add the acid drop-by-drop while swirling the flask regularly

  5. End-point is when the indicator changes colour, indicating all the alkali has been neutralised

  6. Record the volume of acid needed to neutralise the alkali (called the titre)

  7. Repeat to get similar results and take the mean
• Melting point of pure vs impure substances

  • Mixture/impure: melt gradually over a range of temperatures
  • Pure: sharp melting point
• Impurities

  Usually decrease the melting point and increase the boiling point
• Investigating how temperature affects solubility (using ammonium chloride)

  1. Make a saturated solution by adding excess ammonium chloride to water in a boiling tube

  2. Stir the solution and put the boiling tube in a water bath at 25°C

  3. After 5 minutes, check that all the excess solid has sunk and the solution has reached 25°C

  4. Filter to remove the undissolved solid

  5. Evaporate the filtrate to obtain the ammonium chloride that was dissolved at 25°C

  6. Repeat the process at different water bath temperatures
• Separating substances using solubility

  1. Add an organic solvent

  2. Shake the mixture - only one substance will dissolve

  3. The organic and inorganic solutions will form two layers

  4. Separate the layers using a separating funnel

  5. Separate the substance from the solution using crystallisation
• Determining the water content of hydrated crystals (copper(II) sulfate)

  1. Weigh the mass of the hydrated crystals in a crucible

  2. Heat the crystals to remove the water

  3. Stop heating when the mass is constant (by cooling and reweighing)

  4. Calculate the difference in mass between the start and final masses

  5. Use the difference in mass to calculate the number of moles of water lost