Investigating Decay

• Investigating Decay


  1. Measure out 5 cm³ of lipase solution and add it to a test tube

  2. Measure out 5 cm³ of milk and add it to a different test tube

  3. Add 5 drops of phenolphthalein indicator to the tube containing milk

  4. Measure out 2 cm³ of sodium carbonate solution and add it to the tube containing milk and phenolphthalein

  5. Put both tubes into a water bath set to 30 °C and leave them to reach the temperature of the water bath

  6. Use a calibrated dropping pipette to put 1 cm³ of the lipase solution into the milk tube and start a stopwatch

  7. Stir the contents of the tube with a glass rod

  8. Stop the stopwatch as soon as the solution loses its pink colour

  9. Repeat the experiment at a range of different temperatures (e.g. 10 °C, 20 °C, 40 °C, 50 °C)

  10. Calculate the mean time taken for the colour change to occur at each temperature

  11. Calculate the rate of decay using the formula: Rate = 1000 / time
• Phenolphthalein indicator


  Has a pink colour when the pH is around 10 but becomes colourless when the pH falls below 8.3
• Lipase breaks down milk, causing the pH of the milk to decrease
• Adding sodium carbonate solution makes the milk solution alkaline, turning it pink
• Cooling the water bath below room temperature can be done by adding ice