decay prac

• You can investigate decay by observing action of lipase on a sample of alkaline milk. This practical looks at the effects of temperature on rate of decay.
• The indicator used is called phenolphthalein - it is pink when pH is 10, but goes colourless when pH drops below 8.3
• 1. Measure 5cm^3 of lipase using a measuring cylinder and add to a test tube. Label test tube with 'L'.
  2. Measure 5cm^3 of milk and pour into another test tube
  3. add 5 drops of phenolphthalein to milk tube

  
• 4. measure 7cm^3 of sodium carbonate solution and add it to milk tube. This makes the solution alkaline, turning the indicator pink

  5. put both test tubes into a water bath set to 30C and leave them to reach the temperature. Stick a thermometer in milk tube.

  6. once tubes have reached 30C, use a pipette to put 1cm^3 of lipase solution into milk and start a stopwatch immediately.

  
• 7. stir contents of tube with a glass rod. Enzyme starts to decompose milk

  8. when solution loses its pink colour, stop the stopwatch and record how long it took for this colour change

  9. repeat experiment with different temperatures - make sure to do each temperature three times to calculate a mean

  10. use the formula rate = 1000/ time to calculate rate of decay. Unit is s^-1