RP10 - the effect of temperature on rates of decay

• How can you investigate decay?

  By observing the action of the enzyme lipase on a sample of milk that has been made alkaline - when the lipase breaks the milk down - the pH of the milk decreases
• what is the first step when investigating decay?

  measure out 5cm$^3$of lipase solution and add it to a test tube - label it with an ‘L’ for lipase
• what should you do after measuring the lipase solution?

  measure out 5cm$^3$of milk and add it to a different test tube
• what should you do after measuring out the milk?

  add 5 drops of phenolphthalein indicator to the tube containing milk
• what should you do after adding the indicator?

  measure out 7cm$^3$of sodium carbonate solution and add it to the tube containing milk and phenolphthalein - this makes the solution in the tube turn alkaline so it should turn pink
• what should you do after adding the sodium carbonate solution?

  put both tubes into a water bath set to 30 degrees and leave them until they reach the temperature - use a thermometer to check this
• what should you do when both tubes have reached 30 degrees?

  use a calibrated dropping pipette (pipette with a scale) to put 1cm$^3$of the lipase solution into the milk tube and start a stopwatch immediately
• what should you do after adding the lipase solution to the milk tube?

  stir the contents with a glass rod - the enzyme will start to decompose the milk
• when should you stop the stopwatch?

  as soon as the solution loses its pink colour
• what should you record after stopping the stopwatch?

  how long the colour change took
• what should you do after recording the results?

  repeat the experiment at a range of different temperatures