decay rpa

• 1. measurements

  measure 5cm^3 of lipase solution + add it to a test tube + label this tube w an "L" for lipase

  measure out 5cm^3 of milk + add it to a different test tube

  Add 5 drops of phenolphthalein indicator containing milk

  measure out 7cm^3 of sodium carbonate solution + add it to the tube containing milk + the indicator --> making it alkaline + turning it pink.
• 2. method 


  put both tubes into a water bath set to 30 degrees + leave them to equilibrate to the temp in the bath + stick a thermometer into the milk tube to check

  once the tubes reached 30 degrees , use calibrated dropping pipette to put 1cm^3 of the lipase solution into the milk tube + start a stop watch right away

  stir the contents of the tube w a glass rod + enzymes will begin to decompose the milk

  when solution loses its pink colour -> stop stopwatch + record how long the colour change took in a table

  repeat experiment at different temps , three times to calculate a mean time
• rate = 1000/time
• When bacteria anaerobically respire, sugars in milk produce lactic acid.
• RPA Sample:

  Milk - contains lipids to be digested Phenophthalein indicator - pink at pHs above 8.2 , colourless below pH 8.2. Sodium carbonate - so the milk is alkaline at the start of the experiment bile salts- increase the SA of the lipid , to increase the rate of enzyme action.
• reaction

  lipid --> fatty acids + glycerol
• the production of fatty acids lowers the pH
• The time taken for the indicator to become colourless can be used to calculate rate of reaction
• step 1: To 5cm^3 milk in a boiling tube add : 2 drops of Phenophthalein indicator solution , 5cm^3 of sodium carbonate + 1cm^3 of bile salts.
• Step 2

  Equilibrate this boiling tube + a test tube of lipase (5cm^3) at the temperature to be tested, checking this using a thermometer Step 3: add the lipase from the boiling tube in to the 'milk' boiling tube and start timing. step 4: stir the sample until solution turns white ( colourless)
• step 5


  record the time taken for the colour to change to white, in seconds step 6: repeat steps 1-5 three times for each temperature.