decay

• aim - to investigate the effect temperature has on the rate of decay of fresh milk by measuring the pH change
• 1 - using a pipette , measure 5 cm cubed of lipase solution into a test tube
• 2- label another test tube 'milk' and add 5 drops of the indicator of cresol red. Then add 5 cm cubed of milk and 7 cm cubed of sodium carbonate solution to the milk test tube
• 3 - in the milk test tube, the solution should go purple, because sodium carbonate solution is alkaline and cresol red is purple in alkaline conditions
• 4 - place a thermometer in the milk test tube. place both test tubes into a beaker of water at our first chosen temperature , 20 degrees. wait until the temperature in the solutions is the same as the water in the beaker
• 5 - use a pipette to transfer 1cm cubed of lipase solution to test tube containing milk and stir the solution, start a timer
• 6 - the enzyme lipase will start to break down fat molecules in the milk , releasing fatty acids causing the milks solution to become acidic , the indicator cresol red turns yellow
• 7 - when indicator turns yellow, stop timer and record results. repeat experiment at a different range of temperatures
• independent variable - temperature
• dependent variable - time taken for milk solution to turn yellow
• control variable - volumes of different solutions
• make sure test tube is clean, any lipase will trigger an early reaction
• at a higher temperature, reaction will take place quicker as enzymes work quicker
• fungi and bacteria cause decay