Required Practicals - Decay Flashcards
(27 cards)
What is the goal of the decay practical?
To investigate the effect of temperature on the rate of decay of fresh milk by measuring pH change.
What is the apparatus list of the decay practical?
-a small beaker of full fat milk or single cream
-a small beaker of sodium carbonate solution
-a small beaker of lipase solution
-250cm3 beaker
-boiling tubes
-marker pen
-10cm3 plastic syringes
-thermometer
-A kettle
-Cresol red
-ice
What is the method for the decay practical?
-label a boiling tube ‘lipase’ and add 5cm3 of lipase solution
-label a boiling tube ‘milk’ and add five drops of Cresol red solution
-Use a calibrated dropping pipette to add 5cm3 of milk to the ‘milk’ boiling tube
-Use another pipette to add 7cm3 of sodium carbonate solution to the ‘milk’ tube. The solution should be purple
-Put a thermometer into the ‘milk’ tube.
-Set up a water bath.
-Put both boiling tubes into the water bath. Wait until the contents reach the same temperature as water bath.
-Use another dropping pipette to transfer 1cm3 of lipase from the ‘lipase’ tube to the ‘milk’ tube. Immediately start the stopclock.
-Stir the contents of the ‘milk’ boiling tube until the solution turns yellow.
-Record the time taken for the colour to change to yellow.
-Repeat the investifation for different temperatures of water bath.
-Record results in a table.
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What happens if milk is left at room temperature?
It goes sour
Why does milk go sour at room temperature?
bacteria in the milk start the decay process.
the bacteria use enzymes to produce acidic molecules
How do we model decay in the decay practical?
Using lipase enzyme
What do we do first in the decay practical?
Measure 5cm3 of lipase solution into a test tube
What do we do second in the decay practical?
Add 5 drops of cresol red indicator and add 5cm3 of milk and 7cm3 of sodium carbonate solution
Which indicator is used in the decay practical?
Cresol red
What colour is the milk test tube in the decay practical? Why is this?
Purple, as the solution is alkaline due to the sodium carbonate solution
What is the third step of the decay practical?
Place a thermometer in the milk test tube and record the temperature after putting them in a beaker of water.
What is the fourth step of the decay practical?
Use a pipette to transfer 1cm3 of lipase solution to the test tube containing milk.
Stir the solution and start a timer.
What happens after lipase is added to the milk test tube in the decay practical?
Lipase enzyme will start to break down lipid molecules in the milk, releasing fatty acids, causing the solution to become acidic
What happens to cresol red indicator when in acidic solution?
It changes to yellow
What do we do when cresol red solution turns yellow in the decay practical?
Stop timing and record results
How do we repeat the decay practical experiment?
Repeat at a range of different temperatures.
What is the independent variable in the decay practical?
The temperature
What is the dependent variable in the decay practical?
The time taken for milk solution to turn yellow
What are the control variables in the decay practical?
The volumes of the different solutions
These include:
lipase
milk
sodium carbonate solution
cresol red
What kind of test tube do we use in the decay practical?
A clean test tube
Why do we need to use a clean test tube in the decay practical?
Any traces of lipase will trigger the reaction before we are ready
What is the problem with the decay practical?
The point at which the cresol red has fully turned yellow is subjective so results may vary.
How can we combat the problems with subjectivity in the decay practical?
Sharing data with other groups and calculating a mean
Why is the time taken for the cresol red to turn yellow high at low temperatures in the decay practical?
Enzymes work slowly at lower temperatures.
