Required Practical 10: Decay PAPER 2

Question 1

In the required practical decay what do you investigate.

Answer 1

Describe how to investigate the effect of temperature on the rate of decay of fresh milk by measuring the pH change.

Question 2

Decay is —- process so it is very hard to observe.

Answer 2

very slow

Question 3

Decay is very slow process so it is very hard to …

Answer 3

observe.

Question 4

Decay is very slow process so it is very hard to observe. This means that we use …

Answer 4

the enzyme lipase to model decay.

Question 5

Decay is very slow process so it is very hard to observe. This means that we use the enzyme lipase to model decay.
What we are looking at is not strictly decay but it should …

Answer 5

give results that approximate to what we would see with decay.

Question 6

Firstly, we start by labelling a test tube …

Answer 6

‘lipase’

Question 7

Secondly, use pipette to place —— of lipase solution into the test tube.

Answer 7

5cm3

Question 8

Thirdly, we label another test tube …

Answer 8

milk

Question 9

Fourthly, add ———– in the milk labeled test tube.

Answer 9

five drops of the indicator cresol red.

Question 10

Fifthly, we now add ———- and 7cm3 of sodium carbonate to the milk test tube.

Answer 10

5cm3 of milk

Question 11

Fifthly, we now add 5cm3 of milk and ———- to the milk test tube.

Answer 11

7cm3 of sodium carbonate

Question 12

Fifthly, we now add 5cm3 of milk and 7cm3 of sodium carbonate to the milk test tube. At this point the solution should be —– because carbonate solution is alkaline.

Answer 12

purple

Question 12

Fifthly, we now add 5cm3 of milk and 7cm3 of sodium carbonate to the milk test tube. At this point the solution should be purple because …

Answer 12

carbonate solution is alkaline

Question 13

—— is purple in alkaline conditions.

Answer 13

Cresol red

Question 14

Sixthly, we place a ——- in the milk labeled test tube.

Answer 14

thermometer

Question 15

Seventhly, place both test tubes in a ——— at the first chosen temperature usually 20c which is around room temperature.

Answer 15

water bath

Question 16

Eighthly, use a pipette to transfer ———— to the test tube containing milk and stir well.

Answer 16

1cm3 of lipase solution

Question 17

Ninthly, we start a …

Answer 17

timer

Question 18

Ninthly, we start a timer. The enzyme lipase will start to …

Answer 18

break down the fat molecules in the milk.

Question 19

Ninthly, we start a timer. The enzyme lipase will start to break down the fat molecules in the milk. This releases ——- and this causes the milk solution to become acidic.

Answer 19

fatty acids

Question 20

Ninthly, we start a timer. The enzyme lipase will start to break down the fat molecules in the milk. This releases fatty acids and this causes the milk solution to become …

Answer 20

acidic

Question 21

In acidic solutions, the indicator cresol red changes to …

Answer 21

yellow

Question 22

Once the solution turns yellow …

Answer 22

stop timing and record the results.

Question 23

Now repeat the experiment at a …

Answer 23

range of different temperature

Question 24

The independent variable is the …

Answer 24

temperature.

Question 25

The dependent variable is the …

Answer 25

time taken for the milk solution to turn yellow.

Question 26

You must —— the test tubes for the milk solution for each experiment.

Answer 26

clean

Question 27

Because we are looking for a change in colour, it may be difficult to …

Answer 27

decide the exact point to stop the timer.

Question 28

After the experiment we should plot a …

Answer 28

graph