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Arjun investigates the effect of pH on an enzyme called catalase. He uses catalase to break down hydrogen peroxide into oxygen and water. Arjun records how much oxygen is collected in five minutes. The table shows his results. volume of oxygen collected every 5 min in cm3

pH value first attempt

second attempt

third attempt

mean

6

18.3

18.6

18.4

18.4

7

27.3

27.5

26.9

27.2

8

22.1

22.3

12.6

19.0

9

12.5

12.6

12.2

10

7.4

7.1

6.9

7.1

11

3.1

3.3

3.0

3.1

(a) Arjun has calculated the mean for each pH except pH 9. (i)

Calculate the mean for pH 9. answer ........................................... cm3

(ii)

[1]

Describe and explain the pattern seen in the mean results. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [2]

(b) When Arjun calculated the mean for pH 8 he used all three values. Arjun’s teacher tells him that he should not have done that. Explain why his teacher gave him this advice. ................................................................................................................................................... ................................................................................................................................................... .............................................................................................................................................. [2] [Total: 5]

Š OCR 2012

B3 question 4  
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