Change In Ph


- 10mL of hydrogen peroxide was added to each of 5 test tubes
- Universal indicator was added to each test tube
- Hydrochloric acid or sodium hydroxide was added to each test tube and colour changes noted, so that the test tubes had pH’s of about 2, 4, 7, 10 and 12
- 5 small cubes were cut from a potato, all about the same size, using a scalpel OR fresh plant or animal tissue (liver)
- One potato cube OR liver was placed in each test tube with hydrogen peroxide
- After 5 minutes, the height of foam (bubbles) formed was measured for each test tube

- Potato cubes provided the catalase enzyme which catalyses the decomposition of hydrogen peroxide into oxygen and water
- If pH (concentration of hydrogen ions in solution) changes, charge pattern on the enzyme surface changes, altering the shape of its active site. Enzymes will have highest rate of reaction at their optimal pH. At varying pH’s rate of reaction will be decreased, and the enzyme may be denatured at extremes of pH

Enzyme and source: Catalase (liver or potato)
Substrate: Hydrogen peroxide
Chemical reaction catalysed: decomposition of hydrogen peroxide into water and oxygen
Evidence of enzyme activity: fizzing effect
Determining enzyme activity: measure height of bubbles formed
Independent variable: pH of the solutions in the test tubes
Dependent Variable: height of the foam formed