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Experiment 10. The effect of pepsin on egg white suspension

(a) Label four test-tubes 1-4.

(b) Into each tube place about 5 cm3 (20 mm in test-tube) egg white suspension.

(c) To tubes 2,3 and 4 add three drops of dilute hydrochloric acid.

(d) Using a graduated pipette or syringe place 1 cm3 1% pepsin solution in a clean test- tube and heat it over a small Bunsen flame until the liquid boils. Add the boiled pepsin to the egg-white suspension in tube 4.

(e) Prepare a water bath in a 250 cm3 beaker or jar by mixing hot and cold water from the tap to attain a temperature of about 40 °C. Have the beaker about half full.

(f) Using a graduated pipette or syringe, add 1 cm3 1% pepsin to tubes 1 and 3 only.

(g) Place all four tubes in the water bath and copy the table below into your notebook.

(h) After five or six minutes remove the four tubes from the water bath and replace them in the test-tube rack. Compare the appearance of the contents and fill in your table of results.

|Tube |Contents |Results |
|1 |Egg-white suspension & pepsin | |
|2 |Egg-white suspension & HCl | |
|3 |Egg-white suspension, pepsin & HCl | |
|4 |Egg-white suspension, boiled pepsin & HCl | |

Experiment 10. Discussion

1 Why, do you suppose, does the egg white suspension used in the experiment look cloudy?


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