4.1 (d) To conduct a qualitative test for protein
Teacher Notes
Apparatus required per class group of 24 students
Biuret solution
48 ml
Boiling tubes
24
Boiling tube racks
12
Distilled water
Protein solution
24 ml
Advance preparation
o Prepare Biuret solution or alternatively order from suppliers.
Advance chemical preparation
(a) Biuret reagent.
o Dissolve 1.5 g copper (11) sulphate-5-water crystals, 6 g potassium sodium tartrate4-water in 500 ml of distilled water.
o Add 375 ml of a 2M sodium hydroxide solution while stirring. If a precipitate occurs
add 1 g of potassium iodide.
o Pour this mixture into a 1000 ml volumetric flask and dilute to 1 litre.
o Mix well. Label this solution CORROSIVE, as the sodium hydroxide solution is
corrosive. This solution will keep.
(b) Protein solution (albumen solution 1% w/v)
o Dissolve 1g of albumen in 100 ml of distilled water.
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If Biuret solution is not available then sodium hydroxide solution and copper sulfate
solution may be used. The method here is to add 2 ml NaOH and 2-3 drops CuSO4
solution to 2 ml protein solution in a boiling tube. A purple- violet colour is a positive
result
(c) Copper sulfate solution.
o Dissolve 1g of copper sulfate in distilled water and make up to 100 ml.
.
(d)Sodium hydroxide solution (1% w/v)
o Wearing safety goggles dissolve 10 g sodium hydroxide pellets in water and make
up to 100 ml with distilled water. Stir to dissolve. (Care: much heat evolved). Label
CORROSIVE.
Safety precautions
o Biuret reagent is corrosive. See MSDS for further information.
Expected outcome of experiment
o A positive result for proteins is a lilac colour.
o A negative result for proteins is a blue colour.
Disposal and post-experiment work
o Excess sodium hydroxide solution can be diluted and flushed down the drain.
o Excess Biuret reagent can be stored but should be labelled corrosive.
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4.1 (d) To conduct a qualitative test for protein
Student Notes
Apparatus required per group
o 4 ml Biuret solution
o 2 boiling tubes
o Test tube rack
o 2 ml Protein solution
o Distilled water
Assembled apparatus
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Method:
1. Label two boiling tubes ‘A’ and ‘B’.
2. Place 2 ml of the protein solution into tube A.
3. Place 2 ml of water into tube B. This acts as the control.
4. Add 2 ml of Biuret solution into each tube.
5. Swirl both tubes.
6. Record result.
7. At the end of the experiment, clean all of the equipment and replace it in its correct
place.
Results:
Sample
Initial colour
Final colour
A – Protein solution
B – Water
Conclusion/Comment
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