PAG 09 - 9.1 : Biuret’s Test

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5 Terms

1
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What biological molecule does the Biuret test detect?

Proteins (specifically, it detects the presence of peptide bonds)

2
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Outline the method for the Biuret test

1.) Add 2 cm³ of the liquid food sample to a clean test tube.

2. ) Add an equal volume (2 cm³) of Biuret reagent (or add sodium hydroxide solution followed by a few drops of dilute copper(II) sulfate solution).

3.) Mix gently (do not heat) and observe the colour change.

3
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What is a positive and negative result for the Biuret test?

  • Positive: Turns from pale blue to lilac / purple

  • Negative: Remains pale blue.


4
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Why must you NOT heat the sample during the Biuret test?

  • Heating is unnecessary for the reaction and can cause side reactions or interfere with observing the true colour change.


5
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What is the main safety precaution when using Biuret reagent?

  • Biuret reagent contains sodium hydroxide, which is corrosive (an irritant to skin and eyes).

  • Wear eye protection and wash off any spills immediately.