BASIC CONCEPTS
(MCQ)
What does the Biuret test detect?
A. Lipids
B. Reducing sugars
C. Proteins
D. Starch
Answer: C
Explanation: The Biuret test detects proteins by identifying peptide bonds that link amino acids together.
(MCQ)
What color is Biuret reagent before reaction?
A. Blue
B. Green
C. Yellow
D. Colorless
Answer: A
Explanation: The reagent is blue due to copper(II) sulfate.
(MCQ)
A blue solution after adding reagent indicates:
A. High protein
B. No protein
C. Moderate protein
D. Contamination
Answer: B
Explanation: No color change means no peptide bonds detected.
(MCQ)
What is the first step in the Biuret test?
A. Heating sample
B. Adding sodium hydroxide
C. Recording results
D. Cooling sample
Answer: B
Explanation: The solution must first be made alkaline.
(MCQ)
Why is the Biuret test important?
A. Identifies proteins in samples
B. Detects DNA
C. Tests for sugars
D. Measures lipids
Answer: A
Explanation: It’s used to confirm the presence of proteins in biological samples.
(True/False)
The Biuret test detects free amino acids effectively.
Answer: False
Explanation: Free amino acids do not have enough peptide bonds; the test requires at least two peptide bonds to give a positive result.
(MCQ)
What condition is necessary for the Biuret reaction?
A. Acidic environment
B. Neutral environment
C. Alkaline environment
D. Dry conditions
Answer: C
Explanation: The reaction requires an alkaline solution, usually provided by sodium hydroxide.
(True/False)
A light purple color indicates low protein concentration.
Answer: True
Explanation: The intensity of purple reflects protein concentration.
(MCQ)
Why is sodium hydroxide added first?
A. To cool solution
B. To remove proteins
C. To add color
D. To make it alkaline
Answer: D
Explanation: Alkaline conditions are required for the reaction.
(True/False)
The Biuret test can be used in food analysis.
Answer: True
Explanation: It helps determine protein content in foods.
(MCQ)
What structure in proteins is responsible for a positive Biuret test?
A. Hydrogen bonds
B. Peptide bonds
C. Ionic bonds
D. Disulfide bonds
Answer: B
Explanation: The Biuret reagent reacts specifically with peptide bonds in proteins.
(MCQ)
What ion interacts with peptide bonds?
A. Na⁺
B. Cu²⁺
C. Cl⁻
D. H⁺
Answer: B
Explanation: Copper(II) ions form a complex with peptide bonds.
(MCQ)
Which color indicates the highest protein concentration?
A. Blue
B. Light purple
C. Deep violet
D. Green
Answer: C
Explanation: Deep violet indicates many peptide bonds.
(True/False)
Heating is required for the Biuret test.
Answer: False
Explanation: Unlike Benedict’s test, this reaction occurs at room temperature.
(MCQ)
Which sample would give a positive result?
A. Oil
B. Glucose solution
C. Egg white
D. Salt solution
Answer: C
Explanation: Egg white contains albumin protein.
(True/False)
A dipeptide may give a weak positive result.
Answer: True
Explanation: A dipeptide has one peptide bond, so the reaction is weak or sometimes barely detectable.
(True/False)
The reagent changes color even without proteins.
Answer: False
Explanation: Without peptide bonds, the solution remains blue.
(MCQ)
Which order represents increasing protein concentration?
A. Blue → Light purple → Deep violet
B. Violet → Blue → Purple
C. Green → Blue → Red
D. Yellow → Purple → Blue
Answer: A
Explanation: This reflects increasing peptide bond presence.
(MCQ)
What equipment is used to mix solutions?
A. Pipette
B. Stirring rod or gentle shaking
C. Thermometer
D. Balance
Answer: B
Explanation: Proper mixing ensures uniform reaction.
(MCQ)
A negative test result means:
A. High protein
B. Lipids present
C. High sugar
D. No peptide bonds
Answer: D
Explanation: No peptide bonds = no protein detected.
(MCQ)
The Biuret test is an example of what type of reaction?
A. Acid-base reaction
B. Redox reaction
C. Complex formation
D. Precipitation reaction
Answer: C
Explanation: Copper ions form a complex with peptide bonds, producing a color change.
(MCQ)
What color indicates a positive Biuret test?
A. Red
B. Yellow
C. Purple/violet
D. Orange
Answer: C
Explanation: The purple color indicates protein presence.
(True/False)
The Biuret test produces a green color for proteins.
Answer: False
Explanation: The characteristic positive color is purple, not green.
(True/False)
Safety precautions are still required in this test.
Answer: True
Explanation: Sodium hydroxide is corrosive, so PPE is necessary.
(MCQ)
Which factor affects the result?
A. Concentration
B. Mixing
C. Reagent amount
D. All of the above
Answer: D
Explanation: All these influence the accuracy of the result.