Chemical tests for Aloes MCQs With Answer

Chemical tests for Aloes are essential in B.Pharm studies to identify major phytoconstituents such as anthraquinone glycosides (aloin), free anthraquinones (aloe‑emodin), polysaccharides (acemannan), flavonoids and tannins. This concise overview covers classical chemical reactions—Bornträger test, hydrolysis for combined anthraquinones, ferric chloride for phenolics, Molisch for carbohydrates, foam test for saponins—along with instrumental confirmations like TLC and colorimetric assays used in quality control and identification. Understanding reagents, extraction solvents, stepwise hydrolysis, interpretation of color changes and potential false positives strengthens practical skills in pharmacognosy, standardization and analytical phytochemistry. These tests are vital for herbal standardization, stability assessment and safe formulation of aloe‑based products.
Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is the primary purpose of the Bornträger test when applied to aloe extracts?

• To detect saponins in Aloe gel
• To identify anthraquinone aglycones after extraction
• To quantify polysaccharide (acemannan) content
• To determine heavy metal contamination

Correct Answer: To identify anthraquinone aglycones after extraction

Q2. Which solvent is classically used to extract anthraquinones from aloe for the Bornträger test?

• Water
• Ether
• Benzene or chloroform
• Acetone

Correct Answer: Benzene or chloroform

Q3. When anthraquinone glycosides (like aloin) are present, what preparatory step is required before a Bornträger test will detect the aglycone?

• Alkaline precipitation
• Acid hydrolysis to liberate aglycone
• Neutralization with sodium bicarbonate
• Direct visualization under visible light

Correct Answer: Acid hydrolysis to liberate aglycone

Q4. In the Bornträger test, which reagent is added after organic extraction to reveal a positive anthraquinone reaction?

• Dilute hydrochloric acid
• Ammonia (NH4OH)
• Ferric chloride solution
• Lead acetate solution

Correct Answer: Ammonia (NH4OH)

Q5. A positive Bornträger test typically produces which colour in the alkaline aqueous layer?

• Blue‑green
• Pink to red or violet
• Yellow to brown
• Black precipitate

Correct Answer: Pink to red or violet

Q6. Which test is most appropriate for rapid qualitative detection of polysaccharides such as acemannan in aloe gel?

• Molisch test
• Keller‑Kiliani test
• Dragendorff’s test
• Bornträger test

Correct Answer: Molisch test

Q7. What is the expected result of the Molisch test for aloe polysaccharides?

• Persistent foam formation
• Formation of a violet ring at the interface
• Red precipitate
• Green coloration

Correct Answer: Formation of a violet ring at the interface

Q8. Which test is commonly used to indicate the presence of phenolic compounds and tannins in aloe extracts?

• Ferric chloride test
• Ninhydrin test
• Iodine test
• Salkowski test

Correct Answer: Ferric chloride test

Q9. The foam (froth) test is used to detect which class of constituents in aloe?

• Alkaloids
• Saponins
• Anthraquinones
• Polysaccharides

Correct Answer: Saponins

Q10. Periodic acid–Schiff (PAS) staining of an aloe extract is used to confirm which component?

• Proteins
• Polysaccharides (mucopolysaccharides/acemannan)
• Alkaloids
• Unsaturated lipids

Correct Answer: Polysaccharides (mucopolysaccharides/acemannan)

Q11. Which analytical technique provides separation and identification of aloin and aloe‑emodin with high specificity after chemical tests?

• Thin layer chromatography (TLC)
• Simple boiling test
• Gravimetric analysis
• Paper chromatography only

Correct Answer: Thin layer chromatography (TLC)

Q12. After TLC separation, which visualization reagent is commonly used to detect anthraquinones under visible light?

• Anisaldehyde‑sulfuric acid reagent
• Dragendorff’s reagent
• Biuret reagent
• Ammonium molybdate

Correct Answer: Anisaldehyde‑sulfuric acid reagent

Q13. Which of the following best describes why acid hydrolysis is applied to aloe extracts before some chemical tests?

• To remove polysaccharides that interfere with coloration
• To cleave glycosidic bonds and release aglycones like aloe‑emodin
• To precipitate proteins for clearer extracts
• To oxidize anthraquinones into non‑reactive forms

Correct Answer: To cleave glycosidic bonds and release aglycones like aloe‑emodin

Q14. Which reagent would you use to test for reducing sugars present after hydrolysis of aloin?

• Molisch reagent
• Benedict’s reagent
• Ferric chloride
• Salkowski reagent

Correct Answer: Benedict’s reagent

Q15. A false positive in the Bornträger test can arise from which interference if precautions are not taken?

• Residual acidic medium in extract
• Presence of chlorophyll alone
• Non‑hydrolyzed polysaccharides
• Residual solvent such as benzene

Correct Answer: Residual acidic medium in extract

Q16. Which statement about aloin is correct?

• Aloin is a simple phenolic acid found in aloe latex
• Aloin is an anthraquinone glycoside present in aloe latex
• Aloin is a polysaccharide responsible for gel viscosity
• Aloin is a volatile oil component

Correct Answer: Aloin is an anthraquinone glycoside present in aloe latex

Q17. For quantitative estimation of total anthraquinones in aloe, which approach is usually combined with chemical tests?

• Turbidimetric assay
• UV‑visible spectrophotometry after hydrolysis
• Gravimetric precipitation with lead acetate
• pH titration

Correct Answer: UV‑visible spectrophotometry after hydrolysis

Q18. Which of the following is a correct procedural sequence to perform a Bornträger test on aloe containing glycosides?

• Extract with water → add ammonia → observe color
• Hydrolyze with dilute acid → extract aglycones with organic solvent → add ammonia → observe color
• Extract with benzene → add ferric chloride → observe precipitate
• Perform TLC first, then heat with NaOH

Correct Answer: Hydrolyze with dilute acid → extract aglycones with organic solvent → add ammonia → observe color

Q19. Which chemical test specifically differentiates free anthraquinones from combined (glycosidic) anthraquinones without hydrolysis?

• Bornträger test on direct extract
• Kedde test
• Liebermann‑Burchard test
• Froth test

Correct Answer: Bornträger test on direct extract

Q20. If an aloe sample gives a strong PAS positive but negative Benedict’s test, what is most likely present?

• Low molecular weight reducing sugars only
• High molecular weight polysaccharides (e.g., acemannan)
• Free anthraquinone aglycones
• Saponins causing interference

Correct Answer: High molecular weight polysaccharides (e.g., acemannan)

Q21. Which safety consideration is most important when performing classical Bornträger extraction in a teaching lab?

• Use of UV light only in a fume hood
• Avoid inhalation/exposure to organic solvents like benzene; use fume hood and alternatives
• Heat acids in closed containers
• Neutralize ammonia with concentrated acid immediately

Correct Answer: Avoid inhalation/exposure to organic solvents like benzene; use fume hood and alternatives

Q22. Which reagent is used to demonstrate general phenolic hydroxyl groups giving a blue‑green colour with aloe phenolics?

• Ferric chloride
• Biuret reagent
• Millon’s reagent
• Molisch reagent

Correct Answer: Ferric chloride

Q23. In TLC analysis, what is the advantage of using UV detection followed by post‑chromatographic derivatization for aloe anthraquinones?

• UV detection removes the need for standards
• Combining both increases sensitivity and helps identify non‑UV‑visible compounds
• Derivatization causes degradation, simplifying patterns
• There is no advantage; only one method should be used

Correct Answer: Combining both increases sensitivity and helps identify non‑UV‑visible compounds

Q24. Which of the following indicates a positive Keller‑Kiliani test and is relevant to which compound class (even if not primary in aloe)?

• Reddish brown colour indicating cardiac glycosides
• Green precipitate indicating alkaloids
• Violet ring indicating polysaccharides
• Yellow foam indicating saponins

Correct Answer: Reddish brown colour indicating cardiac glycosides

Q25. For routine quality control of commercial aloe gel, which two tests are most commonly combined?

• Benedict’s and Salkowski tests
• Bornträger test for anthraquinones and PAS/Molisch for polysaccharides
• Dragendorff’s and Mayer’s tests for alkaloids
• TLC for essential oils and foam test for saponins

Correct Answer: Bornträger test for anthraquinones and PAS/Molisch for polysaccharides

Q26. Which observation suggests degradation of anthraquinone glycosides during improper storage of aloe samples?

• Increased viscosity of gel
• Enhanced Bornträger positive without hydrolysis due to aglycone formation
• Loss of PAS positivity
• Persistent foam in water extract

Correct Answer: Enhanced Bornträger positive without hydrolysis due to aglycone formation

Q27. When performing a Bornträger test, why is it important to separate organic and aqueous layers carefully?

• To ensure complete removal of polysaccharides
• To prevent transfer of solvent which may mask colour development in alkaline layer
• Because anthraquinones dissolve only in water
• To oxidize anthraquinones in the organic layer

Correct Answer: To prevent transfer of solvent which may mask colour development in alkaline layer

Q28. Which of these is a typical Rf behaviour for aloe‑related anthraquinones on silica TLC with moderately non‑polar mobile phase?

• Very low Rf (near origin) due to extreme polarity
• Moderate Rf values allowing separation from polar polysaccharides
• No migration at all; they remain fixed on the plate
• Rf values greater than 1.5

Correct Answer: Moderate Rf values allowing separation from polar polysaccharides

Q29. Which confirmatory approach is appropriate if a Bornträger test is ambiguous?

• Repeat Bornträger immediately without changes
• Perform TLC with standard anthraquinone markers and chemical derivatization
• Assume negative and discard sample
• Use only the Molisch test for confirmation

Correct Answer: Perform TLC with standard anthraquinone markers and chemical derivatization

Q30. Which description best summarizes the role of chemical tests for aloes in the B.Pharm curriculum?

• They are obsolete and replaced entirely by instrumental methods
• They provide rapid, low‑cost screening for phytoconstituents and guide further instrumental analysis
• They are useful only for detecting adulteration with synthetic drugs
• They only measure toxicity and have no role in identification

Correct Answer: They provide rapid, low‑cost screening for phytoconstituents and guide further instrumental analysis

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