Question:

Which of the following statements is not true about glucose?

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Schiff's reagent tests for aldehydes, and glucose, being an aldose, will give a positive result.
Updated On: Jun 10, 2025
  • It is an aldose.
  • On heating with HI it forms n-hexane.
  • It exists in furanose form.
  • It does not give Schiff's test. 
     

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The Correct Option is A

Approach Solution - 1

The question asks which statement about glucose is not true. Let's evaluate each option:

  • Glucose is an aldose: Glucose is indeed an aldose, as it contains an aldehyde group at the first carbon. Hence, this statement is true.
  • On heating with HI, glucose forms n-hexane: This is a characteristic reaction where the entire glucose molecule reduces to n-hexane when treated with hydrogen iodide. Thus, this statement is also true.
  • It exists in furanose form: Glucose typically forms a pyranose ring when cyclized, not a furanose form. Therefore, this statement is not true about glucose.
  • It does not give Schiff's test: Glucose does not give a positive Schiff's test because while it contains an aldehyde group, it forms a stable cyclic hemiacetal form that typically doesn't react with Schiff's reagent. Hence, this statement is true.

Considering the analysis above, the statement that is not true about glucose is: It exists in furanose form.

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Approach Solution -2

Step 1: Understanding glucose's properties. Glucose is an aldose (option A) and forms n-hexane on heating with HI (option B). It can exist in the furanose form (option C) as well.

 Step 2: Schiff's test. Glucose, being an aldehyde, will give a positive Schiff's test, which detects aldehydes. 

Step 3: Conclusion. Thus, the statement that glucose does not give Schiff's test is incorrect, corresponding to option (D). 

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