Biomolecules

Chemistry · Class 12

Simulation · Chemistry · Class 12

Invert sugar: the reading falls through zero

"Invert sugar: the reading falls through zero" is a free, interactive Class 12 Chemistry simulation for NEET and JEE, built on the NCERT section "Disaccharides and the glycosidic link" in Biomolecules. A polarimeter reading as sucrose hydrolyses to equal moles of glucose (+52.5°) and fructose (−92.4°): the angle falls through zero and ends negative. NEET has asked about this idea 1 time in 10 years of papers. JEE Main asked 50 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).

From the lesson Disaccharides and the glycosidic link in Biomolecules. Change the values and watch what happens.

Invert sugar: the reading falls through zeroChemistry · Class 12

What it shows

NCERT §10.1.3

A polarimeter reading as sucrose hydrolyses to equal moles of glucose (+52.5°) and fructose (−92.4°): the angle falls through zero and ends negative.

Controls

3 to try

  • Slider% sucrose hydrolysed 0–100
  • Toggleacid catalyst / invertase (rate only)
  • Readoutsmoles of each sugar, observed rotation

Try this

Find the percentage hydrolysed at which the rotation crosses zero (≈76%)

Common mistake

Sucrose itself turns laevorotatory.

In NEET

10 years of papers

Asked 1 time in 10 years of NEET.

See the past questions: Biomolecules (Chemistry), Biomolecules (chapter)

In JEE Main

42 shifts analysed

50 questions from Biomolecules across the 42 JEE Main shifts Lumi has analysed (2017–2026).

See the past questions

The idea behind it

NCERT §10.1.3

  • Two monosaccharides join by losing a water molecule, leaving an oxide bridge between them. A link between sugar units through oxygen is a glycosidic linkage. Dilute acid or enzymes hydrolyse it back.
  • If both reducing groups (the aldehydic or ketonic carbons) are used up in the link, the disaccharide is non-reducing. If one stays free it is reducing.
  • Sucrose: C1 of α-D-glucose joined to C2 of β-D-fructose. Both reducing carbons are in the bond, so sucrose is a non-reducing sugar.
  • Sucrose is dextrorotatory. Its hydrolysis gives equal moles of D-(+)-glucose (+52.5°) and D-(–)-fructose (–92.4°). Fructose's laevorotation is the larger, so the mixture is laevorotatory.
  • The sign of rotation flips from (+) to (–) on hydrolysis; the product is called invert sugar.
  • Maltose: two α-D-glucose units, C1 of one joined to C4 of the other. The second unit's C1 can open to a free aldehyde in solution, so maltose is reducing.
  • Lactose (milk sugar): β-D-galactose and β-D-glucose linked from C1 of galactose to C4 of glucose. The glucose unit's C1 can give a free aldehyde, so lactose is reducing.

Questions

5 answers

What does the "Invert sugar: the reading falls through zero" simulation show?
A polarimeter reading as sucrose hydrolyses to equal moles of glucose (+52.5°) and fructose (−92.4°): the angle falls through zero and ends negative.
What mistake does the "Invert sugar: the reading falls through zero" simulation fix?
A common mistake it clears up: sucrose itself turns laevorotatory.
Has NEET asked about this idea?
Yes. NEET has asked about this idea 1 time in 10 years of papers.
Does JEE Main ask questions from Biomolecules?
Yes. JEE Main asked 50 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).
Is this simulation free?
Yes. It is free and runs in the browser on a phone or a laptop. It belongs to the lesson "Disaccharides and the glycosidic link" in Biomolecules (Class 12 Chemistry).

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