Vidaara.orgClass 12 · Chemistry
CodeVID-C12-14-T1-01
Assignment — Carbohydrates
Name: ____________________
Roll No.: __________
Date: ____________
General Instructions
- All questions are compulsory.
- Section A carries 1 mark each, Section B 2 marks, Section C 3 marks and Section D 5 marks.
- Show all working for Sections B, C and D. Only final answers are given at the end — for full solutions, raise your doubts with your teacher.
Section A — Multiple Choice Questions
5 × 1 = 5 marks
1.
Glucose is an:
- A.aldopentose
- B.ketohexose
- C.aldohexose
- D.ketopentose
2.
Which sugar is non-reducing?
- A.Maltose
- B.Sucrose
- C.Glucose
- D.Lactose
3.
Starch gives a blue colour with iodine because of its component:
- A.amylopectin
- B.cellulose
- C.amylose
- D.glycogen
4.
Hydrolysis of sucrose gives:
- A.glucose only
- B.two glucose units
- C.glucose + fructose
- D.glucose + galactose
5.
The D/L notation of a sugar is decided by the chiral carbon:
- A.nearest the –CHO
- B.farthest from the –CHO
- C.C1
- D.bearing CH2OH only
Section B — Short Answer (2 marks)
3 × 2 = 6 marks
6.
Define monosaccharide and give two examples.
7.
Why is maltose a reducing sugar but sucrose is not?
8.
Name the monosaccharides obtained on hydrolysis of lactose.
Section C — Short Answer (3 marks)
2 × 3 = 6 marks
9.
Explain mutarotation of glucose.
10.
Distinguish starch, glycogen and cellulose by their glucose linkages and role.
Section D — Long Answer (5 marks)
1 × 5 = 5 marks
11.
Describe the cyclic (Haworth) structure of glucose, define the anomeric carbon and anomers, and explain why open-chain glucose fails to give certain aldehyde reactions (e.g. Schiff's test).
Answer Key
Section A — Multiple Choice Questions
- (C) aldohexose
- (B) Sucrose
- (C) amylose
- (C) glucose + fructose
- (B) farthest from the –CHO
Section B — Short Answer (2 marks)
- A carbohydrate that cannot be hydrolysed into a simpler sugar, e.g. glucose and fructose.
- Maltose retains one free anomeric (potential aldehyde) group; in sucrose both anomeric carbons are bonded in the glycosidic linkage.
- D-galactose and D-glucose.
Section C — Short Answer (3 marks)
- Freshly dissolved α- or β-D-glucose changes its optical rotation until both reach a common equilibrium (+52.5°), because each anomer opens to the open-chain form and recloses, interconverting α and β.
- Starch: α-1,4 + α-1,6, plant energy store; glycogen: like amylopectin but more branched, animal store in liver/muscle; cellulose: β-1,4 linear, structural fibre, indigestible by humans.
Section D — Long Answer (5 marks)
- Glucose exists mainly as a six-membered pyranose ring formed by addition of the C5–OH to the C1 –CHO. C1 becomes a new chiral centre, the anomeric carbon, giving α-D-glucose (C1–OH down) and β-D-glucose (C1–OH up), the two anomers; they interconvert by mutarotation. Because in solution glucose is overwhelmingly cyclic with very little free –CHO present at any moment, typical aldehyde tests such as Schiff's test and the NaHSO3 addition are not given, even though it reduces Tollens'/Fehling's where the equilibrium is continuously pulled toward the open chain.
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