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CBSE Class 12 chemistry practical, Organic / biochemistry tests · Organic qualitative analysis

Source: CBSE Class 12 chemistry practical syllabus · use your school laboratory manual (NCERT Lab Manual where your school uses it).

Tests for carbohydrates, fats, and proteins in foodstuffs (Class 12 chemistry practical)

You test small portions of foods such as rice, oil, egg albumin, or potato for reducing sugar, starch, fat, and protein.

Use school food samples — do not bring unknown materials from home without permission.

Published practice page. Concentrations, masses, and numerical answers come from your school laboratory manual and your own readings — not invented here. Not yet reviewed by a named chemistry reviewer. Version 1.0.0, updated 2026-10-03.

Safety — read before you start

Safety warning. Practise here. Perform the real experiment only in your school lab, with your teacher present.

  • Benedict’s and biuret reagents contain copper salts that are harmful if swallowed.
  • Iodine solution stains and irritates skin and eyes.
  • Heat Benedict’s mixtures in a water bath — hot glass burns.

Wear: Lab coat, Splash goggles, Gloves, as your teacher directs.

Follow your teacher’s disposal instructions. Do not pour leftovers down a household drain.

Loads only after you tap. Use the lab hands to pick up and use equipment (pointer hidden in the scene). Falls back to a flat diagram if WebGL is unavailable.

Aim

To detect the presence of carbohydrates (reducing sugar and/or starch), fats, and proteins in the food samples listed in your laboratory manual.

Methods and quantities can differ between schools. Follow your teacher's instructions.

Apparatus and chemicals

Apparatus and chemicals
ItemNote
Test tubesSeveral for parallel tests.
Water bathFor Benedict’s test heating.
Spot plate or filter paperGrease-spot test for fat.
Mortar and pestle (optional)Grind solid food with water.
Food samples (food)Teacher-supplied items only.
Benedict’s reagent (Benedict)For reducing sugars after heating.
Iodine solution (I2)Blue-black with starch.
Biuret reagent (biuret)Violet with peptide bonds (protein).
Distilled water (H2O)Extract aqueous portion of food.
Test tubes for carbohydrate, fat, and protein food tests
Run Benedict’s, iodine, grease-spot, and biuret tests on school-supplied foods. Record only the colours and changes you see.

Theory and reaction

Open

Reducing sugars reduce Cu2+ in Benedict’s to Cu2O (brick-red precipitate on heating).

Starch forms a blue-black complex with iodine.

Fats leave a translucent permanent spot on paper (grease-spot test) or sudan dye if manual uses it.

Proteins give biuret test: violet colour with copper ions in alkaline solution (peptide bonds).

Iodine indicates starch; biuret reagent gives violet colour with proteins.

Procedure

  1. Prepare aqueous extract of each solid food by grinding with a little water and filtering if needed.
  2. Benedict’s test: mix extract with Benedict’s, heat gently in water bath. Note colour change.Safety: Hot tubes — hold with holder. Benedict contains copper — do not ingest.
  3. Iodine test: add iodine drop to extract or cut surface of potato/rice. Note blue-black.
  4. Grease-spot: rub a little sample on filter paper or observe oil directly. Hold to light — translucent spot indicates fat.
  5. Biuret test: add biuret reagents to protein-rich extract (e.g. albumin). Note violet/lilac.

Observation table

Enter the readings from your school lab in the practical file below. This page does not fill them in for you.

Type the readings in your practical file

Calculation

No calculation. Tabulate which macronutrients each food contains.

Result

Complete a table: sample versus presence (+/−) of reducing sugar, starch, fat, and protein as your observations support.

Precautions

  • Label tubes — iodine and Benedict look similar in some lighting.
  • Use tiny food amounts.
  • Do not taste laboratory samples.

Viva questions

Answer one question at a time. The full answers stay closed until you open them.

Question 1 of 4

Benedict’s test detects primarily…

Answer choices

Pick an answer first.

Show all questions and answers

  1. Benedict’s test detects primarily…

    Answer: Reducing sugars. Reason: Reducing sugars reduce Cu(II) to Cu(I) oxide on heating.

  2. Iodine test is specific for…

    Answer: Starch. Reason: Starch–iodine gives blue-black colour.

  3. Biuret test indicates…

    Answer: Peptide/protein presence. Reason: Peptide bonds form violet copper complex in alkaline medium.

  4. A permanent translucent grease spot suggests…

    Answer: Fat or oil present. Reason: Lipids leave oily residue on paper.

Common mistakes

  • Calling all sugars ‘starch’ because iodine was skipped.
  • Not heating Benedict’s and missing reducing sugar.
  • Interpreting wet paper translucency from water alone as fat.

Frequently asked questions

Can I do this at home?
No. Use this page to practise the order of steps and viva. Do the real experiment only in your school laboratory, with your teacher present.

Your practical file

Name, school, and roll number are optional and are not sent anywhere.

The practical file opens on this device.

Review

Not yet reviewed by a named chemistry reviewer. Published for practice only — follow your teacher and laboratory manual for quantities and safety.

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