CBSE Class 12 Chemistry Analysis Of Food Worksheet

CBSE Class 12 Chemistry Analysis of Food. CBSE issues sample papers every year for students for class 12 board exams. Students should solve the CBSE issued sample papers to understand the pattern of the question paper which will come in class 12 board exams this year. The sample papers have been provided with marking scheme. It’s always recommended to practice as many CBSE sample papers as possible before the board examinations. Sample papers should be always practiced in examination condition at home or school and the student should show the answers to teachers for checking or compare with the answers provided. Students can download the sample papers in pdf format free and score better marks in examinations. Refer to other links too for latest sample papers.

Question. Outline the systematic chemical tests, observations, and inferences required to identify two unknown food samples as either protein or carbohydrate.
Answer:
To systematically identify protein and carbohydrate components in food samples, a series of qualitative tests are performed as outlined in the experiment table below:
 

* Preparation of Tollens' Reagent: Clean a test tube thoroughly with a small volume of sodium hydroxide (\( \text{NaOH} \)) solution, then add about \( 1\text{ mL} \) of silver nitrate (\( \text{AgNO}_3 \)) solution. A dark precipitate will form; add ammonium hydroxide (\( \text{NH}_4\text{OH} \)) solution dropwise with care until the precipitate is just barely dissolved.

Result: Based on the experimental observations, the given sample A is identified as Protein and sample B is identified as Carbohydrate.
In simple words: Proteins are identified by a purple color in the Biuret test or a yellow precipitate with nitric acid. Carbohydrates are confirmed when they reduce Fehling's solution to form a red-brown solid or produce a shiny silver layer with Tollens' reagent.

Exam Tip: Always make sure to use a water bath when heating mixtures for Fehling's and Tollens' tests, as direct heating over a flame can cause uneven reaction rates or cracking of the glass tube.

Question. Detail the laboratory chemical tests, observations, and corresponding chemical inferences used to detect aldehydes, carboxylic acids, primary amines, and phenols in an organic sample.
Answer:
The identification of different organic functional groups is carried out systematically by performing functional-group-specific chemical reactions as detailed below:
 

In simple words: Organic compounds are identified by distinct behaviors: aldehydes form silver mirrors; carboxylic acids fizz with baking soda and smell fruity with alcohol; amines dissolve in acid and form red-orange dyes; phenols turn violet with iron chloride.

Exam Tip: For the azo-dye test, keeping the reactants strictly below \( 5^\circ\text{C} \) is critical. If the temperature rises, the diazonium salt intermediate decomposes, preventing the formation of the colored dye.