Maharashtra Board Class 11 Chemistry Chapter 3 Basic Analytical Techniques Solutions

11th Chemistry Chapter 3 Exercise Basic Analytical Techniques Solutions Maharashtra Board

Basic Analytical Techniques Class 11 Exercise Question Answers Solutions Maharashtra Board

Class 11 Chemistry Chapter 3 Exercise Solutions Maharashtra Board

Chemistry Class 11 Chapter 3 Exercise Solutions

1. Choose the Correct Option

 

Question A.Which of the following methods can be used to seperate two compounds with different solubilities in the same solvent?
a. Fractional crystallization
b. Crystallization
c. Distillation
d. Solvent extraction
Answer: (a) Fractional crystallization
In simple words: Fractional crystallization is used to separate solids with different solubilities in the same solvent by varying the temperature.

🎯 Exam Tip: Remember that fractional crystallization relies on different solubility properties, making it distinct from other separation methods.

 

Question B.Which of the following techniques is used for seperation of glycerol from soap in soap industry?
a. Distillation under reduced pressure
b. Fractional distillation
c. Filtration
d. Crystallization
Answer: (a) Distillation under reduced pressure
In simple words: Glycerol is separated from soap in industrial processes using distillation under reduced pressure because glycerol has a high boiling point and can decompose at atmospheric pressure.

🎯 Exam Tip: Reduced pressure distillation is ideal for separating high-boiling liquids that are prone to decomposition at their normal boiling points.

 

Question C.Which technique is widely used in industry to seperate components of mixture and also to purify them?
a. Steam distillation
b. Chromatography
c. Solvent extraction
d. Filtration
Answer: (b) Chromatography
In simple words: Chromatography is a powerful and versatile separation technique widely used in industry to separate and purify components from complex mixtures.

🎯 Exam Tip: Chromatography's widespread industrial application stems from its ability to separate a diverse range of compounds, making it a key technique in many fields.

 

Question D.A mixture of acetone and benzene can be seperated by the following method :
a. Simple distillation
b. Fractional distillation
c. Distillation under reduced pressure
d. Sublimation
Answer: (b) Fractional distillation
In simple words: Acetone and benzene have relatively close boiling points, making fractional distillation the suitable method to separate them efficiently.

🎯 Exam Tip: Fractional distillation is chosen over simple distillation when the boiling points of the components in a mixture are close.

 

Question E.Colourless components on chromatogram can not be observed by the following:
a. Using UV light
b. Using iodine chamber
c. Using the spraying reagent
d. Using infrared light
Answer: (d) Using infrared light
In simple words: Infrared light is generally used for structural analysis rather than visualizing colorless components on a chromatogram, which typically relies on UV light, iodine, or specific spraying reagents.

🎯 Exam Tip: Methods like UV light, iodine chambers, or spraying reagents are standard for visualizing colorless compounds in chromatography; infrared light has a different analytical purpose.

 

2. Answer the Following

 

Question A.Which of the following techniques is used for purification of solid organic compounds?
a. Crystallisation
b. Distillation
Answer: Solid (crude/impure) organic compounds can be purified by crystallization.
In simple words: Crystallization is the primary method for purifying solid organic compounds by forming pure crystals from a solution.

🎯 Exam Tip: Crystallization is a fundamental technique for purifying solid organic compounds, relying on solubility differences.

 

Question B.What do you understand by the terms
a. residue
b. filtrate.
Answer:
a. Residue: In the process of filtration, the insoluble (undissolved) impurities which remain on the filter paper are called residue.
b. Filtrate: In the process of filtration, the liquid which pass through the filter paper and collected in the beaker is called filtrate.
In simple words: Residue is the solid left on the filter paper, while filtrate is the liquid that passes through it during filtration.

🎯 Exam Tip: Clearly distinguishing between residue and filtrate is crucial for understanding filtration, a basic separation technique.

 

Question C.Why is a condenser used in distillation process?
Answer: In the process of distillation, a liquid is converted into its vapour and the vapour is then condensed back to liquid on cooling. The condenser has a jacket with two outlets through which water is circulated. Hence, to provide efficient cooling, a condenser is used.
In simple words: A condenser rapidly cools hot vapor back into liquid during distillation, making the process efficient and recovering the purified substance.

🎯 Exam Tip: The condenser's role in distillation is to convert vapor back to liquid, ensuring efficient recovery of the purified substance.

 

Question D.Why is paper moistened before filtration?
Answer: Before filtration, filter paper is moistened with appropriate solvent to ensure that it sticks to the funnel and does not let the air to pass through the leaks.
In simple words: Moisten filter paper before filtration to secure it to the funnel and prevent air leaks, ensuring efficient liquid flow through the paper.

🎯 Exam Tip: Moistening the filter paper is a practical step to create a good seal, preventing bypass of liquid and ensuring effective filtration.

 

Question E.What is the stationary phase in Paper Chromatography?
Answer: Paper chromatography is a type of partition chromatography in which a special quality paper, namely Whatman paper 1 is used. The water trapped in the fibres of the paper acts as stationary phase.
In simple words: In paper chromatography, the stationary phase is the water adsorbed within the fibers of the cellulose paper.

🎯 Exam Tip: For paper chromatography, remember that the embedded water molecules, not the paper itself, constitute the stationary phase, facilitating partition.

 

Question F.What will happen if the upper outlet of the condenser is connected to the tap instead of the lower outlet?
Answer:

• If water enters through upper outlet of condenser, the water will quickly flow down under the influence of gravity. This allows only a small section of the condenser to be cooled enough.
• If water enters through lower outlet of condenser, the entire condenser will be filled with water before it leaves out providing maximum cooling to the condenser. This results in maximum recovery of purified liquid.

Hence, water must be allowed to enter through lower outlet of condenser during distillation process.
In simple words: Connecting the tap to the upper outlet cools only a small section of the condenser, while connecting to the lower outlet ensures the entire condenser fills with water for maximum cooling and efficient recovery.

🎯 Exam Tip: Proper water flow (bottom-to-top) in a condenser is critical for maintaining maximum cooling efficiency throughout the distillation process.

 

Question G.Give names of two materials used as stationary phase in chromatography.
Answer:
1. Alumina
2. Silica gel
In simple words: Alumina and silica gel are common solid materials used as stationary phases in various chromatography techniques.

🎯 Exam Tip: Alumina and silica gel are widely used adsorbents for stationary phases due to their excellent adsorptive properties.

 

Question H.Which properties of solvents are useful for solvent extraction?
Answer:

• Organic compound must be more soluble in the organic solvent, than in water.
• Solvent should be immiscible with water and be able to form two distinct layers.

In simple words: For effective solvent extraction, the target compound must be more soluble in the extracting solvent than in water, and the two solvents must be immiscible, forming separate layers.

🎯 Exam Tip: Immiscibility and differential solubility are the two key properties required for solvents in effective solvent extraction.

 

Question I.Why should spotting of mixture be done above the level of mobile phase ?
Answer:

• If spotting of a mixture is done at the level of mobile phase, then solvent will come in contact with the sample spot.
• Sample spot will dissolve in the mobile phase and its components will move all over the plate resulting in no distinct separation.

Hence, spotting of mixture should be done above the level of mobile phase.
In simple words: Spotting the mixture above the mobile phase level prevents the sample from dissolving directly into the solvent pool, ensuring proper separation as the mobile phase ascends.

🎯 Exam Tip: Always spot above the mobile phase line to ensure the sample undergoes chromatographic separation rather than simply dissolving into the solvent.

 

Question J.Define : a. Stationary phase b. Saturated solution
Answer:
a. Stationary phase: Stationary phase is a solid or a liquid supported on a solid which remains fixed in a place and on which different solutes are adsorbed to a different extent.
b. Saturated solution: A saturated solution is a solution which cannot dissolve additional quantity of a solute.
In simple words: A stationary phase is the fixed material in chromatography that separates components, while a saturated solution holds the maximum amount of dissolved solute at a given temperature.

🎯 Exam Tip: Understand these fundamental definitions, as they are key to grasping separation techniques and solution properties in chemistry.

 

Question K.What is the difference between simple distillation and fractional distillation?
Answer:

No.	Simple distillation	Fractional distillation
i.	If in a mixture the difference in boiling points of two liquids is appreciable/large, they are separated from each other using the simple distillation.	If in a mixture the difference in boiling points of two liquids is not appreciable/large, they are separated from each other using the fractional distillation.
ii.	Simple distillation assembly is used.	fractionating column is fitted in distillation assembly.
e.g.	Mixture of acetone (b.p. 329 K) and water (b.p. 373 K) can be separated by this method.	Mixture of acetone (b.p. 329 K) and methanol (b.p. 337.7 K) can be separated by this method.

In simple words: Simple distillation separates liquids with large boiling point differences, while fractional distillation is used for liquids with close boiling points, employing a fractionating column for better separation.

🎯 Exam Tip: The main differentiating factor is the boiling point difference between components; large differences use simple distillation, small differences require fractional distillation.

 

Question L.Define a. Solvent extraction
b. Distillation.
Answer:
a. Solvent extraction: Solvent extraction is a method used to separate an organic compound present in an aqueous solution, by shaking it with a suitable organic solvent in which the compound is more soluble than water.
b. Distillation: The process in which liquid is converted into its vapour phase at its boiling point and the vapour is then condensed back to liquid on cooling is known as distillation.
In simple words: Solvent extraction uses a second, immiscible solvent to pull a compound from one liquid to another based on solubility, while distillation separates liquids by boiling them into vapor and then condensing them back.

🎯 Exam Tip: Both solvent extraction and distillation are separation techniques, but they rely on different physical principles: differential solubility and boiling point differences, respectively.

 

Question M.List the properties of solvents which make them suitable for crystallization.
Answer: The solvent to be used for crystallization should have following properties:

• The compound to be crystallized should be least or sparingly soluble in the solvent at room temperature but highly soluble at high temperature.
• Solvent should not react chemically with the compound to be purified.
• Solvent should be volatile so that it can be removed easily.

In simple words: A good crystallization solvent should poorly dissolve the compound when cold but well when hot, not react with the compound, and be easily removable afterward.

🎯 Exam Tip: Choosing the right solvent is crucial for successful crystallization; solubility, reactivity, and volatility are key considerations.

 

Question N.Name the different types of Chromatography and explain the principles underlying them.
Answer: Depending on the nature of the stationary phase i.e., whether it is a solid or a liquid, chromatography is classified into adsorption chromatography and partition chromatography.
i. Adsorption chromatography: This technique is based on the principle of differential adsorption. Different solutes are adsorbed on an adsorbent to different extent.
Adsorption chromatography is further classified into two types:
1. Column chromatography
2. Thin-layer chromatography
ii. Partition chromatography: This technique is based on continuous differential partitioning of components of a mixture between stationary and mobile phases. For example, paper chromatography
In simple words: Chromatography types are adsorption, where separation depends on how strongly compounds stick to a solid stationary phase, and partition, where compounds distribute differently between a stationary liquid and a mobile liquid phase.

🎯 Exam Tip: Remember the two main principles: adsorption involves compounds sticking to a solid, while partition involves compounds distributing between two liquid phases.

 

Question O.Why do we see bands separating in column chromatography?
Answer:

• In column chromatography, the solutes get adsorbed on the stationary phase and depending on the degree to which they are adsorbed, they get separated from each other.
• The component which is readily adsorbed are retained on the column and others move down the column to various distances forming distinct bands.

Hence, we see bands separating in column chromatography.
In simple words: Components separate into distinct bands in column chromatography because they adsorb to the stationary phase at different strengths, causing some to move slower and others faster down the column.

🎯 Exam Tip: The formation of bands in column chromatography is a direct result of differential adsorption, where stronger adsorption leads to slower movement and greater retention.

 

Question P.How do you visualize colourless compounds after separation in TLC and Paper Chromatography?
Answer:
i. Thin-layer chromatography (TLC): If components are colourless but have the property of fluorescence then they can be visualized under UV light, or the plate can be kept in a chamber containing a few iodine crystals. The iodine vapours are adsorbed by the components and the spots appear brown. Also, spraying agent like ninhydrin can also be used (for amino acids).
ii. Paper Chromatography: The spots of the separated colourless components may be observed either under ultra-violet light or by the use of an appropriate spraying agent.
In simple words: Colorless compounds in TLC and paper chromatography are visualized by using UV light (if fluorescent), an iodine chamber (for brown spots), or a chemical spraying reagent that reacts to produce colored spots.

🎯 Exam Tip: Remember these three common visualization techniques-UV light, iodine, and spraying reagents-for detecting colorless compounds in chromatography.

 

Question Q.Compare TLC and Paper Chromatography techniques.
Answer:

Chromatography technique	TLC	Paper chromatography
Principle	It is based on the principle of differential adsorption. Different solutes are adsorbed on an adsorbent to different extent.	It is based on continuous differential partitioning of components of a mixture between stationary and mobile phases.
Stationary phase	Solid (adsorbent like silica gel or alumina over a glass plate)	Liquid (water trapped in the fibres of a Paper)
Mobile phase	Liquid (single solvent/mixture of solvents)	Liquid (single solvent/mixture of solvents)
Visualization of components of a mixture	Similar to TLC the coloured components are visible as coloured spots and the colourless components are observed under UV light or using a spraying agent.	The spots of the separated colourless components may be observed either under ultra-violet light or by the use of an appropriate spraying agent.

In simple words: TLC uses a solid adsorbent for differential adsorption, while paper chromatography uses trapped water for differential partitioning; both separate components based on their interaction with stationary and mobile phases.

🎯 Exam Tip: Focus on the nature of the stationary phase and the underlying principle (adsorption vs. partition) to distinguish between TLC and paper chromatography.

 

3. Label the Diagram And Explain The Process In Your Words.

 

ℹ️ चित्र व्याख्या (Diagram Explanation): यह एक निर्वात निस्पंदन (filtration under suction) सेटअप का चित्र है। इसमें एक बुचनर फ़नल को एक बुचनर फ्लास्क पर रबर कॉर्क की सहायता से फिट किया गया है। फ़नल में एक छिद्रित प्लेट और उसके ऊपर एक गीला फ़िल्टर पेपर होता है, जबकि फ्लास्क के साइडआर्म को वैक्यूम पंप से जोड़कर आंशिक निर्वात बनाया जाता है, जिससे निस्पंदन तेजी से होता है और अशुद्धियाँ फिल्टर पेपर पर अवशेष के रूप में और शुद्ध तरल फ्लास्क में निस्पंद के रूप में एकत्रित होता है।

Answer:When filtration is carried out using a vacuum pump it is called filtration under suction. It is a faster and more efficient technique than simple filtration. The diagram is as follows:
ii. Procedure:

• The assembly for filtration under suction consists of a thick wall conical flas with a sidearm (Buchner flask).
• The flask is connected to a safety bottle by rubber tube through the side arm.
• Buchner funnel (a special porcelain funnel with a porous circular bottom) is fitted on the conical flask with the help of a rubber cork.
• A circular filter paper of correct size is placed on the circular porous bottom of the Buchner funnel and the funnel is placed on the flask.
• Filter paper is moistened with a few drops of water or solvent.
• Suction is created by starting the pump and filtration is carried out.

iii. Crystals are collected on the filter paper and filtrate in the flask.
In simple words: Filtration under suction uses a vacuum pump to create negative pressure, drawing liquid through a filter paper in a Buchner funnel much faster and more efficiently than standard gravity filtration.

🎯 Exam Tip: Understand that filtration under suction significantly speeds up the separation of solids from liquids, making it a highly efficient method in laboratory settings.