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Q8.24:
Explain the principle of paper chromatography.
Solution :
Theoretical Foundation: Principles of Partition Chromatography
Paper chromatography is a specific application of partition chromatography. The fundamental principle governing this technique is the differential distribution (partitioning) of components of a mixture between two immiscible phases: a stationary phase and a mobile phase [Per the Nernst Distribution Law].
Step 1: Definition of Phases
- Stationary Phase: A strip of chromatographic paper made of cellulose. Cellulose fibers contain adsorbed water molecules, which serve as the immobilized liquid phase.
- Mobile Phase: A suitable organic solvent or mixture of solvents that travels up the paper strip via capillary action.
Step 2: Mechanism of Separation
The mixture to be separated is applied as a spot near the bottom of the cellulose paper. When the solvent (mobile phase) rises through the paper by capillary action, the individual components of the mixture partition themselves between the water held in the paper (stationary phase) and the moving solvent (mobile phase) [Based on the principle of differential solubility].
Step 3: Determination via Retardation Factor ($R_f$)
The extent to which each component moves is constant for a given set of experimental conditions. This is quantified by the Retardation Factor ($R_f$), defined by the ratio of the distance traveled by the substance to the distance traveled by the solvent front [Per IUPAC chromatographic conventions].
The mathematical expression is:
$R_f = \frac{\text{Distance travelled by the substance from the baseline}}{\text{Distance travelled by the solvent front from the baseline}}$
Analytical Summary
| Feature | Description |
|---|---|
| Phase Interaction | Components with higher solubility in the mobile phase travel faster; those with higher affinity for the stationary water phase travel slower. |
| Separation Basis | Differential rates of migration based on partitioning coefficients ($K_d$). |
Final Solution: Paper chromatography relies on the partition of mixture components between a stationary aqueous phase held in cellulose fibers and a mobile organic solvent phase, causing separation based on varying solubilities and resulting in characteristic $R_f$ values for each component.
More Questions from Class 11 Chemistry Organic Chemistry – Some Basic Principles and Techniques EXERCISES
- Q8.1: What are hybridisation states of each carbon atom in the following compounds ? $CH_2=C=O$, $CH_3CH=CH_2$, $(CH_3)_2CO$, $CH_2=CHCN$, $C_6H_6$
- Q8.10: Explain why alkyl groups act as electron donors when attached to a $\pi$ system.
- Q8.11 (a): Draw the resonance structures for the following compounds. Show the electron shift using curved-arrow notation. (a) $C_6H_5OH$
- Q8.11 (b): Draw the resonance structures for the following compounds. Show the electron shift using curved-arrow notation. (b) $C_6H_5NO_2$
- Q8.11 (c): Draw the resonance structures for the following compounds. Show the electron shift using curved-arrow notation. (c) $CH_3CH=CHCHO$
- Q8.11 (d): Draw the resonance structures for the following compounds. Show the electron shift using curved-arrow notation. (d) $C_6H_5–CHO$
- Q8.11 (e): Draw the resonance structures for the following compounds. Show the electron shift using curved-arrow notation. (e) $C_6H_5–C^+H_2$
- Q8.11 (f): Draw the resonance structures for the following compounds. Show the electron shift using curved-arrow notation. (f) $CH_3CH=CHC^+H_2$
- Q8.12: What are electrophiles and nucleophiles ? Explain with examples.
- Q8.13 (a): Identify the reagents shown in bold in the following equations as nucleophiles or electrophiles: (a) $CH_3COOH + HO^– \rightarrow CH_3COO^–+H_2O$
- Q8.13 (b): Identify the reagents shown in bold in the following equations as nucleophiles or electrophiles: (b) $CH_3COCH_3+ C^–N \rightarrow (CH_3)_2C(CN)(OH)$
- Q8.13 (c): Identify the reagents shown in bold in the following equations as nucleophiles or electrophiles: (c) $C_6H_6 + CH_3C^+O \rightarrow C_6H_5COCH_3$
- Q8.14 (a): Classify the following reactions in one of the reaction type studied in this unit. (a) $CH_3CH_2Br + HS^– \rightarrow CH_3CH_2SH + Br^–$
- Q8.14 (b): Classify the following reactions in one of the reaction type studied in this unit. (b) $(CH_3)_2C = CH_2 + HCl \rightarrow (CH_3)_2ClC – CH_3$
- Q8.14 (c): Classify the following reactions in one of the reaction type studied in this unit. (c) $CH_3CH_2Br + HO^– \rightarrow CH_2 = CH_2 + H_2O + Br^–$
- Q8.14 (d): Classify the following reactions in one of the reaction type studied in this unit. (d) $(CH_3)_3C– CH_2OH + HBr \rightarrow (CH_3)_2CBrCH_2CH_2CH_3 + H_2O$
- Q8.15: What is the relationship between the members of following pairs of structures ? Are they structural or geometrical isomers or resonance contributors ? (c)
- Q8.15: What is the relationship between the members of following pairs of structures ? Are they structural or geometrical isomers or resonance contributors ? (b)
- Q8.15: What is the relationship between the members of following pairs of structures ? Are they structural or geometrical isomers or resonance contributors ? (a)
- Q8.16: For the following bond cleavages, use curved-arrows to show the electron flow and classify each as homolysis or heterolysis. Identify reactive intermediate produced as free radical, carbocation and carbanion. (c)
- Q8.16: For the following bond cleavages, use curved-arrows to show the electron flow and classify each as homolysis or heterolysis. Identify reactive intermediate produced as free radical, carbocation and carbanion. (d)
- Q8.16: For the following bond cleavages, use curved-arrows to show the electron flow and classify each as homolysis or heterolysis. Identify reactive intermediate produced as free radical, carbocation and carbanion. (b)
- Q8.16: For the following bond cleavages, use curved-arrows to show the electron flow and classify each as homolysis or heterolysis. Identify reactive intermediate produced as free radical, carbocation and carbanion. (a)
- Q8.17 (a): Explain the terms Inductive and Electromeric effects. Which electron displacement effect explains the following correct orders of acidity of the carboxylic acids? (a) $Cl_3CCOOH > Cl_2CHCOOH > ClCH_2COOH$
- Q8.17 (b): Explain the terms Inductive and Electromeric effects. Which electron displacement effect explains the following correct orders of acidity of the carboxylic acids? (b) $CH_3CH_2COOH > (CH_3)_2CHCOOH > (CH_3)_3C.COOH$
- Q8.18 (a): Give a brief description of the principles of the following techniques taking an example in each case. (a) Crystallisation
- Q8.18 (b): Give a brief description of the principles of the following techniques taking an example in each case. (b) Distillation
- Q8.18 (c): Give a brief description of the principles of the following techniques taking an example in each case. (c) Chromatography
- Q8.19: Describe the method, which can be used to separate two compounds with different solubilities in a solvent S.
- Q8.2: Indicate the $\sigma$ and $\pi$ bonds in the following molecules : $C_6H_6$, $C_6H_{12}$, $CH_2Cl_2$, $CH_2=C=CH_2$, $CH_3NO_2$, $HCONHCH_3$
- Q8.20: What is the difference between distillation, distillation under reduced pressure and steam distillation ?
- Q8.21: Discuss the chemistry of Lassaigne’s test.
- Q8.22: Differentiate between the principle of estimation of nitrogen in an organic compound by (i) Dumas method and (ii) Kjeldahl’s method.
- Q8.23: Discuss the principle of estimation of halogens, sulphur and phosphorus present in an organic compound.
- Q8.25: Why is nitric acid added to sodium extract before adding silver nitrate for testing halogens?
- Q8.26: Explain the reason for the fusion of an organic compound with metallic sodium for testing nitrogen, sulphur and halogens.
- Q8.27: Name a suitable technique of separation of the components from a mixture of calcium sulphate and camphor.
- Q8.28: Explain, why an organic liquid vaporises at a temperature below its boiling point in its steam distillation ?
- Q8.29: Will $CCl_4$ give white precipitate of AgCl on heating it with silver nitrate? Give reason for your answer.
- Q8.3: Write bond line formulas for : Isopropyl alcohol, 2,3-Dimethylbutanal, Heptan-4-one.
- Q8.30: Why is a solution of potassium hydroxide used to absorb carbon dioxide evolved during the estimation of carbon present in an organic compound?
- Q8.31: Why is it necessary to use acetic acid and not sulphuric acid for acidification of sodium extract for testing sulphur by lead acetate test?
- Q8.32: An organic compound contains 69% carbon and 4.8% hydrogen, the remainder being oxygen. Calculate the masses of carbon dioxide and water produced when 0.20 g of this substance is subjected to complete combustion.
- Q8.33: A sample of 0.50 g of an organic compound was treated according to Kjeldahl’s method. The ammonia evolved was absorbed in 50 ml of 0.5 M $H_2SO_4$. The residual acid required 60 mL of 0.5 M solution of NaOH for neutralisation. Find the percentage composition of nitrogen in the compound.
- Q8.34: 0.3780 g of an organic chloro compound gave 0.5740 g of silver chloride in Carius estimation. Calculate the percentage of chlorine present in the compound.
- Q8.35: In the estimation of sulphur by Carius method, 0.468 g of an organic sulphur compound afforded 0.668 g of barium sulphate. Find out the percentage of sulphur in the given compound.
- Q8.36: In the organic compound $CH_2 = CH – CH_2 – CH_2 – C \equiv CH$, the pair of hydridised orbitals involved in the formation of: $C_2 – C_3$ bond is:
- Q8.37: In the Lassaigne’s test for nitrogen in an organic compound, the Prussian blue colour is obtained due to the formation of:
- Q8.38: Which of the following carbocation is most stable ?
- Q8.39: The best and latest technique for isolation, purification and separation of organic compounds is:
- Q8.4: Give the IUPAC names of the following compounds : (a)
- Q8.4: Give the IUPAC names of the following compounds : (b)
- Q8.4: Give the IUPAC names of the following compounds : (c)
- Q8.4: Give the IUPAC names of the following compounds : (d)
- Q8.4: Give the IUPAC names of the following compounds : (e)
- Q8.4 (f): Give the IUPAC names of the following compounds : (f) $Cl_2CHCH_2OH$
- Q8.40: The reaction: $CH_3CH_2I + KOH(aq) \rightarrow CH_3CH_2OH + KI$ is classified as :
- Q8.5 (a): Which of the following represents the correct IUPAC name for the compounds concerned ? (a) 2,2-Dimethylpentane or 2-Dimethylpentane
- Q8.5 (b): Which of the following represents the correct IUPAC name for the compounds concerned ? (b) 2,4,7-Trimethyloctane or 2,5,7-Trimethyloctane
- Q8.5 (c): Which of the following represents the correct IUPAC name for the compounds concerned ? (c) 2-Chloro-4-methylpentane or 4-Chloro-2-methylpentane
- Q8.5 (d): Which of the following represents the correct IUPAC name for the compounds concerned ? (d) But-3-yn-1-ol or But-4-ol-1-yne.
- Q8.6 (a): Draw formulas for the first five members of each homologous series beginning with the following compounds. (a) H–COOH
- Q8.6 (b): Draw formulas for the first five members of each homologous series beginning with the following compounds. (b) $CH_3COCH_3$
- Q8.6 (c): Draw formulas for the first five members of each homologous series beginning with the following compounds. (c) H–CH=CH2
- Q8.7 (a): Give condensed and bond line structural formulas and identify the functional group(s) present, if any, for : (a) 2,2,4-Trimethylpentane
- Q8.7 (b): Give condensed and bond line structural formulas and identify the functional group(s) present, if any, for : (b) 2-Hydroxy-1,2,3-propanetricarboxylic acid
- Q8.7 (c): Give condensed and bond line structural formulas and identify the functional group(s) present, if any, for : (c) Hexanedial
- Q8.8: Identify the functional groups in the following compounds (c)
- Q8.8: Identify the functional groups in the following compounds (b)
- Q8.8: Identify the functional groups in the following compounds (a)
- Q8.9: Which of the two: $O_2NCH_2CH_2O^–$ or $CH_3CH_2O^–$ is expected to be more stable and why?
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