Q23
5 marksLong AnswerSection A

(a) State two properties of carbon which lead to a very large number of carbon compounds. (b) Why does micelle formation take place when soap is added to water ? Why are micelles not formed when soap is added to ethanol ? OR Explain isomerism. State any four characteristics of isomers. Draw the structures of possible isomers of butane, C4H10C_4H_{10}.

Chemical Reactions and Equations
Carbon Compounds and Chemical Properties
Official Answer

(a) The two properties of carbon that lead to a very large number of carbon compounds are:

  1. Catenation: Carbon has the unique ability to form bonds with other atoms of carbon, giving rise to large molecules. This property is called catenation.
  2. Tetravalency: Since carbon has a valency of four, it is capable of bonding with four other atoms of carbon or atoms of some other mono-valent element.

(b) Micelle Formation:

  • In Water: Soap molecules are sodium or potassium salts of long-chain carboxylic acids. They have a hydrophilic (water-loving) head and a hydrophobic (water-fearing) hydrocarbon tail. When added to water, the molecules arrange themselves in a cluster called a micelle, where the hydrophobic tails are tucked into the interior to stay away from water, while the ionic heads face outwards into the water.
  • In Ethanol: Micelles are not formed in ethanol because the hydrophobic hydrocarbon tail of the soap is soluble in ethanol (an organic solvent). Therefore, the molecules do not need to cluster to hide their tails from the solvent.

OR


Isomerism: The phenomenon in which compounds have the same molecular formula but different structural arrangements of atoms is called structural isomerism.


Characteristics of Isomers:

  1. They have the same molecular formula.
  2. They have different structural formulas (different connectivity).
  3. They possess different physical properties such as melting points and boiling points.
  4. They may exhibit different chemical properties.

Structures of Isomers of Butane (C4H10C_4H_{10}):

  1. n-butane: A straight chain of four carbon atoms.

CH3−CH2−CH2−CH3CH_3-CH_2-CH_2-CH_3

  1. Iso-butane (2-methylpropane): A branched chain where one carbon is attached to the middle carbon of a three-carbon chain.

CH3−CH(CH3)−CH3CH_3-CH(CH_3)-CH_3

CatenationTetravalencyHydrophilicHydrophobicMicelleStructural IsomerismButaneIsobutane

Marking Scheme

  • 1Stating Catenation and Tetravalency with brief descriptions (2 marks)
  • 2Explanation of micelle formation in water (hydrophilic/hydrophobic interaction) (1.5 marks)
  • 3Explanation of why micelles don't form in ethanol (solubility of tail) (1.5 marks)
  • 4OR: Definition of Isomerism (1 mark)
  • 5OR: Four characteristics of isomers (2 marks)
  • 6OR: Correct structures of n-butane and isobutane (2 marks)

Hint

Think about carbon's valency and its ability to link with itself. For micelles, remember 'like dissolves like'—the tail is oily and likes organic solvents like ethanol.

Quick Oral Answer

Carbon forms a large number of compounds primarily due to catenation and its tetravalent nature. Isomers are molecules that share the same chemical formula but have different shapes.

Analysis & Explanation

This question explores the versatility of carbon, which is briefly touched upon in the chapter 'Chemical Reactions and Equations' through compounds like methane (CH4CH_4) and glucose (C6H12O6C_6H_{12}O_6). (a) Catenation allows carbon to form long chains, branched chains, or rings, while tetravalency allows it to bond with a variety of elements like Oxygen, Hydrogen, and Nitrogen. (b) Micelle formation is a result of the dual nature of soap molecules. Water is a polar solvent, forcing the non-polar tails to aggregate. Ethanol, being an organic solvent, interacts favorably with the non-polar tails, so no aggregation (micelle) occurs. The OR section on isomerism highlights that molecular formula alone does not define a substance; the spatial arrangement (structure) is critical, as seen in the two forms of butane.

Common Mistakes

  1. 1Confusing the number of isomers for butane (there are only 2) with pentane (which has 3).
  2. 2Stating that micelles form in ethanol because it is a liquid.
  3. 3Forgetting to show all hydrogen atoms when drawing structures.

Interesting Facts

The chemical formula for marble, CaCO3CaCO_3, is the same as that for limestone and chalk, as mentioned in the NCERT text regarding whitewashing.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2011?

This question carries 5 marks in the CBSE Class 10 Science 2011 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Chemical Reactions and Equations" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Carbon Compounds and Chemical Properties" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2011 paper?

This is a Long Answer question from Section A in the CBSE Class 10 Science 2011 paper.