Class 10 Science Chapter 4 Carbon and its Compounds NCERT Solutions 2026 PDF Download
📝 Introduction
Carbon and its Compounds is arguably the most significant chapter in Class 10 Chemistry as it introduces Organic Chemistry. Carbon is a unique element capable of forming millions of compounds due to its properties of catenation (self-linking) and tetravalency. In this chapter, students will learn about covalent bonding and the versatile nature of carbon. You will explore hydrocarbons (Alkanes, Alkenes, Alkynes), functional groups, homologous series, and isomers. The chapter also covers the chemical properties of carbon compounds (Combustion, Oxidation, Addition, Substitution) and important industrial compounds like Ethanol and Ethanoic Acid, concluding with the chemistry of Soaps and Detergents.
[Image of electron dot structure of methane]🔑 Key Concepts & Formulas
- Covalent Bond: Bond formed by sharing electron pairs between atoms. Carbon forms 4 covalent bonds.
- Versatile Nature:
- Catenation: Carbon's ability to form long chains and rings with other Carbon atoms.
- Tetravalency: Carbon has a valency of 4, allowing it to bond with 4 other atoms.
- Hydrocarbons:
- Alkanes: Saturated ($C_nH_{2n+2}$), Single bonds.
- Alkenes: Unsaturated ($C_nH_{2n}$), Double bonds.
- Alkynes: Unsaturated ($C_nH_{2n-2}$), Triple bonds.
- Homologous Series: A family of compounds with the same functional group and similar chemical properties, differing by a $-CH_2$ unit.
- Saponification: Hydrolysis of an ester (fat/oil) with a base (NaOH) to form Soap and Glycerol.
- Micelles: Clusters of soap molecules that trap dirt/grease in water.
📚 Part 1: NCERT Solutions (In-Text & Exercises)
Q1: What would be the electron dot structure of carbon dioxide which has the formula CO₂?
Ans: Carbon (Z=6) has 4 valence electrons. Oxygen (Z=8) has 6. Carbon shares 2 electrons with one Oxygen and 2 electrons with another Oxygen to complete octets for all three atoms.
Structure: $O :: C :: O$ or $O = C = O$
Q2: What are the two properties of carbon which lead to the huge number of carbon compounds we see around us?
Ans:
1. Catenation: The unique ability of carbon to form bonds with other carbon atoms, giving rise to large molecules (long chains, branched chains, and rings).
2. Tetravalency: With a valency of 4, carbon can bond with four other atoms of carbon or atoms of other monovalent elements like Hydrogen, Chlorine, etc.
Q3: What will be the formula and electron dot structure of cyclopentane?
Ans: Cyclopentane is a cyclic alkane with 5 carbon atoms bonded in a ring.
Formula: $C_5H_{10}$
Structure: 5 Carbon atoms in a pentagon shape, connected by single bonds. Each Carbon is bonded to 2 Hydrogen atoms.
Q4: How can ethanol and ethanoic acid be differentiated on the basis of their physical and chemical properties?
Ans:
- Physical: Ethanol has a pleasant smell, while Ethanoic acid smells like vinegar (pungent). Ethanol's melting point is lower than Ethanoic acid.
- Chemical: Ethanoic acid reacts with Sodium Carbonate ($Na_2CO_3$) to release $CO_2$ gas (effervescence), whereas Ethanol does not react with carbonates.
Q5: Explain the mechanism of the cleaning action of soaps.
Ans: Soap molecules have two ends: a hydrophilic (water-loving) ionic head and a hydrophobic (water-fearing) carbon tail.
1. When added to water, the hydrophobic tails attach to dirt/grease, and hydrophilic heads point outwards into the water.
2. This forms a structure called a Micelle.
3. Agitation pulls the dirt (trapped in the center of the micelle) into the water, washing it away.
Q6: Why does micelle formation take place when soap is added to water? Will a micelle be formed in other solvents such as ethanol also?
Ans: Micelles form because the hydrocarbon chains of soap are hydrophobic (insoluble in water) and cluster together away from water, while the ionic heads are hydrophilic.
No, micelles will not form in ethanol because the hydrocarbon tail of soap is soluble in ethanol (organic solvent), so there is no need to form clusters to hide from the solvent.
Q7: What is an oxidising agent?
Ans: Oxidising agents are substances capable of supplying oxygen to other substances or removing hydrogen from them. Example: Alkaline $KMnO_4$ (Potassium Permanganate) or Acidified $K_2Cr_2O_7$ (Potassium Dichromate) are used to oxidise alcohols to carboxylic acids.
Q8: Explain the formation of scum when hard water is treated with soap.
Ans: Hard water contains Calcium ($Ca^{2+}$) and Magnesium ($Mg^{2+}$) salts. When soap (Sodium salt of fatty acid) reacts with these ions, it forms Calcium or Magnesium salts of fatty acids which are insoluble in water. This insoluble precipitate is called scum.
⚡ Part 2: 15 Extra Practice Questions (PYQ Style)
Short Answer Type Questions
Q1: Define Isomerism. Draw isomers of Butane ($C_4H_{10}$).
Ans: Isomerism is the phenomenon where compounds have the same molecular formula but different structural formulae.
Isomers of Butane:
1. n-Butane: Straight chain ($CH_3-CH_2-CH_2-CH_3$)
2. Iso-Butane: Branched chain ($CH_3-CH(CH_3)-CH_3$)
Q2: Why do covalent compounds have low melting and boiling points?
Ans: Covalent compounds have strong bonds within the molecule but weak intermolecular forces (Van der Waals forces) between different molecules. Little energy is required to break these weak forces, resulting in low melting/boiling points.
Q3: What is a Homologous Series? State two characteristics.
Ans: It is a series of compounds with the same functional group and similar chemical properties, where successive members differ by a $-CH_2$ unit.
Characteristics:
1. Similar chemical properties.
2. Gradation in physical properties (e.g., boiling point increases with mass).
Q4: Write the equation for the reaction of Ethanol with Sodium metal.
Ans: Ethanol reacts with Sodium to produce Sodium Ethoxide and Hydrogen gas.
$2C_2H_5OH + 2Na \rightarrow 2C_2H_5ONa + H_2 \uparrow$
Q5: Draw the Electron Dot Structure of Sulphur molecule ($S_8$).
Ans: Sulphur atoms are arranged in a ring (crown shape). Each Sulphur atom shares 1 electron with the Sulphur on its left and 1 with the Sulphur on its right to complete its octet (6 valence + 2 shared).
Science Chapters
- Ch 1: Chemical Reactions
- Ch 2: Acids, Bases and Salts
- Ch 3: Metals and Non-Metals
- Esterification: Reaction of Acid + Alcohol to form Ester (Sweet smelling).
$CH_3COOH + C_2H_5OH \xrightarrow{Acid} CH_3COOC_2H_5 + H_2O$ - Saponification: Hydrolysis of Ester with a Base (NaOH) to form Soap and Alcohol.
$CH_3COOC_2H_5 + NaOH \rightarrow CH_3COONa + C_2H_5OH$
Long Answer Type Questions
Q6: Explain Esterification and Saponification with chemical equations.
Ans:
Q7: How would you distinguish experimentally between an Alcohol and a Carboxylic Acid?
Ans:
1. Litmus Test: Acid turns blue litmus red. Alcohol has no effect.
2. Sodium Bicarbonate Test: Add a pinch of $NaHCO_3$. Acid reacts to release bubbles of $CO_2$ (brisk effervescence). Alcohol does not react.
Q8: Explain the addition reaction with an example. Why is it important in industry?
Ans: Unsaturated hydrocarbons add hydrogen in the presence of catalysts (Nickel/Palladium) to form saturated hydrocarbons.
$R_2C=CR_2 + H_2 \xrightarrow{Ni} R_2CH-CHR_2$
Use: It is used in the hydrogenation of vegetable oils (unsaturated fat) to form Vanaspati Ghee (saturated fat).
Competency Based Questions
Q9: Why are detergents preferred over soaps for laundry in hard water regions?
Ans: Detergents (ammonium or sulphonate salts) do not form insoluble precipitates (scum) with the Calcium and Magnesium ions present in hard water. They remain effective and lather well even in hard water, unlike soaps which get wasted forming scum.
Q10: Compound X ($C_2H_6O$) on oxidation gives Y ($C_2H_4O_2$). X reacts with Y in presence of acid to give sweet smelling Z. Identify X, Y, Z.
Ans:
X: Ethanol ($C_2H_5OH$)
Y: Ethanoic Acid ($CH_3COOH$) - formed by oxidation of X.
Z: Ethyl Ethanoate ($CH_3COOC_2H_5$) - Ester formed by X + Y.
Q11: Draw the structure of Hexanal.
Ans: Hexanal is an aldehyde with 6 carbons.
Structure: $CH_3-CH_2-CH_2-CH_2-CH_2-CHO$.
Q12: Why does Carbon not form $C^{4+}$ or $C^{4-}$ ions?
Ans:
1. Forming $C^{4+}$ requires removing 4 electrons, which needs huge energy.
2. Forming $C^{4-}$ involves holding 10 electrons with only 6 protons, which is unstable due to repulsion.
Hence, carbon shares electrons.
Q13: Name the allotrope of carbon used as a lubricant and conduct electricity.
Ans: Graphite. It is slippery because its layers can slide over each other (lubricant) and has free electrons (conductor).
Q14: What is the role of concentrated Sulphuric acid in esterification?
Ans: Concentrated $H_2SO_4$ acts as a dehydrating agent. It removes water formed during the reaction, shifting the equilibrium forward to produce more ester.
Q15: What happens when ethanol is heated with excess conc. $H_2SO_4$ at 443 K?
Ans: Dehydration occurs. Ethanol loses a water molecule to form Ethene.
$C_2H_5OH \xrightarrow{Hot Conc. H_2SO_4} CH_2=CH_2 + H_2O$