Solutions-Class-10-CBSE-NCERT-Science-Chapter-4-Carbon and Its Compounds

Since, atomic number of C is 6, its electronic configuration would be K-2, L-4.

Similarly, atomic number of oxygen is 8. Hence, its electronic configuration would be K-2, L-6.

To achieve stable electronic configuration of nearest noble gas, carbon needs 4 electrons, while oxygen needs 2 electrons. So, in CO₂ molecule, each of oxygen atom share two electrons from carbon. Thus, oxygen and carbon both attain their stable octet. The electron dot structure of CO2 is as follows

Since, atomic number of S is 16, its electronic electronic configuration would be K-2, L-8, M-6.

To achieve stable electronic configuration of the nearest noble gas, each sulphur needs 2 electrons. The electron dot structure of S₈ is as follows.

Pentane (C₅H₁₂) has a skeleton of five carbon atoms which can be arranged in straight chain or in the form of chain containing one or two branches. Molecular formula C₅H₁₂ accounts for the following three isomers.

Two main properties which led the carbon to form a huge number of carbon compounds are

• catenation
• tetravalency of carbon

General formula of cycloalkane =C_nH_2n

In cyclopentane, n = 5, ∴ Formula of cyclopentane, C₅H₁₀

Electron dot structure of cyclopentane :

Structural isomers for bromopentane: There are three structural isomers for bromopentane depending on the position of Br at carbon 1, 2, 3. Position 4 and 5 are same as 1, 2.

(i) Bromoethane (because of two carbons attach through single bonded, word root is 'eth' and for bromine group, prefix used is 'bromo').

(ii) methanal (because of single carbon, word root is 'meth' and for functional group  suffix 'al' is used).

(iii) 1-hexyne (because of 6 carbons, word root is 'hex' and for triple bond, suffix is 'yne'). Also, triple bond is located at first position so position of triple bond is indicated in IUPAC name.

Conversion of ethanol to ethanoic acid is oxidation because

• Oxygen is added up to ethanol by oxidising agent like alkaline potassium permanganate or acidified potassium dichromate.
• The product of the reaction is not CO₂ and water. Further no heat or light is produced.

Ethyne with oxygen gives enough heat that can be used for welding whereas if it is burnt in air which contains nitrogen and other inactive gaseous contents, sufficient oxygen is not available for burning ethyne to give the required heat.

2CH≡CH + 5O₂ -> 4CO² + 2H₂O + Heat + Light

Alcohol and carboxylic acid can be distinguished experimentally by two reactions:

(i) Reaction with base Alcohols do not react with base like NaOH, KOH while carboxylic acids react with base to form salt and water.

e.g. CH₃COOH + NaOH → CH₃COONa + H₂O

CH3CH2OH + NaOH → No reaction

(ii) Reaction with sodium bicarbonate Carboxylic acids react with sodium bicarbonate rapidly to give brisk effervescence of CO₂ gas while alcohols do not react.

e.g. CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂ ↑

CH₃CH₂OH + NaHCO₃ → No reaction

Oxidising agents are substances which give oxygen to another substance.

Example : Alkaline potassium permanganate or acidified potassium dichromate can give oxygen to alcohols to convert them into carboxylic acids.

No, because detergent does not form scum with hard water.

• When soap solution is made and dirty clothes are soaked in it, then micelles formation occurs. This results in the formation of an emulsion (a stable suspension of small droplets of one liquid in another with which is immiscible).
• To wash away the loosen dirt particles in the form of micelles from the surface of the cloth, it is either scrubbed mechanically or beaten or agitated in washing machine.

(b) 7 covalent bonds.

(c) ketone.

(b) the fuel is not burning completely.

If the bottom of the vessel is getting blackened, it means that the air holes are blocked and fuel is getting wasted as it is not burning completely.

Covalent bond/s is formed by sharing of electrons so that the combining atom/s complete their outermost shell. In CH₃Cl, this happens as follows:

• Three hydrogen atoms complete (K = 1 + 1 = 2) their shells by sharing three electrons (one electron each) of carbon atom.
• Chlorine completes its outer shell (L = 7 + 1 = 8) by sharing its one out of seven electrons with one electron of carbon atom.
• Thus carbon atom shares in all its four electrons with three of three hydrogen atoms and one of chlorine atom and completes its outer shell (L = 4+3+1 = 8).

A series of similarly constituted compounds in which the members present have the same functional group, similar chemical properties and any two successive members in a particular series differ in their molecular formula by (-CH₂) unit, is called a homologous series.

e.g. Alkane series C_nH_2n+2

CH₄ - Methane

C₂H₆ - Ethane

C₃H₈ - Propane

C₄H₁₀ - Butane

C₅H₁₂ – Pentane

(i) Distinctions based on physical properties are as

(a) Smell Ethanoic acid has a pungent smell while ethanol has a pleasant smell.

(b) Melting point Ethanol has lower melting point (156 K) than ethanoic acid (290 K).

(c) Physical state Ethanoic acid is solid (glacial acetic acid) in winters but ethanol is always a liquid.

(ii) Distinctions based on chemical properties are as :

(a) Reaction with sodium hydrogen carbonate On adding a small amount of sodium hydrogen carbonate to ethanoic acid, carbon dioxide gas is evolved with brisk effervescence. However, no such reaction takes place in case of ethanol.

CH₃COOH + NaHCO₃ → CH₃COONa + CO₂ ↑ + H₂O

C₂H₅OH+ NaHCO₃ → No reaction

(b) Reaction with base Ethanoic acid reacts with both sodium hydroxide (NaOH) and potassium hydroxide (KOH) to form corresponding salt and water. Ethanol fails to react with either of these.

CH₃COOH + NaOH → CH₃COONa + H₂O

CH₃COOH + KOH → CH₃COOK + H₂O

• When soap is at the water's surface, the hydrophobic 'tail' is insoluble in water, and the soap aligns along the surface, with the ionic end in water and the hydrocarbon 'tail' extending out of water.
• Inside water, these molecules have a distinct orientation that keeps the hydrocarbon part out. This is accomplished by arranging molecules in clusters with hydrophobic tails in the inside and ionic ends on the exterior. This structure is known as a micelle.
• Micelle does not develop in all types of solvent. It will form in solvents in which soap is soluble.
• g. Soap is insoluble in ethanol, hence, no micelle formation takes place.

• Carbon burns in oxygen (air) to form carbon dioxide and water.
• During this reaction, a large amount of heat and light is released.
• Further once ignited, carbon and its compounds keep on burning without the requirement of additional energy. Hence, they are used as fuels.

C + O₂ → CO₂ +Heat +Light

When soap is added to a sample of hard water, calcium and/or magnesium ions present in hard water react with soap forming insoluble calcium/magnesium soap which is a sticky and greasy mass (called scum) and thus no lather is formed.

Soap is alkaline in nature. Hence, it turns red litmus paper blue and have no effect on the blue litmus paper.

Hydrogenation : The addition of hydrogen to unsaturated hydrocarbons in the presence of catalyst is known as hydrogenation.

Industrial application : When hydrogen gas is made to pass through vegetable oil in the presence of nickel catalyst, it changes to solid fat (ghee).

Vegetable oils + H₂ \(\frac{Nickel}{Heat}→\) Fat (ghee)

Unsaturated hydrocarbons like alkenes and alkynes (containing double and triple bond respectively) undergo addition reactions and their general formula are C_nH_2n and C_nH_2n-2 respectively.

Thus, C₃H₆, and C₂H₂ will undergo addition reactions.

• Butter contains saturated compounds while cooking oil contains unsaturated compounds.
• Since, unsaturated compounds are oxidised by alk. KMnO₄ with disappearance of its pink colour.
• Therefore, when cooking oil is treated with a few drops of alk. KMnO₄, pink colour of KMnO₄ With butter, however, the pink colour of KMnO₄ does not disappear.

• The cleansing action of soaps and detergents is due to their capacity to reduce the surface tension of water and retain its suspension in water. When soap is dissolved in water is hydrophobic ends attach themselves to dirt and remove it from the cloth.
• Soap solution appear cloudy because the ion aggregate to form spherical clusters which forms micelles that are large enough to scatter light.