Carbon and Its CompoundsClass 10 Chemistry NCERT Solutions

The correct answer is (b) 7 covalent bonds.

Explanation: The structure of ethane ($\mathrm{C}_{2} \mathrm{H}_{6}$) is:

CC

To determine the number of covalent bonds, we count all the single bonds between the atoms:

Total number of covalent bonds = 1 (C-C bond) + 6 (C-H bonds) = 7 covalent bonds.

The correct answer is (c) ketone.

Therefore, butanone is a four-carbon compound containing a ketone functional group.

The correct answer is (b) the fuel is not burning completely.

Explanation: When a fuel burns in an insufficient supply of oxygen (air), it undergoes incomplete combustion. This process produces soot, which is essentially unburnt carbon. This black soot gets deposited on the bottom of the cooking vessel, making it black. A clean, blue flame indicates complete combustion, while a yellow, sooty flame indicates incomplete combustion.

A covalent bond is a chemical bond formed by the mutual sharing of electrons between atoms to achieve a stable electron configuration, similar to that of a noble gas.

In the formation of chloromethane ($\mathrm{CH}_{3} \mathrm{Cl}$):

This structure shows how the sharing of electrons results in the formation of stable covalent bonds, holding the atoms together in the molecule.

CC(=O)O

** (b) Hydrogen Sulphide ($\mathrm{H}_{2} \mathrm{S}$):**

S

** (c) Propanone ($\mathrm{CH}_{3} \mathrm{COCH}_{3}$):**

CC(C)=O

** (d) Fluorine molecule ($\mathrm{F}_{2}$):**

FF

A homologous series is a series of organic compounds that have the same functional group and similar chemical properties. The successive members of the series differ from each other by a $-\mathrm{CH}_{2}$ group.

The general formula for this series is $\mathrm{C}_{n} \mathrm{H}_{2n+1} \mathrm{OH}$.

In this series, each compound has the alcohol functional group (-OH) and each successive compound differs by a $-\mathrm{CH}_{2}$ unit.

Ethanol and ethanoic acid can be differentiated based on the following properties:

Micelle formation occurs when soap is dissolved in water due to the unique structure of soap molecules. A soap molecule has two distinct parts:

When soap is added to water, the hydrophilic heads are attracted to the water molecules, while the hydrophobic tails are repelled by them. To minimize this repulsion, the hydrophobic tails cluster together at the core, away from the water. The hydrophilic heads arrange themselves on the outer surface, facing the water. This spherical aggregation of soap molecules is called a micelle.

No, a micelle will not be formed if soap is added to a solvent like ethanol. This is because ethanol is an organic solvent, and the hydrophobic hydrocarbon tail of the soap molecule is soluble in it. Since the tail is not repelled by the solvent, there is no driving force for the molecules to aggregate into a micelle structure. The soap molecules will simply dissolve in ethanol.

Carbon and its compounds are widely used as fuels for several reasons:

For these reasons, carbon and its compounds are the primary sources of energy for domestic and industrial purposes.

Hard water contains dissolved salts of calcium ($\mathrm{Ca}^{2+}$) and magnesium ($\mathrm{Mg}^{2+}$) ions.

Soap consists of sodium or potassium salts of long-chain carboxylic acids (fatty acids). For example, sodium stearate ($\mathrm{C}_{17} \mathrm{H}_{35} \mathrm{COONa}$).

When soap is added to hard water, a chemical reaction occurs where the calcium and magnesium ions present in the water displace the sodium or potassium ions from the soap molecules. This results in the formation of insoluble calcium and magnesium salts of the fatty acids. This insoluble, curdy precipitate is called scum.

For example, the reaction with calcium ions is:

$2\mathrm{C}_{17} \mathrm{H}_{35} \mathrm{COONa(aq)} + \mathrm{Ca}^{2+}\mathrm{(aq)} \rightarrow (\mathrm{C}_{17} \mathrm{H}_{35} \mathrm{COO})_{2} \mathrm{Ca(s)} + 2\mathrm{Na}^{+}\mathrm{(aq)}$ (Soap) + (Calcium ions in hard water) $\rightarrow$ (Calcium stearate - Scum) + (Sodium ions)

Scum interferes with the cleaning action of soap because a significant amount of soap is wasted in reacting with the hard water ions before it can begin to form lather and clean.

Soaps are salts of a strong base (like NaOH or KOH) and a weak acid (a long-chain carboxylic acid).

When soap is dissolved in water, it undergoes hydrolysis, which produces a small amount of hydroxide ions ($\mathrm{OH}^{-}$), making the solution slightly alkaline or basic.

Because the soap solution is basic:

Hydrogenation: Hydrogenation is a chemical reaction that involves the addition of hydrogen ($\mathrm{H}_{2}$) across a double or triple bond in an unsaturated organic compound. This reaction is typically carried out in the presence of a metal catalyst, such as nickel (Ni), palladium (Pd), or platinum (Pt). The process converts unsaturated hydrocarbons (alkenes and alkynes) into saturated hydrocarbons (alkanes).

Reaction Example: $\mathrm{CH}_{2}=\mathrm{CH}_{2} + \mathrm{H}_{2} \xrightarrow{\text{Ni catalyst}} \mathrm{CH}_{3}-\mathrm{CH}_{3}$ (Ethene - Unsaturated) $\rightarrow$ (Ethane - Saturated)

Industrial Application: The most significant industrial application of hydrogenation is the hardening of vegetable oils to produce solid or semi-solid fats like vanaspati ghee or margarine. Vegetable oils are liquids at room temperature because they contain unsaturated fatty acids (with double bonds). Hydrogenation converts these double bonds into single bonds, raising the melting point of the oil and turning it into a solid or semi-solid fat, which is more stable and has a longer shelf life.

Addition reactions are characteristic of unsaturated hydrocarbons, which are compounds containing double or triple bonds between carbon atoms (alkenes and alkynes).

Let us analyze the given hydrocarbons:

Saturated hydrocarbons (alkanes) undergo substitution reactions, not addition reactions.

Therefore, the hydrocarbons that will undergo addition reactions are the unsaturated ones: $\mathrm{C}_{3} \mathrm{H}_{6}$ and $\mathrm{C}_{2} \mathrm{H}_{2}$.

A common test to differentiate between saturated and unsaturated hydrocarbons is the Bromine Water Test.

This test provides a clear visual distinction between saturated and unsaturated hydrocarbons.

The cleaning action of soap is based on the unique structure of its molecules, which allows them to act as an emulsifying agent between oil and water.