Textbook - Carbon and its Compounds Questions in English

(N/A) The electron dot structure of $CO_2$ is formed by the sharing of electrons between one carbon atom and two oxygen atoms.
Carbon has $4$ valence electrons,and each oxygen atom has $6$ valence electrons.
To achieve a stable octet configuration,the carbon atom shares $2$ electrons with each of the two oxygen atoms,resulting in two double bonds.
This sharing is represented by the electron dot structure where the shared pairs of electrons are placed between the atoms:
(Image: $1067-$s1)

(N/A) sulphur molecule consists of eight atoms of sulphur $(S_8)$ joined together in a puckered ring structure.
Each sulphur atom has $6$ valence electrons and requires $2$ more electrons to complete its octet.
Therefore,each sulphur atom forms two single covalent bonds with two adjacent sulphur atoms.
The electron dot structure shows each sulphur atom sharing two electrons with its neighbors,resulting in a crown-shaped ring.

(B) Three structural isomers are possible for pentane $(C_{5}H_{12})$:
$(i)$ $n$-pentane: $CH_{3}-CH_{2}-CH_{2}-CH_{2}-CH_{3}$
$(ii)$ Isopentane ($2$-methylbutane): $CH_{3}-CH(CH_{3})-CH_{2}-CH_{3}$
$(iii)$ Neopentane ($2$,$2$-dimethylpropane): $C(CH_{3})_{4}$

(A) The two unique properties of carbon that lead to the formation of a vast number of carbon compounds are:
$(i)$ Catenation: It is the unique ability of carbon atoms to form strong covalent bonds with other carbon atoms,resulting in the formation of long chains,branched chains,or ring structures.
$(ii)$ Tetravalency: Carbon has a valency of $4$,which allows it to form covalent bonds with four other atoms of carbon or atoms of other monovalent elements like hydrogen,oxygen,nitrogen,or halogens.

(N/A) The chemical formula for cyclopentane is $C_5H_{10}$.
Cyclopentane is a cyclic hydrocarbon with five carbon atoms arranged in a ring. Each carbon atom is bonded to two other carbon atoms and two hydrogen atoms.
The electron dot structure represents the sharing of electrons between atoms to form covalent bonds. In the structure,each carbon atom shares electrons with two adjacent carbon atoms and two hydrogen atoms to complete its octet,while each hydrogen atom shares an electron to complete its duplet.
[Image Description: $A$ pentagonal ring of five carbon atoms,where each carbon is bonded to two hydrogen atoms.]

(N/A) $(i)$ Ethanoic acid $(CH_{3}COOH)$:
$H-C(H)(H)-C(=O)-OH$
$(ii)$ Yes,structural isomers are possible for bromopentane $(C_{5}H_{11}Br)$. Three common isomers are:
$1$. $1$-Bromopentane: $CH_{3}-CH_{2}-CH_{2}-CH_{2}-CH_{2}-Br$
$2$. $2$-Bromopentane: $CH_{3}-CH_{2}-CH_{2}-CH(Br)-CH_{3}$
$3$. $3$-Bromopentane: $CH_{3}-CH_{2}-CH(Br)-CH_{2}-CH_{3}$

(N/A) $(i)$ Butanone: $CH_{3}CH_{2}COCH_{3}$
Structure: $CH_{3}-CH_{2}-C(=O)-CH_{3}$
$(ii)$ Hexanal: $CH_{3}CH_{2}CH_{2}CH_{2}CH_{2}CHO$
Structure: $CH_{3}-CH_{2}-CH_{2}-CH_{2}-CH_{2}-CHO$

(N/A) The chemical reaction is represented as: $\text{CH}_3\text{CH}_2\text{OH} \xrightarrow{[O]} \text{CH}_3\text{COOH}$.
An oxidation reaction is defined as the addition of oxygen or the removal of hydrogen from a substance.
In the conversion of ethanol $(\text{CH}_3\text{CH}_2\text{OH})$ to ethanoic acid $(\text{CH}_3\text{COOH})$, an oxygen atom is added to the molecule.
Since oxygen is added to ethanol to form ethanoic acid, this process is classified as an oxidation reaction.

(N/A) The chemical reaction for the combustion of ethyne is: $2HC \equiv CH + 5O_2 \to 4CO_2 + 2H_2O + \text{Heat}$.
When ethyne is burnt in air,it produces a sooty flame due to incomplete combustion caused by the limited supply of oxygen in the air.
However,when ethyne is burnt with pure oxygen,it undergoes complete combustion,producing a clean,high-temperature flame reaching approximately $3000 \, ^\circ C$.
This oxy-acetylene flame provides the necessary heat for welding metals.
It is not possible to attain such a high temperature using only air,which is why a mixture of ethyne and air is not used for welding.

(A) We can distinguish between an alcohol and a carboxylic acid based on their reaction with carbonates and hydrogen carbonates.
Carboxylic acids react with metal carbonates and metal hydrogen carbonates to evolve $CO_2$ gas,which turns lime water milky.
Reaction: $\text{Metal Carbonate} / \text{Metal Hydrogen carbonate} + \text{Carboxylic acid} \rightarrow \text{Salt} + \text{Water} + \text{Carbon dioxide}$.
Alcohols,on the other hand,do not react with carbonates or hydrogen carbonates,so no gas is evolved.

(D) Oxidising agents are substances that have the ability to add oxygen to other substances or remove hydrogen from them during a chemical reaction.
Examples include alkaline potassium permanganate $(KMnO_4)$ and acidified potassium dichromate $(K_2Cr_2O_7)$.
These substances facilitate the oxidation process by providing oxygen to the reactant.

(NO) Detergents are ammonium or sulphonate salts of long-chain carboxylic acids. Unlike soap,they do not react with calcium $(Ca^{2+})$ and magnesium $(Mg^{2+})$ ions present in hard water to form scum. They produce a good amount of lather regardless of whether the water is hard or soft. This means that detergents perform equally well in both soft and hard water. Therefore,detergents cannot be used to check whether water is hard or not.

(N/A) soap molecule has two parts,namely hydrophobic and hydrophilic. With the help of these,it attaches to the grease or dirt particle and forms a cluster called a micelle. These micelles remain suspended as a colloid. To remove these micelles (which entrap the dirt),it is necessary to agitate the clothes to dislodge them from the fabric surface.

(B) The molecular formula of ethane is $C_2H_6$.
In this molecule,there is one $C-C$ single bond.
Each carbon atom is bonded to three hydrogen atoms,forming three $C-H$ bonds per carbon atom.
Therefore,there are $6$ $C-H$ bonds and $1$ $C-C$ bond.
Total number of covalent bonds = $6 + 1 = 7$.

(C) Butanone is a $4$-carbon ketone with the chemical formula $CH_3COCH_2CH_3$.
The suffix '-one' in the name 'butanone' indicates the presence of a ketone functional group $(>C=O)$.

(D) When fuel does not burn completely,it produces soot (carbon particles) due to incomplete combustion. This soot deposits on the bottom of the cooking vessel,causing it to turn black.

(N/A) Carbon can neither lose four of its electrons nor gain four electrons as both the processes require a large amount of energy and would make the system unstable. Therefore,it completes its octet by sharing its four electrons with other carbon atoms or with atoms of other elements. The bonds that are formed by sharing electrons are known as covalent bonds. In covalent bonding,both the atoms share the valence electrons,i.e.,the shared electrons belong to the valence shells of both the atoms.
Here,carbon requires $4$ electrons to complete its octet,while each hydrogen atom requires one electron to complete its duplet. Also,chlorine requires one electron to complete its octet. Therefore,all of these share the electrons and as a result,carbon forms $3$ bonds with hydrogen and one with chlorine to form $CH_3Cl$.

(N/A) The electron dot structure of ethanoic acid $(CH_3COOH)$ involves sharing of electrons between carbon,hydrogen,and oxygen atoms to complete their octets/duplets.
(See the provided image for the structural representation).
$(b)$ The electron dot structure of hydrogen sulfide $(H_2S)$ involves the sulfur atom sharing one electron each with two hydrogen atoms to form two covalent bonds,completing the octet of sulfur and the duplet of hydrogen.
(See the provided image for the structural representation).

(N/A) Propanone: The chemical formula of propanone is $CH_3COCH_3$. In this structure,the central carbon atom is double-bonded to an oxygen atom and single-bonded to two other carbon atoms. Each of these two carbon atoms is further bonded to three hydrogen atoms.
(Image provided in the original context shows the electron sharing between atoms.)
$(b)$ $F_2$: Fluorine has $7$ valence electrons. To achieve a stable octet,two fluorine atoms share one pair of electrons,forming a single covalent bond.

(N/A) homologous series is a group of organic compounds that have the same functional group and similar chemical properties,and in which successive members differ by a $-CH_2$ unit.
For example,the alkane series is a homologous series with the general formula $C_nH_{2n+2}$.
$1$. Methane: $CH_4$
$2$. Ethane: $C_2H_6$ (or $CH_3CH_3$)
$3$. Propane: $C_3H_8$ (or $CH_3CH_2CH_3$)
$4$. Butane: $C_4H_{10}$ (or $CH_3CH_2CH_2CH_3$)
In this series,each successive member differs by a $-CH_2$ group,which corresponds to a molecular mass difference of $14 \ u$.

(N/A) Physical Properties:
$1$. Odour: Ethanol has a pleasant,characteristic alcoholic odour,whereas ethanoic acid has a pungent,vinegar-like smell.
$2$. Melting Point: The melting point of ethanoic acid is $17\,^{\circ}C$,which is below room temperature,causing it to freeze in winter. Ethanol has a much lower melting point $(-114\,^{\circ}C)$ and remains liquid at room temperature.
Chemical Properties:
$1$. Reaction with Carbonates/Hydrogencarbonates: Ethanoic acid reacts with metal carbonates and metal hydrogencarbonates to evolve $CO_{2}$ gas,which turns lime water milky. Ethanol does not react with these compounds.
Reaction:
$2CH_{3}COOH + Na_{2}CO_{3} \longrightarrow 2CH_{3}COONa + H_{2}O + CO_{2} \uparrow$
$CH_{3}CH_{2}OH + Na_{2}CO_{3} \longrightarrow \text{No reaction}$

(A) Micelles are formed when soap is added to water because soap molecules are amphiphilic,containing a hydrophobic hydrocarbon tail and a hydrophilic ionic head.
In water,the hydrophobic tails cluster together to avoid contact with water,while the hydrophilic heads face outward,forming a spherical structure called a micelle.
Micelles will not be formed in other solvents like ethanol.
This is because the hydrocarbon chains of soap molecules are soluble in organic solvents like ethanol,preventing the aggregation required to form micelles.

(N/A) Most carbon compounds release a significant amount of heat and light when burned in air.
Saturated hydrocarbons burn with a clean flame and produce no smoke.
Carbon compounds used as fuels possess high calorific values,meaning they release a large amount of energy per unit mass.
Due to these properties,carbon and its compounds are widely used as fuels for most applications.

(N/A) Soap does not work properly in hard water. Soap is a sodium or potassium salt of long-chain fatty acids. Hard water contains dissolved salts of calcium $(Ca^{2+})$ and magnesium $(Mg^{2+})$. When soap is added to hard water,the calcium and magnesium ions present in the water displace the sodium or potassium ions from the soap molecules. This reaction results in the formation of an insoluble white precipitate known as scum. Because of this reaction,a significant amount of soap is wasted before any lather can be formed.

(A) Soap is basic in nature because it is a salt of a strong base and a weak acid.
Basic substances turn red litmus paper blue.
Blue litmus paper does not change its colour in a basic solution.
Therefore,red litmus will turn blue,and blue litmus will remain blue.

(N/A) Hydrogenation is the chemical process of adding hydrogen to a molecule. In organic chemistry,it typically involves the addition of hydrogen to unsaturated hydrocarbons (containing double or triple bonds) in the presence of catalysts like palladium $(Pd)$ or nickel $(Ni)$ to produce saturated hydrocarbons.
The general reaction is:
$R_2C=CR_2 + H_2 \xrightarrow{Ni \text{ catalyst}} R_2CH-CHR_2$
Its primary industrial application is the hydrogenation of vegetable oils. Vegetable oils contain long chains of unsaturated fatty acids. By hydrogenating these oils in the presence of a nickel catalyst,they are converted into saturated fats,which are solid at room temperature,commonly known as vanaspati ghee (hydrogenated vegetable fat).

(B) Addition reactions are characteristic of unsaturated hydrocarbons,which contain at least one double or triple bond between carbon atoms.
$1$. $C_{2}H_{6}$ (Ethane) and $C_{3}H_{8}$ (Propane) are alkanes (saturated hydrocarbons).
$2$. $CH_{4}$ (Methane) is an alkane (saturated hydrocarbon).
$3$. $C_{3}H_{6}$ (Propene) is an alkene (unsaturated hydrocarbon).
$4$. $C_{2}H_{2}$ (Ethyne) is an alkyne (unsaturated hydrocarbon).
Therefore,$C_{3}H_{6}$ and $C_{2}H_{2}$ undergo addition reactions.

(N/A) The bromine water test is commonly used to differentiate between saturated and unsaturated hydrocarbons.
When bromine water (a reddish-brown liquid) is added to an unsaturated hydrocarbon,the bromine reacts with the double or triple bonds,causing the reddish-brown color to disappear (decolorize).
In contrast,saturated hydrocarbons do not react with bromine water under normal conditions,so the reddish-brown color remains unchanged.

(N/A) Cleansing action of soaps:
$1$. Soap molecules consist of two parts: a long hydrocarbon chain which is hydrophobic (water-repelling) and an ionic head which is hydrophilic (water-attracting).
$2$. When soap is dissolved in water,the hydrophobic ends attach themselves to the dirt particles,which are typically oily or greasy in nature.
$3$. The hydrophilic ends remain pointed outwards towards the water.
$4$. These molecules arrange themselves in a spherical structure called a 'micelle',with the dirt trapped at the center.
$5$. The negatively charged ionic heads create a repulsive force between micelles,preventing them from re-attaching to the cloth.
$6$. Finally,the dirt is rinsed away along with the water,leaving the cloth clean.

(A) The $IUPAC$ naming rules are applied as follows:
$(i)$ $CH_3-CH_2-Br$: This is a two-carbon chain with a bromine substituent. The prefix for bromine is 'bromo' and the alkane is 'ethane'. Thus,it is named Bromoethane.
$(ii)$ $H-CHO$: This is a one-carbon aldehyde. The prefix for one carbon is 'meth-' and the suffix for aldehyde is '-al'. Thus,it is named Methanal.
$(iii)$ $CH_3-CH_2-CH_2-CH_2-C \equiv CH$: This is a six-carbon chain with a triple bond at the first position. The prefix for six carbons is 'hex-' and the suffix for an alkyne is '-yne'. Since the triple bond starts at the first carbon,it is named Hex$-1-$yne.