Class 10 Science Chapter 4 Previous Year Questions - Carbon and its compounds

Ans: (c)

The correct answer is (c) because carbon compounds generally do not conduct electricity well (bad conductors), and they have weak forces of attraction between their molecules, which means the molecules can move around easily. This explains why carbon compounds often exist as gases or liquids rather than solids.

Ans: (A) (i) A series of carbon compounds in which the same functional group substitutes for hydrogen in a carbon chain / Series of compounds having same functional group and similar chemical properties.
(ii) Because melting point and boiling point increase with molecular mass.
(iii) Because chemical properties of organic compounds are solely determined by their functional group which remains same in a homologous series.
(iv) (i) Aldehyde: Propanal

(ii) Ketone: Propanone

OR
(B) (i) Ethanol Structure:  

(ii) Ethene is formed

( Note: Deduct ½ mark if the conditions required are not mentioned in the equation)
Concentrated Sulphuric acid acts as a dehydrating agent.
(iii) Ethene

Ans: (a)
In a homologous series of carbon compounds, like alkanes or alkynes, each member differs from the next by a specific group of atoms (—CH₂), which is explained in statement (A). As the size of the molecules increases (more carbon and hydrogen atoms), their melting and boiling points also generally increase, as stated in (B). Thus, both (A) and (B) are correct, making option (a) the right answer.

Ans: (a) (i) Carbon cannot form C⁴⁺ cations because removal of 4 electrons from a carbon atom would require a large amount of energy and it cannot form C^4- anion because it would be difficult for the nucleus with 6 protons to hold 10 electrons.
Thus it shares electrons to form covalent compounds.
(ii) A series of compounds in which the same functional group substitutes for hydrogen in a carbon chain / series of compounds having same functional group and similar chemical properties.
CH₃CHO, C₂H₅CHO (any other consecutive members)
(iii) Structure of cyclohexane (C₆H₁₂)

OR
(b) (i) Ethanol – C₂H₅OH  
(ii)

NOTE: Name of the product for each reaction is given in bold letters under the reaction.

Ans: (b)
The correct structural formula for cyclohexane is shown in option (b). Cyclohexane, C₆H₁₂ , is a cyclic hydrocarbon with a six-membered ring structure, where each carbon atom is bonded to two other carbon atoms and two hydrogen atoms. This configuration ensures all carbon-carbon bonds are single, fitting the description and structure in option (b).

Ans: (b)
The hydrocarbons C₄H₁₀ (butane), C₅H₁₂ (pentane), and C₂H₆ (ethane) are all alkanes, which are saturated hydrocarbons containing only single bonds. However, C₇H₁₄ is an alkene, which has at least one double bond. Therefore, option (b) is different from the others.

Ans: (a) CH₃Br
C₂H₅Br
(b) (i) Aldehyde (ii) Ketone
(c) The colour of KMnO₄ disappears;
KMnO₄ acts as an oxidizing agent.

OR
(c) Ethene Conc. H₂SO₄ acts as a dehydrating agent.

Ans: (b)

Benzene (C₆H₆) has a unique structure with alternating single and double bonds between its carbon atoms, often represented as a hexagon with a circle in the center. In this structure, there are 3 actual double bonds and the remaining 3 bonds are single bonds, but due to resonance, it’s commonly shown as having 3 double bonds and 3 single bonds. So, the correct answer is (d) 3 and 3. It seems the answer you provided is incorrect.

Ans: 

(i) Low melting points and boiling points - Weak intermolecular forces of attraction.
(ii) Non-conductors of electricity - Bonding in these compounds does not give rise to any ions. / Covalent bonds or sharing of electrons do not form any charged particles.

Ans: (a) Compounds formed by carbon and hydrogen only.
(b) Tetravalency and Catenation
(c) (i)

(c) (ii)  Compounds with identical molecular formula but different structures
Two isomers of butane C₄H₁₀

Ans:
Carbon dioxide; Water

Ans:

(i) Oxygen is added to ethanol to produce ethanoic acid. 

(ii) Alkaline potassium permanganate or Acidified potassium dichromate

(iii)

(iv) It is oxidation reaction while other is combustion reaction/ burning of ethanol is exothermic while other is endothermic.

Ans: As carbon has four valence electrons and it can neither loose nor gain four electrons thus, it attains noble gas configuration only by sharing of electrons. Thus, it forms covalent compounds. The existence of large number of compounds is due to some unique properties of carbon which are:
(i) Carbon atoms possess an unique property to link together to form very long chains. This property is referred to as catenation.
A large number of carbon atoms can join together to form straight chains, branched chains and rings as shown below:

(ii) Due to small size and presence of four valence electrons, a carbon atom can form multiple bonds with some other carbon atoms as well as with other atoms like oxygen, nitrogen etc., This increases the variety of compounds formed by it and hence the number of compounds is tremendously increased.
Due to small size, the nucleus of carbon atom can hold its shared pairs of electrons strongly. As a result, the bonds that carbon forms with most of the other elements such as hydrogen, oxygen, nitrogen, etc. are very strong there by making these compounds exceptionally stable.

Ans: (i) Structural isomers of butane are the following:


(iii) (a) Three homologue of alcohol are the following:CH₃OH, CH₃CH₂OH, CH₃CH₂CH₂OH
Third homologue of alcohol is CH₃CH₂CH₂OH
(b) Three homologue of aldehyde are the following:
HCHO, CH₃CHO, CH₃CH,CHO
Third homologue of aldehyde is CH₃CH₂CHO.
(iv) (a) Benzene (b) But-1-ene
(v) Z = 7,

Ans: (i) The process in which compounds of carbon react with oxygen to give carbon dioxide, water, heat and light, is known as combustion. Alkanes burn in air and release large amount of heat, therefore can be used as excellent fuels.

(ii) Oxidation is a process in which oxygen is added to a substance.

(iii) Hydrogenation means addition of hydrogen to an unsaturated compound.

(iv) When alcohol is added to carboxylic acid in the presence of acid catalyst then, a fruity smelling ester is formed. This process is called esterification.

(v) Esters react in the presence of an acid or a base to give the alcohol and carboxylic acid. This reaction is known as saponification because it is used in the preparation of soap.

Ans: Carbon can form only covalent compounds because carbon can neither gain nor lose four electrons to acquire stable octet. The only way by which it can acquire the nearest noble gas configuration is by sharing its valence electrons with other C-atoms or atoms of other elements. Hence, carbon forms compounds mainly by covalent bonding.

Ans: (a) (i) Methane (CH₄)
(ii) Propane (CH₃CH₂CH₃) or C₃H₈
(b) Due to weak intermolecular forces of attraction, covalent compounds generally have low melting and boiling points.

Ans: Covalent compounds have low melting and boiling points because the forces of attraction between molecules of covalent compounds are very weak. On applying a small amount of heat these molecular forces break.

Ans: Diamond

Ans: Carbon has atomic number 6 with four electrons in the valence shell. If it gains four electrons in order to complete its octet, it will lead to the formation of C^4- anion. The addition of four electrons in valence shell j will result in strong electronic repulsions between eight I electrons now present in valence shell. Hence, it will be : difficult for the nucleus to hold on to ten electrons. On the other hand, if it loses four electrons, it forms C⁴⁺ cation. It would require a large amount of energy to remove four electrons. Hence, carbon prefers to share its valence electrons with other atoms of carbon to attain noble gas configuration. The bond formed is known as covalent bond.

Ans: (a) Formation of oxygen molecule:

(b) Formation of nitrogen molecule:

Ans: Carbon can form only covalent compounds because carbon can neither gain nor lose four electrons to acquire stable octet. The only way by which it can acquire the nearest noble gas configuration is by sharing its valence electrons with other C-atoms or atoms of other elements. Hence, carbon forms compounds mainly by covalent bonding.

Ans: (i) Due to weak intermolecular forces of attraction, carbon compounds generally have low melting and boiling points.
(ii) Carbon compounds do not contain ions and hence, are generally poor conductors of electricity.
(iii) Carbon can form only covalent compounds because carbon can neither gain nor lose four electrons to acquire stable octet. The only way by which it can acquire the nearest noble gas configuration is by sharing its valence electrons with other C-atoms or atoms of other elements.

Ans: 

(b) 

Ans: (a) (i) Methane (CH₄)
(ii) Propane (CH₃CH₂CH₃) or C₃H₈
(b) Due to weak intermolecular forces of attraction, covalent compounds generally have low melting and boiling points.

Ans: (a) C₃H₆(or C_nH_2n, n = 3) i.e, alkene series thus, has one double covalent bond.
(b) C₄H₆ (or C_nH_2n-2, n = 4) i.e., alkyne series.
The first member of alkyne series is ethyne (C₂H₂) HC ≡ CH.
(c) C₆H₁₂ can form ring structure of C-atoms.

(d) Alkane series: C_n H_2n+2
Only C₃H₈ is a member of alkane series CH₃ — CH₂ — CH₃

Ans: (a) General formula of alkyne C_nH_{2n - 2}
For C_xH₂, 2n - 2 = 2 ⇒ n = 2 ∴ x = 2.
For C₃H_y, n = 3, y = 2n - 2 = 2 x 3 - 2 = 4
Hence, x = 2, y = 4
(b) A is ethyne (C₂H₂) and B is propyne (C₃H₄).

Ans: A homologous series is the family of organic compounds having the same functional group, similar chemical properties but the successive (adjacent members of the series differ by a —CH2 unit or 14 mas units.
(i) As the molecular mass increases in a homologous series, melting and boiling points also increases.
(ii) Chemical properties remains same for the members of homologous series because they all have same functional group.

Ans: 

These are called structural isomers as they have the same j molecular formula i.e., C₄H₁₀ but different structures. As i the molecular formula is C₄H₁₀, common name of this | compound is butane. i The alkyne of four carbon atoms is butyne. Its structure i is as follows:

The molecular formula of butyne is C₄H₆.

Ans: (i) Molecular formula of benzene is C₆H₆.

(ii) Number of single bonds = 9
Number of double bonds = 3
(iii) Alkynes are the unsaturated hydrocarbons that contain at least one triple bond between two carbon atoms (—C ≡ C—)

Ans: (a) Aldehyde (—CHO) group.
(b) C_nH_2nO
(c) Compound (i) is propanal, and compound (ii) is ethanal. They belong to the same homologous series where each successive compound differs from each other by a—CH₂ unit.
Other member of same homologous series:

Ans:  Covalent bonds are formed by sharing of electron pair between two atoms. Covalently bonded molecules are observed to have stronger bonds within the molecule but intermolecular forces are weak.

Ans: Covalent compounds do not contain ions and hence, are generally poor conductors of electricity.

Ans: A cyclic unsaturated carbon compound is a compound that contains a carbon ring with one or more double or triple bonds between the carbon atoms. An example of a cyclic unsaturated carbon compound is benzene, which has a ring of six carbon atoms with alternating double bonds.

Ans: Carbon has the unique ability to form bonds with other atoms of carbon, giving rise to large molecules. This property is called catenation. Carbon shows catenation due to its small size and stronger carbon-carbon bond strength. As we move down the group, the element-element bond energies decrease rapidly. For this reason, other elements of this group show little or no catenation property.

Ans: (i) 5% solution of KMnO₄ is prepared by adding 5 g of KMnO₄ in 95 g of water.
(ii) Here alkaline KMnO₄ acts as an oxidising agent. It oxidises ethanol to ethanoic acid by donating nascent oxygen. If excess of KMnO₄ is added the purple colour will persist indicating no more alcohol is left and reaction stops.
(iii)

Ans: (a) Isomers are those molecules which have the same molecular formula but different structural formulae i.e., show different properties and the phenomenon is called isomerism. The structures of possible isomers of butane (C₄H₁₀) are:
(b) The compound 'X’ is an unsaturated compound (alkene or alkyne) which burn in air with a yellow sooty flame (producing black smoke).
(c) Alkaline KMnO₄ acts as an oxidising agent which oxidise alcohol (—OH) to corresponding carboxylic acid (—COOH).

Ans: (a) A homologous series is the family of organic compounds having the same functional group, similar chemical properties but the successive (adjacent) members of the series differ by a —CH₂ unit or 14 mass units.
For example, alkane series has general formula C_nH_{2n + 2}.
First member of homologous series of alkane is methane, i.e., CH₄.
Second member of homologous series of alkane is ethane, i.e., C₂H₆.
Third member of homologous series of alkane is propane i.e., C₃H₈.
(b) (i) Carboxylic acids react with alcohols in the presence of a little concentrated sulphuric acid to form pleasant smelling esters. This reaction is called esterification reaction.

(ii) Those reactions in which atoms or group of atoms are simply added to a double or triple bond without the elimination of any atom or molecule, are known as addition reactions.

Ans: (a) (i) When ethanol is heated with cone. H₂SO₄ at 443 K, ethene is obtained due to dehydration of ethanol.

(ii) When 5 % alkaline KMn04 solution is added drop by drop to warm ethanol then it gets oxidised to ethanoic acid.

(b) Addition reactions: Those reactions in which atoms or group of atoms are simply added to a double or triple bond without the elimination of any atom or molecule, are known as addition reactions.
Substitution reactions: The reactions which involve the displacement or substitution of an atom or a group of atoms in an organic compound by another atom or group of atoms, are known as substitution reactions. Saturated hydrocarbons are fairly unreactive and inert in the presence of most of the reagents. However, in presence of sunlight, hydrocarbons undergo rapid substitution reactions. e.g.,

Ans: (a) As the molecular mass of Y is 30 g mol^-1, it is ethane (C₂H₆ = 12 x 2 + 6 x 1 = 30).
‘X’ is ethene (CH₂ = CH₂) which decolourises Br₂^- water and burns with a smoky flam.



(c) No. we are not able to check if water is hard by using a detergent as detergent works well in hard water as well. This is because calcium and magnesium salts of detergents are soluble in water and hence, detergents can be used for washing even in hard water.

Ans: A homologous series is defined as a group of compounds having the same functional group, similar chemical properties in which the successive members differ by a -CH₂ group or 14 mass unit.
For example, in alkane homologous series, the general formula is C_nH_2n+2 i.e.; first three members are CH₄. C₂H₆ and C₃H₈ where two successive members differ by -CH₂ group.
Characteristics of homologous series: 

• All compounds in the series can be represented by a general formula, e.g., for alcohol it is C_nH_2n+1OH, for alkane C_nH_2n+2, for alkene C_nH_2n and for alkynes C_nH_2n-2, where, n = 1, 2, 3..... 
• All compounds in the series have similar chemical properties. 
• All members of the series, show a gradual change in their physical properties.
• Physical properties generally increase as the molecular mass increases.

Ans: As X reacts with conc. H₂SO₄ to give an alkene so it should be an alcohol as cone. H₂SO₄ acts as a dehydrating agent. The reaction of X with Na also confirms that it is an alcohol because alcohols react with Na metal to evolve colourless hydrogen gas.

Here, cone H₂SO₄ acts as a dehydrating agent i.e., helps in the removal of water.

Ans: (a) Due to catenation, carbon forms covalent bonds with the constituent elements in the carbon compounds, hence it does not have mobile electrons and carbon compounds do not dissociate themselves into ions and hence, they are poor conductor of electricity.
(b) Structure:

Name: Cyclopentane
Number of single bonds: 15

Ans: (a)
 
(b) when ethanol is treated with sodium metal observation received are-
Hydrogen gas is evolved and it behaves like an acid.
(c) structure of cyclohexane is below-

(d) Name of the compound is Ethanal and it is an Acetaldehyde 

Ans: The molecular formula of first two members of homologous series having - Cl functional group are CH₃CI and CH₃CH₂CI.

Ans: The molecular formula of first two members of homologous series having - OH functional group are CH₃OH and CH₃CH₂OH.

Ans: Homologous series of alkenes have general formula, C_nH_2n whose first member is ethene.
2^nd member of homologous series of alkenes is C₃H₆ i.e., propene.
3^rd member of homologous series of alkenes is C₄H₈ i.e., butene.

Ans: Methane, CH₄ is an alkane. Alkanes have general formula, C_nH_2n+2.
2^nd member of homologous series of alkanes is C₂H₆ i.e., ethane.
3^rd member of homologous series of alkanes is C₃H₈ i.e., propane.

Ans: All unsaturated hydrocarbons (containing double or triple bonds) have tendency to get converted to saturated hydrocarbons (single bonds) by adding small molecules such as hydrogen (H₂), halogens (X₂), etc. Such reactions are called addition reactions. Compound with the molecular formula C₄H₈ belongs to alkene series (C_nH_2n). Hence, it will undergo addition reaction.

Ans: The molecules of soap are sodium or potassium salts of long-chain carboxylic acids. Detergents are generally ammonium or sulphonate salts of long chain carboxylic acids.
Difference between Soap and Detergent
Soaps:
(i) Soaps are sodium salts of long chain carboxylic acids.
(ii) The ionic group in soap is -COO^-Na⁺.
(iii) Soaps are not useful when water is hard.
Detergents
(i) Detergents are the odium salt of long chain benzene sulphonic acids.
(ii) The ionic groups in detergents is SO₃^-Na⁺ or SO₄^-Na⁺.
(iii) Detergent can be used for washing purpose even when water is hard
Cleansing action of soap can be described as follows:
The soap molecule is generally represented as RCOONa. In solution, it ionises to form RCOO^- and Na⁺. Each soap molecule has a polar head group (carboxylate ion, COO^- group) and a long nonpolar hydrocarbon tail (R group from long chain fatty acid). The polar head attracts the polar water molecule and is called hydrophilic end and the nonpolar tail attracts the water-insoluble oily or greasy dirt particles.

Ans: Compounds consisting of carbon and hydrogen are known as hydrocarbons.
(a) Saturated hydrocarbons: Alkanes (C_nH_2n+2) are the compounds of carbon that have a single bond.

(b) Unsaturated hydrocarbons: The compounds of carbon having double bonds are alkene (C_nH_2n) and having triple bonds are alkyne (C_nH_2n-2). The reaction which converts unsaturated hydrocarbons to saturated hydrocarbons i.e. alkenes to alkane is known as hydrogenation reaction. It is used to obtain ghee from oil.

Ans. (i) C₂H₄ belongs to alkene series having general formula, C_nH_2n.
Thus, next homologue will be C₃H_2x3 = C₃H₆
(ii) C₄H₆ belongs to alkyne series having general formula, C_nH_2n-2.
Thus, next homologue will be C₅H_2x5-2 = C₅H₈ 

Ans: (a) CH₃ - CH₂ - OH: Ethanol (Alcohol)
(b) 

Ans: Saturated hydrocarbons (alkanes) have general formula, C_nH_2n+2. Among the given compounds, only C₄H₁₀ and C₆H₁₄ satisfy the above formula. Thus, these are saturated hydrocarbons. Unsaturated hydrocarbons have the general formula C_nH_2n (alkene) and C_nH_2n-2 (alkyne).

Ans: An alcohol with three carbon atoms in its molecule is propanol. The structure of propanol is

Ans: An alcohol with four carbon atoms is butanol and its structure is:

Ans: An aldehyde with four carbon atoms is butanal and its structure is:

Ans: Carbon has the unique ability to form bonds with other atoms of carbon, giving rise to large molecules. This property is called catenation. Carbon shows catenation due to its small size and stronger carbon-carbon bond strength.

Ans: The general formula of the alkane series is C_nH_2n+2. For fourth member of alkane series, n = 4
∴ C₄H_{2 x 4 + 2} = C₄ H₁₀ i.e., butane.

Ans: A homologous series is the family of organic compounds having the same functional group, similar chemical properties but the successive (adjacent) members of the series differ by a —CH₂ unit or 14 mass units.

Ans: (i) When ethanol reacts with ethanoic acid in presence of cone. H₂SO₄, ethyl ethanoate is formed which belongs to the class of ester compounds, having fruity smell.

(ii) The above reaction is called esterification which occurs in presence of cone. H₂SO₄ which acts as a dehydrating agent and helps in the removal of water. Cone. H₂SO₄ also acts as a catalyst to speed up the reaction.

Ans: Ethanoic acid reacts with sodium as well as sodium hydroxide to form sodium ethanoate.

Ans: Ethanoic acid reacts with Na₂CO₃ to form sodium ethanoate and CO₂ gas is liberated.

With sodium hydrogen carbonate it forms sodium ethanoate.

With NaOH It forms sodium ethanoate.

Ans: Tests for distinguishing between an alcohol and a carboxylic acid are:
(i) Litmus test: When we place a drop of carboxylic acid on blue litmus paper it turns red while alcohol will not change the colour of blue litmus paper.
(ii) Sodium hydrogen carbonate test/sodium carbonate
test: If a pinch of NaHCO₃ or Na₂CO₃ is added to two test tubes containing alcohol and carboxylic acid respectively, then test tube containing carboxylic acid will show the evolution of colourless gas with brisk effervescence while test tube containing alcohol does not show any reaction.

Ans: A micelle is a submicroscopic aggregate of molecules with non-polar groups on the inside and hydrophilic groups on the outside. If ethanol is used in place of water, micelle will not be formed as the solution will not have any polar part.

Ans: Homologous series of alkenes have general formula, C_nH_2n whose first member is ethene.
2nd member of homologous series of alkenes is C₃H₆ i.e., propene.

Ans: Alkanes have general formula, C_nH_{2n + 2}.
2^nd member of homologous series of alkanes is C₂H₆ i.e., ethane.

Ans: General formula, C_nH_2n-2 belongs to alkyne series. The second member of this series is propyne i.e., (C₃H₄) or CH₃—C≡CH.

Ans: The structural formula of ethane (C₂H₆) is
There are total 7 covalent bonds. Six C — H covalent bonds and one C — C covalent bond.

Ans: Butane (C₄H₁₀) has the following structural formula as:

Total number of covalent bonds is 13 in which there are 10C — H and 3C - C covalent bonds.

Ans: The process of adding hydrogen to an unsaturated compound is called hydrogenation. For example, the hydrogenation of ethene leads to the formation of ethane.

Conditions for Hydrogenation
(i) Presence of an unsaturated compound (i.e. an unsaturated hydrocarbon)
(ii) Presence of a catalyst such as finely divided palladium or nickel
In case of the hydrogenation of vegetable oils, liquid unsaturated fatty acids are converted into solid saturated fatty acids.