Synonyms
More meanings
Tip: select a single word for meaning & synonyms.
Select multiple words normally to copy text.
Carbon and its Compounds: Class 10 Science answers, notes
Get summaries, questions, answers, solutions, notes, extras, PDF and guides for Chapter 4 Carbon and its Compounds: Class 10 Science textbook, which is part of the syllabus for students studying under SEBA (Assam Board), NBSE (Nagaland Board), TBSE (Tripura Board), CBSE (Central Board), MBOSE (Meghalaya Board), BSEM (Manipur Board), WBBSE (West Bengal Board), and all other boards following the NCERT books. These solutions, however, should only be treated as references and can be modified/changed.
If you notice any errors in the notes, please mention them in the comments
Summary
Carbon is a very special element, found in many things like our food, clothes, and bodies. It forms strong bonds with itself and other elements, creating a huge variety of compounds. Carbon atoms share electrons to form covalent bonds. With four electrons to share, carbon forms four bonds, a property called tetravalency. Carbon also links with other carbon atoms to make long chains, branches, or rings; this is known as catenation. It’s like carbon atoms can hold hands with many friends in different ways.
Hydrocarbons are compounds made of only carbon and hydrogen. Saturated hydrocarbons, like alkanes, have only single bonds between carbon atoms. Unsaturated ones, such as alkenes and alkynes, have double or triple bonds and are generally more reactive. Other atoms, like oxygen, can join these carbon chains, forming functional groups that give the compounds special properties. For instance, alcohols have an -OH group, and carboxylic acids have a -COOH group. A homologous series is a set of compounds with the same functional group, where each member differs from the next by a -CH2- unit.
Carbon exists in different forms called allotropes. These include diamond, which is very hard; graphite, which is slippery and conducts electricity; and fullerenes, which are shaped like a football. Carbon compounds undergo several important chemical reactions. They burn in air, a process called combustion, to produce carbon dioxide, heat, and light. Alcohols can be changed into carboxylic acids through oxidation. Unsaturated compounds can have hydrogen added to them to become saturated in an addition reaction. In substitution reactions, one type of atom in a compound is replaced by another.
Ethanol and ethanoic acid are two important carbon compounds. Ethanol is an alcohol used in drinks, as a solvent, and in medicines. Ethanoic acid, also known as acetic acid, is what gives vinegar its sour taste and is used as a preservative.
Soaps and detergents help us clean things. Their molecules have two different ends: one end loves water (hydrophilic), and the other end loves oil (hydrophobic). When soap is used, the oil-loving ends stick to oily dirt, while the water-loving ends face the water. This forms tiny clusters called micelles, which trap the dirt inside. These micelles, with the dirt, are then washed away with water. Detergents work in a similar way and are also effective in hard water. Long ago, people thought carbon compounds could only be made by living things due to a ‘vital force’, but a scientist named Friedrich Wöhler proved this wrong by making urea in the laboratory.
Textbook solutions
Intext Questions and Answers I
1. What would be the electron dot structure of carbon dioxide which has the formula CO₂?
Answer:
2. What would be the electron dot structure of a molecule of sulphur which is made up of eight atoms of sulphur? (Hint – The eight atoms of sulphur are joined together in the form of a ring.)
Answer:
Intext Questions and Answers II
1. How many structural isomers can you draw for pentane?
Answer: Three structural isomers are possible for pentane.
2. What are the two properties of carbon which lead to the huge number of carbon compounds we see around us?
The two characteristic features seen in carbon that lead to the huge number of carbon compounds we see around us are catenation and tetravalency.
Two factors noticed in the case of carbon are:
(i) Carbon has the unique ability to form bonds with other atoms of carbon, giving rise to large molecules. This property is called catenation. These compounds may have long chains of carbon, branched chains of carbon or even carbon atoms arranged in rings. In addition, carbon atoms may be linked by single, double or triple bonds.
(ii) Since carbon has a valency of four, it is capable of bonding with four other atoms of carbon or atoms of some other mono-valent element.
3. What will be the formula and electron dot structure of cyclopentane?
Answer: The formula is C₅H₁₀.
4. Draw the structures for the following compounds.
(i) Ethanoic acid
(ii) Bromopentane*
(iii) Butanone
(iv) Hexanal.
*Are structural isomers possible for bromopentane?
Answer:
There are many structural isomers possible for bromopentane.
5. How would you name the following compounds?
Answer: (i) This compound has two carbon atoms and a bromo functional group. It is a haloalkane, and using the prefix ‘bromo’, it would be named Bromoethane.
(ii) This compound has one carbon atom and an aldehyde functional group. Using the suffix ‘-al’ and modifying ‘methane’, it would be named Methanal.
(iii) This is a six-carbon chain with a triple bond. It is an alkyne, and using the suffix ‘-yne’ with ‘hexane’, it would be named Hexyne.
Intext Questions and Answers III
1. Why is the conversion of ethanol to ethanoic acid an oxidation reaction?
Answer: The conversion of ethanol to ethanoic acid is an oxidation reaction because it involves the addition of oxygen to ethanol. Substances like alkaline potassium permanganate or acidified potassium dichromate act as oxidising agents in this reaction. These oxidising agents are “capable of adding oxygen to others,” and in this specific case, they are “oxidising alcohols to acids, that is, adding oxygen to the starting material,” which is ethanol, to form ethanoic acid.
2. A mixture of oxygen and ethyne is burnt for welding. Can you tell why a mixture of ethyne and air is not used?
Answer: A mixture of ethyne and air is not used for welding because ethyne is an unsaturated hydrocarbon, and for welding, a very high temperature is required, which is achieved through complete combustion. Air provides a limited supply of oxygen compared to pure oxygen. Burning ethyne with air would likely lead to incomplete combustion because “unsaturated carbon compounds will give a yellow flame with lots of black smoke” when the oxygen supply is insufficient. Furthermore, “limiting the supply of air results in incomplete combustion…giving a sooty flame.” Such incomplete combustion produces a cooler and less efficient flame, unsuitable for welding. To achieve the necessary high temperatures, ethyne is burnt with pure oxygen, which ensures a “sufficiently oxygen-rich mixture” for complete combustion, resulting in a very hot and clean flame.
Intext Questions and Answers IV
1. How would you distinguish experimentally between an alcohol and a carboxylic acid?
Answer: To distinguish experimentally between an alcohol and a carboxylic acid, the following methods based on their described properties can be used:
One method involves testing the reaction with carbonates or hydrogencarbonates. For instance, ethanoic acid, which is a carboxylic acid, reacts with carbonates and hydrogencarbonates to give rise to a salt, carbon dioxide, and water. The production of carbon dioxide can be observed as effervescence, and the gas can be tested, for example, with lime-water. Alcohols are not described as giving this reaction with carbonates or hydrogencarbonates.
Another experimental distinction can be made using litmus paper. Carboxylic acids are characterised by their acidic nature. For example, 5-8% solution of acetic acid in water is called vinegar. Dilute acetic acid would be indicated as acidic by a litmus test, turning blue litmus paper red. Alcohols like ethanol are generally neutral and would typically not cause such a change in litmus paper.
2. What are oxidising agents?
Answer: Oxidising agents are substances that are capable of adding oxygen to others. For example, alkaline potassium permanganate or acidified potassium dichromate are oxidising agents because they oxidise alcohols to acids, which involves adding oxygen to the starting material. Hence, they are known as oxidising agents.
Intext Questions and Answers V
1. Would you be able to check if water is hard by using a detergent?
Answer: No. When checking for hard water with soap, an insoluble substance (scum) is observed, which is caused by the reaction of soap with the calcium and magnesium salts that cause the hardness of water. Detergents, however, are generally sodium salts of sulphonic acids or ammonium salts with chlorides or bromides ions. The charged ends of these detergent compounds do not form insoluble precipitates with the calcium and magnesium ions in hard water. Thus, they remain effective in hard water. Since detergents do not form the characteristic insoluble precipitates that soap does in hard water, one would not be able to check if water is hard by observing for such a precipitate when using a detergent.
2. People use a variety of methods to wash clothes. Usually after adding the soap, they ‘beat’ the clothes on a stone, or beat it with a paddle, scrub with a brush or the mixture is agitated in a washing machine. Why is agitation necessary to get clean clothes?
Answer: Most dirt is oily in nature and, as is commonly known, oil does not dissolve in water. To clean clothes, we use soap, which consists of molecules that are sodium or potassium salts of long-chain carboxylic acids. These molecules have two ends with differing properties: a hydrophilic end that interacts with water, and a hydrophobic end that interacts with oily hydrocarbons.
When soap is added to water, its molecules form structures called micelles. In this formation, the hydrophobic ends of the molecules cluster together towards the center, trapping the oily dirt particle. The ionic, hydrophilic ends face outwards, interacting with the surrounding water. This process forms an emulsion in the water, allowing the soap micelle to pull the dirt out of the fabric and suspend it in the water.
People use a variety of methods to wash clothes, such as beating them on a stone, scrubbing with a brush, or using a washing machine. This agitation is necessary to provide the mechanical action that helps dislodge the oily dirt from the cloth fibers. The physical movement ensures that the soap molecules can effectively surround the dirt particles to form micelles. Once the dirt is trapped within these micelles and suspended in the water, agitation helps keep them from redepositing onto the fabric, allowing them to be easily rinsed away. This is how we are able to wash our clothes clean.
Exercise Questions and Answers
1. Ethane, with the molecular formula C₂H₆ has
(a) 6 covalent bonds.
(b) 7 covalent bonds.
(c) 8 covalent bonds.
(d) 9 covalent bonds.
Answer: (b) 7 covalent bonds.
2. Butanone is a four-carbon compound with the functional group
(a) carboxylic acid.
(b) aldehyde.
(c) ketone.
(d) alcohol.
Answer: (c) ketone.
3. While cooking, if the bottom of the vessel is getting blackened on the outside, it means that
(a) the food is not cooked completely.
(b) the fuel is not burning completely.
(c) the fuel is wet.
(d) the fuel is burning completely.
Answer: (b) the fuel is not burning completely.
4. Explain the nature of the covalent bond using the bond formation in CH₃Cl.
Answer: Carbon has four valence electrons and shares one electron each with three hydrogen atoms, resulting in covalent bonds. It also shares one electron with a chlorine atom, forming a covalent bond as well. However, due to the higher electronegativity of chlorine, the C-Cl bond is polar in nature.
5. Draw the electron dot structures for
(a) ethanoic acid.
Answer:
(b) H₂S.
Answer:
(c) propanone.
Answer:
(d) F₂.
Answer:
6. What is an homologous series? Explain with an example.
Answer: A homologous series is a series of carbon compounds that have different numbers of carbon atoms but contain the same functional group. An example of this is the alkane homologous series, which includes methane, ethane, propane, butane, and so on. The general formula for this series is CnH2n+2, and there is a difference of -CH2 unit between each successive compound.
7. How can ethanol and ethanoic acid be differentiated on the basis of their physical and chemical properties?
Answer: Ethanol and ethanoic acid can be differentiated based on the following properties: ethanol is a liquid at room temperature with a pleasant smell, while ethanoic acid has a melting point of 17°C and a vinegar-like smell. Ethanol does not react with metal carbonates, but ethanoic acid reacts with metal carbonates to form a salt, water, and carbon dioxide. Ethanol does not react with NaOH, but ethanoic acid reacts with NaOH to form sodium ethanoate and water. Ethanol is oxidized to form ethanoic acid in the presence of acidified KMnO4, but no reaction occurs with ethanoic acid in the presence of acidified KMnO4.
8. Why does micelle formation take place when soap is added to water? Will a micelle be formed in other solvents such as ethanol also?
Answer: When soap is dissolved in water and clothes are placed in the soapy solution, soap molecules form a structure called a micelle. The hydrophobic ends of the soap molecules surround a particle of grease to form a spherical micelle, with the hydrophilic ends on the outside of the sphere and the hydrophobic ends towards the center. Micelles will not be formed in solvents such as ethanol because ethanol is not as polar as soap.
9. Why are carbon and its compounds used as fuels for most applications?
Answer: Carbon and its compounds are used as fuels for most applications because they release a large amount of heat upon combustion due to their high percentage of carbon and hydrogen. Carbon compounds used as fuel have an optimum ignition temperature, high calorific values, and are easy to handle, and their combustion can be controlled.
10. Explain the formation of scum when hard water is treated with soap.
Answer: Hard water often contains calcium and magnesium salts, and when soap is added to it, the soap molecules react with these salts to form a precipitate. This precipitate floats as an off-white layer on the water, known as scum. The formation of scum interferes with the cleansing properties of soap in hard water.
11. What change will you observe if you test soap with litmus paper (red and blue)?
Answer: Since soap is basic in nature, it will turn red litmus blue. However, the color of blue litmus will remain blue.
12. What is hydrogenation? What is its industrial application?
Answer: Hydrogenation is a reaction where unsaturated hydrocarbons add hydrogen in the presence of catalysts such as palladium or nickel to give saturated hydrocarbons.
Its industrial application is commonly the hydrogenation of vegetable oils using a nickel catalyst. Vegetable oils generally have long unsaturated carbon chains, and through hydrogenation, they are converted to fats which have saturated carbon chains.
13. Which of the following hydrocarbons undergo addition reactions: C₂H₆, C₃H₈, C₃H₆, C₂H₂, and CH₄.
Answer: The hydrocarbons that undergo addition reactions are C₃H₆ and C₂H₂.
14. Give a test that can be used to differentiate between saturated and unsaturated hydrocarbons.
Answer: A test that can be used to differentiate between saturated and unsaturated hydrocarbons is observing the nature of the flame upon combustion. Saturated hydrocarbons will generally give a clean flame. Unsaturated carbon compounds will generally give a yellow flame with lots of black smoke, which can result in a sooty deposit.
15. Explain the mechanism of the cleaning action of soaps.
Answer: The cleaning action of soaps is based on the structure of soap molecules and their interaction with oil/dirt and water. Most dirt is oily in nature and oil does not dissolve in water. Soap molecules are sodium or potassium salts of long-chain carboxylic acids. Each soap molecule has two parts: a long hydrocarbon chain (hydrophobic end) that interacts with oil/grease, and an ionic end (hydrophilic end) that interacts with water.
When soap is used for cleaning, the hydrophobic ends of the soap molecules attach themselves to the oily dirt, while the hydrophilic ends remain oriented towards the water. This leads to the formation of structures called micelles, where the oily dirt is trapped in the center of the micelle, and the outer surface of the micelle is composed of the ionic ends of the soap molecules. These micelles, containing the dirt, are suspended in the water. The micelles stay in solution as a colloid and will not come together to precipitate because of ion-ion repulsion between the charged outer surfaces of the micelles. Thus, the dirt suspended in the micelles is easily rinsed away with water, allowing clothes or surfaces to become clean. This formation of an emulsion of oil in water by soap helps in pulling out the dirt.
Extras
Additional MCQs (Knowledge Based)
1. What is the primary type of chemical bond formed by carbon atoms in its compounds?
A. Ionic
B. Covalent
C. Metallic
D. Hydrogen
Answer: B. Covalent
2. An element has an atomic number of 6. How many valence electrons does this element possess?
A. 2
B. 6
C. 4
D. 8
Answer: C. 4
3. Diamond : Rigid three-dimensional structure :: Graphite : ____________.
A. Spherical molecules
B. Linear chains
C. Hexagonal layers
D. Tetrahedral units
Answer: C. Hexagonal layers
4. Which of the following hydrocarbons will readily undergo an addition reaction?
A. Methane (CH₄)
B. Ethane (C₂H₆)
C. Propene (C₃H₆)
D. Propane (C₃H₈)
Answer: C. Propene (C₃H₆)
5. This allotrope of carbon is known for its ability to conduct electricity. Identify the allotrope.
A. Diamond
B. Graphite
C. Fullerene
D. Coal
Answer: B. Graphite
6. Identify the odd one out from the following functional groups.
A. -OH (Alcohol)
B. -CHO (Aldehyde)
C. -Cl (Halo)
D. -COOH (Carboxylic acid)
Answer: C. -Cl (Halo)
7. Identify the key properties of carbon that enable it to form a vast number of compounds:
| Property | Description |
| P | It is tetravalent. |
| Q | It readily forms ionic bonds. |
| R | It exhibits catenation. |
| S | It is a noble gas. |
A. P and Q
B. Q and S
C. P and R
D. R and S
Answer: C. P and R
8. Which of the following is NOT a typical characteristic of most covalent compounds?
A. Low melting point
B. Soluble in water
C. Poor electrical conductivity
D. Low boiling point
Answer: B. Soluble in water
9. What is the general formula for alkenes?
A. CₙH₂ₙ₊₂
B. CₙH₂ₙ
C. CₙH₂ₙ₋₂
D. CₙHₙ
Answer: B. CₙH₂ₙ
10. The process of converting vegetable oils into solid fats by reaction with hydrogen is known as:
A. Saponification
B. Esterification
C. Hydrogenation
D. Combustion
Answer: C. Hydrogenation
11. What gas is produced when ethanol reacts with metallic sodium?
A. Oxygen
B. Carbon dioxide
C. Hydrogen
D. Methane
Answer: C. Hydrogen
12. Which substance is commonly used as an oxidizing agent to convert ethanol to ethanoic acid?
A. Concentrated H₂SO₄
B. Nickel catalyst
C. Alkaline KMnO₄
D. Sodium hydroxide
Answer: C. Alkaline KMnO₄
13. A compound has the formula CH₃COOH. What is its IUPAC name?
A. Methanoic acid
B. Ethanol
C. Ethanoic acid
D. Propanone
Answer: C. Ethanoic acid
14. The sweet-smelling compounds formed by the reaction of an alcohol with a carboxylic acid are called:
A. Aldehydes
B. Ketones
C. Ethers
D. Esters
Answer: D. Esters
15. What is the term for the property of carbon that allows it to form long chains and rings by bonding with itself?
A. Tetravalency
B. Isomerism
C. Catenation
D. Allotropy
Answer: C. Catenation
16. Given below are descriptions of different carbon-based structures. Select the one that describes a fullerene.
| Structure | Description |
| W | Rigid 3D network, very hard |
| X | Layers of hexagonal arrays, conducts electricity |
| Y | Spherical molecule, e.g., C-60 |
| Z | Long chain of single-bonded carbons |
A. W
B. X
C. Y
D. Z
Answer: C. Y
17. With reference to hydrocarbons, complete the following:
Saturated : Alkanes :: Unsaturated with triple bonds : ____________.
A. Alkenes
B. Cycloalkanes
C. Alkynes
D. Arenes
Answer: C. Alkynes
18. Which reaction will occur if methane is treated with chlorine in the presence of sunlight?
A. Addition
B. Combustion
C. Substitution
D. Polymerization
Answer: C. Substitution
19. This substance is added to industrial ethanol to make it unfit for drinking. Identify the substance or process.
A. Water
B. Methanol
C. Acetic acid
D. Filtration
Answer: B. Methanol
20. Identify the incorrect statement regarding homologous series.
A. Members have similar chemical properties.
B. Successive members differ by a -CH₂- unit.
C. Members have the same functional group.
D. Physical properties remain constant.
Answer: D. Physical properties remain constant
21. Identify the products of complete combustion of a hydrocarbon like methane:
| Item | Product |
| P | Carbon monoxide |
| Q | Water |
| R | Carbon dioxide |
| S | Hydrogen gas |
A. P and Q
B. Q and R
C. P and S
D. R and S
Answer: B. Q and R
22. Which of the following is NOT a fossil fuel?
A. Coal
B. Petroleum
C. Natural gas
D. Ethanol
Answer: D. Ethanol
23. The functional group -CHO is characteristic of which class of organic compounds?
A. Alcohols
B. Aldehydes
C. Ketones
D. Carboxylic acids
Answer: B. Aldehydes
24. What is the melting point of pure ethanoic acid?
A. 100 K
B. 273 K
C. 290 K
D. 373 K
Answer: C. 290 K
25. The cleansing action of soap is due to the formation of:
A. Precipitates
B. Esters
C. Micelles
D. Acids
Answer: C. Micelles
26. Why are detergents more effective than soaps in hard water?
A. They are stronger acids.
B. Their charged ends don’t form scum.
C. They are more soluble in oil.
D. They have shorter carbon chains.
Answer: B. Their charged ends don’t form scum.
27. How many covalent bonds are present in a molecule of ethane (C₂H₆)?
A. 6
B. 7
C. 8
D. 5
Answer: B. 7
28. Butanone is a four-carbon compound. Which functional group does it contain?
A. Carboxylic acid
B. Aldehyde
C. Ketone
D. Alcohol
Answer: C. Ketone
29. If the bottom of a cooking vessel is getting blackened on the outside, it indicates:
A. The food is overcooked.
B. The fuel is wet.
C. Incomplete fuel combustion.
D. The vessel is new.
Answer: C. Incomplete fuel combustion.
30. What is the valency of carbon?
A. 1
B. 2
C. 3
D. 4
Answer: D. 4
Additional MCQs (Competency Based)
1. Assertion (A): Ethanol can be converted into ethene by heating it with concentrated sulphuric acid at 443 K.
Reason (R): Concentrated sulphuric acid acts as an oxidising agent in this reaction.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (c) A is true but R is false.
2. Assertion (A): Carbon forms a vast number of compounds, far exceeding those formed by all other elements combined.
Reason (R): Carbon exhibits the unique properties of tetravalency, allowing it to form four covalent bonds, and catenation, the ability to form long chains, branched chains, and rings with other carbon atoms.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (a) Both A and R are true and R is the correct explanation of A.
3. Assertion (A): Soaps are not effective cleansing agents in hard water.
Reason (R): Hard water contains dissolved salts of calcium and magnesium which react with soap to form an insoluble precipitate called scum.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (a) Both A and R are true and R is the correct explanation of A.
4. Assertion (A): Methane (CH₄) readily undergoes addition reactions with reagents like hydrogen or chlorine.
Reason (R): Methane is a saturated hydrocarbon, meaning it contains only single covalent bonds between its carbon and hydrogen atoms.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (d) A is false but R is true.
5. A student observes that when a particular liquid fuel is burned in a lamp with a limited air supply, the bottom of a glass beaker held above the flame quickly turns black with soot. When the air supply to the lamp is increased, the flame becomes less yellow and the soot formation is significantly reduced. What is the most likely reason for the initial blackening of the beaker?
(a) The fuel is primarily composed of saturated hydrocarbons which always produce soot.
(b) The fuel is undergoing complete combustion due to the limited air supply.
(c) There is an insufficient supply of oxygen, leading to incomplete combustion of the fuel.
(d) The fuel contains a high amount of non-combustible impurities.
Answer: (c) There is an insufficient supply of oxygen, leading to incomplete combustion of the fuel.
6. A student is given two unlabeled test tubes. One contains a saturated hydrocarbon (e.g., hexane) and the other an unsaturated hydrocarbon (e.g., hexene). To distinguish between them, the student needs a reagent that will show a visible chemical change primarily with the unsaturated hydrocarbon. Which of the following reagents would be most suitable for this purpose?
(a) A few drops of alkaline potassium permanganate solution.
(b) Dilute sodium hydroxide solution.
(c) Blue litmus solution.
(d) Concentrated hydrochloric acid.
Answer: (a) A few drops of alkaline potassium permanganate solution.
7. A chemist is attempting to synthesize a compound known for its pleasant, fruity smell, often used as a flavouring agent or in perfumes. The chemist reacts an alcohol with a carboxylic acid in the presence of a few drops of concentrated sulphuric acid as a catalyst. What type of compound is the chemist most likely trying to synthesize?
(a) An aldehyde
(b) A ketone
(c) An ester
(d) An ether
Answer: (c) An ester
8. A student is performing two different reactions with ethanol. Reaction 1: Ethanol is warmed gently with a 5% solution of alkaline potassium permanganate. Reaction 2: Ethanol is heated to 443 K with excess concentrated sulphuric acid. What are the likely major organic products, P1 from Reaction 1 and P2 from Reaction 2?
(a) P1 = Ethene, P2 = Ethanoic acid
(b) P1 = Ethanoic acid, P2 = Ethene
(c) P1 = Ethanal, P2 = Diethyl ether
(d) P1 = Methane, P2 = Acetic acid
Answer: (b) P1 = Ethanoic acid, P2 = Ethene
9. Consider the information: “Vegetable oils generally have long unsaturated carbon chains while animal fats have saturated carbon chains. The reaction of unsaturated hydrocarbons with hydrogen in the presence of catalysts like palladium or nickel to give saturated hydrocarbons is commonly used in the hydrogenation of vegetable oils.” A food product label states it is made with “hydrogenated vegetable oil.” What chemical change has most likely occurred in the vegetable oil during this process?
(a) Saturated carbon chains have been converted to unsaturated carbon chains.
(b) The length of the carbon chains in the oil has been significantly increased.
(c) Unsaturated carbon chains in the oil have been converted to saturated carbon chains.
(d) The vegetable oil has been mixed with animal fats to increase its saturation level.
Answer: (c) Unsaturated carbon chains in the oil have been converted to saturated carbon chains.
10. The allotropes of carbon, diamond and graphite, exhibit vastly different physical properties. Diamond is known as the hardest natural substance, while graphite is soft, smooth, and slippery. Another key difference is that “Graphite is also a very good conductor of electricity unlike other non-metals that you studied in the previous Chapter.” Which of the following correctly pairs an allotrope of carbon with one of its distinct physical properties as described?
(a) Diamond – Good conductor of electricity
(b) Graphite – Hardest known substance
(c) Fullerene – Smooth and slippery
(d) Graphite – Smooth and slippery
Answer: (d) Graphite – Smooth and slippery
11. The following data shows the melting and boiling points for four different carbon compounds:
| Compound | Melting point (K) | Boiling point (K) |
| Acetic acid (CH₃COOH) | 290 | 391 |
| Chloroform (CHCl₃) | 209 | 334 |
| Ethanol (CH₃CH₂OH) | 156 | 351 |
| Methane (CH₄) | 90 | 111 |
Based on this data, which compound has the largest temperature range over which it exists as a liquid under standard pressure?
(a) Acetic acid
(b) Chloroform
(c) Ethanol
(d) Methane
Answer: (c) Ethanol
12. Match the compound in Column A with its characteristic property or primary use in Column B.
| Column A (Compound) | Column B (Property/Use) |
| (i) Ethanoic acid | 1. Sweet-smelling substance |
| (ii) Ester | 2. Used as a preservative in pickles |
| (iii) Methane | 3. Good conductor of electricity |
| (iv) Graphite | 4. Major component of bio-gas |
Codes:
(a) (i)–2, (ii)–1, (iii)–4, (iv)–3
(b) (i)–1, (ii)–2, (iii)–3, (iv)–4
(c) (i)–2, (ii)–4, (iii)–1, (iv)–3
(d) (i)–3, (ii)–1, (iii)–2, (iv)–4
Answer: (a) (i)–2, (ii)–1, (iii)–4, (iv)–3
13. Match the type of covalent bond in Column A with a molecule in Column B where it is a defining feature between two specific atoms (other than C-H bonds).
| Column A (Bond Type) | Column B (Molecule) |
| (i) Single Covalent Bond (C-C) | 1. Oxygen (O₂) |
| (ii) Double Covalent Bond (O=O) | 2. Sodium Chloride (NaCl) (Ionic) |
| (iii) Triple Covalent Bond (N≡N) | 3. Ethane (C₂H₆) |
| (iv) Ionic Bond | 4. Nitrogen (N₂) |
Codes:
(a) (i)–3, (ii)–1, (iii)–4, (iv)–2
(b) (i)–1, (ii)–3, (iii)–2, (iv)–4
(c) (i)–3, (ii)–4, (iii)–1, (iv)–2
(d) (i)–2, (ii)–1, (iii)–4, (iv)–3
Answer: (a) (i)–3, (ii)–1, (iii)–4, (iv)–2
14. Match the chemical reaction type in Column A with the most appropriate chemical transformation described in Column B.
| Column A (Reaction Type) | Column B (Transformation) |
| (i) Combustion | 1. Ethene + Hydrogen → Ethane |
| (ii) Addition | 2. Methane + Chlorine → Chloromethane + Hydrogen chloride |
| (iii) Substitution | 3. Ethanol + Alkaline KMnO₄ → Ethanoic acid |
| (iv) Oxidation (specific) | 4. Methane + Oxygen → Carbon dioxide + Water |
Codes:
(a) (i)–4, (ii)–1, (iii)–2, (iv)–3
(b) (i)–1, (ii)–4, (iii)–3, (iv)–2
(c) (i)–4, (ii)–2, (iii)–1, (iv)–3
(d) (i)–3, (ii)–1, (iii)–4, (iv)–2
Answer: (a) (i)–4, (ii)–1, (iii)–2, (iv)–3
15. Match the functional group name in Column A with its correct chemical formula representation in Column B.
| Column A (Functional Group) | Column B (Formula) |
| (i) Aldehyde | 1. -OH |
| (ii) Ketone | 2. -COOH |
| (iii) Alcohol | 3. -CHO |
| (iv) Carboxylic Acid | 4. -CO- (within a chain) |
Codes:
(a) (i)–1, (ii)–2, (iii)–3, (iv)–4
(b) (i)–2, (ii)–1, (iii)–4, (iv)–3
(c) (i)–3, (ii)–1, (iii)–4, (iv)–2
(d) (i)–3, (ii)–4, (iii)–1, (iv)–2
Answer: (d) (i)–3, (ii)–4, (iii)–1, (iv)–2
16. Arrange the following steps in the correct experimental sequence for the formation and detection of an ester from an alcohol and a carboxylic acid.
(i) Gently warm the mixture in a water bath for at least five minutes.
(ii) Add a few drops of concentrated sulphuric acid to the mixture.
(iii) Take approximately 1 mL of ethanol and 1 mL of glacial acetic acid in a test tube.
(iv) Pour the resulting mixture into a beaker containing 20-50 mL of water and carefully smell the mixture.
(a) (iii) → (ii) → (i) → (iv)
(b) (ii) → (iii) → (i) → (iv)
(c) (iii) → (i) → (ii) → (iv)
(d) (i) → (ii) → (iii) → (iv)
Answer: (a) (iii) → (ii) → (i) → (iv)
17. Arrange the following saturated hydrocarbons in increasing order of the number of carbon atoms they contain.
(i) Propane
(ii) Methane
(iii) Ethane
(iv) Butane
(a) (ii) → (iii) → (i) → (iv)
(b) (i) → (ii) → (iii) → (iv)
(c) (iv) → (i) → (iii) → (ii)
(d) (ii) → (i) → (iv) → (iii)
Answer: (a) (ii) → (iii) → (i) → (iv)
18. The process of making soap, known as saponification, involves the alkaline hydrolysis of esters (like fats or oils). Arrange the following conceptual stages in the correct order for saponification.
(i) Formation of an alcohol and the sodium salt of a long-chain carboxylic acid.
(ii) Interaction of a long-chain fatty acid ester (e.g., vegetable oil) with a strong alkali like sodium hydroxide.
(iii) The sodium salt of the long-chain carboxylic acid, which is the soap, precipitates or separates.
(iv) Heating the mixture to facilitate the reaction.
(a) (ii) → (iv) → (i) → (iii)
(b) (iv) → (ii) → (iii) → (i)
(c) (ii) → (i) → (iv) → (iii)
(d) (i) → (ii) → (iv) → (iii)
Answer: (a) (ii) → (iv) → (i) → (iii)
19. Arrange the general steps for testing if a gaseous product from a reaction is carbon dioxide using lime water.
(i) Observe if the lime water turns milky.
(ii) Allow the reaction that produces the gas to occur.
(iii) Pass the gas produced through freshly prepared lime water.
(iv) Carefully collect or direct the gas produced from the reaction vessel.
(a) (ii) → (iv) → (i) → (iii)
(b) (ii) → (iv) → (iii) → (i)
(c) (iv) → (ii) → (iii) → (i)
(d) (ii) → (iii) → (iv) → (i)
Answer: (b) (ii) → (iv) → (iii) → (i)
20. Consider the melting points (in Kelvin) for the following carbon compounds: Acetic acid (290 K), Chloroform (209 K), Ethanol (156 K), Methane (90 K). If these four compounds, initially in their liquid or gaseous state at room temperature (around 298K), are cooled down simultaneously, which compound will be the first to solidify?
(a) Acetic acid
(b) Chloroform
(c) Ethanol
(d) Methane
Answer: (a) Acetic acid
21. The first three members of the homologous series of alcohols are methanol (CH₃OH), ethanol (C₂H₅OH), and propanol (C₃H₇OH). What is the difference in molecular mass between ethanol (C₂H₅OH) and propanol (C₃H₇OH)? (Atomic masses: C=12 u, H=1 u, O=16 u)
(a) 12 u
(b) 14 u
(c) 16 u
(d) 30 u
Answer: (b) 14 u
22. The general formula for alkenes, which are unsaturated hydrocarbons containing one carbon-carbon double bond, is CnH₂n. If a particular alkene has a molecular mass of 42 u, what is the value of ‘n’ for this alkene? (Atomic masses: C=12 u, H=1 u)
(a) 2
(b) 3
(c) 4
(d) 5
Answer: (b) 3
23. The molecular formula of ethane is C₂H₆. Its structural formula shows each carbon atom bonded to three hydrogen atoms and one other carbon atom. How many covalent bonds are present in one molecule of ethane?
(a) 6
(b) 7
(c) 8
(d) 9
Answer: (b) 7
24. A homologous series of compounds, such as alkanes (methane, ethane, propane, butane, etc.), shows a gradation in physical properties as the number of carbon atoms in the chain increases. What trend is generally observed for the boiling points of alkanes as the number of carbon atoms increases from one to four?
(a) Boiling points decrease significantly.
(b) Boiling points remain relatively constant.
(c) Boiling points fluctuate unpredictably without a clear trend.
(d) Boiling points increase steadily.
Answer: (d) Boiling points increase steadily.
25. Pentane (C₅H₁₂), a saturated hydrocarbon, can exist in different structural forms while having the same molecular formula. These different forms are known as structural isomers. Which of the following statements is true regarding the structural isomers of pentane?
(a) They have different molecular formulae but similar structural arrangements and physical properties.
(b) They have the same molecular formula and the exact same structural arrangement, leading to identical properties.
(c) They have different molecular formulae and, consequently, different structural arrangements and physical properties.
(d) They have the same molecular formula but different structural arrangements, which can lead to differences in their physical properties.
Answer: (d) They have the same molecular formula but different structural arrangements, which can lead to differences in their physical properties.
Additional Questions and Answers
1. What is a covalent bond?
Answer: Bonds which are formed by the sharing of an electron pair between two atoms are known as covalent bonds.
2. How many valence electrons does a carbon atom possess?
Answer: In the case of carbon, it has four electrons in its outermost shell, so carbon has four valence electrons.
3. What is the valency of carbon?
Answer: Carbon has a valency of four because it has four valence electrons and is capable of bonding with four other atoms of carbon or atoms of some other mono-valent element.
4. Why are most carbon compounds poor conductors of electricity?
Answer: Most carbon compounds are poor conductors of electricity because the bonding in these compounds does not give rise to any ions. Since the electrons are shared between atoms and no charged particles are formed, such covalent compounds are generally poor conductors of electricity.
5. What is the product when a carbon compound is completely burnt in oxygen?
Answer: When carbon compounds such as methane (CH₄) or ethanol (CH₃CH₂OH) are burnt in oxygen, they produce carbon dioxide (CO₂) and water (H₂O), along with heat and light. Carbon, in all its allotropic forms, burns in oxygen to give carbon dioxide along with the release of heat and light.
6. Define catenation.
Answer: Carbon has the unique ability to form bonds with other atoms of carbon, giving rise to large molecules. This property is called catenation.
7. What are allotropes of carbon?
Answer: Allotropes of carbon are the different forms in which the element carbon occurs in nature, with widely varying physical properties. In these different forms, such as diamond, graphite, and fullerenes, the carbon atoms are bonded to one another in different manners.
8. Name two allotropes of carbon.
Answer: Two allotropes of carbon are diamond and graphite.
9. To what shape is the C₆₀ fullerene molecule compared?
Answer: The C-60 fullerene molecule, which has carbon atoms arranged in its structure, is compared to the shape of a football.
10. What is a saturated hydrocarbon?
Answer: Saturated hydrocarbons are carbon compounds that contain only carbon and hydrogen, in which the carbon atoms are linked by only single bonds between them. These are also called alkanes.
11. What is an unsaturated hydrocarbon?
Answer: Unsaturated hydrocarbons are carbon compounds that contain only carbon and hydrogen, having double or triple bonds between their carbon atoms. Those containing one or more double bonds are called alkenes, and those containing one or more triple bonds are called alkynes.
12. Give the general formula for alkenes.
Answer: The general formula for alkenes can be written as CₙH₂ₙ, where n = 2, 3, 4.
13. What are structural isomers?
Answer: Structural isomers are compounds with an identical molecular formula but different structures.
14. What is meant by a functional group in organic chemistry?
Answer: A functional group is a heteroatom or a group containing these, which is attached to a carbon chain. These functional groups confer specific properties to the compound, regardless of the length and nature of the carbon chain. The presence of a functional group decides the properties of the carbon compound.
15. Which functional group is represented by –OH?
Answer: The functional group –OH is characteristic of alcohols.
16. Which functional group is characteristic of ketones?
Answer: The functional group characteristic of ketones is a carbonyl group where a carbon atom is double-bonded to an oxygen atom (-C=O), and this carbon atom is bonded to two other carbon atoms within the carbon chain.
17. What is esterification?
Answer: Esterification is a reaction in which esters are most commonly formed by the reaction of an acid and an alcohol. For example, ethanoic acid reacts with absolute ethanol in the presence of an acid catalyst to give an ester.
18. What is saponification?
Answer: Saponification is the reaction where an ester, on treating with sodium hydroxide (an alkali), is converted back to alcohol and sodium salt of carboxylic acid. This reaction is known as saponification because it is used in the preparation of soap.
19. Why is absolute alcohol dangerous if consumed?
Answer: Intake of even a small quantity of pure ethanol, called absolute alcohol, can be lethal.
20. What is the common name for a dilute solution of ethanoic acid?
Answer: A 5-8% solution of acetic acid (the common name for ethanoic acid) in water is called vinegar.
21. What is the systematic name for vinegar?
Answer: Vinegar is a 5-8% solution of acetic acid in water. The systematic name of acetic acid, which is the main active component of vinegar, is ethanoic acid.
22. What are micelles?
Answer: Micelles are structures formed by soap molecules in water. They are clusters of molecules in which the hydrophobic tails are in the interior of the cluster and the ionic ends are on the surface of the cluster. One end of the soap molecules is towards the oil droplet while the ionic-end faces outside, forming an emulsion in water.
23. Why do detergents remain effective in hard water?
Answer: Detergents remain effective in hard water because the charged ends of detergent compounds, which are generally sodium salts of sulphonic acids or ammonium salts with chlorides or bromides ions, do not form insoluble precipitates with the calcium and magnesium ions present in hard water.
24. Describe the structure of graphite and explain how it differs from diamond.
Answer: Both diamond and graphite are formed by carbon atoms; the difference lies in the manner in which the carbon atoms are bonded to one another. In diamond, each carbon atom is bonded to four other carbon atoms forming a rigid three-dimensional structure. In graphite, each carbon atom is bonded to three other carbon atoms in the same plane giving a hexagonal array. One of these bonds is a double-bond, and thus the valency of carbon is satisfied. The graphite structure is formed by the hexagonal arrays being placed in layers one above the other.
25. Account for the contrasting electrical properties of diamond and graphite.
Answer: The different structures of diamond and graphite result in them having very different physical properties, even though their chemical properties are the same. Diamond is the hardest substance known, while graphite is smooth and slippery. Graphite is also a very good conductor of electricity, unlike other non-metals, which contrasts with diamond’s electrical properties. This difference in electrical conductivity arises from their distinct atomic arrangements and bonding.
26. Discuss how the property of catenation in carbon leads to the immense variety of its compounds.
Answer: Carbon has the unique ability to form bonds with other atoms of carbon, giving rise to large molecules. This property is called catenation. These compounds may have long chains of carbon, branched chains of carbon, or even carbon atoms arranged in rings. In addition, carbon atoms may be linked by single, double, or triple bonds. The carbon-carbon bond is very strong and hence stable. This stability and versatility in bonding through catenation give us the large number of compounds with many carbon atoms linked to each other, leading to an immense variety.
27. Compare saturated and unsaturated hydrocarbons with respect to their bonding and chemical reactivity.
Answer: Saturated hydrocarbons are compounds of carbon which are linked by only single bonds between the carbon atoms. These compounds are normally not very reactive.
Unsaturated hydrocarbons are compounds of carbon having double or triple bonds between their carbon atoms. These unsaturated carbon compounds are more reactive than the saturated carbon compounds.
28. Outline the steps involved in naming a ketone according to IUPAC nomenclature.
Answer: Naming a ketone involves the following method:
- (i) Identify the number of carbon atoms in the compound. For example, a compound having three carbon atoms would have the root name propane.
- (ii) Since a ketone group is present, it is indicated in the name of the compound with a suffix. For ketones, the suffix is ‘-one’.
- (iii) If the name of the functional group is to be given as a suffix, and the suffix of the functional group begins with a vowel (like ‘o’ in ‘one’), then the name of the carbon chain is modified by deleting the final ‘e’ and adding the appropriate suffix. For example, a three-carbon chain with a ketone group would be named by taking Propane, removing ‘e’ to get propan, and adding ‘one’, resulting in propanone.
29. Write and balance the chemical equation for the combustion of methane.
Answer: Methane (CH₄) undergoes combustion, which is an oxidation reaction, to give carbon dioxide and water along with the release of heat and light. The balanced chemical equation is:
CH₄ + 2O₂ → CO₂ + 2H₂O + heat and light
30. Explain the oxidation of ethanol to ethanoic acid, naming a suitable oxidising agent.
Answer: Ethanol (CH₃–CH₂OH) can be oxidised to ethanoic acid (CH₃COOH). This conversion involves adding oxygen to the starting material. Substances capable of adding oxygen to others are known as oxidising agents. Alkaline potassium permanganate (KMnO₄) with heat, or acidified potassium dichromate (K₂Cr₂O₇) with heat, are suitable oxidising agents for converting alcohols like ethanol to carboxylic acids like ethanoic acid.
The reaction is: CH₃–CH₂OH –(Alkaline KMnO₄ + Heat or Acidified K₂Cr₂O₇ + Heat)–> CH₃COOH.
31. Describe the hydrogenation (addition) reaction used to convert unsaturated vegetable oils into saturated fats.
Answer: Unsaturated hydrocarbons add hydrogen in the presence of catalysts such as palladium or nickel to give saturated hydrocarbons. This reaction is commonly used in the hydrogenation of vegetable oils using a nickel catalyst. Vegetable oils generally have long unsaturated carbon chains. Through hydrogenation, these unsaturated chains are converted into saturated carbon chains, characteristic of animal fats. Catalysts are substances that cause a reaction to occur or proceed at a different rate without the reaction itself being affected.
The general reaction shows an unsaturated compound with a double bond reacting with hydrogen in the presence of a nickel catalyst to form a saturated compound:
R₂C=CR₂ + H₂ –(Nickel catalyst)–> R₂CH-CHR₂.
32. Explain the substitution reaction between methane and chlorine in sunlight, including the products formed.
Answer: Saturated hydrocarbons like methane are fairly unreactive and are inert in the presence of most reagents. However, in the presence of sunlight, chlorine is added to hydrocarbons in a very fast reaction. In this reaction, chlorine can replace the hydrogen atoms one by one. It is called a substitution reaction because one type of atom (hydrogen) or a group of atoms takes the place of another (chlorine). For methane and chlorine, one product formed is chloromethane (CH₃Cl) along with hydrogen chloride (HCl). A number of products are usually formed with the higher homologues of alkanes if more hydrogen atoms are substituted.
The initial reaction is: CH₄ + Cl₂ –(in the presence of sunlight)–> CH₃Cl + HCl.
33. Outline the reactions of ethanoic acid with (a) sodium hydroxide and (b) sodium carbonate, giving balanced equations.
Answer:
- (a) Reaction with sodium hydroxide: Like mineral acids, ethanoic acid reacts with a base such as sodium hydroxide to give a salt (sodium ethanoate, also commonly called sodium acetate) and water.
The balanced equation is: NaOH + CH₃COOH → CH₃COONa + H₂O - (b) Reaction with sodium carbonate: Ethanoic acid reacts with carbonates like sodium carbonate to give rise to a salt, carbon dioxide, and water. The salt produced is commonly called sodium acetate.
The balanced equation is: 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂
34. Contrast the behaviour of soap and detergent in hard water, explaining the cause of any differences.
Answer: When bathing or washing with soap in hard water, foam is formed with difficulty, and an insoluble substance called scum remains. This scum is caused by the reaction of soap with the calcium and magnesium salts present in hard water, which cause its hardness. Consequently, a larger amount of soap is needed.
This problem is overcome by using detergents. Detergents are generally sodium salts of sulphonic acids or ammonium salts with chlorides or bromides ions, both having a long hydrocarbon chain. The charged ends of these detergent compounds do not form insoluble precipitates with the calcium and magnesium ions in hard water. Therefore, detergents remain effective in hard water, unlike soap which forms scum.
35. Explain how ethanol is dehydrated to form ethene, including the role of the acid catalyst.
Answer: Heating ethanol at 443 K with excess concentrated sulphuric acid results in the dehydration of ethanol to give ethene. In this reaction, a water molecule is removed from the ethanol molecule. The reaction is: CH₃ – CH₂OH –(Hot Conc. H₂SO₄)–> CH₂ = CH₂ + H₂O. The concentrated sulphuric acid acts as a dehydrating agent, which means it removes water from ethanol.
