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Summary of the Chapter-4-Carbon and its Compounds with Key-Points:
- Carbon is a highly versatile element that serves as the foundation for all living organisms and many everyday materials.
- Its ability to form a wide range of compounds is due to its tetravalency and the property of catenation.
- Covalent bonds occur when two atoms share electrons to complete their outermost electron shells.
- Carbon forms covalent bonds with other carbon atoms as well as elements like hydrogen, oxygen, sulfur, nitrogen, and chlorine.
- It can also create compounds with double and triple bonds between carbon atoms, which may take the form of straight chains, branched chains, or rings.
- Carbon's ability to form chains leads to the creation of homologous series, where the same functional group is attached to carbon chains of varying lengths.
- Functional groups such as alcohols, aldehydes, ketones, and carboxylic acids give carbon compounds distinct properties.
- Carbon compounds are essential sources of fuel.
- Ethanol and ethanoic acid are examples of carbon compounds that play a significant role in our daily lives.
- Soaps and detergents work due to the presence of both hydrophobic and hydrophilic parts, which allow them to emulsify oily dirt for easier removal.
1. What is the percentage of carbon in the Earth's crust?
(A) 0.02%
(B) 0.2%
(C) 2.0%
(D) 3.0%
Explanation: Carbon constitutes only 0.02% of the Earth's crust in the form of minerals like carbonates, hydrogen carbonates, coal, and petroleum.
2. Why do most carbon compounds have low melting and boiling points?
(A) Because they form ionic bonds
(B) Because the forces of attraction between their molecules are weak
(C) Because they are metals
(D) Because they have strong intermolecular forces
Explanation: The weak intermolecular forces in covalently bonded carbon compounds lead to low melting and boiling points.
3. What is the atomic number of carbon?
(A) 4
(B) 6
(C) 8
(D) 12
Explanation: The atomic number of carbon is 6, meaning it has 6 protons and 6 electrons.
4. How many covalent bonds does carbon form in a methane molecule (CH4)?
(A) 1
(B) 2
(C) 3
(D) 4
Explanation: Carbon forms four covalent bonds with four hydrogen atoms in methane, satisfying its tetravalency.
5. What is the electron configuration of carbon?
(A) 2, 4
(B) 1, 5
(C) 2, 2
(D) 2, 6
Explanation: Carbon has two electrons in its first shell and four electrons in its second shell, leading to the electron configuration 2, 4.
6. Why doesn't carbon form C4- or C4+ ions easily?
(A) Because gaining or losing four electrons requires a lot of energy
(B) Because carbon has too many neutrons
(C) Because carbon is a metal
(D) Because carbon cannot form ions
Explanation: Forming C4- would make it difficult for six protons to hold ten electrons, and losing four electrons to form C4+ would require a significant amount of energy.
7. What type of bond is formed when two hydrogen atoms share electrons?
(A) Ionic bond
(B) Covalent bond
(C) Metallic bond
(D) Hydrogen bond
Explanation: Hydrogen atoms form a covalent bond by sharing their electrons to achieve a stable electron configuration.
8. In which of the following carbon allotropes is each carbon atom bonded to four other carbon atoms?
(A) Graphite
(B) Diamond
(C) Fullerene
(D) Coal
Explanation: In diamond, each carbon atom is covalently bonded to four other carbon atoms, forming a rigid three-dimensional structure.
9. Which of the following is a correct characteristic of graphite?
(A) It is a good conductor of electricity
(B) It is the hardest known natural substance
(C) It forms single covalent bonds
(D) It is an insulator
Explanation: Unlike other non-metals, graphite is a good conductor of electricity because of the free-moving electrons between its layers.
10. What property allows carbon atoms to form long chains and rings?
(A) Combustion
(B) Catenation
(C) Substitution
(D) Decomposition
Explanation: Catenation is the ability of carbon atoms to form long chains and rings by bonding with other carbon atoms.
11. What type of bonds are present in unsaturated hydrocarbons?
(A) Single bonds only
(B) Double or triple bonds
(C) Ionic bonds
(D) Hydrogen bonds
Explanation: Unsaturated hydrocarbons contain either double or triple bonds between carbon atoms, making them more reactive than saturated hydrocarbons.
12. What is the general formula for alkanes?
(A) CnH2n
(B) CnH2n+2
(C) CnH2n-2
(D) CnHn
Explanation: Alkanes are saturated hydrocarbons with the general formula CnH2n+2, where "n" is the number of carbon atoms.
13. Which of the following is an example of a saturated hydrocarbon?
(A) Ethene
(B) Propane
(C) Ethyne
(D) Benzene
Explanation: Propane is an alkane, a saturated hydrocarbon that contains only single bonds between carbon atoms.
14. Which functional group is present in alcohols?
(A) —CHO
(B) —OH
(C) —COOH
(D) —C=O
Explanation: Alcohols contain the —OH (hydroxyl) group attached to a carbon chain.
15. What is the product when ethanol is heated with concentrated sulfuric acid?
(A) Methane
(B) Ethene
(C) Ethane
(D) Ethanoic acid
Explanation: Heating ethanol with concentrated sulfuric acid leads to the dehydration of ethanol, forming ethene, an unsaturated hydrocarbon.
16. What is the molecular formula of ethanoic acid?
(A) C2H5OH
(B) CH3COOH
(C) CH4
(D) C2H6
Explanation: Ethanoic acid, also known as acetic acid, has the molecular formula CH3COOH.
17. Which type of reaction occurs when unsaturated hydrocarbons react with hydrogen in the presence of a catalyst?
(A) Substitution reaction
(B) Addition reaction
(C) Decomposition reaction
(D) Combustion reaction
Explanation: Unsaturated hydrocarbons undergo addition reactions with hydrogen in the presence of a catalyst like nickel or palladium, leading to the formation of saturated hydrocarbons.
18. What is the IUPAC name of the compound with the molecular formula CH3CH2OH?
(A) Methanol
(B) Ethanol
(C) Propanol
(D) Butanol
Explanation: Ethanol is the common name for CH3CH2OH, an alcohol with two carbon atoms.
19. What happens when ethanoic acid reacts with sodium carbonate?
(A) Hydrogen gas is released
(B) Sodium acetate, carbon dioxide, and water are formed
(C) Sodium chloride is formed
(D) No reaction occurs
Explanation: Ethanoic acid reacts with sodium carbonate to produce sodium acetate, carbon dioxide, and water.
20. Which one of the following is a homologous series?
(A) Methane, methanol, ethene
(B) Ethene, propane, butyne
(C) Methane, ethane, propane
(D) Methanol, methanoic acid, methanone
Explanation: A homologous series is a group of compounds that have the same functional group and follow a general formula, such as alkanes (CnH2n+2).
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