Prepare for exams with solved exercises on Organic Chemistry, designed according to the PTB curriculum. Cover key topics like functional groups, reactions, and isomerism to boost your understanding.
Short Questions:
1. What is meant by the term catenation? Give an example of a compound that displays catenation.
- Catenation is the ability of an element, particularly carbon, to form long chains and rings by bonding with atoms of the same element. This property allows for the formation of a vast variety of organic compounds.
- Example: Alkanes like hexane (C₆H₁₄) show catenation as they consist of long chains of carbon atoms.
2. How is coal formed?
- Coal formation occurs over millions of years from the remains of plants that have been buried under sediment. The high temperature and pressure conditions cause chemical and physical changes, transforming the plant material into peat, then into lignite, and finally into coal.
3. What is the importance of natural gas?
- Natural gas is a crucial energy source. It is used for heating, electricity generation, and as a fuel for vehicles. It is also a raw material in the production of chemicals, fertilizers, and hydrogen.
4. Justify that organic compounds are used as food.
- Organic compounds, such as carbohydrates, proteins, and fats, are essential nutrients found in food that provide energy and are necessary for growth and the maintenance of life.
5. How are alkyl radicals formed? Explain with examples.
- Alkyl radicals are formed by the removal of one hydrogen atom from an alkane.
- Example: Removing a hydrogen atom from methane (CH₄) forms a methyl radical (CH₃·).
6. What is the difference between n-propyl and isopropyl radicals? Explain with structure.
- n-Propyl radical: It is derived from propane by removing a hydrogen atom from the terminal carbon (CH₃-CH₂-CH₂·).
- Isopropyl radical: It is formed by removing a hydrogen atom from the middle carbon of propane (CH₃-CH·-CH₃).
7. Explain different radicals of butane.
- Butane can form two types of radicals:
- n-Butyl radical: Formed by removing a hydrogen atom from the terminal carbon (CH₃-CH₂-CH₂-CH₂·).
- sec-Butyl radical: Formed by removing a hydrogen from the second carbon (CH₃-CH₂-CH·-CH₃).
- iso-Butyl radical: Formed by removing a hydrogen atom from the branch carbon (CH₃-CH·-CH₃).
- tert-Butyl radical: Formed by removing a hydrogen atom from the central carbon (C·(CH₃)₃).
8. Define functional group with an example.
- A functional group is a specific group of atoms within a molecule that is responsible for the characteristic chemical reactions of that molecule.
- Example: The hydroxyl group (-OH) in alcohols.
9. What is an ester group? Write down the formula of ethyl acetate.
- An ester group has the structure -COO-, where a carbonyl (C=O) is bonded to an oxygen atom that is also bonded to another carbon chain.
- Formula of ethyl acetate: CH₃COOCH₂CH₃.
10. Write down the dot and cross formulae of propane and n-butane.
- Propane (C₃H₈): Show three carbon atoms bonded with eight hydrogen atoms in a linear chain arrangement.
- n-Butane (C₄H₁₀): Show four carbon atoms bonded with ten hydrogen atoms in a linear chain arrangement.
11. Define structural formula. Draw the structural formulae of n-butane and isobutane.
- A structural formula represents the arrangement of atoms within a molecule, showing how they are connected.
- n-Butane: CH₃-CH₂-CH₂-CH₃
- Isobutane: (CH₃)₂CH-CH₃
12. Write classification of coal.
- Coal classification:
- Peat: Early stage, with low carbon content.
- Lignite: Soft coal with higher carbon than peat.
- Bituminous coal: Harder with more carbon, commonly used in industries.
- Anthracite: Highest carbon content, hardest type.
13. What are heterocyclic compounds? Give two examples.
- Heterocyclic compounds are organic compounds containing rings that include atoms other than carbon, such as nitrogen, oxygen, or sulfur.
- Examples: Pyridine and furan.
14. Why are benzene and other homologous compounds of benzene called aromatic compounds?
- Benzene and its homologs are called aromatic compounds because they contain a conjugated system of pi electrons that are delocalized over the ring structure, making them stable and often having a distinct aroma.
Extensive Questions:
1. (a) How is coal formed? What are the different types of coal?
- Coal formation occurs from dead plant material that is buried and subjected to high pressure and temperature over millions of years.
- Types of coal:
- Peat
- Lignite
- Bituminous coal
- Anthracite
1. (b) Write down the composition and uses of different types of coal.
- Peat: Low carbon, used as a fuel in some regions.
- Lignite: 25-35% carbon, used for electricity generation.
- Bituminous coal: 45-86% carbon, used in industry and electricity generation.
- Anthracite: Over 86% carbon, used for heating.
2. What is destructive distillation of coal?
- Destructive distillation is the process of heating coal in the absence of air to break it down into products like coke, coal tar, and ammonia.
3. Write a detailed note on functional groups of alkenes and alkynes. How are they identified from other compounds?
- Alkenes contain a carbon-carbon double bond (C=C), while alkynes have a carbon-carbon triple bond (C≡C).
- They can be identified by their unsaturation, which gives them characteristic reactions like addition reactions.
4. Give some uses of organic compounds in our daily life.
- Organic compounds are used in medicines, food additives, fuels, and cosmetics.
5. Write down the characteristics of homologous series.
- Homologous series have similar structures, gradual variation in physical properties, and the same functional group.
6. Why are organic compounds numerous?
- The catenation ability of carbon, along with various functional groups, allows for the formation of a vast array of compounds.
7. What are amines? Explain the different types of amines giving an example of each type.
- Amines are organic derivatives of ammonia, classified as:
- Primary amines (R-NH₂): e.g., Methylamine.
- Secondary amines (R₂-NH): e.g., Dimethylamine.
- Tertiary amines (R₃-N): e.g., Trimethylamine.
8. Describe the functional group of an alcohol. How are alcoholic groups identified?
- Alcohol functional group: -OH (hydroxyl group).
- Identified by their reaction with sodium, forming hydrogen gas, or by oxidation to carbonyl compounds.
9. Differentiate between aldehydic and ketonic functional groups. How are both identified from each other?
- Aldehydes (R-CHO) have the carbonyl group at the end of the carbon chain, while ketones (R-CO-R’) have the carbonyl group within the chain.
- Tests: Tollens’ test gives a silver mirror with aldehydes but not with ketones.
10. Identify the functional groups in the following compounds. Also give the names of the functional groups:
- Vinegar: Carboxylic acid (-COOH)
- Ant sting: Formic acid (HCOOH)
- Citrus fruit: Citric acid (carboxylic acid groups)
- Sour milk: Lactic acid (carboxylic and hydroxyl groups)Here are the answers to the exercise questions as per the given numbering:
