Question 8(2019)
Identify the substances italicised : The organic compound which when solidified, forms an ice like mass.
Glacial acetic acid
Key Concepts Covered
This question tests your understanding of the following concepts from the chapter Organic Chemistry: Question, Substances, Italicised, Organic, Compound, Solidified. These are fundamental topics in Chemistry that students are expected to master as part of the ICSE Class 10 curriculum.
A thorough understanding of these concepts will help you answer similar questions confidently in your ICSE examinations. These topics are frequently tested in both objective and subjective sections of Chemistry papers. We recommend revising the relevant section of your textbook alongside practising these solved examples to build a strong foundation.
How to Approach This Question
Read the question carefully and identify what is being asked. Break down complex questions into smaller parts. Use the terminology and concepts discussed in this chapter. Structure your answer logically — begin with a definition or key statement, then provide supporting details. Review your answer to ensure it addresses all parts of the question completely.
Key Points to Remember
- Balance chemical equations before solving numerical problems.
- Learn the periodic table trends and exceptions.
- Understand reaction mechanisms, not just outcomes.
- Use correct IUPAC nomenclature in your answers.
Practice more questions from Organic Chemistry — Chemistry, Class 10 ICSE
Chapter Overview: Organic Chemistry
Organic Chemistry is the study of carbon compounds. Carbon's unique ability to form four covalent bonds and catenate (form long chains) makes organic chemistry vast and diverse. The ICSE syllabus covers hydrocarbons (alkanes, alkenes, alkynes), their nomenclature (IUPAC), structural formulae, isomerism, and characteristic reactions. Alkanes (CnH2n+2) are saturated hydrocarbons that undergo substitution reactions. Alkenes (CnH2n) and alkynes (CnH2n−2) are unsaturated and undergo addition reactions. Students learn homologous series, functional groups, and the distinction between saturated and unsaturated compounds. The chapter introduces alcohols (with −OH group) and carboxylic acids (with −COOH group) as basic functional group chemistry. Students must write structural formulae, name compounds using IUPAC rules, and understand reactions like combustion, substitution, and addition. Practical tests like decolourising bromine water or acidified KMnO4 to distinguish between saturated and unsaturated compounds are important.
Key Concepts & Homologous Series
| Term / Series | Details |
|---|---|
| Catenation | Ability of carbon to form bonds with other carbon atoms, creating chains and rings |
| Homologous Series | Family of compounds with same general formula and functional group, differing by CH2 |
| Alkanes | CnH2n+2; single bonds only; saturated (e.g., CH4, C2H6) |
| Alkenes | CnH2n; one C=C double bond; unsaturated (e.g., C2H4, C3H6) |
| Alkynes | CnH2n−2; one C≡C triple bond; unsaturated (e.g., C2H2, C3H4) |
| Isomerism | Compounds with same molecular formula but different structural arrangements |
| Functional Group | Atom or group responsible for characteristic chemical properties (−OH, −COOH, C=C) |
| IUPAC Naming | Prefix (substituent) + Root (chain length) + Suffix (functional group) |
Must-Know Concepts
- Carbon prefixes: Meth- (1C), Eth- (2C), Prop- (3C), But- (4C), Pent- (5C)
- Combustion: CH4 + 2O2 → CO2 + 2H2O (complete); 2CH4 + 3O2 → 2CO + 4H2O (incomplete)
- Substitution: CH4 + Cl2 → CH3Cl + HCl (in presence of UV light)
- Addition: C2H4 + Br2 → C2H4Br2 (ethene decolourises bromine water)
- Unsaturated compounds decolourise bromine water and acidified KMnO4; saturated compounds do not
- Ethanol: C2H5OH; Ethanoic acid: CH3COOH (vinegar); Ester: CH3COOC2H5 (fruity smell)
- Isomers of butane (C4H10): n-butane and isobutane (2-methylpropane)
Saturated vs Unsaturated Hydrocarbons
| Feature | Saturated (Alkanes) | Unsaturated (Alkenes/Alkynes) |
|---|---|---|
| Bonds | Only single bonds (C−C) | Double (C=C) or triple (C≡C) bonds |
| Typical Reaction | Substitution | Addition |
| Bromine Water | No decolourisation | Decolourised |
| Combustion | Clean blue flame | Smoky/luminous flame (higher C%) |
Important Diagrams to Practice
- Structural formulae of first five members of alkanes, alkenes, and alkynes
- Isomers of butane and pentane with structural formulae
- Laboratory preparation of ethylene from ethanol (dehydration)
Common Mistakes
- Writing wrong general formulae (alkenes are CnH2n, NOT CnH2n+2)
- Confusing substitution (alkanes) with addition (alkenes) reactions
- Not showing all bonds in structural formulae
- IUPAC naming errors: not selecting the longest carbon chain or wrong numbering
- Forgetting conditions (UV light for substitution, Ni catalyst for hydrogenation)
Scoring Tips
- Draw clear structural formulae showing every C-H and C-C bond
- For IUPAC naming: identify longest chain, number from the end nearest to substituent/functional group
- Always mention conditions (catalyst, temperature, UV) in reaction equations
- Practice writing isomers for C4H10, C5H12, and C4H8
Frequently Asked Questions
Why is carbon's chemistry so vast?
Carbon has four valence electrons and can form four strong covalent bonds. Its small size allows strong C-C bonds, enabling catenation (long chains, branches, rings). This versatility leads to millions of organic compounds.
How do you test whether a hydrocarbon is saturated or unsaturated?
Add bromine water to the hydrocarbon. If the orange-brown colour of bromine water is decolourised, the compound is unsaturated (alkene or alkyne). If the colour persists, it is saturated (alkane).
What is the difference between structural isomers?
Structural isomers have the same molecular formula but different structural arrangements of atoms. For example, n-butane has a straight chain while isobutane (2-methylpropane) has a branched chain. They have different physical properties despite the same formula.