Q1: What is the general formula for alkanes? (a) CₙH₂ₙ (b) CₙH₂ₙ₊₂ (c) CₙH₂ₙ₋₂ (d) CₙHₙ
Solution:
Ans: (b) Explanation: Alkanes are saturated hydrocarbons where all carbon valencies are fully satisfied with single bonds, giving them the general formula CₙH₂ₙ₊₂
Q2: Which property of carbon allows it to form chains of identical atoms? (a) Electronegativity (b) Tetravalency (c) Catenation (d) Combustibility
Solution:
Ans: (c) Explanation: Catenation is the tendency of carbon to form chains of identical atoms through self-linking, which is maximum in carbon due to high C-C bond energy.
Q3: What is the functional group present in carboxylic acids? (a) -OH (b) -CHO (c) -COOH (d) -CO-
Solution:
Ans: (c) Explanation: Carboxylic acids contain the carboxylic group (-COOH) as their functional group, which gives them their acidic character due to replaceable hydrogen.
Q4: Which reaction is used to prepare ethane from methyl iodide using sodium? (a) Substitution reaction (b) Addition reaction (c) Wurtz reaction (d) Cracking reaction
Solution:
Ans: (c) Explanation: The Wurtz reaction involves treating alkyl halides like methyl iodide with sodium to form higher alkanes, producing ethane from two methyl iodide molecules.
Q5: What type of isomerism occurs when compounds have the same molecular formula but different functional groups? (a) Chain isomerism (b) Position isomerism (c) Functional isomerism (d) Metamerism
Solution:
Ans: (c) Explanation: Functional isomerism occurs when two or more compounds possess the same molecular formula but contain different functional groups in their structures.
Fill in the Blanks
Q1: Carbon forms four covalent bonds and exhibits _____.
Solution:
Ans: tetravalency
Q2: Alkenes are also called _____ because they form oily products.
Solution:
Ans: olefins
Q3: The general formula of alkynes is _____.
Solution:
Ans: CₙH₂ₙ₋₂
Q4: Each member of a homologous series differs from the preceding one by _____ group.
Solution:
Ans: CH₂
Q5: Ethanol reacts with acetic acid to form ethyl acetate and water in a reaction called _____.
Solution:
Ans: esterification
True or False
Q1: Organic chemistry is the chemistry of all carbon compounds including oxides and carbonates.
Solution:
Ans: False Explanation: Organic chemistry studies specific carbon compounds except oxides, carbonates and carbides, which are excluded from this branch.
Q2: Methane can be prepared by adding water to aluminium carbide at room temperature.
Solution:
Ans: True Explanation: When aluminium carbide reacts with water at room temperature, it produces methane gas along with aluminium hydroxide as products.
Q3: Ethene molecule has all bond angles equal to 120 degrees.
Solution:
Ans: True Explanation: Ethene is a planar molecule where all bond angles, including H-C-H and H-C=C, are equal to 120 degrees.
Q4: Alkanes are more reactive than alkenes under ordinary conditions.
Solution:
Ans: False Explanation: Alkanes are relatively unreactive under ordinary conditions and are called paraffins, whereas alkenes are more reactive due to double bonds.
Q5: The hydroxyl group (-OH) is the functional group of alcohols.
Solution:
Ans: True Explanation: Alcohols are hydroxyl derivatives of alkanes where the hydroxyl group (-OH) serves as their characteristic functional group.
Match the Following
Column A
Column B
1. Hydrocarbons
A. Contains carbon-carbon triple bond
2. Alkenes
B. Maximum in carbon due to high C-C bond energy
3. Alkynes
C. Organic compounds with only carbon and hydrogen
4. Catenation
D. Group of compounds differing by CH₂ group
5. Homologous series
E. Contains carbon-carbon double bond
Solution:
Ans:
1 - C: Hydrocarbons are organic compounds composed entirely of carbon and hydrogen atoms only, such as methane and ethane.
2 - E: Alkenes are unsaturated aliphatic hydrocarbons that contain a carbon-carbon double bond with general formula CnH2n.
3 - A: Alkynes are unsaturated hydrocarbons containing a carbon-carbon triple bond, also called acetylenic linkage, with general formula CnH2n-2.
4 - B: Catenation is the tendency to form chains of identical atoms and is maximum in carbon due to maximum C-C bond energy.
5 - D: A homologous series is a group of organic compounds where successive compounds differ by a CH₂ group and 14 amu.
Short Answer Questions
Q1: Explain the concept of tetravalency in carbon and why it is important.
Solution:
Ans: Carbon exhibits tetravalency, meaning it forms four covalent bonds by mutually sharing its four valence electrons with other atoms. This property makes carbon tetravalent. The tetravalency of carbon, combined with catenation, allows it to form diverse organic compounds with single, double and triple bonds. This unique characteristic enables carbon to create straight, branched and closed chain structures, forming the basis of millions of organic compounds.
Q2: What are isomers? Explain with an example.
Solution:
Ans: Isomers are compounds that have the same molecular formula but different structural formulas, and this phenomenon is called isomerism. The differences arise from variations in the mode of linking atoms or the arrangement of atoms in space. For example, butane and isobutane both have the molecular formula C₄H₁₀ but possess different structural arrangements. They are two distinct compounds with different physical and chemical properties despite having identical molecular formulas.
Q3: Describe the characteristics of a homologous series.
Solution:
Ans: A homologous series shows several characteristics. Each member differs from the preceding one by a CH₂ group and 14 amu. All members share a general formula, like CₙH₂ₙ₊₂ for alkanes. Physical properties show gradation as molecular mass increases. Chemical properties exhibit gradient similarity, as methane and ethane both react with chlorine similarly. All members can be prepared by the same general method, such as preparing alcohols from alkyl halides.
Q4: How is ethanol prepared industrially? Describe one method.
Solution:
Ans: Ethanol is prepared industrially through two main methods. The first method is hydration of ethene, where ethene reacts with water in the presence of a catalyst to form ethanol. The second method is fermentation of carbohydrates, where sugars from materials like molasses or grains are broken down by enzymes in yeast under anaerobic conditions. This process converts carbohydrates into ethanol and carbon dioxide, making it economically viable for large-scale production.
Q5: What are the chemical properties of acetic acid when it reacts with alkalis?
Solution:
Ans: Acetic acid is a weak acid that reacts with alkalis to form salt and water through neutralisation reactions. When acetic acid reacts with sodium hydroxide, it produces sodium acetate and water. Similarly, when it reacts with ammonium hydroxide, it forms ammonium acetate and water. These reactions demonstrate the acidic nature of acetic acid as it neutralises basic substances. The reactions are typical acid-base reactions showing the chemical behaviour of carboxylic acids.
Long Answer Questions
Q1: Analyse the structure and bonding in ethene. Explain how its structure influences its chemical reactivity compared to alkanes.
Solution:
Ans: Ethene has two carbon atoms linked by a double covalent bond formed by sharing two pairs of electrons. It contains four C-H single bonds and one C=C double bond. The molecule is planar with all bond angles equal to 120 degrees. This structure makes ethene more reactive than alkanes because the double bond is a region of high electron density. Alkanes have only single bonds and are saturated, making them relatively unreactive under ordinary conditions. Ethene readily undergoes addition reactions where the double bond breaks, allowing new atoms to attach, whereas alkanes primarily undergo substitution reactions.
Q2: Compare and contrast chain isomerism and position isomerism. Justify your answer with appropriate reasoning about their causes.
Solution:
Ans: Chain isomerism occurs when compounds have the same molecular formula but different arrangements of carbon atoms in straight or branched chains. The carbon skeleton itself differs between isomers. Position isomerism occurs when compounds have the same molecular formula but differ in the position of a substituent atom or functional group on the carbon chain. The carbon skeleton remains the same but the location of groups varies. Both arise from differences in atomic arrangement, but chain isomerism involves structural framework changes while position isomerism involves location changes. These differences significantly affect physical and chemical properties of compounds.
Q3: Evaluate the significance of homologous series in the systematic study of organic compounds. How does it help predict properties?
Solution:
Ans: Homologous series are significant because they enable systematic study of organic compounds by grouping similar compounds together. Members share similar structures and chemical properties, making it easier to understand patterns. The series helps predict properties of unknown members if properties of first few members are known, reducing experimental work. Since physical properties show gradation with increasing molecular mass, interpolation becomes possible. Chemical properties remain similar throughout the series, allowing prediction of reactions. All members can be prepared by similar methods, providing systematic synthetic approaches. This organization simplifies the vast field of organic chemistry considerably.
The document Worksheet with Solutions: Organic Chemistry - Hydrocarbons is a part of the Class 10 Course Chemistry Class 10 ICSE.
FAQs on Worksheet with Solutions: Organic Chemistry - Hydrocarbons
1. What are hydrocarbons?
Ans. Hydrocarbons are organic compounds that consist entirely of hydrogen and carbon atoms. They are the fundamental building blocks of organic chemistry and can be classified into aliphatic hydrocarbons (which include alkanes, alkenes, and alkynes) and aromatic hydrocarbons.
2. What is the general formula for alkanes?
Ans. The general formula for alkanes is CₙH₂ₙ₊₂, where n represents the number of carbon atoms in the molecule. Alkanes are saturated hydrocarbons, meaning they contain only single bonds between carbon atoms.
3. How are alkenes different from alkanes?
Ans. Alkenes are unsaturated hydrocarbons that contain at least one double bond between carbon atoms, whereas alkanes are saturated hydrocarbons with only single bonds. The general formula for alkenes is CₙH₂ₙ.
4. What is the significance of the structural isomerism in hydrocarbons?
Ans. Structural isomerism in hydrocarbons occurs when compounds have the same molecular formula but different structural arrangements of atoms. This leads to variations in physical and chemical properties, making it significant in understanding the diverse nature of organic compounds.
5. Can you explain the process of cracking in relation to hydrocarbons?
Ans. Cracking is the process of breaking down larger hydrocarbon molecules into smaller, more useful ones, often through the application of heat or catalysts. This is important in the petroleum industry to convert heavy oils into lighter fractions like petrol and diesel.
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