Chapter 13: Organic Chemistry

1. Encircle the correct answer.

(i) Condensed structural formula for butane is

(a) CH₃ - CH₂ - CH₃

(b) CH₃ - CH₂ - CH₂ - CH₃

(c) CH₃ - CH₂ - CH₂ - CH₂ - CH₃

(d) CH₃ - CH₃

Answer: (b) CH₃ - CH₂ - CH₂ - CH₃

Explanation: Butane has four carbon atoms. Its condensed structural formula is CH₃-CH₂-CH₂-CH₃.

(ii) CH₃ - CH₂ - CH₃ is the chemical formula for

(a) Ethane

(b) Propane

(c) Butane

(d) Pentane

Answer: (b) Propane

Explanation: The formula CH₃-CH₂-CH₃ has three carbon atoms, which corresponds to propane.

(iii) Which compound is not a saturated hydrocarbon?

(a) CH₄

(b) C₂H₆

(c) CH₂=CH₂

(d) CH₃ - CH₂ - CH₃

Answer: (c) CH₂=CH₂

Explanation: Saturated hydrocarbons contain only single bonds (alkanes). CH₂=CH₂ (ethene) contains a double bond, making it an unsaturated hydrocarbon (alkene).

(iv) Stem "But" stands for how many Carbon atoms.

(a) 2

(b) 3

(c) 4

(d) 5

Answer: (c) 4

Explanation: The prefix "But-" in organic nomenclature indicates a chain of four carbon atoms (e.g., butane, butene, butanol).

(v) The functional group C=O is found in.

(a) Alcohols

(b) Ketones

(c) Carboxylic acids

(d) Esters

Answer: (b) Ketones

Explanation: The carbonyl group (C=O) is the functional group found in both aldehydes and ketones. In ketones, the carbonyl carbon is bonded to two carbon atoms (R-CO-R').

(vi) In which of the following compounds, oxygen is attached to two alkyl carbon atoms?

(a) Alcohol

(b) Phenol

(c) Ether

(d) Ester

Answer: (c) Ether

Explanation: In an ether (R-O-R'), the oxygen atom is bonded to two alkyl or aryl carbon atoms.

(vii) Which of the following is an alcohol?

(a) CH₃ - CH₂ - O - CH₂ - CH₃

(b) CH₃ - CH₂ - COOH

(c) C₂H₅ - OH

(d) CH₃ - CH₂ - OH

Answer: (c) C₂H₅ - OH and (d) CH₃ - CH₂ - OH (Both are alcohols, as they contain the -OH functional group. Option (c) is ethanol and option (d) is also ethanol.)

(viii) The functional group of amines is

(a) -OH

(b) -COOH

(c) -NH₂

(d) -CHO

Answer: (c) -NH₂

Explanation: The amino group (-NH₂) is the functional group of amines.

(ix) Ethanoic acid contains functional group

(a) -OH

(b) -CO

(c) -COOH

(d) -CHO

Answer: (c) -COOH

Explanation: Ethanoic acid (CH₃COOH) contains the carboxyl group (-COOH).

2. Give short answer.

(i) What is catenation?

Answer: Catenation is the ability of an atom to form covalent bonds with other atoms of the same element, creating long chains or rings. Carbon exhibits strong catenation due to its small size and the high strength of C-C bonds. This property allows carbon to form millions of different organic compounds with diverse structures.

(ii) Define Isomerism.

Answer: Isomerism is the phenomenon where two or more compounds have the same molecular formula but different structural formulas or spatial arrangements of atoms. These compounds are called isomers. They have different physical and chemical properties. Isomerism is common in organic chemistry due to the tetravalency of carbon.

(iii) Give three examples of unsaturated compound.

Answer: Three examples of unsaturated compounds:

1. Ethene (C₂H₄): Contains a carbon-carbon double bond.

2. Ethyne (C₂H₂): Contains a carbon-carbon triple bond.

3. But-2-ene (C₄H₈): Contains a carbon-carbon double bond.

(iv) Define a functional group.

Answer: A functional group is a specific group of atoms within a molecule that is responsible for the characteristic chemical reactions of that molecule. It determines the physical and chemical properties of the compound and allows us to classify organic compounds into families (e.g., alcohols, aldehydes, carboxylic acids).

(v) What is the difference between an alkane and an alkyne?

Answer:

3. Identify the following compounds on the basis of functional groups they contain and encircle the functional group.

CH₃-CH=CH₂, CH₃-CH₂-COOH, CH₃-C(=O)-CH₃, CH₃-CH₂-CHO, CH₃-CH₂-O-CH₂-CH₃, H-C(=O)-OH

Answer:

CH₃-CH=CH₂: Alkene (Functional group: C=C) CH₃-CH₂-COOH: Carboxylic acid (Functional group: -COOH)

CH₃-C(=O)-CH₃: Ketone (Functional group: -CO-) CH₃-CH₂-CHO: Aldehyde (Functional group: -CHO) CH₃-CH₂-O-CH₂-CH₃: Ether (Functional group: -O-)

H-C(=O)-OH: Carboxylic acid (Functional group: -COOH)

4. What is the name of alkane having four carbon atoms in the chain?

Answer: The alkane having four carbon atoms in the chain is butane (C₄H₁₀). Its IUPAC name is butane. It has two isomers: n-butane and isobutane (2-methylpropane).

5. Give the structural formula of two simple alkanes and one alkyne.

Answer:

Alkane 1 (Methane): CH₄ Alkane 2 (Ethane): CH₃-CH₃ Alkyne (Ethyne): H-C[source symbol unavailable]C-H

6. What is meant by the term functional group? (Refer to Question 2(iv))

7. Identify the type of following compounds as an alcohol, aldehyde or ketone:

(a) HCHO, which is used to manufacture polymers, such as urotropine which is used to treat urinary tract infection.

Answer: HCHO is formaldehyde, which is an aldehyde.

(b) CH₃COCH₃, which is used in nail polish remover.

Answer: CH₃COCH₃ is acetone, which is a ketone.

(c) CH₃CH₂OH, which is used in the preparation of many organic substances such as plastics, cosmetics, tinctures etc.

Answer: CH₃CH₂OH is ethanol, which is an alcohol.

8. Give molecular formula of a compound containing C, H and O and single bonds. List all the possible functional groups this compound can have?

Answer: A compound containing C, H, and O with only single bonds could be an alcohol or an ether.

Molecular Formula Example: C₂H₆O

Possible Functional Groups:

Alcohol: -OH (e.g., ethanol, CH₃CH₂OH) Ether: -O- (e.g., dimethyl ether, CH₃OCH₃)

9. Give the condensed structural formulas of the following compounds and classify each on the basis of functional group.

(a) (Diagram of a molecule with a C=C double bond and an -OH group)

Answer: The compound is CH₂=CH-OH (ethenol). Functional group: Alcohol (and alkene).

(b) (Diagram of a molecule with an -O- linkage)

Answer: The compound is CH₃-O-CH₃ (dimethyl ether). Functional group: Ether.

10. The diagram represents an organic compound that contains three different elements. (Diagram: X-X-X-Y-Z-X, where X, Y, Z are different elements)

Answer: The compound contains three different elements (X, Y, Z). Based on the structure, it could be an organic compound with functional groups containing Y and Z. For example, if Y is O and Z is H, it could be an alcohol. If Y is O and Z is another carbon chain, it could be an ether.

11. Vinyl chloride (PVC) is a polymer. It is used for making vinyl sheets, drainage pipes, wire insulation etc. It is obtained from vinyl chloride.

(Diagram: H₂C=CHCl) Classify Vinyl chloride as saturated or unsaturated compound.

Answer: Vinyl chloride (CH₂=CHCl) contains a carbon-carbon double bond. Therefore, it is an unsaturated compound.

12. For each of the following, sketch the structural formulas of a two-carbon compound containing the indicated functional group.

(a) alcohol

Answer: CH₃-CH₂-OH (Ethanol)

(b) aldehyde

Answer: CH₃-CHO (Ethanal)

(c) carboxylic acid

Answer: CH₃-COOH (Ethanoic acid)

(d) alkene

Answer: CH₂=CH₂ (Ethene)

13. Aspirin is a mild painkiller and fever reducer. It is manufactured from salicylic acid. (Diagram of salicylic acid with -COOH and -OH groups) Select functional groups present in it and encircle them. Justify your selection.

Answer: The functional groups present in salicylic acid are:

Carboxyl group (-COOH): Responsible for its acidic properties. Hydroxyl group (-OH): A phenolic hydroxyl group, which contributes to its reactivity. These groups are circled on the benzene ring structure.

18. Construct the general formula for an alkane, an alkene, alkyne and an alcohol containing 4 carbon atoms.

Answer:

Alkane (C₄H₁₀): CH₃-CH₂-CH₂-CH₃ (Butane)

Alkene (C₄H₈): CH₂=CH-CH₂-CH₃ (But-1-ene)

Alkyne (C₄H₆): HC[source symbol unavailable]C-CH₂-CH₃ (But-1-yne) Alcohol (C₄H₉OH): CH₃-CH₂-CH₂-CH₂-OH (Butan-1-ol)

19. Water adds to ethene according to the following reaction

CH₂=CH₂ + H₂O [source symbol unavailable] CH₃CH₂OH Compare the functional groups in the reactant and product molecules.

Answer:

Reactant (Ethene): Contains a carbon-carbon double bond (C=C), which is the functional group of alkenes. Product (Ethanol): Contains a hydroxyl group (-OH), which is the functional group of alcohols. The reaction converts an alkene (unsaturated) into an alcohol (saturated with an -OH group).

CONCEPT ASSESSMENT EXERCISE 13.1

Write the molecular formulae of the following compounds using general formulae

1. Alkane containing (i) 4 carbon atoms (ii) 6 carbon atoms

Answer: General formula: CₙH₂ₙ₊₂

(i) C₄H₁₀ (Butane)

(ii) C₆H₁₄ (Hexane)

2. Alkene containing (i) 3 carbon atoms (ii) 4 carbon atoms

Answer: General formula: CₙH₂ₙ

(i) C₃H₆ (Propene)

(ii) C₄H₈ (Butene)

3. Alkyne containing (i) 3 carbon atoms (ii) 4 carbon atoms

Answer: General formula: CₙH₂ₙ₋₂

(i) C₃H₄ (Propyne)

(ii) C₄H₆ (Butyne)

4. Alcohol containing (i) 2 carbon atoms (ii) 3 carbon atoms

Answer: General formula: CₙH₂ₙ₊₁OH

(i) C₂H₅OH (Ethanol)

(ii) C₃H₇OH (Propanol)

CONCEPT ASSESSMENT EXERCISE 13.2

Give the molecular, structural and condensed structural formulas for

(a) Butane

Answer:

Molecular Formula: C₄H₁₀ Structural Formula: CH₃-CH₂-CH₂-CH₃ (full displayed structure with all bonds) Condensed Structural Formula: CH₃CH₂CH₂CH₃

(b) Hexane

Answer: Molecular Formula: C₆H₁₄ Structural Formula: CH₃-CH₂-CH₂-CH₂-CH₂-CH₃ Condensed Structural Formula: CH₃(CH₂)₄CH₃

(c) Octane

Answer: Molecular Formula: C₈H₁₈

Structural Formula: CH₃-CH₂-CH₂-CH₂-CH₂-CH₂-CH₂-CH₃ Condensed Structural Formula: CH₃(CH₂)₆CH₃

CONCEPT ASSESSMENT EXERCISE 13.3

Choose saturated and unsaturated compounds from the following.

(i) CH₃-CH₂-CH₃

Answer: Saturated (Alkane)

(ii) CH₃-C[source symbol unavailable]CH

Answer: Unsaturated (Alkyne)

(iii) CH₃-CH=CH₂

Answer: Unsaturated (Alkene)

(iv) CH₂=CH-CH=CH₂

Answer: Unsaturated (Diene)

CONCEPT ASSESSMENT EXERCISE 13.4

A to E are the structural formulas of some organic compounds. (Diagrams A to E showing different carbon skeletons) Give the letters which represents

1. A branched chain compound.

Answer: E (The structure has a branch on the main chain).

2. A cyclic compound.

Answer: C (The structure is a ring).

3. Two straight chain compounds.

Answer: A and B (Both have unbranched carbon chains).

CONCEPT ASSESSMENT EXERCISE 13.5

Classify the following compound as alcohol, ether or phenol.

(a) CH₃CH₂OCH₂CH₃

Answer: Ether (Diethyl ether)

(b) CH₃CH₂CH₂OH

Answer: Alcohol (Propan-1-ol)

(c) C₆H₅OH

Answer: Phenol (Benzenol)

(d) C₂H₅OH

Answer: Alcohol (Ethanol)

CONCEPT ASSESSMENT EXERCISE 13.6

Identify the following compounds as an aldehyde, or a ketone or a carboxylic acid.

(a) CH₃COCH₂CH₃

Answer: Ketone (Butanone)

(b) CH₃CH₂CH(=O)

Answer: Aldehyde (Propanal)

(c) CH₃CH₂COOH

Answer: Carboxylic acid (Propanoic acid)

Prepare a chart showing differences between organic and inorganic compounds.

Answer: (Guide for the project)

Title: Organic vs. Inorganic Compounds. Section 1: Organic Compounds

Definition: Compounds containing carbon, usually with hydrogen. Examples: Methane, ethanol, glucose, proteins. Properties: Covalent bonding, low melting/boiling points, generally flammable, soluble in organic solvents, slow reactions.

Section 2: Inorganic Compounds

Definition: Compounds generally lacking carbon-hydrogen bonds. Examples: Water, salts, metals, minerals. Properties: Ionic or covalent bonding, high melting/boiling points, generally non-flammable, soluble in water, fast reactions.

Comparison Table: Include a table comparing bonding, solubility, conductivity, melting/boiling points, and reactivity. Visuals: Use images of organic products (e.g., plastic, food) and inorganic products (e.g., salt, water, metals) to illustrate the differences.