Class 10 Chemistry — Chapter 08: Organic Chemistry

Board: Federal Board

1. Multiple Choice Questions (MCQs)

i. Which of the following correctly represents the formula for but-2-ene?

a) \(\mathrm{CH_3CH=CHCH_3}\)
b) \(\mathrm{CH_2=CHCH_2CH_3}\)
c) \(\mathrm{CH_3CH_2CH=CH_2}\)
d) \(\mathrm{CH_3C\equiv CCH_3}\)

Correct Answer: a) \(\mathrm{CH_3CH=CHCH_3}\)

Concept: But-2-ene is an alkene containing four carbon atoms, with the double bond located between carbon-2 and carbon-3.

ii. Given the molecular formula \(\mathrm{C_4H_{10}O}\), which compound is most likely to be represented by this formula?

a) Butanoic acid
b) Butan-1-ol
c) But-2-ene
d) Butanal

Correct Answer: b) Butan-1-ol

Concept: Saturated monohydric alcohols follow the general formula \(\mathrm{C_nH_{2n+1}OH}\) (or \(\mathrm{C_nH_{2n+2}O}\)). For \(n=4\), this corresponds to \(\mathrm{C_4H_{10}O}\) (butanol).

iii. Which of the following is the correct IUPAC name for the compound with the formula \(\mathrm{CH_3CH_2CH_2COOH}\)?

a) Butanoic acid
b) Propanoic acid
c) Butanal
d) Butanol

Correct Answer: a) Butanoic acid

Concept: The carbon chain has four carbon atoms in total, including the carbonyl carbon of the \(\mathrm{-COOH}\) group. The suffix for carboxylic acids is “-oic acid”.

iv. Identify the statement which is true regarding propan-1-ol and propan-2-ol.

a) Both have identical condensed structural formula.
b) They have the same molecular formula.
c) They are different compounds with the same structural formula.
d) Propan-1-ol is a carboxylic acid, and propan-2-ol is an ester.

Correct Answer: b) They have the same molecular formula.

Concept: Propan-1-ol and propan-2-ol are position isomers. They share the same molecular formula \(\mathrm{C_3H_8O}\) but differ in the position of the \(\mathrm{-OH}\) functional group on the carbon chain.

v. Name the compound that can be formed by the esterification of methanol and propanoic acid.

a) Methyl propanoate
b) Propyl methanoate
c) Ethyl propanoate

Correct Answer: a) Methyl propanoate

Concept: In ester naming, the alkyl group comes from the alcohol (methanol → methyl), and the carboxylate part comes from the acid (propanoic acid → propanoate).

vi. Which of the following molecules contains an \(\mathrm{-OH}\) functional group?

a) Butane
b) Ethene
c) Butan-1-ol
d) But-2-yne

Correct Answer: c) Butan-1-ol

Concept: Alcohols contain the hydroxyl functional group (\(\mathrm{-OH}\)). Butan-1-ol is a primary alcohol.

vii. If a compound ends in “-oic acid”, what functional group must it contain?

a) \(\mathrm{-OH}\)
b) \(\mathrm{-COOH}\)
c) \(\mathrm{-C=O}\)
d) \(\mathrm{-C\equiv C-}\)

Correct Answer: b) \(\mathrm{-COOH}\)

Concept: The suffix “-oic acid” designates carboxylic acids, characterized by the carboxyl group (\(\mathrm{-COOH}\)).

viii. Which formula corresponds to an ester that could be formed from butan-1-ol and ethanoic acid?

a) \(\mathrm{CH_3CH_2CH_2CH_2COOCH_3}\)
b) \(\mathrm{CH_3COOCH_2CH_2CH_2CH_3}\)
c) \(\mathrm{CH_3CH_2CH_2CH_2COOH}\)
d) \(\mathrm{CH_3CH_2COOCH_3}\)

Correct Answer: b) \(\mathrm{CH_3COOCH_2CH_2CH_2CH_3}\)

Concept: Ethanoic acid provides the \(\mathrm{CH_3CO-}\) acyl group, and butan-1-ol provides the \(\mathrm{-CH_2CH_2CH_2CH_3}\) alkyl group.

ix. Which structural formula represents butan-1-ol?

a) \(\mathrm{CH_3CH_2CH_2CH_2OH}\)
b) \(\mathrm{CH_3CH_2CH_2COOH}\)
c) \(\mathrm{CH_3CH_2CH=CH_2}\)
d) \(\mathrm{CH_3CH=CHCH_3}\)

Correct Answer: a) \(\mathrm{CH_3CH_2CH_2CH_2OH}\)

Concept: Butan-1-ol is a straight-chain four-carbon primary alcohol with the hydroxyl group at carbon-1.

x. Identify the compound based on the following information: It has the formula \(\mathrm{C_3H_8O}\) and the name ends with “-ol”.

a) Propanoate
b) Propan-2-ol
c) Propane
d) Propanoic acid

Correct Answer: b) Propan-2-ol

Concept: A three-carbon alcohol with formula \(\mathrm{C_3H_8O}\) ending in “-ol” is either propan-1-ol or propan-2-ol.

xi. Which of the following names is incorrect for the given formula?

a) But-2-ene: \(\mathrm{CH_3CH=CHCH_3}\)
b) But-1-ene: \(\mathrm{CH_2=CHCH_2CH_3}\)
c) Butane: \(\mathrm{CH_3CH_2CH_2CH_3}\)
d) Butan-2-ol: \(\mathrm{CH_3CH(OH)CH_2CH_3}\)

Answer: All provided name-formula pairings match standard IUPAC conventions. The supplied material does not identify an incorrect option.

2. Short Answer Questions

i. Define the term displayed structural formula in organic chemistry.

Answer: A displayed structural formula shows every individual atom and every covalent bond explicitly in a two-dimensional layout, using lines to represent shared electron pairs (single, double, or triple bonds). It clearly portrays the exact connectivity of all atoms in the molecule.

ii. Explain the difference between an alkane and an alkene.

Alkane: A saturated hydrocarbon containing only single covalent bonds (\(\mathrm{C-C}\) and \(\mathrm{C-H}\)) with the general formula:

Alkene: An unsaturated hydrocarbon containing at least one carbon-carbon double bond (\(\mathrm{C=C}\)) with the general formula:

iii. How can you distinguish between an alcohol and a carboxylic acid by their structural formulae?

Alcohol: Contains a hydroxyl group (\(\mathrm{-OH}\)) attached to a saturated carbon atom.

Carboxylic Acid: Contains a carboxyl functional group (\(\mathrm{-COOH}\)), where a carbonyl group (\(\mathrm{-C=O}\)) and a hydroxyl group (\(\mathrm{-OH}\)) are bonded to the same carbon atom.

iv. Write the name for \(\mathrm{CH_3-CH_2-CH_2-CH_2-OH}\).

Answer: Butan-1-ol (or 1-butanol).

v. Describe the process of esterification.

Answer: Esterification is a condensation reaction in which a carboxylic acid reacts with an alcohol in the presence of an acid catalyst (such as concentrated sulfuric acid, \(\mathrm{H_2SO_4}\)) under heat to form an ester and water.

vi. Given the condensed structural formula \(\mathrm{CH_3CH_2CH_3}\), what is the displayed structural formula?

Answer: The compound is propane (\(\mathrm{C_3H_8}\)). Its displayed formula explicitly shows all single bonds:

        H       H       H
        |       |       |
    H - C  -  C  -  C - H
        |       |       |
        H       H       H

vii. Give displayed structural formulae for (i) Ethanol and (ii) Ethanoic acid.

(i) Ethanol (\(\mathrm{CH_3CH_2OH}\)):

        H       H
        |       |
    H - C  -  C - O - H
        |       |
        H       H

(ii) Ethanoic acid (\(\mathrm{CH_3COOH}\)):

        H       O
        |       ||
    H - C  -  C - O - H
        |
        H

viii. Identify the type of organic compounds from the given names and give the normal structural formula of each compound.

a. Propyne

• Type: Alkyne (\(\mathrm{-C\equiv C-}\))

• Structure: \(\mathrm{CH_3-C\equiv CH}\)

b. Propanoic acid

• Type: Carboxylic acid (\(\mathrm{-COOH}\))

• Structure: \(\mathrm{CH_3-CH_2-COOH}\)

c. Propan-2-ol

• Type: Alcohol (\(\mathrm{-OH}\))

• Structure: \(\mathrm{CH_3-CH(OH)-CH_3}\)

d. Methyl propanoate

• Type: Ester (\(\mathrm{-COO-}\))

• Structure: \(\mathrm{CH_3-CH_2-COO-CH_3}\)

ix. Identify the type of compound given the name “but-2-ene”.

Answer: It is an alkene (an unsaturated hydrocarbon with a carbon-carbon double bond, \(\mathrm{C=C}\)).

x. Draw the structural formula of but-1-ene and but-2-ene and explain the difference between them.

Answer:

But-1-ene:

But-2-ene:

Difference: They are position isomers. They have the same molecular formula (\(\mathrm{C_4H_8}\)) but differ in the location of the double bond.

xi. Draw the displayed formula of ethyl butanoate.

Answer:

xii. Given the displayed formula \(\mathrm{CH_3COOCH_2CH_3}\), identify the alcohol and carboxylic acid used to form the ester.

Carboxylic Acid: Ethanoic acid (\(\mathrm{CH_3COOH}\))

Alcohol: Ethanol (\(\mathrm{CH_3CH_2OH}\))

xiii. From the displayed formula \(\mathrm{CH_3-C\equiv C-CH_3}\), identify the compound and its type.

Compound Name: But-2-yne

Compound Type: Alkyne (contains a carbon-carbon triple bond, \(\mathrm{-C\equiv C-}\)).

xiv. Design the synthesis pathway for converting butan-1-ol into but-1-ene.

Answer:

• Method: Acid-catalyzed dehydration.

• Condition: Heat butan-1-ol with concentrated sulfuric acid (\(\mathrm{H_2SO_4}\)) at \(170^\circ\mathrm{C}\).

• Equation:

3. Long Questions

i. Discuss the significance of functional groups in organic chemistry and provide examples.

Answer:

A functional group is a specific atom or group of atoms within organic molecules that dictates their chemical reactivity and physical properties, regardless of the length of the carbon chain.

Examples:

1. Hydroxyl group (\(\mathrm{-OH}\)): Found in alcohols (e.g., ethanol). It confers hydrogen bonding and solubility in water.

2. Carboxyl group (\(\mathrm{-COOH}\)): Found in carboxylic acids (e.g., ethanoic acid). It confers acidic properties.

3. Carbon-carbon double bond (\(\mathrm{-C=C-}\)): Found in alkenes (e.g., ethene). It undergoes addition reactions.

ii. How can you differentiate alkenes, alcohols, and carboxylic acids by looking at their structural formulae?

Alkenes: Contain a carbon-carbon double bond (\(\mathrm{-C=C-}\)) with no oxygen atoms.

Alcohols: Contain a hydroxyl group (\(\mathrm{-OH}\)) attached to a saturated carbon.

Carboxylic Acids: Contain a carboxyl group (\(\mathrm{-COOH}\)) with both a carbonyl (\(\mathrm{C=O}\)) and hydroxyl (\(\mathrm{OH}\)) group on the same carbon.

iii. Explain the reaction between an alcohol and a carboxylic acid to form an ester.

Answer:

• This reaction is known as esterification (a condensation reaction).

• The \(\mathrm{-OH}\) group from the carboxylic acid combines with the hydrogen atom from the alcohol’s hydroxyl group to form water (\(\mathrm{H_2O}\)).

• The remaining organic fragments bond together through an ester link (\(\mathrm{-COO-}\)) in the presence of concentrated \(\mathrm{H_2SO_4}\).

iv. Explain the chemical reaction process for forming esters from alcohols and carboxylic acids. Draw the structural and displayed formulas of the ester formed from ethanol and propanoic acid.

Answer:

Reactants:

• Propanoic acid: \(\mathrm{CH_3CH_2COOH}\)

• Ethanol: \(\mathrm{CH_3CH_2OH}\)

Products:

• Ethyl propanoate: \(\mathrm{CH_3CH_2COOCH_2CH_3}\)

• Water: \(\mathrm{H_2O}\)

Equation:

v. Given the esters methyl methanoate, ethyl ethanoate, and butyl butanoate, give the starting materials required to produce these esters.

Answer:

1. Methyl methanoate:

   • Methanoic acid (\(\mathrm{HCOOH}\))

   • Methanol (\(\mathrm{CH_3OH}\))

2. Ethyl ethanoate:

   • Ethanoic acid (\(\mathrm{CH_3COOH}\))

   • Ethanol (\(\mathrm{CH_3CH_2OH}\))

3. Butyl butanoate:

   • Butanoic acid (\(\mathrm{CH_3CH_2CH_2COOH}\))

   • Butan-1-ol (\(\mathrm{CH_3CH_2CH_2CH_2OH}\))

vi. Explain the significance of the suffixes -ane, -ene, -yne, -ol, and -oic acid in naming organic compounds. Provide examples of each with their molecular and displayed formulas.

Answer: Suffixes classify organic compounds into homologous series.

Structural formula examples:

• Ethane: \(\mathrm{CH_3-CH_3}\)

• Ethene: \(\mathrm{CH_2=CH_2}\)

• Ethyne: \(\mathrm{HC\equiv CH}\)

• Ethanol: \(\mathrm{CH_3-CH_2-OH}\)

• Ethanoic acid: \(\mathrm{CH_3-COOH}\)

vii. Compare the functional groups of esters and carboxylic acids. Use specific examples to illustrate your answer.

Answer:

Carboxylic acids (\(\mathrm{-COOH}\)): Contain an acidic hydrogen capable of dissociating into protons (\(\mathrm{H^+}\)). Example: ethanoic acid (\(\mathrm{CH_3COOH}\)).

Esters (\(\mathrm{-COO-}\)): Have the acidic hydrogen replaced by an alkyl group, resulting in neutral, sweet-smelling compounds. Example: methyl ethanoate (\(\mathrm{CH_3COOCH_3}\)).

viii. Develop a table that helps you to determine the type of organic compound based on its structural formula (having two carbon atoms) and functional groups.

4. Think Tank

i. Develop a flowchart or decision tree that helps students determine the type of organic compound based on its molecular formula and functional groups.

Decision Tree Logic:

1. Are oxygen atoms present?

• No: Check for unsaturation:

  • \(\mathrm{C=C}\) → Alkene

  • \(\mathrm{C\equiv C}\) → Alkyne

  • Only single bonds → Alkane

• Yes: Count oxygen atoms:

  • One oxygen atom: Check if it has an \(\mathrm{-OH}\) group (→ Alcohol / Ether) or a \(\mathrm{C=O}\) group.

  • Two oxygen atoms: Check for:

    • \(\mathrm{-COOH}\) → Carboxylic Acid

    • \(\mathrm{-COO-}\) → Ester

ii. Given the molecular formula \(\mathrm{C_3H_6O_2}\), draw all possible structural formulas and identify the type of compound.

Answer: The supplied material lists the following possible isomers and their types:

1. Propanoic Acid (Carboxylic Acid):

   \[
   \mathrm{CH_3-CH_2-COOH}
   \]

2. Methyl Ethanoate (Ester):

   \[
   \mathrm{CH_3-COO-CH_3}
   \]

3. Ethyl Methanoate (Ester):

   \[
   \mathrm{H-COO-CH_2-CH_3}
   \]

Notes by Sir Dilawar
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