Chemistry Notes – Grade 10
National Curriculum Pakistan - NCP
Chapter 8: Organic Compounds
Aligned with National Curriculum Pakistan (Federal Board, NBF, PTB)
Organic Compounds Questions and Answers
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Why is the carbon in the carboxylic acid group always numbered as carbon-1 in the IUPAC naming system?
In carboxylic acids, the carboxyl group (-COOH) is the principal functional group, and IUPAC rules require assigning it the lowest number. It is always carbon-1 to ensure consistency and clarity in naming. -
How does the structure of a carboxylic acid determine its name, and what changes are made to the name of the corresponding alkane?
The name is based on the longest chain containing the -COOH group. The “-e” of the parent alkane is replaced with “-oic acid” to indicate the presence of the carboxylic acid group. -
Why do carboxylic acids have both common names and IUPAC names, and how do they differ?
Common names are traditional and based on source or history, while IUPAC names follow a standardized system. For example, acetic acid is the common name, while ethanoic acid is the IUPAC name. -
What is esterification, and why is a catalyst like dilute sulfuric acid used in this reaction?
Esterification is the reaction between a carboxylic acid and an alcohol to form an ester and water. Dilute sulfuric acid acts as a catalyst and removes water to drive the reaction forward. -
How is the name of an ester determined, and what does each part of the name represent?
An ester’s name combines the alcohol-derived alkyl group and the acid-derived part with “-oate” suffix. For example, methyl ethanoate comes from methanol and ethanoic acid. -
Why do esters typically have pleasant or fruity smells, and what is their relevance in real-world applications?
Esters have molecular structures that interact with olfactory receptors to produce fruity aromas. They are widely used in perfumes, food flavorings, and cosmetics. -
Why does CH₃CH₂COOH react with CH₃OH to form an ester instead of simply mixing?
They undergo a chemical reaction: CH₃CH₂COOH and CH₃OH form methyl propanoate and water. This esterification changes both the structure and properties of the reactants. -
How does the presence of the carboxyl group affect the physical and chemical properties of a compound?
The -COOH group increases polarity and allows hydrogen bonding, making the compound soluble and acidic. It also makes the compound reactive in forming esters and salts. -
What is the name and structural formula of an alkane containing 5 carbon atoms?
The alkane with 5 carbon atoms is called pentane. Its structural formula is CH₃–CH₂–CH₂–CH₂–CH₃, a straight-chain saturated hydrocarbon. -
Write the name and structural formula of an alkene with 6 carbon atoms and a double bond starting on the third carbon.
The compound is named hex-3-ene. Its structural formula is CH₃–CH₂–CH=CH–CH₂–CH₃, with a double bond between carbon 3 and 4. -
Which name is correct for the compound CH₃CH₂CH=CHCH₃: Pent-2-ene or Pent-3-ene?
The correct name is Pent-2-ene. According to IUPAC rules, numbering starts from the end nearer the double bond, placing the double bond between carbons 2 and 3. -
Write the structural formula of an alkyne containing 6 carbon atoms with a triple bond starting on the second carbon.
This compound is named hex-2-yne. Its structure is CH₃–C≡C–CH₂–CH₂–CH₃, where the triple bond starts at carbon 2. -
Write the name, display and structural formula of an alcohol-containing 4-carbon chain with an –OH group on the second carbon atom.
The compound is named butan-2-ol. Its displayed formula is CH₃–CH(OH)–CH₂–CH₃, showing the hydroxyl group on the second carbon. -
Write the structural formulas of the following alcohols: (a) Butan-1-ol and (b) Butan-2-ol.
(a) Butan-1-ol: CH₃–CH₂–CH₂–CH₂OH
(b) Butan-2-ol: CH₃–CH(OH)–CH₂–CH₃
Both are isomers with the formula C₄H₁₀O, differing by the position of the –OH group. -
How are alkynes identified and named in organic chemistry?
Alkynes contain a carbon-carbon triple bond and are named with the suffix “-yne”. The position of the triple bond is indicated by numbering from the nearest end. -
What is the name of the 2-carbon alkyne and what is its structure?
The 2-carbon alkyne is ethyne. Its structural formula is H–C≡C–H, showing a triple bond between two carbon atoms. -
How is the triple bond position determined in naming longer alkynes?
Number the carbon chain from the end nearest the triple bond. The position number of the first carbon in the triple bond is used in the name. -
What is the correct name and structure of an alkyne with 4 carbon atoms and the triple bond starting at carbon 1?
The compound is But-1-yne. Its structure is CH≡C–CH₂–CH₃, where the triple bond begins on the first carbon. -
What is the name of a 4-carbon alkyne if the triple bond starts on the second carbon?
It is named But-2-yne, and its structure is CH₃–C≡C–CH₃, where the triple bond begins from the second carbon atom. -
How are alcohols identified in organic compounds and how are they named?
Alcohols are identified by the presence of a hydroxyl group (–OH) attached to a carbon chain. In naming, the final “e” of the corresponding alkane is replaced by “ol”. -
What is the name and formula of the alcohol with one carbon atom?
The alcohol with one carbon atom is called methanol. Its chemical formula is CH₃OH, consisting of one carbon bonded to three hydrogens and one –OH group. -
What is the name and structure of the alcohol formed from ethane?
The alcohol formed from ethane is ethanol. Its formula is CH₃CH₂OH, where the –OH group is attached to the second carbon in the 2-carbon chain. -
What is the difference between Propan-1-ol and Propan-2-ol?
Propan-1-ol has the –OH group on the first carbon (CH₃CH₂CH₂OH), while Propan-2-ol has it on the second carbon (CH₃CHOHCH₃), making them structural isomers. -
How do you name an alcohol when the –OH group is on a specific carbon atom?
Number the carbon chain from the end closest to the –OH group. Use the number to show its position and replace the “e” in the alkane name with “ol”. -
What is the purpose of the IUPAC system in naming organic compounds?
The IUPAC system standardizes names so chemists worldwide can identify structures clearly, avoiding confusion caused by local or common names. -
How does the IUPAC name of an organic compound reflect its molecular structure?
The IUPAC name shows the number of carbon atoms, positions of bonds, and functional groups, helping to accurately identify the compound’s structure. -
What is meant by the 'stem' in the IUPAC naming of organic compounds?
The stem refers to the base name that indicates the number of carbon atoms in the longest continuous chain of the molecule. -
What is the function of the 'suffix' in naming organic compounds?
The suffix describes the main functional group in the compound, such as “-ane” for alkanes, “-ol” for alcohols, and “-oic acid” for carboxylic acids. -
How would you name a compound with only one carbon atom and single bonds?
The compound is named methane using the stem "meth" for one carbon and the suffix “-ane” for single bonds. Its formula is CH₄. -
What are the stem names for the first ten straight-chain hydrocarbons?
The stems are: Meth (1), Eth (2), Prop (3), But (4), Pent (5), Hex (6), Hept (7), Oct (8), Non (9), and Dec (10). -
What are alkanes and how are they named?
Alkanes are saturated hydrocarbons with only single bonds. They are named using the stem (carbon count) and the suffix “-ane”, e.g., methane, ethane. -
Explain how the name 'propane' reflects its molecular structure.
The name 'propane' uses the stem "prop" to indicate three carbon atoms and the suffix "-ane" to show single bonds. Its formula is CH₃CH₂CH₃. -
What is the general rule for naming alkenes?
Alkenes are named by identifying the longest chain with a double bond and using the suffix "-ene". The position of the double bond is also specified. -
How do you determine the position of a double bond in an alkene?
Number the carbon chain from the end nearest the double bond so that it gets the lowest number. This number is included in the name. -
Give an example of how a 4-carbon alkene with a double bond is named.
But-1-ene is a 4-carbon chain with a double bond starting at carbon 1. Its structure is CH₂=CHCH₂CH₃. -
What is the difference between a displayed formula and a condensed structural formula?
A displayed formula shows all atoms and bonds clearly, while a condensed formula groups atoms (e.g., CH₃, CH₂), omitting bond lines for simplicity. -
Why are condensed structural formulas more commonly used in organic chemistry?
They save time and space, especially for large molecules, while still showing the correct atom sequence and structure. -
How do structural formulas help in understanding organic compounds?
They show how atoms are bonded, helping chemists visualize shapes, reactivity, and mechanisms of molecules. -
What does the structural formula of alkanes reveal about their bonding?
It shows that all bonds are single, indicating saturation. Each carbon forms four bonds with hydrogen or other carbon atoms. -
How do CH₃ and CH₂ groups help simplify the representation of organic molecules?
These groups represent common units in organic chains and simplify the structure by replacing repeated hydrogen atoms. -
Why is methane considered the simplest alkane?
Methane (CH₄) has only one carbon bonded to four hydrogen atoms. It is the base for forming all larger alkanes. -
What does CH₃CH₂CH₃ represent, and how can it be expanded?
It represents propane. Expanded, it is CH₃–CH₂–CH₃, showing three carbon atoms bonded with hydrogen atoms. -
How does a displayed formula represent bond strength?
The number of lines between atoms (1, 2, or 3) indicates single, double, or triple bonds — stronger bonds have more lines. -
What does a structural formula show?
It shows how atoms are joined and arranged in a compound, helping understand molecular layout and bonding.