Frank Brothers Solutions for ICSE Class 10 Chemistry Chapter 11a Organic Compounds

Organic Compounds

Solution 1:
Answer: Urea was the first organic compound synthesized in laboratory by Friedrich Wohler.
In simple words: A German scientist named Friedrich Wohler was the first person to make an organic compound (urea) in his lab, proving that organic substances could be made artificially.

📝 Teacher's Note: This is a landmark discovery in chemistry that broke the "vital force theory" - students should understand this marked the beginning of synthetic organic chemistry. Use this to discuss how scientific theories evolve with new evidence.

🎯 Exam Tip: Always mention both the compound name (urea) and the scientist's name (Friedrich Wohler) for full marks in synthesis-related questions.

Solution 2:
Answer: As the general formula of the homologous series is \(C_nH_{2n-2}\) so they represent Alkynes.
Third member: \(C_4H_6\)
Fifth member: \(C_6H_{10}\)
In simple words: When you see the formula pattern \(C_nH_{2n-2}\), it always means alkynes (compounds with triple bonds). Just substitute n=3 for third member and n=5 for fifth member.

📝 Teacher's Note: Help students memorize the three main homologous series formulas: alkanes (\(C_nH_{2n+2}\)), alkenes (\(C_nH_{2n}\)), and alkynes (\(C_nH_{2n-2}\)). Practice with multiple examples.

🎯 Exam Tip: Always identify the homologous series first by looking at the general formula, then substitute the value of n to find specific members.

Solution 3:
Answer: \(C_3H_6\), \(C_4H_8\) belong to same Homologous series.
In simple words: Both compounds follow the same pattern \(C_nH_{2n}\) (alkenes), so they are part of the same family of compounds with similar properties.

📝 Teacher's Note: Show students how to check if compounds belong to the same series by verifying if they follow the same general formula pattern. This builds pattern recognition skills.

🎯 Exam Tip: To check homologous series membership, substitute n values in the general formula and see if both compounds fit the same pattern.

Solution 4:
Answer:
(a) \(C_3H_8\) : Zero isomers. Alkanes with more than three carbon atoms form isomers.
(b) \(C_4H_{10}\): Two isomer
In simple words: Propane (\(C_3H_8\)) has only one way to arrange its atoms, but butane (\(C_4H_{10}\)) can be arranged in two different ways - straight chain and branched chain.

📝 Teacher's Note: Draw the structures to show students why \(C_3H_8\) has no isomers while \(C_4H_{10}\) has two. Visual representation helps students understand structural possibilities.

🎯 Exam Tip: Remember the rule: alkanes with 4 or more carbon atoms can form isomers. For \(C_4H_{10}\), specifically mention "2 isomers" for full marks.

Solution 5:
Answer: Natural gas and Petroleum are one of the major sources of organic compound.
In simple words: Most of the organic compounds we use come from natural gas and crude oil found underground - these are like treasure chests of carbon compounds.

📝 Teacher's Note: Connect this to real-world applications - petrol, plastics, medicines all come from these sources. Discuss the environmental implications and the search for renewable alternatives.

🎯 Exam Tip: When asked about sources of organic compounds, always mention both "natural gas" and "petroleum" as the primary sources for maximum marks.

Solution 6:
Answer:

In simple words: Organic compounds come from living things and are generally easier to burn and melt, while inorganic compounds come from rocks and minerals and are harder to melt or burn.

📝 Teacher's Note: Use everyday examples like sugar (organic - burns easily) vs salt (inorganic - doesn't burn) to make these differences memorable for students.

🎯 Exam Tip: Learn at least 4 key differences and present them in tabular format for clear, organized answers that examiners appreciate.

Solution 7:
Answer:
(i) Organic compounds are essentially carbon compounds. They show chemical Reaction and their rates are slow.
(ii) One of the products of combustion of organic compounds is always carbon dioxide.
(iii) More than 90% of the known organic compounds are synthesised.
(iv) Vital force theory was discarded by the synthesis of Urea in laboratory.
In simple words: All organic compounds contain carbon, burn to give carbon dioxide, most are man-made in labs, and the old belief that they could only come from living things was proven wrong when urea was made artificially.

📝 Teacher's Note: Connect point (iv) back to Wohler's experiment to reinforce the historical significance. Emphasize how this discovery opened the door to modern pharmaceutical and chemical industries.

🎯 Exam Tip: For fill-in-the-blank questions about organic compounds, remember these four key points - they often appear in exams in this exact format.

Solution 8:
Answer: Organic compounds are large in number due to the following unique properties of Carbon atom:
a) Tetra covalency of carbon: Carbon has four valence shell electrons. Thus it always forms covalent bonds by sharing electrons with other atoms.
b) Catenation: It is the property of combining any number of carbon atoms to form straight chains, branched chains and rings of different sizes.
c) Formation of multiple bonds: Due to small size carbon atom can form multiple bonds with not only carbon but with atoms of other elements like oxygen, nitrogen etc.
d) Isomerism: it forms large number of compounds due to isomerism by means of which compounds having same molecular formula can have different structural formula.
In simple words: Carbon is like a universal connector that can link with 4 other atoms, chain together endlessly, form double and triple bonds, and arrange in different ways to make millions of different compounds.

📝 Teacher's Note: Use building blocks or Lego analogies to help students visualize how carbon's versatility leads to compound diversity. Demonstrate with simple models if available.

🎯 Exam Tip: Always explain all four properties (tetravalency, catenation, multiple bonds, isomerism) with brief definitions for comprehensive answers worth full marks.

Solution 9:
Answer:
(a) A homologous series is a group of organic compounds having similar structures and similar chemical properties.
(b) The difference in molecular formula of any two adjacent homologues in terms of types of atoms is that that they differ by \(CH_2\) group i.e. by one carbon atom and two hydrogen atom.
The difference in the molecular masses of any two adjacent homologues is 14.
In simple words: A homologous series is like a family of similar compounds where each next member has one extra \(CH_2\) unit, making it 14 units heavier than the previous one.

📝 Teacher's Note: Use the alkane series (methane, ethane, propane, butane) as a concrete example to show the \(CH_2\) difference pattern. Calculate molecular masses to demonstrate the "14" difference.

🎯 Exam Tip: Always mention both the \(CH_2\) formula difference and the numerical mass difference of 14 when explaining homologous series for complete answers.

Solution 10:
Answer: Carbon has the unique property of combining any number of carbon atoms to form straight chains, branched chains and rings of different sizes.
Carbon show maximum tendency of catenation due to:
(i) Tetra covalency of carbon and
(ii) Great strength of carbon-carbon bonds.
In simple words: Carbon atoms love to hold hands with each other because they can form 4 strong bonds and the carbon-carbon connection is very stable, allowing them to form long chains and rings.

📝 Teacher's Note: Compare catenation to a human chain where people hold hands strongly - carbon does this but much more efficiently. Discuss why other elements like silicon don't catenate as well.

🎯 Exam Tip: When explaining catenation, always mention both the tetravalency and the strength of C-C bonds as the two main reasons for this unique property.

Solution 11:
Answer: The name and Formulae of one member of each of following are:
(a) Saturated Hydrocarbons:
Formulae: \(CH_4\)
Name: Methane
(b) Unsaturated Hydrocarbons:
Formulae: \(C_2H_4\)
Name: Ethene
In simple words: Saturated hydrocarbons have only single bonds (like methane), while unsaturated ones have double or triple bonds (like ethene with a double bond).

📝 Teacher's Note: Help students remember "saturated" means "full of hydrogen" (no room for more), while "unsaturated" means "can take more hydrogen" due to multiple bonds.

🎯 Exam Tip: Always provide both the molecular formula and the correct IUPAC name. Methane and ethene are the simplest and safest examples to use.

Solution 12:
Answer:
(a) The group formed by the removal of one hydrogen atom from an alkane molecule is called an alkyl group.
(b) The three alkyl groups are:
• Methyl
• Ethyl
• Propyl
Formation of alkyl group:
• Methyl:
\(CH_4 \xrightarrow{-H} CH_3 -\)
• Ethyl:
\(C_2H_6 \xrightarrow{-H} C_2H_5 -\)
• Propyl:
\(C_3H_8 \xrightarrow{-H} C_3H_7 -\)
In simple words: When you remove one hydrogen atom from an alkane, you get an alkyl group - it's like a molecule with one hand free to attach to something else.

📝 Teacher's Note: Show students how alkyl groups act as building blocks in larger molecules. Use hand gestures or molecular models to demonstrate the "removal" concept visually.

🎯 Exam Tip: Always show the formation reaction with the "-H" arrow notation and include the negative charge (-) on the alkyl group for complete representation.

Solution 13:
Answer:
(i) Pentane
(ii) 2,2-dimethylpropane
(iii) Pent-2-ene
(iv) Propyne
In simple words: These are the proper scientific names for different hydrocarbon compounds, following international naming rules that tell us exactly how the atoms are arranged.

📝 Teacher's Note: Emphasize the importance of IUPAC naming system for clear global communication in chemistry. Practice naming with students using simple rules step by step.

🎯 Exam Tip: Learn the IUPAC naming rules systematically - identify the longest chain, number carbons, name branches, and use proper prefixes like "di-" for multiple identical groups.

Solution 14:
Answer: A functional group may be defined as an atom or group of atoms present in a molecule which largely determines its chemical properties.
For Example: -OH- Alcohol, -CHO- Aldehyde
Functional group of:
(i) Alcohol: -OH
(ii) Ketone: >C=O
(iii) Carboxylic acid: -COOH
In simple words: A functional group is like the "active part" of a molecule that decides how it will behave and react - just like how a key's teeth determine which lock it opens.

📝 Teacher's Note: Use everyday analogies like "the functional group is like a person's profession - it determines what they do." Help students identify functional groups in common substances.

🎯 Exam Tip: Always provide the definition, give examples, and draw or write the functional groups clearly with correct symbols (>, =, -) for full marks.

Solution 15:
Answer:
(i) Molecular formula: The formula of an organic compound which represents kind of atoms and the number of each kind of atoms present in one molecule is called molecular formula.
Molecular formula of butane: \(C_4H_{10}\)
(ii) Structural formula: The formula of an organic compound which represents the arrangement of various atoms in one molecule in space is called structural formula.
Structural formula of butane:
[Structural diagram showing H-C-C-C-C-H with all hydrogen atoms]
(iii) Condensed formula: A kind of structural formula which indicates the group of atoms joined together to each of the carbon atom in straight or branched carbon chain is called condensed formula.
Condensed formula of butane: \(CH_3CH_2CH_2CH_3\)
In simple words: Molecular formula tells you what atoms are there, structural formula shows how they're connected in space, and condensed formula is a shorthand way to write the connections.

📝 Teacher's Note: Use the analogy of describing a house - molecular formula is like listing materials, structural formula is the blueprint, and condensed formula is the address format.

🎯 Exam Tip: Practice drawing all three types for the same compound. Examiners often ask for specific formula types, so know the differences clearly.

Solution 16:
Answer: The names of the functional groups are:
-OH : alcohol
>C=O : Ketone
-CHO : Aldehyde
-COOH : Carboxylic acid
In simple words: Each functional group has a specific name that tells chemists exactly what type of compound they're dealing with - like labels on different types of tools.

📝 Teacher's Note: Create flashcards or memory aids to help students remember functional group names and structures. Regular practice with identification exercises helps retention.

🎯 Exam Tip: Learn the functional groups in order of complexity - alcohol (simplest), aldehyde, ketone, carboxylic acid (most complex). Draw structures clearly for visual recognition.

Solution 17:
Answer:

In simple words: Many compounds have both old common names (trivial) and new scientific names (IUPAC) - like how people might have both a nickname and an official name.

📝 Teacher's Note: Explain that trivial names are historical and still used in industry, while IUPAC names follow systematic rules. Both are important for complete chemical literacy.

🎯 Exam Tip: Learn both naming systems as exam questions may use either. IUPAC names follow patterns, while trivial names need to be memorized individually.