1.Why does carbon form covalent bonds rather than ionic bonds? Explain by discussing why carbon cannot form either a $\text{C}^{4+}$ cation or a $\text{C}^{4-}$ anion.
2.What is a covalent bond? Draw the electron-dot structures for the following simple covalent molecules:
- Hydrogen molecule ($\text{H}_2$)
- Oxygen molecule ($\text{O}_2$)
- Nitrogen molecule ($\text{N}_2$)
3.Draw the electron-dot structure and structural formula for a molecule of methane ($\text{CH}_4$). State the valency of carbon and hydrogen in this compound.
4.Draw the electron-dot structures for:
- Water molecule ($\text{H}_2\text{O}$)
- Ammonia molecule ($\text{NH}_3$)
- Carbon dioxide molecule ($\text{CO}_2$)
5.Covalent compounds generally have low melting/boiling points and are poor conductors of electricity. Explain why, contrasting them with ionic compounds.
6.Explain what is meant by "sharing of electrons" in covalent bonding. How does this bonding lead to chemical stability?
7.Name the allotropes of carbon. Contrast diamond and graphite in terms of: (a) hardness, (b) electrical conductivity, and (c) structure.
8.What is a Fullerene? Describe the structure and chemical properties of Buckminsterfullerene ($\text{C}_{60}$).
9.Explain why diamond has an extremely high melting point while graphite is slippery and used as a dry lubricant.
10.Carbon has the unique ability to form millions of stable compounds. Name the two primary properties of carbon that are responsible for this versatile nature.
11.Define "catenation". Why does carbon show an exceptionally high degree of catenation compared to other group 14 elements like silicon?
12.Differentiate between saturated and unsaturated carbon compounds. Draw the structural formula for ethane ($\text{C}_2\text{H}_6$) and ethene ($\text{C}_2\text{H}_4$).
13.What are structural isomers? Draw all possible structural isomers for pentane ($\text{C}_5\text{H}_{12}$) and give their IUPAC names.
14.Draw the structural formula and write the molecular formula for:
- Propane
- Butyne
- Benzene
15.What is a homologous series? State three general characteristics of a homologous series.
16.Explain why consecutive members of a homologous series differ in their molecular mass by 14 u. Name the first three members of the homologous series of alkanes.
17.Draw the structural formulas for cyclohexane ($\text{C}_6\text{H}_{12}$) and benzene ($\text{C}_6\text{H}_6$). State which one is saturated and which one is unsaturated.
18.Why do the physical properties (like melting and boiling points) of members of a homologous series show a regular gradation as the molecular mass increases?
19.Draw the electron-dot structure and structural formula for ethyne ($\text{C}_2\text{H}_2$). What type of covalent bond exists between the carbon atoms?
20.Classify the following as alkanes, alkenes, or alkynes: $\text{C}_3\text{H}_8$, $\text{C}_4\text{H}_8$, $\text{C}_5\text{H}_8$, $\text{C}_2\text{H}_6$, $\text{C}_3\text{H}_6$. Write their general formulas.
29.Write the balanced chemical equations for the combustion of:
- Methane gas
- Ethanol liquid
Is combustion an exothermic or endothermic process?
30.Explain why saturated hydrocarbons generally burn with a clean, blue flame, whereas unsaturated hydrocarbons burn with a yellow, sooty flame. Under what conditions do saturated hydrocarbons burn with a sooty flame?
31.What is an oxidation reaction? How is it different from combustion? Write the chemical equation for the oxidation of ethanol to ethanoic acid using alkaline potassium permanganate ($\text{KMnO}_4$) or acidified potassium dichromate ($\text{K}_2\text{Cr}_2\text{O}_7$).
32.What are oxidizing agents? Name two strong chemical oxidizing agents used in organic chemistry.
33.What is an addition reaction? Write the chemical equation for the industrial hydrogenation of vegetable oils (unsaturated fats) to make vegetable ghee (saturated fats). Name the catalyst used.
34.Why are saturated fatty acids considered unhealthy for consumption, while unsaturated fatty acids (oils) are recommended? Explain in terms of chemical properties.
35.What is a substitution reaction? Write the balanced chemical equation for the reaction of methane with chlorine in the presence of sunlight. Why is this reaction called a substitution reaction?
36.How will you chemically distinguish between a cooking oil (unsaturated) and butter (saturated) using bromine water? Describe the test and observations.
37.State the physical properties of ethanol (state, odour, melting/boiling points, solubility in water). Why is ethanol widely used as a solvent in medicines?
38.Write the balanced chemical equations for the reaction of ethanol with:
- Sodium metal
- Hot concentrated sulphuric acid at 443 K.
State the role of concentrated sulphuric acid in the second reaction.
39.What is denatured alcohol? Why is ethanol denatured, and what substances are added to make it unfit for drinking?
40.State the physical properties of ethanoic acid (acetic acid). What is glacial acetic acid and why is it called so?
41.What is esterification? Write the balanced chemical equation and describe the setup for the preparation of ethyl ethanoate from ethanol and ethanoic acid. What characteristic physical property do esters possess?
42.What is saponification? Write the balanced chemical equation showing the alkaline hydrolysis of an ester using sodium hydroxide. How is this reaction related to soap making?
43.Write balanced equations showing how ethanoic acid reacts with:
- Sodium hydroxide ($\text{NaOH}$)
- Sodium carbonate ($\text{Na}_2\text{CO}_3$)
- Sodium hydrogen carbonate ($\text{NaHCO}_3$)
Describe the diagnostic gas test for the product evolved in the carbonate reactions.
44.How can you chemically distinguish between ethanol and ethanoic acid using: (a) litmus test, (b) sodium hydrogen carbonate test? Describe the observations in each case.
45.What is a soap? State the chemical structure of a soap molecule, identifying its hydrophilic (ionic) head and hydrophobic (hydrocarbon) tail.
46.Explain what a micelle is. Why does micelle formation take place when soap is added to water? Draw a labelled diagram of a micelle.
47.Explain the step-by-step mechanism of the cleaning action of soaps. How does a soap molecule trap oil/grease and suspend it in water to be washed away?
48.Will a micelle be formed when soap is dissolved in an organic solvent like ethanol? Give scientific reasons for your answer.
49.Why do soaps fail to clean clothes in hard water? Name the two main salts present in hard water. Write the chemical equation or describe the formation of scum.
50.What is a synthetic detergent? How does its chemical structure differ from that of soap? Why are detergents able to clean effectively even in hard water?
51.State two advantages and two disadvantages of using synthetic detergents over natural soaps. Explain in terms of biodegradability.
Governments around the world are promoting "Gasohol" — a blend of 10% or 20% anhydrous ethanol with petrol. Ethanol is produced by fermenting molasses obtained from sugarcane juice. When burned, ethanol produces carbon dioxide and water, releasing massive energy.
52.Based on Case Study 1, answer the following:
- Write the balanced chemical equation for the complete combustion of ethanol.
- Why is gasohol considered a cleaner, more eco-friendly fuel than pure petrol?
- Explain how sugarcane acts as a highly efficient solar-to-chemical energy converter.
Anjali is trying to prepare an ester in her chemistry lab. She mixes 2 mL of absolute ethanol with 2 mL of glacial acetic acid in a test tube, adds 3 drops of concentrated sulphuric acid, and heats the tube in a hot water bath for 5 minutes. On pouring the mixture into water, a highly pleasant, sweet-fruity smell fills the room.
53.Based on Case Study 2, answer the following:
- Write the balanced chemical equation for the reaction. What is the name of the ester formed?
- Why did Anjali add concentrated sulphuric acid? State its dual role in this reaction.
- Why did she heat the test tube in a hot water bath rather than directly over the burner flame? Explain based on the physical properties of ethanol.
Ramesh lives in an area with heavy groundwater supply. Whenever he bathes using regular bathing soap, a sticky, white precipitate forms on his skin and the bucket, and he struggles to form a rich lather. His friend suggests switching to a liquid shower gel (a detergent).
54.Based on Case Study 3, answer the following:
- Why does the regular soap form a sticky, white precipitate instead of lather? What is this precipitate called chemically?
- Write the ionic reactions occurring between the sodium soap molecules and the calcium ions present in Ramesh's water supply.
- Why does the shower gel (detergent) form rich lather even in Ramesh's water supply? Explain.
A chemist is examining four consecutive members of a homologous series of alcohols: methanol ($\text{CH}_3\text{OH}$), ethanol ($\text{C}_2\text{H}_5\text{OH}$), propanol ($\text{C}_3\text{H}_7\text{OH}$), and butanol ($\text{C}_4\text{H}_9\text{OH}$). She measures their physical properties and records their boiling points.
55.Based on Case Study 4, answer the following:
- State the general formula for the homologous series of alcohols.
- Why does the boiling point increase regularly from methanol to butanol? Explain in terms of intermolecular forces.
- Predict whether butanol or methanol will have a higher solubility in water, and justify your answer based on molecular structure.
CNG (Compressed Natural Gas) is primarily methane ($\text{CH}_4$), whereas LPG (Liquefied Petroleum Gas) is primarily butane ($\text{C}_4\text{H}_{10}$). During a safety check at a factory, a gas leak is detected. An inspector uses a chemical detector that senses hydrocarbons reacting with chlorine in the presence of UV light.
56.Based on Case Study 5, answer the following:
- Write the balanced chemical equations showing the step-by-step substitution reaction of methane with chlorine under UV light.
- Why is this reaction considered a chain reaction?
- Write the molecular formula and structural isomers of the major LPG constituent, butane.
An organic compound 'A' (molecular formula $\text{C}_2\text{H}_6\text{O}$) is a liquid at room temperature and is the active ingredient in alcoholic drinks. When 'A' is heated with alkaline $\text{KMnO}_4$, it gets oxidized to compound 'B' (molecular formula $\text{C}_2\text{H}_4\text{O}_2$). When compound 'A' reacts with compound 'B' in the presence of concentrated sulphuric acid, a sweet-smelling, fruity compound 'C' is formed. When 'C' is treated with sodium hydroxide, it yields back compound 'A' and a sodium salt of 'B' (compound 'D').
57.Based on the puzzle description, answer the following:
- Identify compounds 'A', 'B', 'C', and 'D'.
- Write down the chemical equations for the conversion of: (a) 'A' to 'B', (b) 'A' and 'B' to 'C'.
- Write the chemical equation for the reaction of 'C' with sodium hydroxide. What is this reaction called?
58.Explain why soap bubbles appear colorful when exposed to sunlight. What physical phenomenon is responsible for this? (Focus on light reflection and thin-film interference).
59.Why is carbon considered a unique element in the periodic table? Discuss catenation and tetravalency in detail.
60.What is coal and petroleum? Explain how they were formed in nature over millions of years. Why are they considered non-renewable resources?
61.Explain the term "Anodising" and why it is used to protect aluminium surfaces. How is it related to the chemical properties of carbon? (Anodising forms a stable oxide layer; carbon is used as electrodes in metallurgy).
62.Write the complete balanced equations for:
- $\text{CH}_3\text{COOH} + \text{NaHCO}_3 \rightarrow$
- $\text{C}_2\text{H}_5\text{OH} + \text{Na} \rightarrow$
- $\text{CH}_3\text{COOC}_2\text{H}_5 + \text{NaOH} \rightarrow$
- $\text{CH}_3\text{CH}_2\text{OH} \xrightarrow{\text{Hot Conc. } \text{H}_2\text{SO}_4} $
63.Explain the difference between soap and detergent in terms of their chemical composition. Which one is biodegradable?
64.A student burns a piece of charcoal (carbon) and a candle (hydrocarbons) side-by-side. Explain the differences in their combustion products, flames, and the nature of the residue left behind.
65.Why are covalent bonds directional in nature while ionic bonds are non-directional? Explain how this directional property leads to structural isomerism in carbon compounds.
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