Exercises
Q1. Ethane, with the molecular formula C2H6 has (a) 6 covalent bonds. (b) 7 covalent bonds. (c) 8 covalent bonds. (d) 9 covalent bonds.
Answer:
The correct answer is (b) 7 covalent bonds. Ethane consists of six C-H bonds and one C-C single bond, making a total of seven covalent bonds.
Q2. Butanone is a four-carbon compound with the functional group (a) carboxylic acid. (b) aldehyde. (c) ketone. (d) alcohol.
Answer:
The correct answer is (c) ketone. The suffix '-one' in butanone indicates the presence of a ketone functional group.
Q3. While cooking, if the bottom of the vessel is getting blackened on the outside, it means that (a) the food is not cooked completely. (b) the fuel is not burning completely. (c) the fuel is wet. (d) the fuel is burning completely.
Answer:
The correct answer is (b) the fuel is not burning completely. Incomplete combustion of fuel produces soot (carbon), which deposits on the bottom of the vessel, making it black.
Q4. Explain the nature of the covalent bond using the bond formation in CH3Cl.
Answer:
In CH3Cl (chloromethane), carbon shares its four valence electrons with three hydrogen atoms and one chlorine atom. Each hydrogen atom shares one electron with carbon to form three C-H single covalent bonds. Chlorine shares one electron with carbon to form one C-Cl single covalent bond. All atoms achieve a stable octet (or duplet for hydrogen) through this sharing of electrons.
Q5. Draw the electron dot structures for (a) ethanoic acid. (b) H2S. (c) propanone. (d) F2.
Answer:
(a) Ethanoic acid (CH3COOH): H:C::C:O::O:H (with two dots representing shared pairs and lone pairs on oxygen atoms). (b) H2S: H:S:H (with two lone pairs on sulfur). (c) Propanone (CH3COCH3): H:C:C::C:H (with C=O double bond and two lone pairs on oxygen). (d) F2: :F:F: (with three lone pairs on each fluorine atom).
Q6. What is an homologous series? Explain with an example.
Answer:
A homologous series is a group of organic compounds having similar structural features and chemical properties, with successive members differing by a -CH2- unit. For example, the alkane series: methane (CH4), ethane (C2H6), propane (C3H8), butane (C4H10). Each member differs from the next by a CH2 group.
Q7. How can ethanol and ethanoic acid be differentiated on the basis of their physical and chemical properties?
Answer:
Physical: Ethanol has a characteristic alcoholic smell and a boiling point of 351 K, while ethanoic acid has a pungent smell of vinegar and a melting point of 290 K (freezes in winter). Chemical: (a) Ethanol does not turn blue litmus red, but ethanoic acid does due to its acidic nature. (b) Ethanol does not react with sodium carbonate/hydrogencarbonate, but ethanoic acid reacts to produce CO2 gas. (c) Ethanol reacts with sodium metal to produce hydrogen gas, while ethanoic acid also produces hydrogen gas but more slowly.
Q8. Why does micelle formation take place when soap is added to water? Will a micelle be formed in other solvents such as ethanol also?
Answer:
Micelle formation occurs because soap molecules have a hydrophilic (water-attracting) ionic end and a hydrophobic (water-repelling) hydrocarbon tail. In water, the hydrophobic tails cluster together away from water, while the ionic heads face outward, forming a spherical structure called a micelle. Micelles will not form in ethanol because ethanol is a non-polar solvent that can dissolve both ends of the soap molecule, so there is no need for the hydrophobic tails to cluster away from the solvent.
Q9. Why are carbon and its compounds used as fuels for most applications?
Answer:
Carbon and its compounds are used as fuels because they have high calorific value, are relatively inexpensive, readily available, and burn completely in air (or oxygen) to produce a large amount of heat and light. They also form easily combustible gases or vapors.
Q10. Explain the formation of scum when hard water is treated with soap.
Answer:
Hard water contains calcium and magnesium salts (like bicarbonates, chlorides, or sulfates). When soap (sodium or potassium salts of long-chain carboxylic acids) is added to hard water, it reacts with calcium and magnesium ions to form insoluble calcium or magnesium salts of the fatty acids. This insoluble precipitate is called scum or curd.
Q11. What change will you observe if you test soap with litmus paper (red and blue)?
Answer:
Soap solution is basic in nature because it is a salt of a weak acid (carboxylic acid) and a strong base (sodium or potassium hydroxide). Therefore, it will turn red litmus paper blue, while blue litmus paper will remain blue.
Q12. What is hydrogenation? What is its industrial application?
Answer:
Hydrogenation is the process of adding hydrogen to unsaturated hydrocarbons (like vegetable oils) in the presence of a catalyst (such as nickel, palladium, or platinum) to convert them into saturated hydrocarbons (fats). Its industrial application is the production of vanaspati ghee (solid fat) from vegetable oils.
Q13. Which of the following hydrocarbons undergo addition reactions: C2H6, C3H8, C3H6, C2H2 and CH4.
Answer:
Addition reactions are a characteristic of unsaturated hydrocarbons (containing double or triple bonds). Among the given: C3H6 (propene) has a double bond and C2H2 (ethyne) has a triple bond. Methane (CH4), ethane (C2H6), and propane (C3H8) are saturated hydrocarbons and undergo substitution reactions, not addition reactions.
Q14. Give a test that can be used to differentiate between saturated and unsaturated hydrocarbons.
Answer:
The bromine water test: Add bromine water (reddish-brown) to the hydrocarbon. Saturated hydrocarbons (like alkanes) will not decolorize bromine water. Unsaturated hydrocarbons (like alkenes and alkynes) will decolorize bromine water by adding bromine across the double/triple bond, turning it from reddish-brown to colorless.
Q15. Explain the mechanism of the cleaning action of soaps.
Answer:
Dirt is usually oily in nature and does not dissolve in water. Soap molecules have a hydrophilic (water-attracting) ionic head and a hydrophobic (water-repelling) hydrocarbon tail. When soap is dissolved in water, the hydrophobic tails are attracted to and surround the oily dirt particles, while the hydrophilic heads face outward. This forms a structure called a micelle. The micelle keeps the oily dirt suspended in water (emulsification). The dirt is then easily rinsed away with water due to ion-ion repulsion between micelles.
Questions from text (numbered in text)
Q1. Why is the conversion of ethanol to ethanoic acid an oxidation reaction?
Answer:
The conversion of ethanol to ethanoic acid involves the addition of an oxygen atom to the ethanol molecule (CH3CH2OH + O2 -> CH3COOH + H2O in the presence of an oxidizing agent). The addition of oxygen constitutes oxidation. Alternatively, there is a loss of hydrogen atoms from the ethanol molecule, which also defines oxidation.
Q2. A mixture of oxygen and ethyne is burnt for welding. Can you tell why a mixture of ethyne and air is not used?
Answer:
A mixture of ethyne and air is not used for welding because air contains only about 21% oxygen. The combustion of ethyne in air is less efficient and produces a flame with a lower temperature (about 2000°C) and a lot of soot due to incomplete combustion. Pure oxygen supports complete combustion of ethyne, producing a very high temperature (about 3000°C) and a clean blue flame suitable for welding.
Q1. How would you distinguish experimentally between an alcohol and a carboxylic acid?
Answer:
Perform a sodium carbonate test: Add a small amount of sodium carbonate (Na2CO3) to the compound. A carboxylic acid will react with sodium carbonate to produce carbon dioxide gas, which turns lime water milky. Alcohol does not react with sodium carbonate. Alternatively, use litmus paper: Carboxylic acid turns blue litmus red, while alcohol does not change the color of litmus paper.
Q2. What are oxidising agents?
Answer:
Oxidizing agents are substances that are capable of adding oxygen to others or removing hydrogen from them. In the context of carbon compounds, examples include alkaline potassium permanganate (KMnO4) and acidified potassium dichromate (K2Cr2O7). These agents oxidize alcohols to carboxylic acids.
Q1. Would you be able to check if water is hard by using a detergent?
Answer:
No, you cannot check if water is hard by using a detergent. Detergents do not form insoluble precipitates (scum) with calcium and magnesium ions present in hard water. They produce lather in both hard and soft water. Soap is used to test hard water, as it forms scum with hard water.
Q2. People use a variety of methods to wash clothes. Usually after adding the soap, they 'beat' the clothes on a stone, or beat it with a paddle, scrub with a brush or the mixture is agitated in a washing machine. Why is agitation necessary to get clean clothes?
Answer:
Agitation helps in the formation of more micelles and ensures that the soap molecules come into close contact with the oily dirt particles on the clothes. The mechanical action of beating, scrubbing, or agitating helps to dislodge the dirt particles from the fabric and suspend them in the water inside the micelles. Without agitation, the micelles would form slowly and the cleaning process would be inefficient.
Exercises (end-of-chapter)
Q1. Ethane, with the molecular formula C2H6 has (a) 6 covalent bonds. (b) 7 covalent bonds. (c) 8 covalent bonds. (d) 9 covalent bonds.
Answer:
The correct answer is (b) 7 covalent bonds. Ethane consists of six C-H bonds and one C-C single bond, making a total of seven covalent bonds.
Q2. Butanone is a four-carbon compound with the functional group (a) carboxylic acid. (b) aldehyde. (c) ketone. (d) alcohol.
Answer:
The correct answer is (c) ketone. The suffix '-one' in butanone indicates the presence of a ketone functional group.
Q3. While cooking, if the bottom of the vessel is getting blackened on the outside, it means that (a) the food is not cooked completely. (b) the fuel is not burning completely. (c) the fuel is wet. (d) the fuel is burning completely.
Answer:
The correct answer is (b) the fuel is not burning completely. Incomplete combustion of fuel produces soot (carbon), which deposits on the bottom of the vessel, making it black.
Q4. Explain the nature of the covalent bond using the bond formation in CH3Cl.
Answer:
In CH3Cl (chloromethane), carbon shares its four valence electrons with three hydrogen atoms and one chlorine atom. Each hydrogen atom shares one electron with carbon to form three C-H single covalent bonds. Chlorine shares one electron with carbon to form one C-Cl single covalent bond. All atoms achieve a stable octet (or duplet for hydrogen) through this sharing of electrons.
Q5. Draw the electron dot structures for (a) ethanoic acid. (b) H2S. (c) propanone. (d) F2.
Answer:
(a) Ethanoic acid (CH3COOH): H:C::C:O::O:H (with two dots representing shared pairs and lone pairs on oxygen atoms). (b) H2S: H:S:H (with two lone pairs on sulfur). (c) Propanone (CH3COCH3): H:C:C::C:H (with C=O double bond and two lone pairs on oxygen). (d) F2: :F:F: (with three lone pairs on each fluorine atom).
Q6. What is an homologous series? Explain with an example.
Answer:
A homologous series is a group of organic compounds having similar structural features and chemical properties, with successive members differing by a -CH2- unit. For example, the alkane series: methane (CH4), ethane (C2H6), propane (C3H8), butane (C4H10). Each member differs from the next by a CH2 group.
Q7. How can ethanol and ethanoic acid be differentiated on the basis of their physical and chemical properties?
Answer:
Physical: Ethanol has a characteristic alcoholic smell and a boiling point of 351 K, while ethanoic acid has a pungent smell of vinegar and a melting point of 290 K (freezes in winter). Chemical: (a) Ethanol does not turn blue litmus red, but ethanoic acid does due to its acidic nature. (b) Ethanol does not react with sodium carbonate/hydrogencarbonate, but ethanoic acid reacts to produce CO2 gas. (c) Ethanol reacts with sodium metal to produce hydrogen gas, while ethanoic acid also produces hydrogen gas but more slowly.
Q8. Why does micelle formation take place when soap is added to water? Will a micelle be formed in other solvents such as ethanol also?
Answer:
Micelle formation occurs because soap molecules have a hydrophilic (water-attracting) ionic end and a hydrophobic (water-repelling) hydrocarbon tail. In water, the hydrophobic tails cluster together away from water, while the ionic heads face outward, forming a spherical structure called a micelle. Micelles will not form in ethanol because ethanol is a non-polar solvent that can dissolve both ends of the soap molecule, so there is no need for the hydrophobic tails to cluster away from the solvent.
Q9. Why are carbon and its compounds used as fuels for most applications?
Answer:
Carbon and its compounds are used as fuels because they have high calorific value, are relatively inexpensive, readily available, and burn completely in air (or oxygen) to produce a large amount of heat and light. They also form easily combustible gases or vapors.
Q10. Explain the formation of scum when hard water is treated with soap.
Answer:
Hard water contains calcium and magnesium salts (like bicarbonates, chlorides, or sulfates). When soap (sodium or potassium salts of long-chain carboxylic acids) is added to hard water, it reacts with calcium and magnesium ions to form insoluble calcium or magnesium salts of the fatty acids. This insoluble precipitate is called scum or curd.
Q11. What change will you observe if you test soap with litmus paper (red and blue)?
Answer:
Soap solution is basic in nature because it is a salt of a weak acid (carboxylic acid) and a strong base (sodium or potassium hydroxide). Therefore, it will turn red litmus paper blue, while blue litmus paper will remain blue.
Q12. What is hydrogenation? What is its industrial application?
Answer:
Hydrogenation is the process of adding hydrogen to unsaturated hydrocarbons (like vegetable oils) in the presence of a catalyst (such as nickel, palladium, or platinum) to convert them into saturated hydrocarbons (fats). Its industrial application is the production of vanaspati ghee (solid fat) from vegetable oils.
Q13. Which of the following hydrocarbons undergo addition reactions: C2H6, C3H8, C3H6, C2H2 and CH4.
Answer:
Addition reactions are a characteristic of unsaturated hydrocarbons (containing double or triple bonds). Among the given: C3H6 (propene) has a double bond and C2H2 (ethyne) has a triple bond. Methane (CH4), ethane (C2H6), and propane (C3H8) are saturated hydrocarbons and undergo substitution reactions, not addition reactions.
Q14. Give a test that can be used to differentiate between saturated and unsaturated hydrocarbons.
Answer:
The bromine water test: Add bromine water (reddish-brown) to the hydrocarbon. Saturated hydrocarbons (like alkanes) will not decolorize bromine water. Unsaturated hydrocarbons (like alkenes and alkynes) will decolorize bromine water by adding bromine across the double/triple bond, turning it from reddish-brown to colorless.
Q15. Explain the mechanism of the cleaning action of soaps.
Answer:
Dirt is usually oily in nature and does not dissolve in water. Soap molecules have a hydrophilic (water-attracting) ionic head and a hydrophobic (water-repelling) hydrocarbon tail. When soap is dissolved in water, the hydrophobic tails are attracted to and surround the oily dirt particles, while the hydrophilic heads face outward. This forms a structure called a micelle. The micelle keeps the oily dirt suspended in water (emulsification). The dirt is then easily rinsed away with water due to ion-ion repulsion between micelles.