Answer The Following Question.
1. What would be the electron dot structure of carbon dioxide which has the formula of CO2?
Ans:
The electron dot structure of CO₂ is: :Ö::C::Ö:
Carbon forms double bonds with each oxygen.
Each oxygen has two lone pairs of electrons.
The structure is linear.
2. What would be the electron dot structure of a molecule of sulphur which is made up of eight atoms of sulphur?
Ans:
The electron dot structure of S₈ is a ring of 8 sulphur atoms, where:
Each sulphur atom forms two single bonds with neighboring sulphur atoms.
Each sulphur atom has 2 lone pairs of electrons.
It forms a puckered ring (crown shape) structure.
3. How many structural isomers can you draw for pentane?
Ans : Pentane (C₅H₁₂) can have three structural isomers. Structural isomers have the same molecular formula but different arrangements of atoms. These are:
4. What are two properties of carbon which lead to the huge number of carbon compounds we see around us?
The two properties of carbon that lead to a huge number of compounds are:
Catenation: The ability of carbon to form bonds with other carbon atoms, creating chains, branches, and rings.
Tetravalency: Carbon can form four covalent bonds with other atoms, allowing it to combine with various elements.
5. What will be the formula and electron dot structure for cyclopentane?
Solution : Formula of cyclopentane is C5H10. The electron dot structure cyclcopentane is:
6. Draw the structure for the following compounds :
(i) Ethanoic acid
(ii) Bromopentane
(iii) Butane
(iv) Hexanal
6. Draw the structure for the following compounds :
(i) Ethanoic acid
(ii) Bromopentane
(iii) Butane
(iv) Hexanal
7. How would you name the following compounds?
Solution :
(i) Bromoethane
(ii) Methanal (Formaldehyde)
(iii) Hexyne
8. Why is the conversion of ethanol and ethanoic acid an oxidation reaction?
The conversion of ethanol to ethanoic acid is considered an oxidation reaction because:
Loss of Hydrogen:
Ethanol (CH3 CH2 OH) loses hydrogen atoms as it gets oxidized to ethanoic acid (CH3 COOH).
Gain of Oxygen:
During the oxidation, oxygen atoms are added to ethanol to form the carboxylic acid group (-COOH) in ethanoic acid.
Reaction: CH3 CH2 OH → CH3 COOH
Here:
[O] represents an oxidizing agent.
Ethanol is oxidized because it gains oxygen and loses hydrogen.
Thus, the addition of oxygen and removal of hydrogen makes this reaction an oxidation process.
9. A mixture of oxygen and ethane is burnt for welding. Can you tell why the mixture of ethane and air is not used?
A mixture of ethane and air is not used for welding because:
Lower Oxygen Content: Air has only 21% oxygen, leading to incomplete combustion.
Lower Flame Temperature: Nitrogen in air absorbs heat, reducing the flame temperature, which is insufficient for welding.
Ethane and oxygen produce a much hotter flame, ensuring complete combustion and efficient welding.
10. Would you be able to check if water is hard by using a detergent?
You cannot directly check if water is hard using a detergent in the same way as you would with soap. Detergents lather in both hard and soft water, unlike soap, which forms scum in hard water. Therefore, detergent is not a reliable method for detecting water hardness.
11. People use a variety of methods to wash clothes. Usually after adding the soap, they beat the clothes on 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?
Ans: Agitation is necessary to get clean clothes because it helps to:
Loosen Dirt and Stains:
Agitation creates movement in the water and soap mixture, which helps to loosen dirt, grease, and stains from the fabric.
Improve Detergent Action:
The friction caused by agitation allows the soap or detergent to spread evenly over the fabric, increasing its effectiveness in breaking down oils and dirt.
Increase Contact Between Dirt and Soap:
The motion ensures that the dirt particles come into contact with the soap or detergent molecules, making it easier to dissolve and remove the dirt.
12. Ethane, with the molecular formula C2H6 has
(a) 6 covalent bonds
(b) 7 covalent bonds
(c) 8 covalent bonds
(d) 9 covalent bonds
Ans : (b) 7 covalent bonds
13. Butanone is a four carbon compound with the functional group
(a) carboxylic acid
(b) aldehyde
(c) ketone
(d) alcohol
Ans : (c) Ketone
14. While cooking, if the bottom of the vessels is getting blackened on the outside, it means that
(a) the fuel is not cooked completely.
(b) the fuel is not burning completely.
(c) the fuel is wet.
(d) the is burning completely.
Ans : (b) the fuel is not burning completely.
15. Explain the nature of the covalent bond using the bond formation in CH3Cl.
Ans: In CH₃Cl (methyl chloride), covalent bonds are formed by the sharing of electrons between atoms:
C-H bonds: Carbon shares one electron with each hydrogen, forming nonpolar covalent bonds.
C-Cl bond: Carbon shares one electron with chlorine, forming a polar covalent bond because chlorine is more electronegative and attracts the shared electrons more.
Thus, the covalent bonds in CH₃Cl result from electron sharing, with the C-H bonds being nonpolar and the C-Cl bond being polar.
16. Draw the electron dot structure for
(a) Ethanoic acid
(b) H2S
(c) Propanone
(d) F2
17. What is a homologous series? Explain with an example.
Ans : A homologous series is a group of organic compounds with the same functional group and similar chemical properties, where each compound differs from the next by a CH2 unit.
18. How can ethanol and Ethanoic acid be differentiated on the basis of their physical and chemical properties?
Ans: Physical Properties:
Ethanol has a lower melting point (156 K) and boiling point (351 K) than ethanoic acid (290 K and 391 K) due to weaker intermolecular forces in ethanol.
Chemical Properties:
Ethanoic acid reacts with sodium hydrogen carbonate, releasing carbon dioxide gas. Ethanol does not react with it.
19. Why does micelle formation take place when soap is added to water? Will a micelle be formed in other solvents such as ethanol also?
Micelle Formation in Water:
Soap molecules have a hydrophilic (water-attracting) head and a hydrophobic (water-repellent) tail. In water, the hydrophobic tails avoid water and form the inner part of a sphere (micelle), with the hydrophilic heads facing outward, trapping oil or dirt inside.
In Ethanol:
Micelle formation does not occur in ethanol because ethanol does not promote the same strong hydrophilic-hydrophobic interaction as water, making the soap molecules less likely to form micelles.
20. Why are carbon and its compounds used as fuels for most applications?
Ans: Carbon and its compounds are used as fuels because:
Combustion of carbon (in the form of coal, charcoal, etc.) produces carbon dioxide (CO₂) and water (H₂O), releasing a large amount of heat and light.
Similarly, carbon compounds (like hydrocarbons in fuels such as petrol, diesel, and natural gas) also release energy when burned, making them efficient for most applications.
Thus, the energy released during combustion of carbon and its compounds is the reason they are widely used as fuels.
21. Explain the formation of scum when hard water is treated with soap.
Ans: Hard water contains calcium and magnesium salts. When soap is added, these salts react with the soap to form insoluble scum. For example, calcium chloride reacts with soap to form calcium stearate (scum), which is not soluble in water and reduces soap’s effectiveness.
22. What change will you observe if you test soap with litmus paper (red and blue)?
Soap (like sodium stearate) is a salt of a weak acid (fatty acid) and a strong base (sodium hydroxide). When soap is dissolved in water, it forms a slightly alkaline solution.
Litmus Test Observation:
The alkaline nature of the soap solution will turn red litmus paper to blue.
Blue litmus paper will remain blue because the solution is basic (alkaline).
Soap in water will turn red litmus paper blue, indicating its alkaline nature.
23. What is hydrogenation? What is its industrial application?
Hydrogenation is the process in which unsaturated hydrocarbons (containing double or triple bonds) react with hydrogen in the presence of a catalyst (like palladium or nickel) to form saturated hydrocarbons (with single bonds).
Industrial Application:
Hydrogenation is used commercially to convert vegetable oils (unsaturated) into vanaspati ghee (saturated fat) by using nickel as a catalyst. This process increases the shelf life and solidifies the oils at room temperature.
24. Which of the following hydrocarbons undergo addition reactions?
C6, C3H8, C3H6, C2 and CH4
Solution : C3H6 and C2H2 will undergo addition reactions.
25. Give a test that can be used to differentiate chemically between butter and cooking oil?
Test to Differentiate Butter and Cooking Oil:
You can use the bromine water test:
Cooking oil contains unsaturated fats, which react with bromine water and decolorize it when shaken.
Butter, which contains mostly saturated fats, does not react with bromine water and does not decolorize it.
Thus, decolorization of bromine water indicates the presence of unsaturated fats (cooking oil).
26. Explain in mechanism of the cleaning action of soap.
Mechanism of the Cleaning Action of Soap:
Soap molecules are made of a hydrophilic (water-attracting) ionic head and a hydrophobic (water-repellent) hydrocarbon tail.
The hydrophilic end faces the water, while the hydrophobic end attaches to oily dirt.
Soap molecules surround the oily dirt, forming a structure called a micelle. In a micelle, the hydrophobic tails trap the oil inside, while the hydrophilic heads face outward, interacting with the water.
When rinsed with water, the micelles are washed away, carrying the dirt with them, thus cleaning the surface (like clothes).