NCERT Solutions For Class 10 Science Chapter 4 Carbon And Its Compounds

NCERT Solutions For Class 10 Science Chapter 4 Carbon And Its Compounds Long Question And Answers

Question 1.

1. What are homologous series of compounds? List any two characteristics of a homologous series.
2. What would be observed by adding a 5% solution of alkaline potassium permanganate drop by drop to warm ethanol taken in a test tube? Write the name of the compound.
3. How would you distinguish experimentally between an alcohol and a carboxylic acid on the basis ofa chemical property?

Answer:

1. Homologous series represent different families of organic compounds into which these are divided. Two characteristics of homologous series are listed.

• All the members in a particular homologous series of families have the same
  characteristic functional group. For example, in organic acids, the functional
  group is the carboxyl group (—COOH).
• Any two consecutive members in a particular family have the same common difference of CH₂ in their molecular formulae.
• For example, the first three members ofthe family of alkanes are CH₄ (methane), C₂H₆ (ethane), and propane (C₃H₈).

2. On adding a 5% solution of alkaline potassium permanganate to ethanol, it will be oxidized to ethanoic acid. The pink color of the solution will be discharged upon warming.

3. A carboxylic acid gives a brisk effervescence when an aqueous solution of sodium hydrogen carbonate (NaHCOa) is added to it. This is due to the evolution of CO₂ gas. However, alcohol will not give any reaction.

⇒ \(\underset{\text { Carboxylic acid }}{\mathrm{ROOH}}+\mathrm{NaHCO}_3 \longrightarrow \underset{\text { Sodium salt }}{\mathrm{RCOONa}}+\mathrm{H}_2 \mathrm{O}+\mathrm{CO}_2\)

Question 2.

1. Give a name to the reaction which takes place between ethanoic acid and ethanol in the presence ofconcentrated sulphuric acid. Write the chemical reaction and name of the product obtained.
2. Explain the following reactions with chemical equations:
   1. Oxidation
   2. Hydrogenation
   3. Substitution

Answer:

1. Esterification:

Ethyl ethanoate is the product formed.

2. Oxidation: Alcohols are converted into carboxylic acid in the presence of oxidizing agent

3. Hydrogenation: Hydrogen reacts with unsaturated hydrocarbonin the presence of catalyst.

4. Substitution: Saturated hydrocarbon reacts with chlorine in the presence of sunlight.

CH₄+Cl₂→ CH₃Cl + HCl

Question 3.

1. How is vinegar made?
2. What is glacial acetic acid1? What is its meltingpoint?
3. Write the name and the formula of the two compounds formed when the ester
4. CH₃COOC₅H₂undergoes saponification.

Answer:

1. Acetic acid in water, 5-8% solution.
2. Pure ethanoic acid, 290 K.
3. Do not ionize completely.
4. CH₃COONa or sodium ethanoate; C₂H₅OH or ethanol.

Question 4. A compound X is formed by the reaction ofa carboxylic acid C₂H₄CO₂ and alcohol in the presence ofa few drops of H₂SO₄. The alcohol on oxidation with alkaline KMnO₄ followed by acidification gives the same carboxylic acid as used in this reaction. Give the names and structures of

1. Carboxylic acid
2. Alcohol, and
3. The compound X.

Also, write the reaction.
Answer:

1. Carboxylic acid as ethanoic acid.
2. Alcohol is ethanol.
3. X is ethyl ethanoate.

⇒ \(\underset{\text { Ethanoic acid }}{\mathrm{CH}_3-\mathrm{COOH}}+\underset{\text { Ethanol }}{\mathrm{C}_2 \mathrm{H}_5 \mathrm{OH}} \longrightarrow \underset{\text { Ethyl ethanoate }}{\mathrm{CH}_3-\mathrm{COOC}_2 \mathrm{H}_5}+\mathrm{H}_2 \mathrm{O}\)

Question 5.

1. In organic compounds, which part largely determines the physical and chemical
   properties.
2. Write a chemical equation to represent the reaction of ethanol with the acidified solution of potassium dichromate.

Answer:

1. In organic compounds, it is the functional group that largely determines the physical and chemical properties of compounds. An organic compound is made up of two parts. These are the alkyl group and the functional group.

Whereas the alkyl group remains the same (size may change) the functional groups change. These are responsible for the characteristics of the compounds.

For example, the properties. Alkanols (-OH is the functional group) are different from those of alkanoic acid (-COOH is the functional group).

2. An acidified solution of potassium dichromate (K₂Cr₂O₇) forms chromic acid (H₂CrO₄). It releases oxygen to bring about the oxidation of ethanol first to ethanal and then to ethanoic acid.

Question 6. An ester has the molecular formula C₄H₈O₂ Write its structural formula. What happens when this ester is heated in the presence ofsodium hydroxide solution? Write the balanced chemical equation for the reaction and name the products. What is the saponification reaction?
Answer:

For the molecular formula C₄H₈O₂ two isomeric esters are possible which differ in structural formula. These are

Both will react with sodium hydroxide upon heating from the sodium salt of the acid and alcohol

1. Ethyl ethanoate:

2. Methyl Propanoate:

Question 7.

1. How will you bring about the following reactions’? Write the concerned chemical equation:

1. Ethanol to Ethene
2. Ethanol to Ethanoic acid

2. Give one example with a chemical equation for the following reactions:

1. Substitution reaction
2. Saponification reaction
3. Combustion reaction

Answer:

Question 8. An organic compound A on heating with cone. H₂SO₄ forms a compound B which on the addition of one mole of hydrogen in the presence of nickel forms a compound ‘C’ One mole of ‘C’ on combustion forms 2 moles of CO₂ and 3 moles of H₂O. Identify the compounds A, B, and C and write the equations for the reactions involved.
Answer:

A-Ethanol

B-Ethene

C-Ethane

Question 9. What are soaps chemically? How do they differ from synthetic detergents? Explain the mechanism and the cleaning action of soap.
Answer:

1. Soap: It is sodium or potassium salt of fatty acid.

Detergents are ammonium or sulphonate salts of long-chain carboxylic acids.

2. Due to micelle formation, ionic-ionic repulsion.

Micelle: It is a structure formed when soap molecules get arranged and aligned along the surface of water with the ionic end in water and the hydrocarbon ‘tail’ protruding out of water.

Question 10.

1. A compound burns with a sooty flame. Is it saturated or unsaturated?
2. With the help of suitable tests, distinguish between ethyl alcohol and acetic acid experimentally.

Answer:

1. Organic compounds mostly contain carbon and hydrogen. Both of them burn in the air to form carbon dioxide and water respectively.

If the combustion is complete, this means that all the carbon atoms present in the compound have fully reacted to form carbon dioxide. In case, the flame is sooty, this means that the combustion is incomplete and there are unburnt carbon particles.

Now, a saturated compound like hexane (C₆H₁₄) has more hydrogen atoms as compared to hexene (C₆H₁₂) which is unsaturated. Both have six carbon atoms in their molecules.

Hexane will require more air or oxygen for complete combustion than hexane. Thus, we may conclude that generally, a saturated compound is more likely to burn with sooty flame as compared to an unsaturated compound.

2. The distinction can be made by the following test: Litmus test. Add a few drops of blue litmus solution in two test tubes containing ethyl alcohol and acetic acid. Its color will change to red in the acid while it will remain unaffected in alcohol.

Sodium hydrogen carbonate test. The distinction can also be made with sodium hydrogen carbonate (NaHCO₃).

⇒ \(\mathrm{CH}_3 \mathrm{COOH}+\mathrm{NaHCO}_3 \longrightarrow \mathrm{CH}_3 \mathrm{COONa}+\mathrm{H}_2 \mathrm{O}+\underset{\text { (effervescence) }}{\mathrm{CO}_2}\)

Question 11.

1. Differentiate between soap and detergent.
2. Explain why, soaps form scum with hard water whereas detergents do not

Answer:

2. Hard water contains ions of calcium and magnesium which react with soap molecules to form insoluble precipitates called soap scum.

⇒ \(\underset{\text { Soap molecule (Sodium stearate) (from hard water) }}{2 \mathrm{C}_{17} \mathrm{H}_{35} \mathrm{COONa}}+\mathrm{Ca}^{2+}\left(\mathrm{Mg}^{2+}\right) \longrightarrow \underset{\begin{array}{c}
\text { White ppt.)(scum) } \\
\text { Calciumstearate }
\end{array}}{\left(\mathrm{C}_{17} \mathrm{H}_{33} \mathrm{COO}\right)_2 \mathrm{Ca}}+2 \mathrm{Na}^{+}\)

Question 12. Two carbon compounds ‘A’and ‘B’have the molecular formula C₃H₈ and C₃H₆ respectively. Which one of the two is most likely to show additional reactions? Justify your answer. Explain with the help of a chemical equation, how an addition reaction is useful in the vegetable ghee industry.
Answer:

The compound ‘A’ with the formula C₃H₈ (propane) is a saturated hydrocarbon and corresponds to the general formula C_nH_2n+2. The compound ‘B’ with formula C₃H₆ (propene) is an unsaturated hydrocarbon and corresponds to the general formula C_nH_2n. It has a double bond (C = C) and is, therefore, unsaturated.

The compound ‘B’ will take part in the addition reactions. As a result, the double bond will change to a single bond.

For example,

The addition reaction is quite useful in the hydrogenation of oils i.e., to convert edible oils like groundnut oil and cottonseed oil which are unsaturated into solid fats which are of a saturated nature.

Question 13.

1. How are carboxylic acids different from mineral acids from an ionization point of view?
2. Describe an activity to show how ethanoic acid reacts with sodium carbonate. Name the gas evolved. How can it be tested?
3. State the principle on which the cleansing action of soap is based.

Answer:

Carboxylic acids (organic acids) are less ionized in solution as compared to mineral acids (HCl, HNO₃, H₂SO_4, etc.) Due to this reason, these are weaker acids than the mineral acids.

Take a small volume of ethanoic acid in a tube. Add a few drops ofsodium carbonate (Na₂CO₃) a solution prepared in water to the tube.

A colorless gas with brisk effervescence will evolve. When the gas is passed through lime water, it will become milky

⇒ \(\mathrm{Na}_2 \mathrm{CO}_3(a q)+2 \mathrm{CH}_3 \mathrm{COOH}(a q) \longrightarrow 2 \mathrm{CH}_3 \mathrm{COONa}(a q)+\mathrm{H}_2 \mathrm{O}(l)+\mathrm{CO}_2(g)\)

⇒  \(\underset{\text { Lime water }}{\mathrm{Ca}(\mathrm{OH})_2(a q)}+\mathrm{CO}_2(\mathrm{~g}) \longrightarrow \underset{\text { (Milky) }}{\mathrm{CaCO}_3(s)+\mathrm{H}_2 \mathrm{O}(l)}\)

The cleaning action of soap is based on its tendency to act as a bridge between water and oil drops containing dirt particles. As a result, oil and water get mixed. They form a stable emulsion also called micelle. This helps in removing oil drops containing dirt particles from clothes. The clothes become clean.

Question 14. Complete the following chemical reactions and write the chemical name ofthe products obtained.

1. CH₂ = CH₂ +HO

2. CHCOOH + NaOH

3.  CH₂CHOH → (H₂SO₄)

4. HCOOH + Na

5. C₂H₅OH → (AlK. KMnO₄)

Answer:

1. \(\mathrm{CH}_2=\mathrm{CH}_2+\mathrm{H}_2 \mathrm{O} \longrightarrow \mathrm{C}_2 \mathrm{H}_5 \mathrm{OH} \text { (Ethanol) }\)

2. \(\mathrm{CH}_3 \mathrm{COOH}+\mathrm{NaOH} \longrightarrow \underset{{\text { Sodium ethanoate }}}{\mathrm{CH}_3 \mathrm{COONa}}+\mathrm{H}_2 \mathrm{O}\)

3.

4. HCOOH + Na → HCOONa (Sodiumacid) + H₂

5.

Question 15.

1. Explain with the help of chemical equation for the following properties of carbon compounds:

1. Addition reaction
2. Substitution reaction

2. Differentiate between vegetable oils and animal fats.

3. What is meant by hydrogenation?

Answer:

1.

1. Addition reaction:  Unsaturated hydrocarbons add hydrogen in the presence of catalysts such as palladium or nickel.

2. Substitution reaction:  One type of atom or group of atoms takes the place of hydrogen.

CH₄ + Cl₂ →CH₃Cl + HCl (in the presence of sunlight)

2. Vegetable oils are unsaturated fatty acids and animal fats are saturated.

3. Adding hydrogen to unsaturated fatty acids.

Question 16.

1. Differentiate between saturated and unsaturated hydrocarbons. Write any two points of difference.

2. Why are carbon compounds:

1. Poor conductors of electricity?
2. Have low melting and boiling points?

3. Name the simplest hydrocarbon and write its formula

Answer:

1. 

2. Most carbon compounds are poor conductors of electricity as they do not ionize. Low melting and boiling points as the intermolecular force of attraction is very low.

3. Simplest hydrocarbon -Methane-CH₄

Question 17. Why is the conversion of ethanol to ethanoic acid an oxidation reaction?
Answer:

The conversion of ethanol to ethanoic acid is an oxidation reaction because oxygen is added to it during this conversion.

A mixture of oxygen and ethyne is burnt for welding. Can you tell why a mixture of ethyne and air is not used?

Ethyne with oxygen gives enough heat that be used for welding whereas if it is burnt in air, sufficient oxygen is not available and it burns with u sooty flame which does not give enough heat to melt metals for welding.

Question 18. 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 in a washing machine. Why is agitation necessary to get clean clothes?
Answer:

The molecules of soap are sodium or potassium salts of long-chain carboxylic acids. The ionic end of soap dissolves in water while the hydrocarbon chain gets attached to oily dirt on the clothes.

Thus, molecules called micelles are formed. When the cloth is agitated by different means, the micelles containing oily or greasy dirt particles get removed from the surface of the dirty cloth and go into the water, and the clothes get cleaned.

Question 19. How would you distinguish experimentally between an alcohol and a carboxylic acid?
Answer:

The distinction between alcohol and carboxylic acid can be made as follows:

Question 20. Explain the nature of the covalent bond using the bond formation in CH₃Cl.
Answer:

Covalent is formed by sharing ofelectrons so that combining atoms complete their outermost shell. In CH₃Cl, this happens as:

Three hydrogen atoms complete (K = 1 +1 = 2) their shells by sharing three electrons (one electron each) of carbon atoms. Chlorine completes its outer shell (L = 7 + 1 = 8) by sharing one out of seven electrons with one electron of a carbon atom.

Thus, the carbon atom shares all its four electrons with three hydrogen atoms and one chlorine atom and completes its outer shell (L = 4 + 3 + 1 = 8). 5.

Question 21. Draw the electron dot structures for

1. Ethanoic acid
2. H₂S
3. Propanone
4. F₂

Answer:

Question 22. Why does micelle formation take place when soap is added to water? Will a micelle be formed in other solvents such as ethanol?
Answer:

Soaps are sodium or potassium salts of long-chain carboxylic acids. The acid end of soap dissolves in water while the carbon chain dissolves in oil. When soap is added to the water, the hydrophilic end (acid end) will align along the surface of the water and the hydrophobic tail (carbon chain) remains out of water.

The cluster of molecules in which the hydrophobic tail is in the interior of the cluster and the ionic ends are on the surface of the cluster is called a micelle. The soap micelles thus help in dissolve the dirt in water and we can wash our clothes clean. No micelle will be formed in other solvents such as ethanol.

Question 23. Give a test that can be used to differentiate chemically between butter and cooking oil.
Answer:

Cooking oil is unsaturated hydrocarbon whereas butter is saturated hydrocarbon. We know that the brown color of bromine disappears when a drop of bromine is added to an unsaturated compound whereas there is no reaction between saturated hydrocarbons and bromine.

Thus, when a drop of bromine is added to cooking oil, its color disappears whereas there is no color change when a drop of bromine is added to butter.

Question 24. Explain the mechanism ofthe cleaning action of soaps.
Answer:

Dirt is generally absorbed in the clothes as an oily material. It cannot be removed with water because it does not mix well with water. But when a cloth with dirt is soaked in soap solution, the dirt and grease attach themselves to the hydrocarbon component of the soap molecule.

The —COONa part of the soap which is attached to the water molecules pulls the hydrocarbon part along with dirt away from the surface of the cloth, thus washing it clean.

Question 25. What is meant by a homologous series of carbon compounds? Write the general formula of

1. Alkene,
2. Alkynes

Draw the structures ofthe first member ofeach series to show the bonding between the two carbon atoms.

Answer:

A homologous series is called a series of organic compounds in which the same functional group substitutes for hydrogen in a carbon chain.

All consecutive members of this series differ by CH₂ unit.

Physical properties show gradation but chemical properties are the same.

The general formula of three compounds A, B, and C is CnH₂n. B has the highest boiling point and C has the lowest boiling point.

Mention the type of compounds A, B, and C.

Question 26. What is a homologous series? Explain with an example.
Answer:

A homologous series is a group of compounds that contain the same functional group but different chain lengths. Thus, these have the same chemical properties but different physical properties.

Two adjacent members ofa homologous scenes differ by a CH₂ unit. Examples CH₃OH, C₂H₅OH, C₃H₇OH, C₄ H₉ OH and C₂H₄, C₃H₆, C₄H₈, C₅H₁₀ two same homologous series respectively.

Question 27. How do diamond and graphite differ in their structures? Is there any effect of structures on the nature of these?
Answer:

1. Diamond and graphite are the two crystalline allotropic forms of carbon.
2. But they differ in their structures. In diamond, all the four valence electrons of carbon atoms are involved.
3. In the covalent bond formation with the electrons of neighboring carbon atoms In graphite, only three electrons participate in the bond formation while the fourth electron is free.
4. Diamond without nny free electrons is a poor conductor of electricity while e with free electrons available is a good conductor.

Question 28. An organic compound ‘X’ has the molecular formula CJi40. It has a pleasant smell. It does not turn blue litmus red; nor does it give any effervescence with sodium hydrogen carbonate solution. Predict the compound. Give its structural formula as well as the IUPAC name.
Answer:

Two different structural formulae are possible for the compound X’ with molecular formula C₂H₄O₂. These are known as functional isomers and may be written as:

StructureI is that of a carboxylic acid, ethanoic acid. Since the compound X’ does not turn blue litmus red and also does not give effervescence with NaHCO₃ solution, it cannot be an acid. As the compound has a pleasant smell, it seems to be an ester with structure 2. Please note that the esters have a pleasant smell. The IUPAC name of the compound is methylmethanoate.

Question 29.

1. Take about 3 mL of ethanol in a test tube and warm it gently in a water bath.
2. Add a 5% solution of alkaline potassium permanganate drop to the solution.
3. What happens to the color of KMnO₄ initially and then in excess? Give reason. Name the product of this reaction.

Answer:

The purple color of alkaline potassium permanganate solution, also known as Baeyer’s reagent gets initially discharged. On adding the reagent in excess, the purple color persists.

Baeyer’s reagent is an oxidizing agent. It provides oxygen to oxidize ethanol to ethanoic acid. Once the oxidation is complete, the further addition ofBaeyer’s reagent imparts the purple color to the solution.

Question 30.

1. Hydrocarbons generally act as fuels. How will you account for this?
2. Why is petrol regarded as a better fuel than kerosene?

Answer:

All hydrocarbons contain carbon and hydrogen. Both these elements are easily oxidized by oxygen to form carbon dioxide and water respectively. These reactions are highly exothermic and are accompanied by the release of a large amount of heat energy. That is why hydrocarbons generally act as fuels.

In petrol, the combustion of hydrocarbons present is complete and they bum with blue flame. However, in kerosene, the combustion is not complete. It burns with smoky flame accompanied by the release of unburnt carbon atoms. Therefore, petrol is regarded as a better fuel than kerosene.

Question 31. Draw the electron dot structure of ethyne and also draw its structural formula.
Answer:

The molecular formula of ethyne is C₂H₂.

Electronic configuration of C = 2, 4 (valence]electrons = 4)

Electronic configuration of H =1 (valence electrons = 1)

The electronic dot structure is

The structural formula is H — C≡ C—H (Ethyne)

Question 32. A salt X is formed and a gas is evolved when ethanoic acid reacts with sodium hydrogen carbonate. Name the salt X and the gas evolved. Describe an activity and draw the diagram ofthe apparatus to prove that the evolved gas is the one that you have named. Also, write the chemical equation ofthe reaction involved.
Answer:

CH₃COOH+NaHCO₃→ CH₃COONa +H₂O+CO₂

X is sodium ethanoate V

The gas evolved is carbon dioxide

Lime water will turn milky, a characteristic property of CO₂ gas.

Question 33.

1. What are hydrocarbons? Give examples.
2. Give the structural differences between saturated and unsaturated hydrocarbons with two examples each.
3. What is a functional group? Give examples of our different functional groups.

Answer:

1. Compounds of carbon and hydrogen are called hydrocarbons.

Examples: Methane, ethane, etc.

2. Saturated hydrocarbons contain carbon-carbon single bonds. Unsaturated hydrocarbons contain at least one carbon-carbon double or triple bond

3. Functional group:

An atom or a group of atoms joined in a specific manner that is responsible for the characteristic chemical properties of the organic compounds.

Examples are the hydroxyl group (—OH), aldehyde group (—CHO), carboxylic group (—COOH), etc.

Question 34. Name the reaction which is commonly used in the conversion of vegetable oils to fats. Explain the reaction involved in detail.
Answer:

Hydrogenation reaction:

Where R is the alkyl group.

Industrial use:

Vegetable oil + H₂ → (Ni,473K) → Vanaspati ghee

Question 35.

1. Write the formula and draw the electron dot structure of carbon tetrachloride.
   
2. What is saponification? Write the reaction involved in this process.
   

Answer:

1. Carbon tetrachloride

2. Saponification is the process of converting esters into salts of carboxylic acids and ethanols by treating them with a base.

CH₃COOC₂H₆ →( NaOH) →  CH₃COONa + C₂H₅OH

Question 36. Esters are sweet-smelling substances and are used in making perfumes. Suggest some activity and the reaction involved in the preparation of an ester with a well-labeled diagram.

Answer:

Activity

• Take 1 mL ethanol (absolute alcohol), 1 mL glacial acetic acid, and a few drops of concentrated sulphuric acid in a test tube.
• Warm in a water bath at about 60°C for at least 15 minutes as shown in the figure (It should not be heated directly on flame as the vapors of ethanol catch fire)
• Pour into a beaker containing 20-50 mL of water and smell the resulting mixture.

Question 37. A compound C(molecularformula, reacts with Na-metal to form a compound R and evolves a gas that burns with a pop sound. Compound C on treatment with alcohol A in the presence of an acid forms a sweet-smelling compound S (molecular formula)

In addition to NaOH to C, it also gives R and water. S on treatment with NaOH solution gives back R and A. Identify C, R, A, and S and write down the reactions involved.

Answer:

C — Ethanoic acid

R— Sodium salt of ethanoic acid (sodium acetate) and gas evolved is hydrogen.

A — Methanol

S — Ester (Methyl acetate)

1. 2CH₃COOH (C) + 2Na → 2CH₃COONa (R) + H₂

2. CH₃COOH  (C) + CH₃OH (A) →(Conc.H₂SO₄)   CH₃COOCH₃ (S) + H₂O

3. CH₃COOH₃ + NaOH → CH₃COONa (R) +  H₂O

4. CH₃COOCH₃ + NaOH→ CH₃COONa(R) +  CH₃ OH (A)

Question 38. Look at the figure and answer the following questions

1. What change would you observe in the calcium hydroxide solution taken in tube B?
2. Write the reaction involved in test tubes A and B respectively.
3. If ethanol is given instead of ethanoic acid, would you expect the same change?
4. How can a solution of lime water be prepared in the laboratory?

Answer:

1. It will turn milky

2. 2CH₃COOH + Na₂CO₃→ 2CH₃COONa + H₂O + CO₂ (Test tube A)

Ca(OH)₂ + CO₂→CaCO₃ + H₂O(Test tube B)

With excess CO₂, milkiness disappears.

CaCO₃ + H₂O + CO₂→ Ca(HCO₃)₂

3. As C₂H₅OH and Na₂CO₃ do not react, a similar change is not expected.

4. The lime water is prepared by dissolving calcium oxide in water and decanting the supernatant liquid.

Question 39. How would you bring about the following conversions? Name the process and write the reaction involved.

1. Ethanol to ethene
2. Propanol to propanoic acid

Write the reaction.

Answer:

1. Dehydration:

2. Oxidation reaction:

Question 40. Draw the possible isomers ofthe compound with molecular formula C₃H₆O and also give their electron dot structures
Answer:

1. CH₃-C=O – CH₃ (Propanone):

2. CH₃CH₂CHO (Propanal):

Question 41. Explain the given reactions with examples:

1. Hydrogenation reaction
2. Oxidation reaction
3. Substitution reaction
4. Saponification reaction
5. Combustion reaction

Answer:

1. Hydrogenation reaction:

Unsaturated hydrocarbons add hydrogen in the presence of a nickel catalyst to give saturated hydrocarbons.

2. Oxidation reaction:

Ethanol is oxidized to ethanoic acid in the presence of alkaline KMnO₄ on heating.

3. Substitution reaction:

In the presence of sunlight, chlorine is added to hydrocarbons.

4. Saponification reaction:

⇒ \(\underset{\text { Ester }}{\mathrm{CH}_3 \mathrm{COOC}_2 \mathrm{H}_5}+\mathrm{NaOH} \longrightarrow \underset{\text { Sodium acetate }}{\mathrm{CH}_3-\mathrm{COO}-\mathrm{Na}}+\underset{\text { Ethanol }}{\mathrm{C}_2 \mathrm{H}_5 \mathrm{OH}}\)

5. Combustion reaction:

Most carbon compounds release n large amount of heat and light on burning.

⇒ \(\mathrm{CH}_4+2 \mathrm{O}_2 \longrightarrow \mathrm{CO}_2+2 \mathrm{H}_2 \mathrm{O}+\text { Heat and ligh }\)

Question 42. An organic compound A on heating with concentrated H₂SO₄ forms a compound B which on the addition of one mole of hydrogen in the presence of Ni forms compound C. One mole of compound C on combustion forms two moles of CO₂ and 3 moles of H₂O. Identify the compounds A, B, and C and write the chemical equations ofthe reactions involved.
Answer:

Since compound C gives 2 moles of CO₂ and 3 moles of H₂O, it shows that it has the molecular formula C₂H₆ (Ethane). C is obtained by adding one mole of hydrogen to compound B so the molecular formula of B should be C₂H₄ (Ethene).

Compound B is obtained by heating compound A with concentrated H₂O₄ which shows it to be an alcohol. So compound A could be C₂H₅OH (Ethanol).

Question 43. Study the variation in the atomic radii of the first group elements given below and arrange them in increasing order.

1. Name the elements that have the smallest and the largest atoms

2. How does the atomic size vary as you go down a group?
Answer:

1. The smallest atom—is lithium and the largest atom is cesium

Question 44. How would you bring about the following conversions? Name the process and write the reaction involved.

1. Ethanol to ethene
2. Propanol to propanoic acid

Answer:

1. By the dehydration of ethanol in the presence of concentrated H₂SO₄

2. By the dehydration of propanol in the presence of alkaline KMnO₄

Question 45. Write an activity to show the acidic nature ofethanol. Give the chemical equation of the reaction taking place.
Answer:

Take ethanol in a test tube and drop a small piece ofsodium about the size of a grain of rice into it. The reaction evolves a colorless gas which is hydrogen.

Hydrogen gas can be tested by bringing a burning splinter/match stick near the mouth of the test tube, it burns with the popping sound. This activity proves that ethanol like other acids releases H gas.

2CH₃CH₂OH + 2Na → 2CH₃CH₂ONa + H₂

Question 46. A student reports to police about the illegal blending of alcohol near his school. He also knew about denatured alcohol.

1. What is denatured alcohol?
2. What would happen if a person consumes denatured alcohol?
3. What value is reflected by a student who reported the matter to the police?

Answer:

1. Denatured alcohol is ethanol when added with poisonous methanol or CuSO₄.
2. On drinking denatured alcohol, a person may die.
3. Value reflected is in society’s decorum of law and order.

Question 47. Mrs. Anju Pandey observed that her cooking utensils are becoming black and the flame other gas stove is yellowish. She complained about it in the gas company and got thegas stove repaired. Answer the following questions based on the above situation.

1. What can be the reason for this sooty flame?
2. How is this problem harmful to our environment?
3. What steps should be taken to stop this process?
4. What values are promoted by Mrs. Pandey?

Answer:

• The inlets for air in the stove get blocked which leads to a yellow flame.
• This problem is harmful to our environment as incomplete combustion results in the formation of oxides which are major pollutants of our environment.
• To prevent this situation, gas or stove burners should be cleaned from time to time.
• Prudence, careful observations, and decision-making.

Question 48. Ethanol, commonly known as alcohol is an excellent solvent, is used in medicines, and is an important chemical compound involved in the synthesis of many chemical compounds.

However, despite its benefits to man, its impact on social behavior has always been questioned. It is considered as a curse in the lives of those who are addicted to alcohol—

‘Alcoholic people are not only lowering their metabolism but anger and rude behavior are also some of its ill effects.

Answer the following questions based on the above information:

1. Comment on the statement—‘Should the production of alcohol be banned?’ Give three valid reasons to justify.
2. As a student, what initiative would you take in the common concern of ‘ Save Life, Do Not Drink’? Give two suggestions.

Answer:

1.

In favor of a negative response:

1. Regulate production and supply.
2. It is used in so many ways for medicines and ornamentation.

In favor of a positive response:

• Cause of death of many people.
• Many adolescents get affected out of it and become addicts, which affects their physical as well as mental health.

2. Initiatives:

1. Drive to spread awareness.
2. Skit/street plays/drama.
3. Organise exhibitions.

Question 49. The element carbon is known to have the unique ability to form bonds with other similar atoms of other elements. The carbon-carbon bond is also known to be very strong and hence stable.

Answer the following questions based on the above information:

1. Name the chemical bond formed between carbon-carbon atoms. How is this bond formed?
2. Which two values are reflected like carbon resulting in its ability to form a maximum number of compounds’?
3. How can these values help strengthen relationships in a family, organization, or even people ofa nation?

Answer:

1. Covalent bond: Sharing of bonds
2. Ability to share, nature to share
3. Sharing of one’s possessions, jobs, and resources with others enables an individual organization or even a society to live happily and comfortably.

Question 50. Write the structural formulae of all the isomers of hexane.
Answer:

Structural formulae of all the isomers of hexane:

Question 51. What is the role of metal or reagents written on arrows in the given chemical reactions?

Answer:

1. Ni acts as a catalyst.
2. Concentrated sulphuric acid acts as a dehydrating agent.
3. Alkaline KMnO₄ acts as an oxidizing agent.

Question 52. Why should we prefer vegetable oils over animal fats for cooking food? Give a balanced chemical equation ofthe reaction for hydrogenation of vegetable oils. Name, the catalysts in this reaction.
Answer:

Animal fats are saturated fatty acids that are harmful to health.

Catalyst: Palladium or Nickel

Question 53. Convert CH₄ into CCl₄ by substituting hydrogen atom with chlorine atom in successive reactions. Why this reaction is referred to as a substitution reaction?
Answer:

CH₄+ Cl₂ →(Sunlight ) → CH₃CI + HCl

CH₃CI + Cl₂ →CH₂Cl₂ + HCl

CH₂Cl₂ + Cl₂ →CCl + HCl

CHCl₃ + Cl₂ → CCl + HCl

Replace the hydrogen atom with a heteroatom (Cl).

Question 54. The organic compound ‘A’ is an essential constituent of wine and beer. Oxidation of ‘A’ yields an organic acid ‘B’ which is present in vinegar. Name the compounds ‘A’ and ‘B’ and write their structural formula. What happens when”A’ and ‘B” react in the presence of an acid catalyst? Write the chemical equation for the reaction.
Answer:

The available information suggests that the compound ‘A’ is ethanol and the compound B formed by the oxidation of‘A’ is ethanoic acid.

Their structural formula is are 

Ethanol (A)

Ethanoic Acid (B)

When ‘A’ and ‘B’ react the presence ofan acid cone. H₂SO₄, the compound is ethyl ethanoate ester with a pleasant smell.