NCERT Exemplar Class 10 Science Chapter 4 Carbon and its Compounds are part of NCERT Exemplar Class 10 Science. Here we have given NCERT Exemplar Class 10 Science Chapter 4 Carbon and its Compounds.
NCERT Exemplar Class 10 Science Chapter 4 Carbon and its Compounds
Multiple Choice Questions (MCQs)
Question. 1 Carbon exists in the atmosphere in the form of
(a) Only carbon monoxide
(b) Carbon monoxide in traces and carbon dioxide
(c) Only carbon dioxide
(d) Coal
Answer. (c)
Explanation: Carbon exists only in the form of carbon dioxide gas (CO2) in air.
Question. 2 Which of the following statements are usually correct for carbon compounds? These
(i) Are good conductors of electricity.
(ii) Are poor conductors of electricity.
(iii) Have strong forces of attraction between their molecules.
(iv) Do not have strong forces of attraction between their molecules.
(a) (i) and (iii)
(b) (ii) and (iii)
(c) (i) and (iv)
(d) (ii) and (iv)
Answer. (d)
Explanation: Carbon having four valence electrons forms only covalent compounds which exhibit less intermolecular attractions and do not have any fre electrons to carry electric current. Therefore, these are poor conductors of electricity.
Question. 3 A molecule of ammonia (NH3) has
(a) Only single bonds
(b) Only double bonds
(c) Only triple bonds
(d) Two double bonds and one single bond
Answer. (a)
Explanation: Ammonia is a covalent molecule in which center nitrogen atom is bonded with three hydrogen atoms through single covalent bond.
Question. 4 Buckminsterfullerene is an allotropic form of
(a) Phosphorus
(b) Sulphur
(c) Carbon
(d) Tin
Answer. (c)
Explanation: Buckminsterfullerene is an allotrope of carbon with 60 carbon atoms which are joined together in a spherical shape.
Question. 5 Which of the following are correct structural isomers of C4H10?
(a) (i) and (iii)
(b) (ii) and (iv)
(c) (i) and (ii)
(d) (iii) and (iv)
Answer. (a)
Explanation: Structural isomers have same molecular formula but different parent chain of carbon atoms in the molecule.
Question. 6 In the following reaction, alkaline KMnO4 acts as:
(a) Reducing agent
(b) Oxidising agent
(c) Catalyst
(d) Dehydrating agent
Answer. (b)
Explanation: KMnO4 acts as oxidising agent as it oxidized CH3CH2OH to CH3COOH by addition of oxygen atom.
Question. 7 Oils on treating with hydrogen in the presence of palladium or nickel catalyst form fats. This is an example of
(a) Addition reaction
(b) Substitution reaction
(c) Displacement reaction
(d) Oxidation reaction
Answer. (a)
Explanation: It is hydrogenation reaction means addition of hydrogen to double bonds of unsaturated compounds found in oil.
Question. 8 In which of the following compounds -OH is the functional group?
(a) Butanone
(b) Butanol
(c) Butanoic
(d) Butanal
Answer. (b)
Explanation: Compounds with –OH functional group are ended with suffix –ol.
C4H9 ─ OH or CH3 ─ CH2 ─ CH2 ─ CH2 ─ OH
Question. 9 The soap molecule has a
(a) Hydrophilic head and a hydrophobic tail
(b) Hydrophobic head and a hydrophilic tail
(c) Hydrophobic head and a hydrophobic tail
(d) Hydrophilic head and a hydrophilic tail
Answer. (a)
Explanation: A soap molecule contains a long hydrocarbon part and a small ionic part of -COONa group. Hydrocarbon chain is hydrophobic or water repelling whereas ionic head is hydrophilic or water attracting group.
Question. 10 Which of the following is the correct representation of electron dot structure of nitrogen?
Answer. (d)
Explanation: Nitrogen molecule is a covalent molecule in which two nitrogen atoms are bonded through triple covalent bond with one lone pair of electrons over each nitrogen atom.
Question. 11 Structural formula of ethyne is
Answer. (a)
Explanation: General formula for alkyne is CnH2n−2. There must be at least one triple bond between carbon atoms. With two carbon atom, the possible structure would be H ─ C ≡ C ─ H.
Question. 12 Identify the unsaturated compounds from the following.
(i) Propane
(ii) Propene
(iii) Propyne
(iv) Chloropropane
(a) (i) and (ii)
(b) (ii) and (iv)
(c) (iii) and (iv)
(d) (ii) and (iii)
Answer. (d)
Explanation: Alkene and alkyne are unsaturated hydrocarbon as they have double and triple covalent bonds between carbon atoms.
Question. 13 Chlorine reacts with saturated hydrocarbons at room temperature in the
(a) absence of sunlight
(b) presence of sunlight
(c) presence of water
(d) presence of hydrochloric acid
Answer. (b)
Explanation: Chlorine shows photochemical substitution reactions with saturated hydrocarbons that occurs in the presence of light.
Question. 14 In the soap micelles
(a) The ionic end of soap is on the surface of the cluster while the carbon chain is in the interior of the cluster
(b) Ionic end of soap is in the interior of the cluster and the carbon chain is out of the cluster
(c) Both ionic end and carbon chain are in the interior of the cluster
(d) Both ionic end and carbon chain are on the exterior of the cluster
Answer. (a)
Explanation: A micelle is a spherical aggregation of soap molecules in water in which hydrocarbon ends are directed towards the centre and ionic ends are directed outwards.
Question. 15 Pentane has the molecular formula C5H12. It has
(a) 5 covalent bonds
(b) 12 covalent bonds
(c) 16 covalent bonds
(d) 17 covalent bonds
Answer. (c)
Explanation: Pentane contains four C-C bonds and twelve C-H covalent bonds.
Question. 16 Structural formula of benzene is:
Answer. (c)
Explanation: Benzene is simplest aromatic compound with six carbon atoms and six H atoms. There are three alternate pi bonds in ring of carbon atoms.
Question. 17 Ethanol reacts with sodium and forms two products. These are
(a) Sodium ethanoate and hydrogen
(b) Sodium ethanoate and oxygen
(c) Sodium ethoxide and hydrogen
(d) Sodium ethoxide and oxygen
Answer. (c)
Explanation: Ethanol (C2H5OH) reacts with sodium to form sodium ethoxide (C2H5ONa) along with liberation of hydrogen gas.
2C2H5OH + 2Na → 2C2H5ONa + H2 ↑
Question. 18 The correct structural formula of butanoic acid is:
Answer. (d)
Explanation: Butanoic acid is a carboxylic acid with four carbon atom and one –COOH group at terminal.
Question. 19 Vinegar is a solution of:
(a) 50% – 60% acetic acid in alcohol
(b) 5% – 8% acetic acid in alcohol
(c) 5% – 8% acetic acid in water
(d) 50%- 60% acetic acid in water
Answer. (c)
Explanation: Vinegar is a 5%-8% aqueous solution of acetic acid.
Question. 20 Mineral acids are stronger acids than carboxylic acids because
(i) Mineral acids are completely ionised.
(ii) Carboxylic acids are completely ionised.
(iii) Mineral acids are partially ionised.
(iv) Carboxylic acids are partially ionised.
(a) (i) and (iv)
(b) (ii) and (iii)
(c) (i) and (ii)
(d) (iii) and (iv)
Ans. (a)
Explanation: Mineral acids like nitric acid, sulphuric acid are stronger than carboxylic acid as they can ionize 100% in their solution.
Question. 21 Carbon forms four covalent bonds by sharing its four valence electrons with four univalent atoms, e.g. hydrogen. After the formation of four bonds, carbon attains the electronic configuration of
(a) Helium
(b) Neon
(c) Argon
(d) Krypton
Answer. (b)
Explanation: Electronic configuration of carbon is 2, 4 hence it contains 4 valence electrons and after formation of 4 covalent bonds, it will get 4 more electrons through them so total would be 10 electrons that is atomic number for Neon gas.
Question. 22 The correct electron dot structure of a water molecule is
Answer. (c)
Explanation: In water molecule, center oxygen atom contains two lone pairs of electrons and form two single covalent bonds with two hydrogen atoms.
Question. 23 Which of the following is not a straight chain hydrocarbon?
Answer. (d)
Explanation: A branched chain hydrocarbon must contain some side chains which are bonded with parent carbon chain.
Question. 24 Which among the following are unsaturated hydrocarbons?
(a) (i) and (iii)
(b) (ii) and (iii)
(c) (ii) and (iv)
(d) (iii) and (iv)
Answer. (c)
Explanation: Unsaturated hydrocarbons have multiple covalent bonds (double or triple bond) like alkene and alkyne.
Question. 25 Which of the following does not belong to the same homologous series?
(a) CH4
(b) C2H6
(c) C3H8
(d) C4H8
Answer. (d)
Explanation: Successive members of same homologous series are differ by -CH2 unit. CH4, C2H6, C3H8 belong to same series that is of alkane and differ by ─CH2 unit but C4H8 does not belong to this.
Question. 26 The name of the compound, CH3 ─ CH2 ─ CHO is:
(a) Propanal
(b) Propanone
(c) Ethanol
(d) Ethanal
Answer. (a)
Explanation: Compound contains three carbon atoms so prop- would be root word and – CHO functional group so suffix will be –al. Hence name would be propane + al = propanal.
Question. 27 The heteroatoms present in CH3 ─ CH2 ─ O ─ CH2 ─ CH2Cl are:
(i) Oxygen
(ii) Carbon
(iii) Hydrogen
(iv) Chlorine
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (iii) and (iv)
(d) (i) and (iv)
Answer. (d)
Explanation: Atoms other than C and H in organic compound are called as heteroatoms.
Question. 28 Which of the following represents saponification reaction?
Answer. (d)
Explanation: Saponification reaction is reaction of ester with base like NaOH to form the parent alcohol and sodium salt of carboxylic acid.
Question. 29 The first member of alkyne homologous series is:
(a) Ethyne
(b) Ethene
(C) Propyne
(d) Methane
Answer. (a)
Explanation: Alkyne is an organic compound with triple covalent bond between two carbon atoms therefore first member of homologous series must have atleast two carbon atoms with one triple bond that is ethyne (CH ≡ CH).
Short Answer Type Questions
Question. 30 Draw the electron dot structure of ethyne and also draw its structural formula.
Answer.
Ethyne is a hydrocarbon with molecular formula C2H2. Here two carbon atoms are bonded together by a triple covalent bond and one hydrogen atom is bonded with each carbon atom through a single covalent bond. Hence the electron dot structure of ethyne molecule can be representes as:
Structural formula of ethyne is: H ─ C ≡ C ─ H
Question. 31 Write the names of the following compounds.
Answer.
(a) Pentanoic acid as it contains five carbon atoms with one –COOH group.
(b) Pentyne as it contains five carbon atoms in a straight chain with one triple covalent bond at terminal.
(c) Heptanal as it contains seven carbon atoms with one –CHO group ( aldehyde group)
(d) Pentanol because it contains 5 carbon atoms with one –OH group.
Question. 32 Identify and name the functional groups present in the following compounds.
Answer.
(a) Functional group: ─ OH
Name of compound: Alcohol
(b) Functional group: ─ COOH
Name of compound: Carboxylic acid
(a) Functional group: >C = O
Name of compound: Ketone
(a) Functional group: ─ C = C ─
Name of compound: Alkene
Question. 33 A compound X is formed by the reaction of a carboxylic acid C2H4O2 and an alcohol in the presence of a 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
(a) Carboxylic acid,
(b) Alcohol and
(c) The compound x. Also write the reaction.
Answer.
(a) Carboxylic acid with molecular formula C2H4O2 is acetic acid or ethanoic acid having the structure as:
(b) Given alcohol forms acetic acid on oxidation with alkaline KMnO4 followed by acidification. Therefore, it must be ethanol with structure CH3 ─ CH2 ─ OH.
(c) Reaction of ethanoic acid with ethanol in presence of a few drops of conc. H2SO4 is an esterification reaction that forms an ester, ethyl ethanoate (CH3COOC2H5).
Question. 34 Why detergents are better cleansing agents than soaps? Explain.
Answer.
Detergents and soaps both are cleansing agents but detergents can be used even in hard water whereas soaps cannot use in hard water.
Soaps forms an insoluble precipitate with calcium and magnesium ions found in hard water. This precipitate is called as scum which sticks to the cloths and makes the cleaning even more difficult.
On the contrary, detergents have charged ends and do not form insoluble precipitates with calcium and magnesium ions.
The cleansing action of detergents is stronger than soaps. They are more soluble in water therefore it is convenient to use them compare to soaps.
Question. 35 Name the functional groups present in the following compounds.
(a) CH3COCH2CH2CH2CH3
(b) CH3CH2CH2COOH
(c) CH3CH2CH2CH2CHO
(d) CH3CH2OH
Answer.
(a) CH3COCH2CH2CH2CH3 – Ketone ( >C=O)
(b) CH3CH2CH2COOH – Carboxylic acid (─ COOH)
(c) CH3CH2CH2CH2CHO – Aldehyde (─ CHO)
(d) CH3CH2OH – Alcohol (─ OH)
Question. 36 How is ethene prepared from ethanol? Give the reaction involved in it.
Answer.
This conversion is possible through dehydration reaction which occurs in the presence of concentrated sulphuric acid or concentrated phosphoric (V) acid, H3PO4 at 160°C.
Question. 37 Intake of small quantity of methanol can be lethal. Comment
Answer.
When methanol is entered in our body, it is metabolized in the liver and form formaldehyde which further converted to formate. Formate is essential for survival because it acts as building block for many biomolecules but high levels of it can cause toxicity.
Formaldehyde also reacts with living cells and can cause coagulation of protoplasm. Excess of methanol in our body also affects the optic nerve and can cause blindness.
Question. 38 A gas is evolved when ethanol reacts with sodium. Name the gas evolved and also write the balanced chemical equation of the reaction involved.
Answer.
When ethanol reacts with sodium metal, it forms sodium ethoxide (C2H5O−Na+) and hydrogen gas is released. The reaction is as follows.
2C2H5OH + 2Na → 2C2H2O−Na+ + H2 ↑
So the gas is hydrogen gas that is evolved during the reaction.
Question. 39 Ethene is formed when ethanol at 443 K is heated with excess of concentrated sulphuric acid. What is the role of sulphuric acid in this reaction? Write the balanced chemical equation of this reaction.
Ans. Conversion of ethanol to ethene is a dehydration reaction which occurs in the presence of excess of concentrated sulphuric acid. Here concentrated sulphuric acid acts as dehydrating agent and remove water molecule from ethanol to form ethene.
Hence concentrated sulphuric acid acts as a dehydrating agent as it removes water molecule.
Question. 40 Carbon, group (14) element in the periodic table, is known to form compounds with many elements.
Write an example of a compound formed with
(a) Chlorine (group 17 of periodic table)
(b) Oxygen (group 16 of periodic table)
Answer.
(a) Carbon (C) exhibits tetravalnecy and form four covalent bonds with other elements. Chlorine atom contains 7 valence electrons and forms one covalent bond with other elements. The compound that is formed by combination of carbon and chlorine is carbon tetrachloride.
Carbon tetrachloride
(b) Oxygen can form two covalent bonds and form carbon dioxide with carbon atom. The center carbon atom is bonded with two oxygen atoms through double covalent bonds. Hence the structure of carbon dioxide would be O=C=O.
Question. 41 In electron dot structure, the valence shell electrons are represented by crosses or dots.
(a) The atomic number of chlorine is 17. Write its electronic configuration.
(b) Draw the electron dot structure of chlorine molecule.
Answer.
(a) Atomic number of chlorine atom is 17. Hence the electronic configuration of Cl (17)would be;
K L M
2 8 7
(b) Chlorine molecule is formed by formation of single covalent bond between two chlorine atoms. The electron dot structure of chlorine molecule is:
Question. 42 Catenation is the ability of an atom to form bonds with other atoms of the same element. It is exhibited by both carbon and silicon. Compare the ability of catenation of the two elements. Give reasons.
Answer.
Both carbon (C) and silicon (Si) are placed in 14th group of the periodic table and have four valence electrons in their valence shell.
Both of them can form four covalent bonds with other elements and can also exhibit the phenomenon of catenation.
Catanation is the self linkage property of atoms due to which they can bond with other similar atoms to form long chain compounds. It depends on the bond energy of atoms.
Out of carbon and silicon, carbon exhibits catenation much more than silicon. This is because of smaller size of carbon and high bond energy of C-C bonds compare to Si-Si bonds. Hence carbon shows catenation to a greater extent than silicon.
Question. 43 Unsaturated hydrocarbons contain multiple bonds between the two c-atoms and show addition reaction. Give the test to distinguish ethane from ethene.
Answer.
Ehene is an unsaturated hydrocarbon as it contains a double covalent bond between two carbon atoms.
Presence of un-saturation or double covalent bond can be distinguished with the help of bromine solution in CCl4. It is an orange colour solution which shows colour change after addition in ethene solution.
The orange colour disappears because of formation of the colourless ethylene dibromide
(CH2Br ─ CH2Br). It is an addition reaction of ethene due to presence of double covalent bond in the molecule.
CH2 = CH2 + Br2 → CH2Br ─ CH2Br
Ethane is a saturated hydrocarbon and cannot show this test. It burns with a clear flame whereas unsaturated hydrocarbons burn with yellow flame and lots of black smoke.
Question. 44 Match the reactions given in Column I with the names given in Column II.
Ans. The matching of Column I and Column II is as given
Question. 45 Write the structural formulae of all the isomers of hexane.
Answer.
Hexane can exhibit five isomers with molecular formula C6H14.
Question. 46 What is the role of metal or reagents written on arrows in the given chemical reactions?
Answer.
(a) Given reaction represents the hydrogenation of alkene which converts alkene to alkane by addition of hydrogen atoms to the carbon atoms included in double bond. Thus, Nickel (Ni) here acts as the catalyst for hydrogenation reaction.
(b) It is the esterification reaction between carboxylic acid and alcohol that forms ester and water molecules. Here concentrated sulphuric acid acts as catalyst as well as dehydrating agent. It provides hydrogen ions to initiate the reaction and also absorbs water molecules so that reaction can form more products.
(c) This reaction involves the conversion of alcohol (ethanol) to carboxylic acid (acetic acid). It is an oxidation reaction and alkaline KMnO4 acts as an oxidising agent for ethanol.
Long Answer Type Questions
Question. 47 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 of the apparatus to prove that the evolved gas is the one which you have named. Also, write the chemical equation of the reaction involved.
Answer.
Ethanoic (CH3COOH) acid reacts with sodium hydrogen carbonate (NaHCO3) to form sodium ethanoate (CH3COONa), water and carbon dioxide gas. Hence salt X is sodium ethanoate and the gas evolved is CO2.The chemical equation of the reaction involved is:
CH3COOH + NaHCO3 → CH3COONa + H2O + CO2
Activity for observing the gas evolved in above reaction:
Set up the apparatus and take sodium hydrogen carbonate in test tube. Add ethanoic acid to it and observe brisk effervescence of carbon dioxide (CO2) gas. Now pass this gas through freshly prepared lime water (Ca(OH)2). It will turn milky due to the formation of insoluble calcium carbonate (CaCO3).
Ca(OH)2 + CO2 → CaCO3 + H2O
(Milky)
Question. 48 (a) What are hydrocarbons? Give examples.
(b) Give the structural differences between saturated and unsaturated hydrocarbons with two examples each.
(c) What is functional group? Give examples of four different functional groups.
Answer.
(a) Compounds which are formed from carbon and hydrogen atoms are called as hydrocarbons. Some common examples of hydrocarbons are methane (CH4), ethane (C2H6), ethene (CH2 = CH2), ethyne (C2H2), cyclohexane (C6H12) and benzene (C6H5).
(b) Saturated hydrocarbons have only C-C bonds means all carbon atoms are bonded with single covalent bonds. The unsaturated hydrocarbons have multiple bonds (double or triple covalent bonds) between carbon atoms.
Examples of saturated hydrocarbons: Methane (CH4), Ethane (CH3 − CH3)
Examples of unsaturated hydrocarbons: Ethene (H2C = CH2), Ethyne (HC CH)
(c) An atom or group of atoms that is responsible for characteristics physical and chemical properties for organic compound is found is called as functional group.
Examples of four functional groups are:
| Name of functional group | Formula of functional group |
| Alcohol | ─ OH |
| Carboxylic acid | COOH |
| Aldehyde | CHO |
| Ketone | >C=O |
Question. 49 Name the reaction which is commonly used in the conversion of vegetable oils to fats. Explain the reaction involved in detail.
Answer.
The reaction that is used to convert vegetable oil to fat is called as hydrogenation reaction. Vegetable oils contain unsaturated hydrocarbons which can exhibit addition reaction with hydrogen to form saturated hydrocarbons or fats. The reaction occurs in the presence of metal catalyst like finely divided nickel or palladium at 200 oC and forms saturated vegetable fats.
The hydrogenation reaction is an industrial method for the manufacturing of vanaspati ghee from vegetable oil.
Here, R is any alkyl group which usually contains a large number of carbon atoms in vegetable oils.
Question. 50 (a) Write the formula and draw electron dot structure of carbon tetrachloride.
(b) What is saponification? Write the reaction involved in this process.
Answer.
(a) The molecular formula of carbon tetrachloride is CC14 and electron dot structure is as below.
Carbon tetrachloride
(b) Alkaline hydrolysis of an ester in the presence of a strong base like sodium hydroxide is called as Saponification. It results the formation of corresponding salts of carboxylic acids and alcohol.
Question. 51 Esters are sweet-smelling substances and are used in making perfumes. Suggest some activity and the reaction involved for the preparation of an ester with well labelled diagram.
Answer.
Activity: Take a test tube and add 1 mL ethanol and 1 mL glacial acetic acid with a few drops of concentrated sulphuric acid. Now heat the solution in water bath for at least five minutes. Pour the content into a beaker containing water and smell the mixture. Sweet smell of ester would be observed.
Reaction of ethanoic acid (CH3COOH) and ethanol (CH3CH2OH) in the presence of concentrated sulphuric acid (H2SO4) forms ethyl ethanoate (CH3COOC2H5) with water.
CH3COOH + CH3CH2OH → CH3COOC2H5 + H2O
Question. 52 A compound C (molecular formula, C2H4O2) reacts with Na metal to form a compound R and evolves a gas which burns with a pop sound. Compound C on treatment with an alcohol A in the presence of an acid forms a sweet smelling compound S (molecular formula, C3H6O2). On addition of NaOH to C, it also gives R and water. S on treatmentwith NaOH solution gives back R and A. Identify C, R, A, S and write down the reactions involved.
Answer.
Compound C with molecular formula C2H4O2 contains two oxygen atoms so it can be either ester or carboxylic acid.
Since it reacts with sodium metal to form compound R and evolves a gas which burns with pop sound, therefore it should be a carboxylic acid which forms sodium alkanoate and hydrogen gas with sodium metal.
2CH3COOH + 2Na → 2CH3COONa + H2 ↑
The gas which burns with pop sound is hydrogen gas.
Reaction of ethanoic acid with alcohol in the presence of an acid (Conc. H2SO4) forms sweet smelling ester. So compound S that is formed due to reaction of ethanoic acid and methanol (A) is methyl ethanoate with molecular formula C3H6O2 and structural formula CH3COOCH3.
Hence compound C = Ethanoic acid (CH3COOH), R = Sodium ethanoate (CH3COONa), A = Methanol (CH3OH) and S = Methyl merhanoate (CH3COOCH3)
Question. 53 Look at the figure and answer the following questions.
(a) What change would you observe in the calcium hydroxide solution taken in tube B?
(b) Write the reaction involved in test tubes A and B respectively.
(c) If ethanol is given instead of ethanoic acid, would you expect the same change?
(d) How can a solution of lime water be prepared in the laboratory?
Answer.
(a) Calcium hydroxide solution in test tube B will react with carbon dioxide gas and turns milky due to the formation of insoluble calcium carbonate (CaCO3).
(b)
Test tube A:
Na2CO3 + 2CH3COOH → 2CH3COONa + CO2 + H2O
Test tube B:
Ca(OH)2 + CO2 → CaCO3 + H2O
(c) Ethanol is weakly acidic and cannot decompose Na2CO3 to give CO2 gas.
(d) Lime water (calcium hydroxide) is usually prepared by the reaction of calcium oxide (quick lime) with water. The supernatent liquid thus formed is decanted or filtered off to get a clear solution of lime water.
Question. 54 How would you bring about the following conversions? Name the process and write the reaction involved.
(a) Ethanol to ethene
(b) Propanol to propanoic acid
Write the reactions.
Answer.
(a) Ethanol can be converted to ethene by dehydration of ethanol in the presence of concentrated sulphuric acid at 170 °C temperature. The reaction is named as dehydration reaction.
(b) Propanol can be converted to propanoic acid by oxidation in the presence of alkaline potassium permanganate and heat. It is named as oxidation reaction.
Question. 55 Draw the possible isomers of the compound with molecular formula C3H6O and also give their electron dot structures.
Answer.
Five isomers possible for the molecular formula C3H6O are listed below.
Question. 56 Explain the given reactions with the examples.
(a) Hydrogenation reaction
(b) Oxidation reaction
(c) Substitution reaction
(d) Saponification reaction
(e) Combustion reaction
Answer.
(a) Hydrogenation reaction: It can be defined as the addition of hydrogen on unsaturatedmolecule to make saturated one.
For example hydrogenation of ethene forms ethane in the presence of metal catalyst like Nickel at high temperature.
(b) Oxidation reaction: Oxidation reaction is addition of oxygen with the help of some oxidizing agent like alkaline potassium dichromate.
For example, oxidation of ethanol forms ethanol, which further oxidize to form ethanoic acid.
(c) Substitution reaction: These reactions involve substituent of one or more part of molecule in the presence of appropriate reagent.
For example, reaction of methane with chlorine gas in the presence of sunlight substitute hydrogen atoms of methane with chlorine atom and form methyl chloride.
(d) Saponification reaction: It is hydrolysis of ester in the presence of strong alkali like sodium hydroxide. It results in the formation of sodium salts of carboxylic acid and alcohol.
CH3COOCH3 + NaOH → CH3COONa + CH3OH
(e) Combustion reaction: Burning of organic compounds in the presence of air forms carbon dioxide and water vapour. This reaction is called as combustion reaction.
CH4 + 2O2 → CO2 + 2H2O + Heat and light
It is an exothermic reaction and releases a large amount of energy in the form of heat.
Question. 57 An organic compound A on heating with concentrated H2SO4 forms a compound B which on addition of one mole of hydrogen in presence of Ni forms a compound C. One mole of compound C on combustion forms two moles of CO2 and three moles of H2O. Identify the compounds A, B and C and write the chemical equation of the reactions involved.
Answer. Combustion of compound C forms two moles of CO2 and three moles of H2O so it must contain two carbon atoms and six hydrogen atoms with molecular formula C2H6 that is ethane.
Ethane is formed by the addition of one mole of hydrogen in the presence of Ni catalyst on compound B. So compound B must be unsaturated hydrocarbon with two carbon atom that is ethene (CH2=CH2).
Hence; A = Ethanol (CH3CH2OH), B = Ethene (CH2 = CH2) and C = Ethane (CH3 ─ CH3)