Revision of Carbon and Its Compounds F

 4. Carbon and Its Compounds  

Specific Properties of Ethanoic Acid

 

 

Soaps and Detergents  

Uniqueness of Carbon  

Formation of Covalent Bonds  

Difference Between Ionic and Covalent Bonds  

Electron Dot Structure  

Saturated and Unsaturated Carbon Compounds  

Chains, Branches and Rings  

Homologous Series of Carbon Compounds  

Nomenclature of Carbon Compounds  

Specific Properties of Ethanol  

General Properties of Carbon Compounds

Lesson: Carbon and its Compounds

Question: 1

Ethane, with the molecular formula C2H6$$ has:

(a) 6 covalent bonds.

(b) 7 covalent bonds.

(c) 8 covalent bonds.

(d) 9 covalent bonds.

Solution:

b

Question:2

Butanone is a four-carbon compound with the functional group:

(a) Carboxylic acid

(b) Aldehyde

(c) Ketone

(d) Alcohol

Solution:

c

Question:3

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.

Solution:

b

Question:4

Explain the nature of the covalent bond using the bond formation in CH3Cl$$.

Solution:

The structure of CH3Cl$$ is given below.

Carbon has four valence electrons. In order to form an octet, it needs four more electrons. It shares 1 electron each with 3 hydrogen atoms and 1 electron with chlorine atom. In this way, chlorine and the three hydrogen atoms attain a stable configuration. Since these bonds are formed because of sharing of electrons, these are therefore called covalent bonds.

Question:5

Draw the electron dot structures for:

(a) Ethanoic acid

(b) H2S$$

(c) Propanone

(d) F2$$

Solution:

Question:6

What is a homologous series? Explain with an example.

Solution:

A series of carbon compounds is said to be homologous when difference between two successive compounds is CH2$$.

Example: Methane, ethane, propane, butane, etc. belong to the alkane homologous series. The general formula of this series is CnH2n+2$$.

Formula of methane: CH4$$

Formula of ethane: CH3CH3$$

Formula of propane: CH3CH2CH3$$

Formula of butane: CH3CH2CH2CH3$$

Here, there is a difference of CH2$$ unit between two successive compounds.

Question:7

How can ethanol and ethanoic acid be differentiated on the basis of their physical and chemical properties?

Solution:

Ethanol and Ethanoic acid can be differentiated on the basis of their following properties:

Ethanol	Ethanoic acid
Physical Properties:
It has a pleasant smell.	It has a pungent vinegar-like smell.
It does not freeze in winter	It freezes in winter.
Chemical Properties:
It does not react with metal carbonates.	It reacts with metal carbonates.
It does not react with NaOH.	It reacts with NaOH.

Question: 8

Why does micelle formation take place when soap is added to water? Will a micelle be formed in other solvents such as ethanol also?

Solution:

A soap molecule has two ends. One end is hydrophilic and the other end is hydrophobic. When soap is dissolved in water and clothes are put in the solution, soap molecules arrange themselves in a cluster.  In this, the hydrophilic end is outside the sphere and hydrophobic end is towards the centre of the sphere.

The dirt present in the clothes is insoluble in water. The hydrophobic ends of the clusters attach themselves to the dirt. This cluster formation in which the dirt is entrapped is called micelle.

Micelles will not be formed in ethanol as it is not as polar as soap.

Question:9

Why is carbon and its compounds used as fuels for most applications?

Solution:

Carbon and its compounds are used as fuel as they have large number of carbon and hydrogen. When burnt in the presence of air, they give a large amount of heat as they have high calorific value. Therefore, carbon and its compounds are used as fuels for most applications.

Question: 10

Explain the formation of scum when hard water is treated with soap.

Solution:

Hard water contains salts of calcium and magnesium. When it is treated with soap, the soap molecules react with these salts and form a precipitate. This precipitate is called scum. A large amount of soap is wasted in the formation of scum before it is used to wash clothes. This makes soap unsuitable to wash clothes in hard water.

Question: 11

What change will you observe if you test soap with litmus paper (red and blue)?

Solution:

Soap is basic in nature. So, it will turn red litmus blue. However, the colour of blue litmus will remain blue.

Question: 12

What is hydrogenation? What is its industrial application?

Solution:

The addition of hydrogen to an unsaturated hydrocarbon to obtain saturated hydrocarbon is called hydrogenation. This reaction is carried out in the presence of catalysts like nickel or palladium.

Industrial application:

·         In petrochemical industries, hydrogenation is used to convert alkenes into alkanes (paraffins) and cycloalkanes.

·         It is also used to prepare vegetable ghee from vegetable oils.

Question: 13

Which of the following hydrocarbons undergo addition reactions?

C2H6, C3H8, C3H6,  C2H2  and CH4$$.

Solution:

C3H6and C2H2$$ are unsaturated hydrocarbons. Unsaturated hydrocarbons undergo addition reactions.

Question: 14

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

Solution:

Butter contains saturated fat while cooking oil has unsaturated fat. All unsaturated carbon compounds decolorize bromine water whereas saturated hydrocarbons do not decolorize bromine water. So, bromine water test can be applied to differentiate between butter and cooking oil.

Question: 15

Explain the mechanism of the cleaning action of soaps.

Solution:

Soap molecules have two ends. One end is hydrophilic and another end is hydrophobic. When soap is dissolved in water, the soap molecules arrange themselves in a cluster. Since the dirt present in the clothes is insoluble in water, the hydrophobic ends of the clusters attach themselves to the dirt. The dirt is entrapped in the cluster. This cluster formation in which the dirt is entrapped is called micelle. These micelles remain suspended in the water. When rinsed, the dirt particles are washed away with water.

Questions

Q1	What are hydrocarbons? What are its types?

Q2	The formula of a hydrocarbon is CnH2n. Name the family to which it belongs and also predict its nature?

Q3	What is the valency of carbon in: HC = CH, CH2 = CH2 and CH3 - CH3?

Q4	What are alcohols?

Q5	What are organic compounds?

Q6	Why is high temperature not beneficial for alcoholic fermentation?

Q7	What are cyclic hydrocarbons?

Q8	Both diamond as well as graphite is made of carbon but then why is diamond a bad conductor of heat and electricity yet graphite is not?

Q9	Draw bond formation of CCl4 and CH4 using Lewis dot structures.

Q10	How are saturated hydrocarbons different from unsaturated hydrocarbons?

Q11	Draw the electron dot structure for (a) Methane (b) Ethane (c) Ethene (d) Ethyne

Q12	What is hydrogenation? Where do we find its application?

Q13	What is isomerism?

Q14	Enumerate any four differences between alkanes and alkenes. How are they alike?

Q15	Explain the tetravalency and the catenation properties of carbon.

Q16	What are allotropes? Name any 3 crystalline allotropic forms of carbon and give two uses of each of them.

Q17	Explain addition and substitution reactions of hydrocarbons.

Q18	What are cyclic hydrocarbons? Explain saturated and unsaturated cyclic hydrocarbons.

Q19	One end of the soap molecule is hydrophilic and while the other end is hydrophobic. How does this help us in keeping our clothes clean?

Q20	Write important uses of: (1) Ethanol and (2) Ethanoic acid.

Questions

Q1	What are hydrocarbons? What are its types?

A1	A compound made up of only carbon and hydrogen is called a hydrocarbon. Hydrocarbons are of two types: Saturated hydrocarbons and unsaturated hydrocarbons.

Q2	The formula of a hydrocarbon is CnH2n. Name the family to which it belongs and also predict its nature?

A2	The hydrocarbon CnH2n belongs to the family of alkenes and it is unsaturated in nature.

Q3	What is the valency of carbon in: HC = CH, CH2 = CH2 and CH3 - CH3?

A3	The valency of carbon is 4, irrespective of the compound it is forming. Not only in the compounds HC = CH, CH2 = CH2 and CH3 - CH3, but in all its compounds, be it saturated or unsaturated, the valency of carbon is 4.

Q4	What are alcohols?

A4	Alcohols are organic compounds in which a hydroxyl group (-OH) is attached to a carbon atom. CH3-OH is an example of an alcohol.

Q5	What are organic compounds?

A5	The compounds of carbon except its carbonates, hydrocarbonate salts and oxides are known as organic compounds.

Q6	Why is high temperature not beneficial for alcoholic fermentation?

A6	High temperature destroys the enzymes such as zymase and invertase, which are needed for fermentation and so high temperature is not beneficial for alcoholic fermentation.

Q7	What are cyclic hydrocarbons?

A7	Hydrocarbons in which carbon atoms are arranged in the form of a ring are called cyclic hydrocarbons. Example: Benzene

Q8	Both diamond as well as graphite is made of carbon but then why is diamond a bad conductor of heat and electricity yet graphite is not?

A8	Diamond is a bad conductor of heat and electricity because there are no free electrons present in it. In diamond each carbon atom is connected to four other carbon atoms. Graphite on the other hand,contains free electrons and is therefore a good conductor of heat and electricity.

Q9	Draw bond formation of CCl4 and CH4 using Lewis dot structures.

A9	Representation of bond formation of CCl4 and CH4 using Lewis dot structures:

Q10	How are saturated hydrocarbons different from unsaturated hydrocarbons?

A10	Saturated hydrocarbons are the hydrocarbons which have only single bonds and are rather inert, that is, non-reactive. These compounds burn in air with a blue, non-sooty flame. These are also known as alkanes. Unsaturated hydrocarbons have double or triple bonds along with single bonds, and are reasonably reactive. These compounds burn in air with a yellow, sooty flame.

Q11	Draw the electron dot structure for (a) Methane (b) Ethane (c) Ethene (d) Ethyne

A11	The electron dot structures are given below:

Q12	What is hydrogenation? Where do we find its application?

A12	The addition of hydrogen to an unsaturated hydrocarbon, to obtain saturated hydrocarbon, is called hydrogenation. This reaction is carried out in the presence of catalysts like nickel or palladium. It is used to prepare vegetable ghee from vegetable oils.

Q13	What is isomerism?

A13	Organic compounds having same molecular formula but different structural formula are known as isomers and the phenomenon is called isomerism. For example, the formula C4H10 represents two possible structural formulae, butane and methyl propane:

Q14	Enumerate any four differences between alkanes and alkenes. How are they alike?

A14

Differences between alkanes and alkenes are as follows: • Alkanes are generally unreactive but alkenes are very reactive. • Alkanes contain only single bonds between carbon atoms, whereas alkenes contain double bonds   between carbon atoms. • Alkanes undergo substitution reactions, whereas alkenes undergo addition reactions. • In reaction with orange-coloured aqueous bromine, alkenes rapidly decolourise aqueous bromine because    a colourless dibromo compound is formed, while alkanes do not do so. Alkenes and alkanes have resemblances too. Both of them being hydrocarbons are flammable, and in complete combustion in the presence of oxygen, they form carbon dioxide and water and also release heat, and are therefore useful as fuels.

Q15	Explain the tetravalency and the catenation properties of carbon.

A15

Tetravalency: A carbon atom has an electronic configuration as 2, 4. It has 4 electrons in its outermost shell. To attain a stable inert gas configuration by having 8 electrons in its L shell or 2 in its K shell, a carbon atoms needs to either remove or add 4 electrons to the L shell. But a carbon atom holds the electrons very tightly and it is not possible either to remove 4 electrons from a carbon atom or add 4 electrons to the atom. So, carbon achieves the inert gas configuration by sharing of electrons. Since a carbon atom requires 4 more electrons to attain stable inert gas configuration, its valency is 4.   Catenation: Carbon is tetravalent. It forms covalent bonds with other atoms to achieve stable configuration. Due to its tetravalency, carbon has the unique property of combining with other carbon atoms to form a long chain or cyclic ring. No other atom has this property of forming long chain through self-linking. This property of self-linking of carbon atoms through covalent bonds to form straight chains or cyclic rings of carbon atoms is called catenation.

Q16	What are allotropes? Name any 3 crystalline allotropic forms of carbon and give two uses of each of them.

A16

The property of an element to exist in more than one form in the same physical state is known as allotropy and the different forms are called allotropes. E.g. Diamond, graphite and fullerene are the crystalline allotropic forms of carbon. Uses of diamond: (a) Due to its hardness it is used in knives for cutting marble, granite and glass and also as an abrasive for     polishing hard surfaces. (b) It is used for ornaments, studded as precious stones.   Uses of graphite: (a) It is used as a powdered lubricant for parts of machineries. (b) It is used for making electrodes of cells.   Uses of fullerene: (a) In pure form, it behaves as an insulator. However, it can be converted into a semiconductor under suitable conditions. (b) In small amounts, it is used to catalyse the photochemical refining industry.

Q17	Explain addition and substitution reactions of hydrocarbons.

A17

Addition reaction of hydrocarbon: The reaction in which an unsaturated hydrocarbon combines with another atom to form another compound is called an addition reaction. So, all hydrocarbons having a double or triple bond can bond with atoms like hydrogen, chlorine, etc. in an addition reaction. The equation shows addition reaction between an unsaturated hydrocarbon and water in presence of an acid catalyst.   Substitution reaction of hydrocarbon: Saturated hydrocarbons contain only carbon-carbon single bond. Hence, they are quite unreactive in the presence of most reagents. They, however, do undergo substitution reaction with chlorine, in the presence of sunlight. Chlorine can substitute the hydrogen atoms one by one from the saturated hydrocarbons. The reaction in which the hydrogen atoms of a saturated hydrocarbon are replaced by some other atoms, it is called a substitution reaction. The equation shows the reaction of methane with chlorine, in the presence of sunlight, to form chloromethane and hydrogen chloride.

Q18	What are cyclic hydrocarbons? Explain saturated and unsaturated cyclic hydrocarbons.

A18	The compounds of carbon which contain a closed ring of carbon atoms are called cyclic hydrocarbons. They can be saturated or unsaturated. Saturated cyclic hydrocarbons are also called cycloalkanes. Examples of saturated cyclic hydrocarbons: Cyclopropane, Cyclobutane. Example of unsaturated cyclic hydrocarbon: Benzene (C6H6)

Q19	One end of the soap molecule is hydrophilic and while the other end is hydrophobic. How does this help us in keeping our clothes clean?

A19

Soaps are molecules in which the two ends have differing properties; one is hydrophilic (it dissolves in water) while the other end is hydrophobic (it dissolves in hydrocarbons of fats and oil). When soap is at the surface of water the hydrophobic end of soap will not be soluble in water and the soap will arrange in a line along the surface of water with the ionic end in water and the hydrocarbon end sticking out of water. Inside water, these molecules have an exclusive direction that keeps the hydrocarbon portion out of the water. This is attained by forming clusters of molecules in which the hydrophobic ends are in the inner side of the cluster and the ionic ends are on the surface of the cluster. This formation is called a micelle. In the form of a micelle, soap is able to clean, since the oily dirt gets collected in the centre of the micelle. The micelles stay as collides in the solution and does not come closer to precipitate due to ion-ion repulsion. Hence the dirt suspended in the micelles is also easily rinsed away. To wash away the loosened dirt particles in the form of micelles from the surface of the cloth, it is scrubbed mechanically, beaten or else agitated in washing machines. The cleaning action of soap has been explained with the help of the following figure.

Q20	Write important uses of: (1) Ethanol and (2) Ethanoic acid.

A20

(1) Uses of ethanol: a. Ethanol (ethyl alcohol) is used for making alcoholic drinks like wines, whiskies, beer, etc. b. It is used for making some medicines like cough syrups, tincture iodine and some tonics. c. It is used for making wood polish. d. It is used for making anti-freeze material for cooling engines of vehicles. (2) Uses of ethanoic acid: a. Vinegar (dilute solution of ethanoic acid in water) is used as a preservative of pickles. b. It is used as a useful reagent in the chemical laboratories. c. It is used for making esters which are used as flavouring agents and perfumes. Lesson: Carbon and its Compounds Question:1 What would be the electron dot structure of carbon dioxide which has the formula CO2$$? Solution: Question:2 What would be the electron dot structure of a molecule of sulphur which is made up of eight atoms of sulphur? (Hint –$$ The eight atoms of sulphur are joined together in the form of a ring.) Solution: Question:3 How many structural isomers can you draw for pentane? Solution: Question:4 What are the two properties of carbon which lead to the huge number of carbon compounds we see around us? Solution: The following are the features due to which carbon atoms can form a large number of compounds: ·         Catenation –$$ Carbon can form bond with other carbon atoms. ·         Tetravalency –$$ The valency of carbon is four. It means that one carbon atom can form bonds with four different atoms. Even if one of these four atoms is changed, a new compound is formed.   Question:5 What will be the formula and electron dot structure of cyclopentane? Solution: The formula of cyclopentane is C5H10$$. Question: 6 Draw the structures for the following compounds. (a) Ethanoic acid (b) Bromopentane* (c) Butanone (d) Hexanal. *Are structural isomers possible for bromopentane? Solution: Question: 7 How would you name the following compounds? Solution: (i)     Bromoethane (ii)  Methanal (formaldehyde) (iii)            Hexyne Question: 8 Why is the conversion of ethanol to ethanoic acid an oxidation reaction? Solution: CH3CH2OH+2[O]  −→−−−−−−−−Alkaline  KMnO4CH3COOH+H2O$$ In this reaction, one oxygen atom is added to ethanol to form ethanoic acid.  Hence, it is an oxidation reaction. Question: 9 A mixture of oxygen and ethyne is burnt for welding. Can you tell why a mixture of ethyne and air is not used? Solution: When a mixture of oxygen and ethyne is burnt for welding, the following reaction takes place: 2 C2H2+5 O2→4 CO2+2 H2O+Heat$$ Due to the presence of oxygen, complete combustion takes place. The air, however, contains limited supply of oxygen. So, when ethyne is burnt in air, it results in incomplete combustion. Question: 10 How would you distinguish experimentally between an alcohol and a carboxylic acid? Solution: An alcohol and a carboxylic acid can be distinguished on the basis of their reaction with carbonates and hydrogen carbonates. On reacting with an acid, a carbonate or a hydrogen carbonate give CO2$$. CO2$$ gas turns lime water milky. 2 CH3COOH+Na2CO3→2 CH3COONa+H2O+CO2CH3COOH+NaHCO3→CH3COONa+H2O+CO2$$ An alcohol, however, does not react with carbonates and hydrogen carbonates. Question: 11 What are oxidising agents? Solution: The substances that give oxygen or replace hydrogen in a chemical reaction are called oxidising agents. Question: 12 Would you be able to check if water is hard by using a detergent? Solution: No, it is not possible to check if water is hard by using detergent as detergents form lather with both hard and soft water. Question: 13 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? Solution: One end of a soap molecule is hydrophobic and the other is hydrophilic. The hydrophobic end attaches to the dirt particles and forms a cluster called micelle. The hydrophilic end remains attached to water. When the cloth is agitated, these micelles get dispersed in water due to which the soap water becomes dirty and the clothes get cleaned. Lesson: Carbon and its Compounds Question: 1 Carbon exists in the atmosphere in the form of: (a) Carbon monoxide only (b) Carbon monoxide in traces and carbon dioxide (c) Carbon dioxide only (d) Coal Solution: b Question:2 Which of the following statements are usually correct for carbon compounds? (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) Solution: d 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 Solution: a Question: 4 Buckminsterfullerene is an allotropic form of: (a) Phosphorus (b) Sulphur (c) Carbon (d) Tin Solution: c Question: 5 Which of the following are correct structural isomers of butane?   (a) (i) and (iii) (b) (ii) and (iv) (c) (i) and (ii) (d) (iii) and (iv) Solution: c Question:6 CH3COOH  −→−−−−−−−−−−−−Heat   +Alkaline KMnO4   CH3COOH  In the above given reaction, alkaline KMnO4 acts as: (a) Reducing agent (b) Oxidising agent (c) Catalyst (d) Dehydrating agent Solution: b 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 Solution: a Question: 8 In which of the following compounds, —OH is the functional group? (a) Butanone (b) Butanol (c) Butanoic acid (d) Butanal Solution: b 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 Solution: a Question: 10 Which of the following is the correct representation of electron dot structure of nitrogen? Solution: d Question: 11 Structural formula of ethyne is: Solution: a 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) Solution: d 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 Solution: b 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 Solution: a 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 Solution: c  Question: 16 Structural formula of benzene is: Solution: c  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 Solution: c Question: 18 The correct structural formula of butanoic acid is: Solution: d  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 Solution: c 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) Solution: a 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 Solution: b Question: 22 The correct electron dot structure of a water molecule is: Solution: c Question: 23 Which of the following is not a straight chain hydrocarbon? Solution: d 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) Solution: c Question: 25 Which of the following does not belong to the same homologous series? (a) CH4 (b) C2H6 (c) C3H8 (d) C4H8 Solution: d Question: 26 The name of the compound CH3—CH2—CHO is: (a) Propanal (b) Propanone (c) Ethanol (d) Ethanal Solution: a 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) Solution: d Question: 28 Which of the following represents saponification reaction? (a) CH3COONa+NaOH  −→−CaO CH4+Na2CO3 (b) CH3COOH+C2H5OH  −→−−H2SO4 CH3−COO−C2H5+H2O (c) 2 CH3COOH+2 Na →2 CH3COONa+H2 (d) CH3COOC2H5+NaOH→CH3COONa+C2H5OH Solution: d Question: 29 The first member of alkyne homologous series is: (a) Ethyne (b) Ethene (c) Propyne (d) Methane Solution: a Question: 30 Draw the electron dot structure of ethyne and also draw its structural formula: Solution: Structural formula of ethyne H         C          C         H Electron dot structure of ethyne ( C2H2 ) Question: 31 Write the names of the following compounds: Solution: (a) Pentanoic acid (b) Butyne (c) Heptanal (d) Pentanol Question: 32 Identify and name the functional groups present in the following compounds. Solution: Question: 33 A compound X is formed by the reaction of a carboxylic acid C2H4O2 and an alcohol in 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. Solution: (a) The carboxylic acid is ethanoic acid. (b) The alcohol is ethanol. (c) X is ethyl ethanoate. The reaction is as follows: CH3COOH+C2H5OH  −→−−H2SO4  CH3COOC2H5+H2OEthanoic acid  Ethanol                    Ethyl ethanoate  Question: 34 Why detergents are better cleansing agents than soaps? Explain. Solution: Detergents are better cleansing agents than soaps. This is because detergents are effective even in hard water whereas, soaps cannot be used in hard water for washing clothes or cleaning dirt. This is because the charged ends of detergents do not react with calcium and magnesium ions in hard water to form insoluble precipitate. Question: 35 Name the functional groups present in the following compounds (a) CH3COCH2CH2CH2CH3 (b) CH3CH2CH2COOH (c) CH3CH2CH2CH2CHO (d) CH3CH2OH Solution: (a) Ketone (b) Carboxylic acid (c) Aldehyde (d) Alcohol Question: 36 How is ethene prepared from ethanol? Give the reaction involved in it. Solution: Ethanol dehydrates on heating with concentrated sulphuric acid at 443 K and gives ethane and water. C2H5OH −→−−−−−−−−443  KHot  conc .  H2SO4  CH2=CH2+H2O  Question: 37 Intake of small quantity of methanol can be lethal. Give comment. Solution: Methanol gets oxidised in the liver and forms methanal. Methanal reacts rapidly with the protoplasm and leads to its coagulation. It also blocks the optic nerves leading to 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. Solution: Hydrogen gas is evolved when ethanol reacts with sodium. The equation for the reaction is: 2 CH3CH2OH+2 Na→2 CH3CH2ONa+H2 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. Solution: When ethanol is heated to form ethane, sulphuric acid acts as a dehydrating agent in the reaction. C2H5OH −→−−−−−−−443  KHot conc . H2SO4  CH2=CH2+H2O  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) Solution: (a) Carbon tetrachloride ( CCl4 ) (b) Carbon dioxide ( CO2 ) 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. Solution: (a) Electronic configuration of chlorine:   K L M Number of electrons 2 8 7 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. Solution: Carbon has a smaller size. Due to its smaller size, carbon exhibits catenation much more than silicon, which has a relatively bigger size. This smaller size makes the C–C bonds strong while the Si–Si bonds are comparatively weaker. Question: 43 Unsaturated hydrocarbons contain multiple bonds between the two C-atoms and show addition reactions. Give the test to distinguish ethane from ethene. Solution: Unsaturated hydrocarbons have double or triple bonds between two carbon atoms. They participate in the addition reaction. Due to the presence of double bond, these molecules can break one of the carbon-carbon bonds and can add other atoms by sharing of electrons with new atoms. Thus, addition reaction results in the formation of a saturated compound. All unsaturated carbon compounds decolorize bromine water whereas all saturated hydrocarbons do not decolorize bromine water. Ethane and ethene can, thus, be distinguished by the bromine water test. Question: 44 Match the reactions given in Column (A) with the names given in column (B). Solution: (a) — (iv) (b) — (i) (c) — (ii) (d) — (iii) Question: 45 Write the structural formulae of all the isomers of hexane. Solution: Question: 46 What is the role of metal or reagents written on arrows in the given chemical reactions? Solution: (a)  Ni acts as a catalyst. (b) Concentrated H2SO4 acts as a catalyst. (c) Alkaline KMnO4 acts as an oxidising agent. 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 chemical equation of the reaction involved. Solution: When ethanoic acid reacts with sodium hydrogen carbonate, sodium ethanoate is formed. Thus, X is sodium ethanoate. Gas evolved is carbon dioxide. Activity: The gas that is evolved is passed through lime water. It turns the lime water milky. This confirms the evolution of carbon dioxide gas in the reaction. CH3COOH+NaHCO3→CH3COONa+H2O+CO2 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 a functional group? Give examples of four different functional groups. Solution: (a)   Hydrocarbons are compounds formed mainly from carbon and hydrogen. E.g. methane, ethene, propyne, butanol. pentanoic acid, etc. (b)   In saturated hydrocarbons, there is no double or triple bond between two carbon atoms. In unsaturated hydrocarbons, there is at least one double or triple bond between two carbon atoms. (c)   Functional group – A functional group is an atom or a group of atoms joined in a specific manner which is responsible for the characteristic chemical properties of the organic compounds. Examples of functional groups includes hydroxyl group (–OH), aldehyde group (–CHO), carboxylic group (–COOH), etc. Question: 49 Name the reaction which is commonly used in the conversion of vegetable oils to fats. Explain the reaction involved in detail. Solution: The reaction which is commonly used in the conversion of vegetable oils to fats is called hydrogenation reaction. This reaction involves the addition of hydrogen to an unsaturated hydrocarbon to obtain saturated hydrocarbon. This reaction is carried out in the presence of a catalyst like nickel or palladium. It can be seen that one of the two bonds between the carbon atoms breaks to accommodate hydrogen and form saturated hydrocarbon. 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. Solution: a)      The chemical formula for carbon tetrachloride is CCl4. (b) Saponification is the process of making soap. It involves conversion of ethyl acetate into salts of carboxylic acids and ethanol by treating them with a base. CH3CO2OH5  −→−−NaOH  CH3COONa+ C2H5OH 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. Solution: Activity ·         Take 1ml of pure ethanol and 1ml ethanoic acid along with a few drops of concentrated sulphuric acid in a test tube. ·         Warm the content in a water-bath at about 60°C for at least 5 minutes. ·         Pour the content into a beaker that contains 20-50 ml of water and smell the resulting mixture. Observation: The mixture smells sweet indicating the formation of ester. The reaction is as follows: CH3COOH+  C2H5OH−→−−H2SO4  CH3COOC2H5+ H2OEthanoic acid  Ethanol         Ester (Ethyl ethanoate) 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. Son treatment with NaOH solution gives back R and A. Identify C, R, A, S and write down the reactions involved. Solution: Here, compound C (molecular formula C2H4O2 ) is ethanoic acid. R is formed when ethanoic acid reacts with sodium. Thus, R is sodium salt of ethanoic acid (sodium acetate) and gas evolved is hydrogen. On reacting with an alcohol A, ethanoic acid forms a compound S (molecular formula C3H6O2 ). Thus, S is an ester (methyl acetate) and alcohol A is methanol. The reactions are: (a)   2 CH3COOH+2 Na→2 CH3COONa+H2      (C)                                       (R) (b)   CH3COOH+  CH3OH−→−−H2SO4  CH3COOC2H5+ H2O      (C)                        (A)                                         (S) (c)   CH3COOH+NaOH→CH3COONa+H2O                                                   (R) (d)   CH3COOH3+NaOH→CH3COONa+CH3OH                                                     (R)            (A) Question: 53 Look at the figure which is given below 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 limewater be prepared in the laboratory? Solution: (a)   Calcium hydroxide solution will turn milky when the gas evolved in the reaction is passed through it. (b) Reactions involved in test tube A 2 CH3COOH+Na2CO3→2 CH3COONa+H2O+CO2 Reactions involved in test tube B Ca(OH)2+CO2→CaCO3+H2O (c) Ethanol ( C2H5OH ) does not react with sodium carbonate ( Na2CO3 ). Hence, a similar change is not expected. C2H5OH+Na2CO3→No change (d)   When calcium oxide is dissolved in water and the supernatant liquid is decanted, lime water is obtained. 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. Solution: (a)   By the dehydration of ethanol in the presence of concentrated H2SO4, C2H5OH −→−−−−−−−443  KHot conc . H2SO4  CH2=CH2+H2O (b)   By the oxidation of propanol using oxidizing agent such as alkaline KMnO4, CH3CH2CH2OH −→−−−−−HeatAIk . KMnO  CH3CH2COOH Question: 55 Draw the possible isomers of the compound with molecular formula C3H6O and also give their electron dot structures. Solution: Question: 56 Explain the given reactions with the examples: (a) Hydrogenation reaction (b) Oxidation reaction (c) Substitution reaction (d) Saponification reaction (e) Combustion reaction Solution: (a)   Hydrogenation reaction : The addition of hydrogen to an unsaturated hydrocarbon to make it saturated is known as hydrogenation reaction. Example: Vegetable oil (Unsaturated fat)+Hydrogen                    →Vegetable ghee (Saturated  fat) (b)   Oxidation reaction: The reaction which involves addition of oxygen to a reactant or removal of hydrogen from a reactant is called oxidation reaction. Example:  Methane reacts with oxygen to form carbon dioxide and water. Here methane is oxidised to carbon dioxide. (c)    Substitution reaction: When an atom or a group of atoms substitutes another atom or a group of atoms from the molecule, it is known as substitution reaction. Example: In the presence of sunlight, chlorine is added to methane to form methyl chloride and hydrochloric acid. CH4+Cl2→CH3Cl+HCl (d)   Saponification: A reaction in which an ester is hydrolysed in the presence of a base is called saponification reaction. Example: It is used in the preparation of soap. CH3COOC2H5+NaOH →CH3COONa+C2H5OH (e) Combustion reaction: A reaction, in which organic compounds burn readily in air to form CO2 and water vapour along with lot of heat, is known as combustion reaction. Example: Methane burns in air to form carbon dioxide and water, releasing large amount of heat and light. CH4+2 O2→CO2+2 H2O+Heat and light Question: 57 An organic compound A on heating with concentrated H2SO4 forms a compound B which on addition of one mole of hydrogen in the presence of Ni forms a 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 of the reactions involved. Solution: One mole of compound C on combustion forms two moles of CO2 and 3 moles of H2O. This means that the compound has at least 2 carbon atoms and 6 hydrogen atoms. Thus, the molecular formula of C is C2H6 (ethane). Compound C, i.e. ethane, is obtained by the addition of one mole of hydrogen ( H2 ) to compound B. Thus, compound B should be C2H4 (ethene). Compound B, i.e. ethene, is obtained by heating the compound A with concentrated H2SO4 which shows it to be an alcohol. So compound A could be C2H5OH (ethanol). CH3CH2OH−→−−−−−−−HotConc.H2SO4  C2H4+ H2O      A                                                             BC2H4+H2→Ni  C2H6     B                                  C2 C2H6+7 O2→4 CO2+6 H2O+Heat and light    C  A is ethanol ( C2H5OH ) B is ethene ( C2H4 ) C is ethane ( C2H6 ) Lesson: Carbon and its Compounds Question: 1 Ethane, with the molecular formula C2H6 has: (a) 6 covalent bonds. (b) 7 covalent bonds. (c) 8 covalent bonds. (d) 9 covalent bonds. Solution: b Question:2 Butanone is a four-carbon compound with the functional group: (a) Carboxylic acid (b) Aldehyde (c) Ketone (d) Alcohol Solution: c Question:3 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. Solution: b Question:4 Explain the nature of the covalent bond using the bond formation in CH3Cl. Solution: The structure of CH3Cl is given below. Carbon has four valence electrons. In order to form an octet, it needs four more electrons. It shares 1 electron each with 3 hydrogen atoms and 1 electron with chlorine atom. In this way, chlorine and the three hydrogen atoms attain a stable configuration. Since these bonds are formed because of sharing of electrons, these are therefore called covalent bonds. Question:5 Draw the electron dot structures for: (a) Ethanoic acid (b) H2S (c) Propanone (d) F2 Solution: Question:6 What is a homologous series? Explain with an example. Solution: A series of carbon compounds is said to be homologous when difference between two successive compounds is CH2. Example: Methane, ethane, propane, butane, etc. belong to the alkane homologous series. The general formula of this series is CnH2n+2. Formula of methane: CH4 Formula of ethane: CH3CH3 Formula of propane: CH3CH2CH3 Formula of butane: CH3CH2CH2CH3 Here, there is a difference of CH2 unit between two successive compounds. Question:7 How can ethanol and ethanoic acid be differentiated on the basis of their physical and chemical properties? Solution: Ethanol and Ethanoic acid can be differentiated on the basis of their following properties: Ethanol Ethanoic acid Physical Properties: It has a pleasant smell. It has a pungent vinegar-like smell. It does not freeze in winter It freezes in winter. Chemical Properties: It does not react with metal carbonates. It reacts with metal carbonates. It does not react with NaOH. It reacts with NaOH. Question: 8 Why does micelle formation take place when soap is added to water? Will a micelle be formed in other solvents such as ethanol also? Solution: A soap molecule has two ends. One end is hydrophilic and the other end is hydrophobic. When soap is dissolved in water and clothes are put in the solution, soap molecules arrange themselves in a cluster.  In this, the hydrophilic end is outside the sphere and hydrophobic end is towards the centre of the sphere. The dirt present in the clothes is insoluble in water. The hydrophobic ends of the clusters attach themselves to the dirt. This cluster formation in which the dirt is entrapped is called micelle. Micelles will not be formed in ethanol as it is not as polar as soap. Question:9 Why is carbon and its compounds used as fuels for most applications? Solution: Carbon and its compounds are used as fuel as they have large number of carbon and hydrogen. When burnt in the presence of air, they give a large amount of heat as they have high calorific value. Therefore, carbon and its compounds are used as fuels for most applications. Question: 10 Explain the formation of scum when hard water is treated with soap. Solution: Hard water contains salts of calcium and magnesium. When it is treated with soap, the soap molecules react with these salts and form a precipitate. This precipitate is called scum. A large amount of soap is wasted in the formation of scum before it is used to wash clothes. This makes soap unsuitable to wash clothes in hard water. Question: 11 What change will you observe if you test soap with litmus paper (red and blue)? Solution: Soap is basic in nature. So, it will turn red litmus blue. However, the colour of blue litmus will remain blue. Question: 12 What is hydrogenation? What is its industrial application? Solution: The addition of hydrogen to an unsaturated hydrocarbon to obtain saturated hydrocarbon is called hydrogenation. This reaction is carried out in the presence of catalysts like nickel or palladium. Industrial application: ·         In petrochemical industries, hydrogenation is used to convert alkenes into alkanes (paraffins) and cycloalkanes. ·         It is also used to prepare vegetable ghee from vegetable oils. Question: 13 Which of the following hydrocarbons undergo addition reactions? C2H6, C3H8, C3H6,  C2H2  and CH4. Solution: C3H6and C2H2 are unsaturated hydrocarbons. Unsaturated hydrocarbons undergo addition reactions. Question: 14 Give a test that can be used to differentiate chemically between butter and cooking oil. Solution: Butter contains saturated fat while cooking oil has unsaturated fat. All unsaturated carbon compounds decolorize bromine water whereas saturated hydrocarbons do not decolorize bromine water. So, bromine water test can be applied to differentiate between butter and cooking oil. Question: 15 Explain the mechanism of the cleaning action of soaps. Solution: Soap molecules have two ends. One end is hydrophilic and another end is hydrophobic. When soap is dissolved in water, the soap molecules arrange themselves in a cluster. Since the dirt present in the clothes is insoluble in water, the hydrophobic ends of the clusters attach themselves to the dirt. The dirt is entrapped in the cluster. This cluster formation in which the dirt is entrapped is called micelle. These micelles remain suspended in the water. When rinsed, the dirt particles are washed away with water.