Carbon and its compounds

Question 1

Question: What is organic chemistry?
Answer: Organic chemistry is the study of carbon compounds of living matter i.e., plants and animals (CO₂, carbonates, bicarbonates etc. do not fall in this category).

Question 2

Question: Give three reasons for the existence of a large number of carbon compounds?
Answer: Catenation The unique property of the 'C' element to be able to form continuous links with other 'C' atoms through covalency called catenation, is one reason for the existence of a large number of organic compounds. Formation of Multiple Bonds Two 'C' atoms can either be linked through a single bond

or a double bond

. This leads to the formation of a variety of organic compounds. Isomerism This property, shown by organic compounds, which have same molecular formula but different structural formulae is also a reason for formation of a large number of organic compounds. Example: For C₄H₁₀ formula there could be two isomers.

Question 3

Question: What are hydrocarbons?
Answer: Compounds containing only the elements carbon and hydrogen are called hydrocarbons. They are a parent class of organic carbon compounds from which all other classes of hydrocarbon sub groupings of compounds can be made. Examples: Ethane (C₂H₄) alkane group; hexene (C₆H₁₂) alkene group; acetylene (C₂H₂) alkyne group and benzene C₆H₆ (arene or aromatic group).

Question 4

Question: What are the different types of covalent bonds found in carbons compounds? Briefly explain with examples.
Answer: There are three classes of covalent bonds, mainly found in hydrocarbons compounds of the aliphatic type:
Alkanes
These hydrocarbons have a single covalent bond between the 'C' atoms throughout the molecule i.e., only one pair of electrons is shared between any two carbon atoms.

Examples: C₂H₆, C₃H₈, C₄H₁₀ ---------


Alkenes
These are aliphatic hydrocarbons in which at least one pair of 'C' atoms are linked by a double bond in the molecule.

Examples:

Alkynes
These are aliphatic hydrocarbons in which at least one pair of 'C' atoms are linked by a triple bond in the molecule

Examples: C₂H₂, C₃H₄, C₄H₆

Question 5

Question: How do the prefixes and suffixes for the open chain hydrocarbons indicate their formula?
Answer: The prefixes meth-, eth-, prop-, but-, pent-, hex-, hept-, oct-, non- deca- indicate that the number of 'C' atoms in the molecule of hydrocarbons is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 respectively. The suffix ane or ene or yne with these, indicate whether they belong to the family of alkane or alkene or alkyne respectively. Examples:

Methane CH4	Methene Does not exist	Methyne Does not exist
Ethane	Ethylene or Ethene	Acetylene or Ethyne
Propane	Propylene or Propene	Propyne

Methane CH₄Methene Does not existMethyne Does not existEthane


Ethylene or Ethene

Acetylene or Ethyne

Propane

Propylene or Propene

Propyne

Question 6

Question: What is the difference between saturated and unsaturated carbon compounds?
Answer: carbon compounds in which all the four valencies of carbon atom are satisfied by forming single covalent bonds are known saturated carbon compounds. For example, ethane:


In unsaturated carbon compounds, at least one or more double covalent bond or triple bonds satisfy the four valencies of a carbon atom. For example, ethylene or acetylene:



The main differences between saturated and unsaturated hydrocarbons are:

Saturated C Saturated compounds	Unsaturated compounds
These compounds contain all single carbon - carbon covalent bond.	These compounds contain at least one double or triple covalent bond.
These compounds are less reactive.	These compounds are more reactive.
Saturated compounds undergo substitution reactions.	Unsaturated compounds under go addition reactions.
These compounds have more number of hydrogen atoms.	The number of hydrogen atoms is less here.

Saturated C Saturated compoundsUnsaturated compoundsThese compounds contain all single carbon - carbon covalent bond.These compounds contain at least one double or triple covalent bond.These compounds are less reactive.These compounds are more reactive.Saturated compounds undergo substitution reactions.Unsaturated compounds under go addition reactions.These compounds have more number of hydrogen atoms.The number of hydrogen atoms is less here.

Question 7

Question: An alcohol and an ether have same molecular formula C₂H₆O. Draw their structural formula, indicating their functional groups.
Answer:


Ether
-OH is the functional group in ethyl alcohol while O- is the functional group in ether. Ethyl alcohol is an isomer of dimethyl ether.

Question 8

Question: What are functional groups? write the functional groups of:
1) acids
2) aldehydes.
Answer: The functional group is an atom, or a group of atoms which can replace one or more hydrogen in a hydrocarbon. This group when present in organic compounds defines the characteristic physical and chemical properties of that particular family of organic compounds.

1) The functional group of acids is -COOH




'R' can be 'H' or alkyl group attached to an carboxylic acid group (-COOH)


2) The functional group of aldehydes is -CHO




'R' can be a 'H' atom or an alkyl group attached to an aldehdye group (-CHO).

Question 9

Question: What are homologous series? Write a short note.
Answer: The extremely large numbers of carbon compounds discovered so far are better and more systematically studied by classifying them into families. Such groupings contain members, which are similar to one another in chemical properties, due to their common functional groups. These families form homologous series.

The properties of such homologous series are:
1) Members of the same family have a general formula. For e.g., for alkanes the general formula is C_nH_2n+2, for alkenes the general formula is C_nH_2n; for alkyne the general formula is C_nH_2n-2

2) They have common methods of preparation

3) Their chemical properties are similar

4) Their physical properties like colour, solubility, density, melting and boiling ponits etc. are graded

5) Each member differs from the next by a CH₂ moiety in its formula

Question 10

Question: Three hydrocarbons have molecular formula:
a)
1) C₄H₈
2) C₂H₂
3) C₃H₈ Identify them.
b) Draw their structural formulae and give their IUPAC names.
Answer: a)

1) In C₄H₈, n = 4 and it fits into the formula C_nH_2n Therefore it is an alkene

2) In C₂H₂, n = 2 and it fits into the formula C_nH_2n-2 Therefore it is an alkyne

3) In C₃H₈, n = 3 and it fits into the formula C_nH_2n+2 Therefore it is an alkane

b)

1) C₄H₈ - alkene - Butene IUPAC name: 1-butene



2) C₂H₂ - alkyne Ethyne - IUPAC name




3) C₃H₈ - alkane - Propane - IUPAC name

Question 11

Question: Draw the two structural formulae for butane and name the isomers.
Answer: Butane is C₄H₁₀ with general formula of alkane C_nH_2n+2.

Question 12

Question: Draw the two isomers for propyl alcohol and name the isomers.
Answer: Propyl alcohol is C₃H₇ - OH

Question 13

Question: What is esterification? Give an example.
Answer: When an alcohol reacts with an acid, it forms ester and water. This process is known as esterification. For example, ethanol reacts with organic acids to form esters. Unlike neutralization, this is a reversible, non-ionic and slow process carried out in the presence of a dehydrating agent like concentrated sulphuric acid.

Question 14

Question: Mention a few important uses of ethanol.
Answer: Ethanol is used in the manufacture of:
1) In manufacturing paints and varnishes
2) As a constituent of alcoholic beverages
3) ether, chloroform, iodoform and other organic compounds
4) In alcohol thermometers and spirit levels.
5) In the manufacture of chemical dyes
6) As a solvent in the manufacture of transparent soaps.

Question 15

Question: Choose and give reason for the one which does not belong to the set: C₂H₂, C₃H₄, C₃H₆
Answer: C₃H₆ because it is an alkene (C_nH_2n) while the other two are alkynes CnH_2n-2.

Question 16

Question: An organic compound A with the formula C₂H₆O gives the compound B with the same number of carbon atoms when oxidized, which further undergoes oxidation to acetic acid. Identify the compound A.
Answer: Compound A is ethanol (C₂H₅OH). It undergoes oxidation to give acetaldehyde (CH₃CHO) with the same number of carbon atoms. Acetaldehyde further undergoes oxidation to give acetic acid (CH₃COOH), again with the same number of carbon atoms.

Question 17

Question: Mention two uses of ethanoic acid.
Answer: Ethanoic acid is used in the manufacture of
1) dyes, perfumes and rayons.
2) rubber from latex and casein from milk. (It is used for coagulation).

Question 18

Question: Why do soaps not give lather with hard water?
Answer: Hard water contains dissolved impurities like salts of calcium chloride, calcium sulphate or calcium carbonate (bicarbonate) and corresponding salts of magnesium. When soap is added to hard water it reacts with the calcium and magnesium salts present in it and forms an insoluble white curd like precipitate of calcium or magnesium stearate.





These impurities do not allow the soap to lather but instead form insoluble scum. Until all the calcium and magnesium ions precipitate from such water, soap will not produce lather with it. Thus, a part of the soap is wasted and washing becomes wasteful.

Question 19

Question: In a molecule of a hydrocarbon, the number of 'C' atoms is '5'. What will be its formula if it is an alkane, alkene, alkyne?
Answer: If the number of 'C' atoms is '5' then the formula of the alkane is C₅H₁₂, the formula of the alkene is C₅H₁₀ and the formula of the alkyne is C₅H₈.

Question 20

Question: How do you convert:
1) Ethane to ethanoic acid
2) Ethanol to ethene. Give conditions and equations relevant to these conversions.
Answer:
1) Ethane to ethanoic acid Ethane when heated with air at 400^oC under 130 atms gets converted to ethanoic acid or acetic acid.





2) Ethanol gets dehydrated by concentrated H₂SO₄ at 170^oC to ethene.

Question 21

Question: Which is the ionic and non-ionic part in sodium stearate soap (C₁₇H₃₅COONa)?
Answer: The sodium stearate soap molecule (C₁₇H₃₅COONa) has a tadpole shaped structure, whose ends have different polarities. One end has a long hydrocarbon CH₃(CH₂)₁₆- chain and is non-ionic or non polar part. The other end is a short ionic or polar part containing -COO^-Na⁺ group.

Question 22

Question: What is saponification? Give an example.
Answer: Saponification is the process where a natural oil or fat is treated with sodium hydroxide solution called lye, to form soap and glycerine. For example, tristearin is heated with lye to give sodium stearate and glycerine.

Question 23

Question: What is alcohol? What is the general formula of alcohol?
Answer: Alcohol is a derivative of alkane, obtained by replacing one 'H' atom of alkane by a - OH group. The general formula of alcohol is C_nH_2n+1OH.

Question 24

Question: What happens when ethyl alcohol is treated with K₂Cr₂O₇ and H₂SO₄?
Answer: When ethyl alcohol is treated with K₂Cr₂O₇ and H₂SO₄ it gets oxidized first to ethanal and then to ethanoic acid.

Question 25

Question: What are the molecular, general and the structural formula for each of the following compounds? Give the names of these compound and the homologous groups to which they belong.

Answer:

Hydrocarbon	Molecular formula	General Formula
	C6H12 (Hexene)	CnH2n (Alkene)
	C8H16 (Cyclooctane)	CnH2n (Cycloalkane)

HydrocarbonMolecular formulaGeneral Formula
C₆H₁₂ (Hexene)

C_nH_2n (Alkene)


C₈H₁₆ (Cyclooctane)C_nH_2n (Cycloalkane)

Question 26

Question: What happens when a mixture of ethyl alcohol, acetic acid and concentrated H₂SO₄ is heated?
Answer: When a mixture of ethyl alcohol, acetic acid and concentrated H₂SO₄ is heated ester formation takes place with the elimination of a water molecule as follows.

Question 27

Question: What are isomers? Give an example.
Answer: Two or more compounds having the same molecular formula but different molecular structures are called isomers of each other. When the compounds with the same molecular formula have their atoms attached in a different order; they have different structures and are called structural isomers of each other. This phenomenon is known as isomerism. The four carbon atom alkane C₄H₁₀ has two isomers:

Question 28

Question: Write the structural formulae of all the possible isomers of C₂H₂Cl₂.
Answer: The structural formulae are:

Question 29

Question: What is 'denatured' alcohol?
Answer: When methyl alcohol is present in a small quantity with ethyl alcohol, it renders the latter unfit for drinking. This is called denatured alcohol.

Question 30

Question: What is the danger of drinking ethyl alcohol by youngsters?
Answer: Large amounts of alcoholic intake, affects the nerves that control respiration, action of pancreas and heart action. Hence it is a health hazard and needs immediate and expensive medical attention. It can therefore cause economic problems for many poor and middle income group families.

Question 31

Question: Describe the cleansing mechanism of soap or detergents?
Answer: All soaps and detergents are polar molecules, which allow for the cleansing action of dirt in water. One end consists of a large non-polar hydrocarbon group that is hydrophobic i.e., repels water but attracts oil and dirt particles. The other end has a highly polar short group that is hydrophilic i.e., attracts water and not oil or dirt.


Soap forms a colloidal solution in water and when soap is applied to the surface of a wet dirty cloth, the non-polar long end hydrocarbon of soap attaches itself to the dirt and grease. The short polar or ionic end of the soap molecule remains attached to water molecules. The latter form very small globules or structures called 'micelles' in which the oily dirt particle is surrounded with the tails of soap molecules carrying negative charge, while the polar head with positive charge interacts with the water. The subsequent mechanical action of rubbing or tumbling dislodges the dirt and grease. These are washed away with excess of water leaving the fabric clean.

Question 32

Question: How can detergents be used for washing in hard water?
Answer: Synthetic detergents are the sodium or potassium salts of sulphonic acids that have cleansing action exactly similar to that of soaps. However, synthetic detergents lather well even in hard water. This is because calcium and magnesium salts of detergents like their sodium and potassium salts are soluble in water. Thus, they do not form insoluble calcium or magnesium salts on reacting with the calcium ions or magnesium ions present therein. This is a major advantage of the cleansing property of detergents over soap.

Question 33

Question: Write the IUPAC names of:











Answer:

Question 34

Question: What is a covalent bond? Explain with an example.
Answer: When a pair of electrons is shared between atoms in such a way that each contributes an electron, covalent bond is formed. It was G.N. Lewis who proposed that sharing of electrons is possible. It may be defined as the attraction between atoms arising due to electron pair sharing. For example, consider the formation of hydrogen molecule (H₂). Each hydrogen atom contributes an electron and the shared pair belongs to both the atoms. By sharing, both the hydrogen atoms acquire the stable, nearest inert gas (He) configuration. This bonding can be represented by the Lewis dot structure as follows:

Question 35

Question: What are the characteristics of covalent compounds?
Answer: The characteristics of covalent compounds are:
1) The molecules are non-ionic and hence do not conduct electricity either in solution or in fused state
2) They are generally gases, liquids or low melting solids because of the weak forces holding the molecules together
3) They are generally insoluble in water or polar solvents but are soluble in non-polar solvents like benzene, ether etc.
4) Covalent bond is rigid and directional

Question 36

Question: What is a functional group? Give some examples.
Answer: An atom or a group of atoms, which makes an organic compound reactive and decides its functions is called a functional group. Examples of functional groups are:

Question 37

Question: Write down the steps involved in IUPAC nomenclature of compound containing functional groups.
Answer: The following four steps are involved in naming the compound containing functional group.

1) Identify the functional group present. This enables us to chose the appropriate suffix or prefix. For example, the functional group present in the following compound is carboxylic acid and the suffix is oic acid


2) Determine the longest continuous chain containing the functional group. The longest continuous chain in the above compound contains five carbon atoms. Therefore the base name is pentane.

3) Following the principle of assigning the lowest possible number to the functional group, the chain is numbered. In the above compound, carboxylic acid carbon is number 1 and the carbon at which the branching is present is carbon 3.

4) Then the name is arrived at. The alkyl group (CH₃ ) at carbon 3 comes as a prefix. Hence, the name of the compound is completed.

Question 38

Question: Write a short note on substitution reactions?
Answer: The replacement of a hydrogen atom of a hydrocarbon molecule by an atom or a group of atoms is known as substitution reaction. Alkanes, due to their structure, can undergo substitution reactions only in the presence of sunlight or ultraviolet light or at high temperatures. For example, methane reacts with chlorine either on heading at 520 - 670 K or on exposure to sunlight to give a mixture of chloro methane.



Arenes, though unsaturated, also undergoes substitution reactions due to special stability associated with electron cloud.

Question 39

Question: What are addition reactions? Which of the following will not give addition reactions and why? Propane, propyne, propene, benzene.
Answer: Addition reactions are those in which one reacting molecule adds on to the multiple bond of the other reacting molecule. In the process, the -bond of the multiple bond is broken and two new ?-bonds are formed. For example, in the case of an alkene, we have




Propane, being a saturated hydrocarbon (no -bond) will not give addition reaction. Arenes are also stable due to delocalisation of -electron cloud and gives addition reaction only in the presence of sunlight. Propene and propyne gives addition reactions under normal conditions.

Question 40

Question: The following organic compounds are popularly known by their common names. Write their structural formulas and IUPAC names.
1) Neopentane
2) Vinyl chloride
3) Iso-butyl bromide
4) Acetonitrile
Answer:

Question 41

Question: What is allotropy? Name some elements which exhibit allotropy.
Answer: Allotropy is the phenomenon of an existence of an element in two or more distinct forms in the same physical state. Elements which exhibit allotropy are:
1) Carbon diamond, graphite, buck minster fullerene
2) Phosphorus White phosphorus, red phosphorus.
3) Sulphur rhombic sulphur, monoclinic sulphur