Carbon and its compounds answers

CARBON AND ITS COMPOUNDS 1. Write the name and formula of the first member of the carbon compounds having functional group .

Ans. Methanal is the first member of the carbon compound having functional group . Its formula is HCHO. 2. What are hydrocarbons?

Ans. Compounds that contain only carbon and hydrogen are known as Hydrocarbons.

E.g. CH4 3. Ethane having molecular formula C2H6 has how many bonds?

Ans. Ethane having molecular formula C2H6 has seven covalent bonds.

4. Define catenation?

Ans. Catenation is the property of carbon to get attached to other carbon atoms. Up to 60 carbon atoms are found to get attached in the shape of a ball (fullerenes).

5. What is the maximum covalency of carbon?

Ans. The maximum covalency of carbon is four since it is capable of forming four covalent bonds.

6. Write down the names and the chemical equations of the products that are obtained by oxidation of ethanol in different stages.

Ans. CrO3

CH3CH2OH

Alkaline

CH3CHO CH3COOH

(Ethanol)

CH3COOH + H2O KMnO4

(Ethanal)

(Ethanoic acid)

CARBON AND ITS COMPOUNDS 7. Distinguish experimentally between alcohol and carboxylic acid.

Ans. Test

Alcohol

Litmus test There will be no colour change Sodium hydrogen No reaction seen carbonate Sodium metal

Carboxylic acid The colour of blue litmus turns red Evolution of CO2 with brisk effervescence

H2 is released with effervescence H2 is released with no effervescence

8. What is ‘Homologous series’ of compounds? List any 2 of its characteristics.

Ans.  Homologous series is a group or family of compounds containing the same functional group but having different chain lengths.  In such series, a same functional group substitutes hydrogen in a carbon chain in a series of compounds. E.g. CH3Cl and C2H5Cl differ by a –CH2 unit.  The two characteristics of homologous series are as follows: 1) As the molecular mass of any homologous series increases, a gradation in physical properties (such as solubility in a particular solvent) is observed due to the increase in the melting and boiling points with increase in their molecular mass.

2) The chemical properties determined by the functional groups remain unchanged in a homologous series.

CARBON AND ITS COMPOUNDS 9. Explain the terms ‘Esterification’ and ‘Saponification’ of carbon compounds with the help of chemical reactions of each.

Ans. a) Esterification – Esterification is the reaction of an alcohol in the presence of concentrated H2SO4 to form a sweet smelling compound. This sweet smelling compound is called as ester.

CH3COOH + C2H5OH (Ethanoic acid) (Ethanol)

Conc. H2SO4

CH3COOC2H5 + H2O (Ethyl ethanoate) (Ester)

b) Saponification – Saponification means hydrolysis of an ester in presence of an alkali (NaOH or KOH) to form an alcohol and sodium salt of the acid. This reaction is generally used in the preparation of soap.

CH3COOC2H5 + NaOH (Ethyl ethanoate)

10. Draw the following structures: a) Ethanoic acid b) Bromopentane c) Butanone d) Hexanal Ans.

CH3COONa + C2H5OH

CARBON AND ITS COMPOUNDS

11. Why does carbon form large number of compounds? Describe the phenomenon of allotropy in carbon compounds.

Ans. ďƒ˜ Carbon forms large number of organic compounds due to the following reasons: 1) It exhibits the property of catenation due to which it can form bond with itself.

2) Carbon forms a large number of organic compounds due to its tetravalency.

3) Carbon also exhibits isomerism.

CARBON AND ITS COMPOUNDS  Allotropy - When an element possesses two or more different forms in the same state, they are called as allotropes and the phenomenon is called as allotropy. E.g. Diamond and graphite.  Carbon exists in two allotropic forms: a) Crystalline – Diamond, graphite, etc. b) Amorphous – Coal, charcoal, etc.  Buckminsterfullerene is the new allotrope of carbon. The properties of diamond and graphite are well known whereas the properties of buckminsterfullerene are being studied.

12. Distinguish between alkenes and alkynes. (3 points each) Ans. Alkene

Alkyne

1. The unsaturated hydrocarbons that 1. The unsaturated hydrocarbons contain a double bond between that contain a triple bond two carbon atoms are called as between two carbon atoms are alkenes called as alkynes 2. General formula for alkenes is 2. General formula for alkynes is CnH2n CnH2n-2 3. For e.g. Ethene, propene, butene 3. For e.g. Ethyne, propyne, butyne

13. Illustrate the following reactions with one example each: a) Combustion b) Oxidation c) Addition Ans. a. Combustion – Carbon compounds undergo combustion to produce CO2 and H2O with the evolution of heat and light.

CH4 + O2

CO2 + H2O + heat and light

CARBON AND ITS COMPOUNDS b. Oxidation – It means ‘controlled combustion’. The substance used for oxidation is called an oxidising agent. E.g. alkaline KMnO4 acidified K2Cr2O7.

CH3CH2OH

Alk. KMnO4/∆

CH3COOH

c. Addition reaction – Unsaturated hydrocarbons such as alkenes and alkynes undergo addition reaction in presence of catalysts.

E.g.

14. What do you mean by hydrocarbons? Write the name and general formula of (i) Saturated hydrocarbons (ii) Unsaturated hydrocarbons And draw the structure of one hydrocarbon of each type.

Ans. Hydrocarbons: The chemical compounds containing carbon and hydrogen are known as hydrocarbons. (i) Saturated hydrocarbons: Compounds of carbon and hydrogen attached in chains, branches or rings, by single covalent bonds are called as saturated hydrocarbons.

For example: Alkane General formula: CnH2n+2

CARBON AND ITS COMPOUNDS (ii) Unsaturated hydrocarbons: Compounds of carbon and hydrogen with either carbon-carbon double bond (C = C) or carbon-carbon triple bond (C ≡ C) in their molecules are called as unsaturated hydrocarbons.

For example: Alkene General formula: CnH2n

Alkyne General formula: CnH2n-2 E.g. Ethyne C2H2 H-C ≡ C-H

15. Complete the following reactions: a) CH3CH2OH

CrO3 CH3COOH

b) 2CH3COOH + Na2CO3 c) CH2 = CH2 + H2

Ni / 3000C

Ans. a) CH3CH2OH

CrO3 CH3COOH

b) 2CH3COOH + Na2CO3

CH3CHO + H2O

2CH3COONa + CO2 + H2O

CARBON AND ITS COMPOUNDS

c) CH2 = CH2 + H2

Ni / 3000C

CH3

CH3

16. Explain what is a detergent with one example. List down two advantages and two disadvantages of detergents over soap. Also explain the mechanism of the cleansing action of detergents.

Ans.  Detergents are sodium salts of substituted benzene sulphonic acids. Detergents are similar to soaps but their hydrocarbon part is obtained from petroleum.

Some examples of detergents are as follows:  Sodium lauryl sulphate  Sodium-n-dodecyl sulphate  The two advantages and disadvantages of detergents over soaps are as follows:  Advantages: 1) Detergents can be used in acidic solutions.

2) Detergents can be used in hard water. They also have a strong cleansing action.  Disadvantages: 1) Detergents are not 100% biodegradable and they also reduce the oxygen content in water.

2) They are accumulated in sewage plants and lakes and cause water pollution and destroy aquatic life.  The mechanism of the cleansing action of detergents is as follows:  A detergent is made up of two components which are: a hydrocarbon tail which is hydrophobic in nature and a polar head which is hydrophilic in nature.  When a detergent is dissolved in water, the molecules gather together to form clusters called as micelles.  The hydrocarbon tail entraps the dirt and grease from the surface of the cloth while the polar head pulls the dirt away from the cloth surface and is directed towards water. Thus, in this way, the cloth gets cleansed.

17. What is isomerism? How many possible isomers are there for a compound with molecular formula C4H10 and C5H12? Draw their structure and write their names.

Ans.  The phenomenon in which the compounds have the same molecular formula but a different structural formula is known as Isomerism.

CARBON AND ITS COMPOUNDS ďƒ˜ Butane (C4H10) has two isomers, one is a straight chain and the other is branched chain. Their structures are as follows:

ďƒ˜ Pentane (C5H12) has three isomers and they are as follows:

CARBON AND ITS COMPOUNDS 18. Explain what are micelles and how does the formation of micelle help in cleaning of clothes.

Ans.  Soaps or detergents mainly consist of two parts having distinct properties. They are as follows: a) Hydrocarbon tail which is hydrophobic (water repelling) b) A polar head which is hydrophilic (water loving)  When soap is added to water, it does not form a true solution instead it gets dispersed in such a way that the ionic end is in water and the hydrophobic part is protruding out of water.  This gives rise to formation of clusters of molecules in which the hydrophobic tails are in the interior of the cluster and the ionic ends are on the surface of the cluster. This formation with a hundreds of soap molecules is called a micelle.  Soap in the form of micelle is capable of cleaning dirt or oily grease, since it is collected in the centre of the micelle. When water is agitated, the micelle containing oily dirt is lifted from the dirty surface and is split into fragments. Due to this, other tails stick to the oil if left.  The negatively charged heads present in water prevents the small globules that are formed from forming aggregates or precipitates because of ion-ion repulsion.  Thus, the dirt suspended in micelles is easily washed or cleansed away.

CARBON AND ITS COMPOUNDS 19. Explain the following terms: a) b) c) d) e)

Emulsifying action Polymerization Methylated spirit Straight and branched chain compounds Substitution reaction

Ans. a) Emulsifying action- Emulsifying action is the action of soaps and detergents on the dirt present in clothes. b) Polymerization – Polymerization is the process in which similar or different molecules combine together in the presence of catalyst to form long chain compounds. c) Methylated spirit – Methylated spirit is ethyl alcohol contaminated with methyl alcohol and other impurities. d) Straight chain compounds - Compounds containing straight chain of carbon atoms are called as straight chain compounds. E.g. Normal butane (C4H10), normal pentane (C5H12), etc.

Branched chain compounds - Compounds containing branched chain of carbon atoms are called as branched chain compounds. E.g. iso-butane (C4H10), pentane (C5H12), etc. e) Substitution reaction – Substitution reactions are reactions in which an atom or group of atoms of a compound is replaced by other atom or group of atoms.

Saturated hydrocarbons give substitution reactions. E.g. Methane in the presence of sunlight undergoes chlorination.

CARBON AND ITS COMPOUNDS 20. a) Ethanol is a fuel which is generally used as a gas supply usually in a spirit lamp. When a beaker is heated by a spirit lamp, a black solid is formed at the bottom of the beaker. Answer the following questions by using the above information. i. What is the name of the black substance formed on the beaker? ii. Why according to you is the black substance formed when ethanol is burned? b) Write the names of other fuels used in the industry. c) Methane is unsaturated whereas methanol is saturated. i. Describe a simple chemical test that would show that ethene is unsaturated. ii. Name other uses of ethene. (Except production of ethanol) Ans. a) i. The black substance formed on the beaker is carbon. ii. On burning, ethanol yields carbon. b) The names of other fuels used in the industry are as follows:  Methane which is also known as marsh gas.  Butane which is the main component of LPG. c) i. The easiest way to show unsaturation of ethene is : On reaction with bromine water and with a solution of dilute acidic KMnO4, ethene discharges colour of bromine water as well as KMnO4. ii. Other uses of ethene are in making plastics, synthetic fibres and other important carbon compounds.