Carbon And It's Compounds
Class: 10 | Chapter: 4
Important Questions & Answer
1. Give the names of the following functional groups:(i) —OH (ii) —COOH
Ans. (i) Alcohol
(ii) Carboxylic acid
2. What is the difference in the molecular formula of any two consecutive members of a homologous series of organic compounds?
Ans. -CH2 is the difference in the molecular formula of any two consecutive members of a homologous series of organic compounds.
3. Why are covalent compounds generally poor conductors of electricity?
Ans. Covalent compounds are generally poor conductors of electricity becouse in covalent compound there are no free electrons to move. All electrons are bonded and hence they are not available for conduction.
4. What is meant by a functional group in an organic compound? Name the functional group present in
(i) CH3CH2OH
(ii) CH3COOH
Ans. Functional group : These are atoms or group of atoms which provides soecific properties to a compound.
(i) Alcohol Group
(ii) Carboxylic Group
5. State two characteristic features of carbon which when put together give rise to large number of carbon compounds.
Ans. 1. Tetravalency : Carbon has valency 4 . So, it can form four bonds.
2. Catenation : This is also called self linking property. Carbon makes bonds with itself and form long chains.
3. Multiplicity : Carbon Shows single bonding, double and triple bonding.
So, it is clear that carbon is a versatile element that's why it is forming a large number of compounds.
6. Write the name and molecular formula of an organic compound having its name suffixed with -ol and having two carbon atoms in the molecule. With the help of a balanced chemical equation indicate what happens when it is heated with excess of conc.H2S04.
Ans. -ol is used for representing alcohol group. It has 2 carbon atoms so, it is C2H5OH i. e. Ethanol.
C2H5OH + Conc. H2SO4 ---------> C2H4 (Ethene) + H2O
7. Write the names and molecular formula of two organic compounds having functional group suffixed as ‘-oic acid’. With the help of a balanced chemical equation and explain what happens when any one of them reacts with sodium hydroxide.
Ans. - Oic acid is used for carboxylic acids. So, we can take any two members of this homologous series like With 1 carbon atom, it is HCOOH ( Methanoic acid) and next with 2 carbon atoms, it is CH3COOH ( Ethanoic acid). CH3COOH + NaOH ---------> CH3COONa + H2O
8. What is a homologous series? Which two of the following organic compounds belongto the same homologous?
CH3 ,C2H6, C2H6O, C2H6O2,CH4O
Ans. Homologous series : A sequenve of compounds having same functional group and chemical properties but differ by -CH2 group . C2H6O and CH4O belong to same homologous series.
9. 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.
Ans. Catenation in carbon is more becouse of it's smaller size and stronger C - C bond.
10. What happens when a small piece of sodium is dropped into ethanol?
Ans. 2C2H5OH + 2Na -----------> 2C2H5ONa + H2
(Ethanol) ( Sodium Ethoxide)
11. What is ethanol? State its two properties. What happens when it is heated with excess of cone. H2SO4 at 443 K? What role does cone. H2SO4 play in this reaction? Write chemical equation of the reaction involved and the structural formula of the main product formed.
Ans. Ethanol is an organic compound having chemical formula C2H5OH. It is second member of alcoholic series.
Properties : 1. It is flammable liquid.
2. It is volatile and having pungent odour.
When Ethanol is heated with excess of conc. H2SO4 at 443 K,
C2H5OH + Conc. H2SO4 ---------> C2H4 (Ethene) + H2O
Here conc. H2SO4 acts as dehydrating agent.
12. With the help of balanced chemical equations explain what happens when ethanol is heated with (i) alkaline solution of potassium permanganate, (ii) excess concentrated sulphuric acid at 443 K. Mention any two uses of ethanol.
Ans. (i) When ethanol is geated with alkaline solution of potassium permanganate, ethanol oxidises to acetic acid ( CH3COOH)
CH3CH2OH + alk. KMnO4 -----------> CH3COOH
Ethanol oxidizing agent Acetic acid
(ii) When Ethanol is heated with excess of conc. H2SO4 at 443 K,
C2H5OH + Conc. H2SO4 ---------> C2H4 (Ethene) + H2O
Here conc. H2SO4 acts as dehydrating agent.
13. How many covalent bonds are there in a molecule of ethane (C2H6)?
Ans. 7 bonds ( 6 C- H bonds + 1 C - C bond)
14. Write the electron dot structure of ethene molecule (C2H4).
Ans.
Ans.
C2H6O2, C2H6O, C2H6, CH4O
Ans. C2H6O and CH4O belong to same homologous series becouse they have same general formula and different by - CH2.
17. Out of HCI and CH3COOH, which one is a weak acid and why? Describe an activity to support your answer.
Ans. CH3COOH is a weak acid Becouse it's dissociation is not complete it gives less no. of H+ ions in the solution and secondly by pH value also, we can get the result. CH3COOH has more pH value than HCl. More is pH value, weeker is the acid.
18. Explain isomerism. State any four characteristics of isomers. Draw the structures of possible isomers of butane, C4H10.
Ans. Isomerism : The phenomenon of two or more compounds having same molecular formula, but different structural formulae and the compounds showing this phenomenon are called isomers.
Characteristics of isomers :
1. Same molecular formula.
2. Different structural formula.
3. Different physical and chemical properties.
4. Same no. of atoms.
Isomers of butane ( C4H10) :
(i)Element carbon forms compounds mainly by covalent bonding.
(ii)Diamond has a high melting point.
(iii)Graphite is a good conductor of electricity.
(iv)Acetylene bums with a sooty flame.
Ans. (i) Carbon forms compounds mainly by covalent bonding becouse to complete octet it can't loose 4 electrons as it needs a lot of energy and it can't gain 4 electrons becouse of repulsion. So, it shares 4 electrons and completes it's octet by covalent bonding.
(ii) Diamond has a high melting point becouse of it's strong gaint structure. In this structure carbon atoms are joined with other 4 carbon atoms and a lot of energy is needed to break this bonding or separate this atoms.
(iii) Graphire is a good conductor of electricity due to presence of free elcetrons in it's structure. In graphite, every carbon atom is bonded to 3 other carbon atoms so, for every carbon one electron is free to move and hence can conduct electricity.
(iv) Acetylene burns with a sooty flame due to it's unsaturated nature. In acetylene, percentage of carbon is more and it is not completely oxidised by oxygen of air , it gives sooty flame.
20. Write the name and formula of the second member of the carbon compounds having functional group —OH.
Ans. It is C2H5OH, ethanol.
21. Write the molecular formulae and the names of the immediate lower and higher homologues of C3H4.
Ans. C3H4 belongs to alkyne series. It's general formula is CnH2n-2. It's lower immediate will be corresponding to n = 2 and higher immediate will be corresponding to n = 3. By putting the values of n, we get lower immediate as C2H2 and higher immediate as C4H6.
22. Define homologous series of organic compounds. List its two characteristics. Write the name and formula of the first member of the series of alkenes.
Ans. Homologous series : A sequenve of compounds having same functional group and chemical properties but differ by -CH2 group .
Characteristics of homologous series : 1. Members of homologous series have same general formula.
2. They have same chemical properties.
3. They show a regular variation in physical properties.
First member of alkenes is ethene, C2H4 .
23. An organic compound A of molecular formula C2H6O on oxidation gives an acid B with the same number of carbon atoms in the molecule as A. Compound A is often used for sterilisation of skin by doctors. Name the compounds A and B. Write the chemical equation involved in the formation of B from A.
Ans. Here B is an acid with two carbon atoms , so it is ethanoic acid ( CH3COOH). We know that alcohols are oxidized to give carboxyluc acids. Here A is an alcohol named Ethyl alcohol ( C2H5OH) . C2H5OH + O2 -------------- > CH3COOH + H2O
24. Which class of carbon compounds is responsible for the depletion of ozone layer at the higher level of the atmosphere?
Ans. Chlorofluorocarbons.
25. Name the functional group present in each of the following compounds: (i) HCOOH (ii) C2H5CHO
Ans. (i) Carboxylic acid
(ii) Aldehyde
26. Write the name and formula of the 2nd member of homologous series having general formula CnH2n.
Ans. Name - propene
Formula - C3H6
27. Write the number of covalent bonds in the molecule of butane.
Ans. 13
28. Write the next homologue of each of the following: (i) C2H4 (ii) C4H6
Ans. (i) C3H6
(ii) C5H8
29.(a) Name the product obtained when ethanol is oxidised by alkaline potassium permanganate. (b) Give an example of an esterification reaction.
Ans. (a) Product with alkaline potassium permanganate is ethanoic acid.
(b) CH3COOH + C2H5OH --------------- > CH3COOC2H5 + H2O
30. Write the name and formula of the first member of the carbon compounds having functional group – COOH.
Ans. Name - Methanoic acid
Formula - HCOOH