CBSE Class 10 Science Carbon and its compounds Assignment Set A

Question : Give reason why carbon can neither form C⁴⁺ cations nor C^4– anions, but forms covalent compounds. Also, state the reason to explain why covalent compounds are bad conductors of electricity and have low melting and boiling points? 
Answer : Carbon cannot form C⁴⁺ cation because removal of 4 electrons from a carbon atom would require a large amount of energy. 
Carbon cannot form C^4– anion because it would be difficult for the nucleus with 6 protons to hold on to 10 electrons.
Hence, carbon atoms share electrons forming covalent compounds. 
Covalent compounds do not form ions/ charged particles and therefore do not conduct electricity. 
Inter-molecular forces of attraction are weak, hence they have low melting and boiling points. 

Question : An aldehyde as well as a ketone can be represented by the same molecular formula, say C₃H₆O. Write their structures and name them. State the scientific relation between the two.
Answer : (i) Propanal (aldehyde); 

(iii) Isomers (same molecular formula but different structural formula/different functional group)

Question : Give a test that can be used to confirm the presence of carbon in a compound. With a valency of 4, how is carbon able to attain noble gas configuration in its compounds? 
Answer : When carbon compound is burnt in the presence of oxygen, a gas is evolved. Gas evolved turns lime water milky.
By sharing its four valence electrons with other elements, carbon attains stable noble gas configuration. 

Question : What are covalent compounds? How are they different from ionic compounds? List any two properties of covalent compounds.
Answer : The compounds that are formed due to sharing of electrons between two atoms/compounds having covalent bonds. 
Ionic compounds are formed due to transfer of electrons from one atom to another/compounds having ionic bonds/compounds having attraction between oppositely charged ions 
(i) They are poor conductors of electricity 
(ii) They have low melting and boiling point. 

Question : What is meant by isomers ? Draw the structure of two isomers of butane, C₄H₁₀. Explain why we cannot have isomers of first three members of alkane series.
Answer : Isomers are the compounds which have the same molecular formula but different structural formula.
Isomers of Butane:

We cannot have isomers of the first three members of the alkane series because of the following laws of isomers:
(i) The parent chain should have the most number of carbon atoms.
(ii) The branching cannot be done from the first and the last carbon atom of the structure. 

Question : The number of carbon compounds is more than those formed by all other elements put together. Justify the statement by giving two reasons.
Answer : (i) Due to self linking ability of carbon/catenation.
(ii) Since carbon has a valency of four it can form bonds with four other atoms of carbon or atoms of some other monovalent element.
(iii) Due to small size of carbon it forms very strong and (or) stable bonds with other elements.

Question : (a) Why most of the carbon compounds are poor conductor of electricity ?
Answer : (a) Carbon compounds form covalent bonds/do not dissociate into ions/do not have charged particles (ions)/do not have free electrons.

Question : Draw the structures of the following compounds and identify the functional group present in them:
(i) Butanoic acid
(ii) Bromopropane
(iii) Butyne 
Answer : 

Question : What is a homologous series of carbon compounds?
Give an example and list its three characteristics.
Answer : A series of compounds in which the same functional group substitutes for hydrogen in a carbon chain is called a homologous series. 
Example: Alkane / Alkene / Alkyne / Alcohol or any other one correct example.
Characteristics:
(i) They have same general formula.
(ii) They have same functional group.
(iii) The difference in the molecular mass of two successive member is 14u.
(iv) The difference in the molecular formula of two successive member is of CH₂ unit.
(v) They have similar chemical properties.

Question : Which compounds are called (i) alkanes, (ii) alkenes and (iii) alkynes ? C₄H₁₀ belongs to which of these? Draw two structural isomers of this compound.
Answer : • Alkane
Saturated hydrocarbon with C–C single bond
• Alkene
Unsaturated Hydrocarbon with double bond in C=C
• Alkyne
Unsaturated Hydrocarbon with triple bond in C ≡ C
• Alkane 
2 structural isomers