CBSE Class 10 Science Carbon And Its Compounds Worksheet Set A

Short Answers

Question : Name the compound CH₃COOH and identify its functional group.
Answer : Acetic acid
Functional group — COOH (Carboxylic acid group)

Question : Write the names of the following compounds.

Answer : (a) Pentanoic acid (b) Butyne (c) Heptanal (d) Pentanol

Question : What are isomers? Draw the structures of two isomers of butane (C₄H₁₀).
Answer : Organic compounds having the same molecular formula but different structural formulae, and hence, different physical and chemical properties are called isomers. n-butane and iso–butane are two isomers of butane (C₄H₁₀).

Question : (a) Give a chemical test to identify the compound CH₃COOH.
(b) Name the gas evolved when this compound acts on solid sodium carbonate. How would you identify this gas?
Answer : (a) To the compound CH₃COOH add some amount of ethanol and then a few drops of concentrated sulphuric acid. Warm the mixture in a water bath for a few minutes. A fruity smell will be given off on account of the formation of an ester. This is a confirmatory test for carboxylic acid. Therefore the compound is identified as acetic acid.

(b) Carbon dioxide. The gas turns clear limewater milky when bubbled through it.
2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂
                                                                  Carbon dioxide

Question : 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 concentrated H₂SO₄?
Answer : Ethanol – C₂H₅OH
When ethanol is heated with excess of concentrated H2SO4 it gets dehydrated to form ethene.

Question : What happens when wood is burnt in a limited supply of oxygen? Name the residue left behind after the reaction and state two advantages of using this residue as a fuel over wood.
Answer : When wood is burnt in a limited supply of oxygen, destructive distillation takes place with the formation of wood charcoal.
The residue left after the reaction is wood charcoal.
Advantages of using wood charcoal over wood:
(a) Wood charcoal burns without smoke.
(b) It does not liberate any poisonous gases on burning.

Question : What is a homologous series? Which two of the following organic compounds belong to the same homologous series?
C₂H₆, C₂H₆O, C₂H₆O₂, CH₄O
Answer : A group of members of the same class of organic compounds, which differ from each other by a – CH₂ group, when arranged in the ascending order of molecular mass is called a homologous series.
CH₄O and C₂H₆O are homologues since they differ by a – CH₂ group.

Question : (a) Describe a chemical test to distinguish between ethanol and ethanoic acid.
(b) Write a chemical equation to represent what happens when hydrogen gas is passed through an unsaturated hydrocarbon in the presence of nickel acting as a catalyst.
Answer : (a) Ethanoic acid liberates carbon dioxide on reacting with carbonates or hydrogen carbonates,while ethanol gives no such reaction.

Question : (a) What is a ‘homologous series’ of substances?
(b) In an organic compound, which parts largely determine its physical and chemical properties?
Answer : (a) A group or series of organic compounds having the same general formula and similar graded physical and chemical properties is called a homologous series.
(b) The functional group of an organic compound determines its physical and chemical properties.

Question : Draw the structures of the following compounds :
(a) Ethanoic acid (b) Butanone
Answer : 

Question : (a) Write the name of the following : (i) CH3CH2COOH (ii) CH3CH2Br
(b) Draw the electron dot structure of ethene.
Answer : (a) (i) Propanoic acid (ii) Bromoethane

Question : What will happen if ethanoic acid reacts with ethanol in the presence of an acid as a catalyst?
Name the reaction. Write the chemical equation for this reaction.
Answer : A sweet smelling compound, ethyl ethanoate (an ester) is formed.
The reaction is known as esterification reaction.

Question : (a) Give a chemical test to distinguish between ethanol and ethanoic acid.
(b) Name the product formed when an organic acid reacts with an alcohol in the presence of an acid catalyst. What is the name assigned to this type of reaction.
Answer : (a) Ethanoic acid liberates carbon dioxide gas on reacting with sodium carbonate or sodium hydrogen carbonate. Ethanol gives no such reaction with sodium carbonate or sodium hydrogen carbonate.
(b) Ester
Esterification

Question : (a) Explain why carbon forms covalent bond? Give two reasons for carbon forming a large number of compounds.
(b) Explain the formation of ammonia molecule.
Answer : (a) Carbon has electronic configuration 2, 4. It could gain four electrons forming C-4 anion or lose 4 electrons to form C+4 cation . Both are not possible due to energy considerations. Carbon overcome this problem by sharing electrons and forming covalent compounds. Two reasons for forming large number of compounds:
(1) Catenation (2) Tetra valency
(b) Formation of NH3 molecule
Three hydrogen atoms each share their 1 electron with nitrogen to form three covalent bonds and
make an ammonia molecule (NH3).

Question : Carbon, a member of group 14, forms a large number of carbon compounds estimated to be about three million. Why is this property not exhibited by other elements of this group? Explain.
Answer : Carbon shows the property of catenation.
It forms strong covalent bonds with other atoms of carbon forming long straight, branched and closed chain compounds.
Carbon is smallest in size in group 14 with tatravalency, it can form double as well as triple bonds,
therefore, it can show property of catenation to maximum extent and forms 3 million compounds other elements cannot show property of catenation to this extent due to larger size form weaker covalent bond and cannot form double or triple bonds.

Question : (a) (i) Name the products formed when ethanol burns in air.
(ii) What two forms of energy are liberated on burning alcohol?
(b) Why is the reaction between methane and chlorine considered as a substitution reaction?
Answer : (a) (i) Ethanoic acid and water
(ii) Heat energy, chemical energy
(b) The reaction between methane and chlorine is considered as a substitution reaction since the hydrogen atoms of methane are replaced by chlorine atoms.

Question : What are covalent compounds? Why are they different from ionic compounds? List their three characteristic properties.
Answer : Those compounds which are formed by equal sharing of electrons are called covalent compounds.
They are different from ionic compounds since ionic compounds are formed by transfer of electrons from one atom to another.
Properties:
(i) They have low melting and boiling points.
(ii) They do not conduct electricity in molten state and in aqueous solution.
(iii) They are mostly insoluble in water but soluble in organic solvents except glucose, sugar, urea, ethyl alcohol, etc.

Question : (a) Name the following compound:

(b) Name the gas evolved when ethanoic acid is added to sodium carbonate. How would you prove the presence of this gas?
Answer : (a) The compound is propanone or acetone (common name).
(b) The gas evolved is carbon dioxide. The presence of this gas can be confirmed by passing it through limewater. The limewater turns milky.

Question : Two non-metals react with each other by sharing electrons to form a compound C.
(i) Name the type of chemical bond in C.
(ii) State whether C will have a high boiling point or a low boiling point.
(iii) State whether C will be soluble in water or in organic solvents.
(iv) State whether C is a good conductor of electricity or not.
Answer : (i) The chemical bond is covalent in nature.
(ii) C will have low boiling point.
(iii) C will dissolve in organic solvents.
(iv) C will not conduct electric current.

Question : Draw the possible isomers of the compound with molecular formula C₃H₆O and also give their electron dot structures.
Answer : 

Question : 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.
Answer : Carbon exhibits catenation much more than silicon or any other element due to its smaller size which makes the C–C bonds strong while the Si–Si bonds are comparatively weaker due to the large size of the atoms.

Question : Match the reaction given in column (A) with the names given in column (B).

Answer : (A) – (iv) (B) – (i) (C) – (ii) (D) – (iii)

Question :  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.
Answer : (a) By the dehydration of ethanol in the presence of concentrated H2SO4

(b) By the oxidation of propanol using oxidising agent such as alkaline KMnO4.

Question : Intake of small quantity of methanol can be lethal. Comment.
Answer : Methanol is oxidised to methanal in the liver. Methanal reacts rapidly with the components of the cells. It causes the protoplasm to coagulate. It also affects the optic nerve causing blindness.

Question : Ethene is formed when ethanol is heated with excess of concentrated sulphuric acid at 443 K.
What is the role of sulphuric acid in this reaction? Write balanced chemical equation of this reaction.
Answer : Sulphuric acid acts as a dehydrating agent.

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 : Burn compound in air/oxygen. Gas evolved turns limewater milky. By sharing its four valence
electrons with other elements.

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 : The following reasons are :
(i) Due to self-linking ability of carbon which is known as catenation.
(ii) Since carbon has valency of four it can form with four other atoms of carbon or atoms of some other monovalent element.
(iii) Due to small size of carbon it forms very strong or stable bonds with other elements.

Question : Which types of compound does carbon generally form? Why is the compound formed by carbon exceptionally stable?
Answer : Carbon generally forms covalent compound. The stability of carbon compounds is attributed to the small size of carbon atom. Due to the small size of carbon atom, the nucleus holds the shared pair of electrons more effectively, thus making the bond stronger.

Question : Samir took ghee in a beaker and heated it. Ghee readily melts and easily boils too, but when he tries to pass electricity through ghee, it does not conduct electricity. Give reason for his observation.
Answer : Ghee is a saturated hydrocarbon or we can say that it is a carbon compound with covalent bond. Covalently bonded molecules are seen to have strong bonds within the molecule, but inter-molecular forces are small. This gives rise to the low melting and boiling points of these compounds.
Since the electrons are shared between atoms and no charged particles are formed, such covalent compounds are generally poor conductor of electricity, that is why ghee did not conduct electricity.

Question : What is meant by functional group in an organic compound? Name the functional group present in :
(a) CH₃CH₂OH (b) CH₃COOH
Answer : Functional group is an atom or group of atoms or reactive part of compound which determines
chemical properties of compounds.
(a) —OH (Alcohol) (b) —COOH (Carboxylic acid)

Question : Give reasons for the following observation :
Air holes of a gas burner have to be adjusted when the heated vessels get blackened by the flame.
Answer : Air holes of a gas burner are made open so that air can pass through them, which is needed for complete combustion, so that heated vessels do not get blackened.

Question : Acetic acid reacts with ethanol in the presence of concentrated H2SO4 to produce a sweet
smelling compound. For this reaction :
(a) Write the name of main product.
(b) Write the balanced chemical equation.
Answer : (a) In this reaction, the main product formed is ethyl ethanoate or ethyl acetate.
(b) The balanced chemical equation is :

Question :  (a) Identify the functional group present in CH₃COOH and CH₃OH.
(b) Name the fourth member of alkene series.
Answer : (a) The functional group present in CH₃COOH and CH₃OH are carboxylic acid group and alcoholic group respectively.
(b) Pentene

Long Answers