CBSE Class 10 Science Carbon and its compounds Assignment Set A

MCQ's

Question : The number of single and double bonds present in benzenes are
(a) 9 and 6
(b) 9 and 3
(c) 12 and 3
(d) 12 and 6
Answer : B

Question : For gas welding used for welding broken pieces of iron, we normally use a mixture of
(a) Ethane and oxygen
(b) Ethene and oxygen
(c) Ethyne and oxygen
(d) Ethene and air
Answer : A

Question : The heteroatoms present is
CH₃ – O – CH₂ – CH₂ (Br)
(a) oxygen
(b) carbon
(c) hydrogen
(d) bromine
Answer : D

Question : Identify the compound that undergoes bromination reaction:

Answer : D

Question : Bromine reacts with saturated hydrocarbon at room temperature in the
(a) absence of sunlight
(b) presence of water
(c) presence of sunlight
(d) presence of hydrochloric acid
Answer : C

Question : Identify the correct way of numbering an organic compound (according to IUPAC)

Answer : A

Question : Which of the following is used to oxidise ethanol to ethanoic acid?
(a) Alkaline KMnO₄
(b) Conc. H₂SO₄
(c)  Acidified K₂Cr₂O₇
(d) All of above
Answer : D

Question : Identify the functional group present in the following compound

(a) aldehyde
(b) bromine
(c) carboxylic
(d) both bromine and carboxylic group
Answer : D

Question : Which of the following is not a straight chain?

Answer : D

Question : The upper and lower homologue of C₂H₅OH are respectively
(a) methyl alcohol and butyl alcohol
(b) ethyl alcohol and propyl alcohol
(c) butyl alcohol and propyl alcohol
(d) propyl alcohol and methyl alcohol
Answer : D

Question : Which is not true about homologous series?
(a) They have same general formula.
(b) They differ from other by CH₃ group.
(c) They have same functional group.
(d) They have same chemical properties.
Answer : B

Question : Ethanoic acid was added to sodium carbonate solution and the gas evolved was tested with a burning splinter. The following four observations were reported. Identify the correct observation.
(a) The gas burns with pop sound and the flame gets extinguished
(b) The gas does not burn but the splinter burns with pop sound
(c) The flame extinguishes and the gas does not burn
(d) The gas burns with a blue flame and the splinter burns brightly
Answer : C

Question : The general formula for alkanes is C_nH_2n+1–CHO. The value of ‘n’ for the first member.
(a) 1
(b) 0
(c) 0.5
(d) 1.1
Answer : B

Question : Name the following aromatic compound

(a) toluene
(b) aniline
(c) phenol
(d) furan
Answer : A

Question : An organic compound ‘X’ has the molecular formula C₃H₆O₂. It has a pleasant smell but does not turn blue limus red. It has structural formula

Very Answer Type Questions :

Question : In saponification process, the fatty acid present in the oils is neutralised by adding
a. Sodium hydroxide
b. Aluminium hydroxide
c. Calcium hydroxide
d. Magnesium hydroxide
Answer : A

Question : Diabetic patients sometimes use this artificial sweeteners
a. Glycerol
b. Cane Sugar
c. Brown Sugar
d. Molasses
Answer : B

Question : This is not true regarding the micelle. 
a. The micelle stay in solution as a colloid
b. Micelle will not come together to precipitate
c. There is ion-ion repulsion
d. The dirt suspended in the micelles is very difficult to get rinsed oil
Answer : D

Question : This is not a characteristic of members of a homologous series. 
a. They possess varying chemical properties
b. Their properties vary in regular and predictable manner
c. Their formulae fit the general molecular formula
d. Adjacent members differ by one carbon and two hydrogen atoms
Answer : A

Question : Temporary hardness of water is due to compound 'A' and can be removed by adding compound 'B'. A and B respectively can be : 
a. Mg(HCO₃)₂, CaCO₃
b. CaSO₄, HCl
c. CaCl₂, MgSO₄
d. Ca(HCO₃)₂,Ca(OH)₂
Answer : D

Question : A gas on passing through ammonical AgNO₃ does not give any precipitate but decolourises alkaline KMnO₄ The gas may be : 
a. C₂H₆
b. C₂H₄
c. C₂H₂
d. C₃H₈
Answer : C

Question : Acetic acid, with the molecular formula CH₃ COOH has
a. 8 covalent bonds
b. 7 covalent bonds
c. 9 covalent bonds
d. 10 covalent bonds.
Answer : A

Question : Consider the chemical formulae CH₃COOH and HCOOCH₃ and choose the incorrect statement:
a. Both have the equal boiling point
b. Both have the equal molecular weight
c. Both have the equal number of covalent bonds
d. Both are not the same compound
Answer : A

Question : The path of light gets illuminated when passed through the solution: 
a. Blood solution(aq)
b. Brine solution (aq)
c. Copper sulphate solution(aq)
d. Acetic acid solution(aq)
Answer : C

Question : The number of structural isomers of the compound having molecular formula C₄H₉Br is :
a. 3
b. 5
c. 4
d. 2
Answer : C

Question : The total number of electrons and the number of electrons involved in the formation of various bonds present in one molecule of propanal (C₂H₅CHO) are respectively :
a. 32 and 20
b. 24 and 20
c. 24 and 18
d. 32 and 18
Answer : A

Question : Ethanol is made unfit for drinking by adding 
a. Propanol
b. Methanal
c. Methanol
d. Ethanal
Answer : C

Question : The general formula CnH₂nO₂ could be for open chain 
a. diketones
b. carboxylic acids
c. diols
d. dialdehydes.
Answer : B

Question : The correct decreasing order of priority for the functional groups of organic compounds in the IUPAC system of nomenclature is
a. –SO₃H, –COOH, –CONH₂, –CHO
b. –CHO, –COOH, –SO₃H, –CONH₂
c. –CONH₂, –CHO, –SO₃H, –COOH
d. –COOH, –SO₃H, –CONH₂, –CHO
Answer : D

Question : The IUPAC name of neopentane is 
a. 2, 2-dimethylpropane
b. 2-methylpropane
c. 2, 2-dimethylbutane
d. 2-methylbutane
Answer : A

Question : Which of the following hydrocarbons undergo addition reactions?
C₂H₆, C₃H₈, C₂H₂ and CH₄
Support your answer by a chemical equation.
Answer : Only C₂H₂ will undergo addition reaction.

Question : Write the next homologue of propanol (CH₃CH₂CH₂OH) and butanal (CH₃CH₂CH₂CHO).
Answer : Next homologue of propanol (CH₃CH₂CH₂OH) is butanol (CH₃CH₂CH₂CH₂OH).
Next homologue of butanal (CH₃CH₂CH₂CHO) is pentanal (CH₃CH₂CH₂CH₂CHO).

Question : What is a functional group? Give examples of four different functional groups.
Answer : Functional group: An atom/group of atoms joined in a specific manner which is responsible for the characteristic chemical properties of the organic compounds. Examples are hydroxyl group
(– OH), aldehyde group (– CHO), ketonic group (C=O ), carboxylic acid group (–COOH), etc.

Question : Complete the following reactions :

Answer : 

3 Marks Question :

Question : Give reasons for the following :
(a) Unsaturated hydrocarbons show addition reactions but not saturated hydrocarbons.
(b) Carbon only forms covalent compounds.
Answer : (a) Unsaturated hydrocarbons such as ethene (C₂H₄) and ethyne (C₂H₂) have double or triple covalent bonds respectively. Hence they show addition reactions to form new single covalent bond while saturated hydrocarbons have only single covalent bonds so they do not show addition reaction.
(b) Carbon has four valence electrons. Thus, it is not in a position to donate/accept four electrons so as to acquire a stable neon gas like structure. Thus, in order to enter into a chemical reaction, it shares its valence electrons with other elements. So it forms only covalent compounds.

Question : (a) Define the term functional group. Identify the functional group present in the following compounds :

(b) What will you observe on adding a 5% alkaline potassium permanganate solution drop by drop to some warm ethanol taken in a test tube? Write the name of the compound formed during the above chemical reaction.
Answer : (a) Functional group : The functional group in an organic compound is an atom or a group of atoms bonded together in such a unique fashion, that it is usually the site of chemical reactivity of an organic molecule.

(b) On adding a 5% alkaline potassium permanganate solution, the pink colour of potassium permanganate fades at once, continue adding drops of potassium permanganate, till the colour stops fading. At this stage the ethanol is completely oxidised to ethanoic acid.

Question : (a) Write the names of :
(i) CH₃ — CH₂ — CHO
(ii) CH₃ — CH₂ — OH
(b) Name the gas evolved when an alcohol reacts with sodium. Give chemical equation for the reaction involved.
(c) Which two of the following compounds belong to same homologous series?
C₂H₆O, C₂H₆O₂, C₂H₆, CH₄O
Answer : (a) (i) Propanal (ii) Ethanol
(b) Ethanol reacts with sodium to give sodium ethoxide and hydrogen gas.
2CH₃CH₂OH    +     2Na     →    2CH₃CH₂ONa      +      H₂(g)
Ethanol                Sodium         Sodium ethoxide       Hydrogen
(c) C₂H₆O and CH₄O are of same homologous series.

Question : What is ethanol? Draw the structure of ethanol molecule. How does ethanol behave with the following:
(a) Sodium
(b) Excess of concentrated sulphuric acid at 443 K?
Write chemical equation for each reaction.
Answer : Ethanol is the second member of the homologous series of alcohols.

Question : An organic compound ‘A’ is an essential constituent of wine and beer. Oxidation of ‘A’ yields an organic acid ‘B’ which is present in vinegar. Name the compounds ‘A’ and ‘B’ and write their structural formula. What happens when ‘A’ and ‘B’ react in the presence of an acid catalyst?
Write the chemical equation for the reaction.
Answer : ethyl alcohol is an essential constituent of wine and beer. Therefore, A is ethyl alcohol. Oxidation of ethyl alcohol gives acetic acid. Vinegar contains acetic acid. Therefore, B is acetic acid.

Question : (a) Distinguish between esterification and saponification reactions of organic compounds.
(b) With a labelled diagram to describe an activity to show the formation of an ester.
OR
Describe an activity to show the formation of an ester in the school laboratory.
Answer : (a) A chemical reaction in which an alcohol reacts with alkanoic acid to form a sweet smelling compound (ester) is called esterification.

A chemical reaction in which an ester gets hydrolysed in the presence of sodium hydroxide to form the constituent alcohol and sodium salt of the alkanoic acid is called saponification.
CH₃COOC₂H₅       +   NaOH        →         CH₃COONa      +      C₂H₅OH
Ethyl ethanoate      Sodium hydroxide       Sodium acetate     Ethanol

(b) Activity
Pour 1 ml of ethanol (absolute alcohol in a test tube).
Pour 1 ml of glacial acetic acid in the alcohol and then a few drops of conc. sulphuric acid.
Warm the contents of the test tube in a hot water bath for 10 minutes.
Pour the contents of the test tube in another beaker containing 20 ml of water.
Smell the contents of the beaker. You will will find a sweet fruity smell. This smell is due to the formation of the ester, ethyl ethanoate.

Question : An ester has the molecular formula C₄H₈O₂.Write its structural formula. What happens when this ester is heated in the presence of sodium hydroxide solution? Write balanced chemical equation for the reaction and name the products. What is a saponification reaction?
Answer : 

The reaction between an ester and an alkali to form the sodium salt of an alkanoic acid and an alcohol is known as saponification.

Question : What is ethanol? State its two properties. What happens when it is heated with excess of concentrated H₂SO₄ at 443 K? What role does concentrated H2SO4 play in this reaction? Write chemical equation of the reaction involved and the structural formula of the main product formed.
Answer : ethanol is the second member of the homologous series of alcohols.
When ethanol is heated with excess of concentrated H₂SO₄ at 443 K it dehydrates to form ethene.

Question : (a) What is vinegar?
(b) Describe with a chemical equation, what happens when sodium hydrogen carbonate reacts with ethanoic acid?
Answer : (a) A 5 – 8% solution of acetic acid in water is known as vinegar.
(b) When sodium hydrogen carbonate reacts with ethanoic acid, carbon dioxide gas is liberated.
CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂

Question : What is ethanoic acid? Write the formula of the functional group present in this acid. What special name is given to its 5 – 8% solution in water? How does ethanoic acid react with sodium carbonate? Write the chemical equation of the reaction and common name of the salt produced.
Answer : Ethanoic acid is the second member of the homologous series of alkanoic acid. Functional group in ethanoic acid is — COOH.5 – 8% solution of ethanoic acid in water is known as vinegar.
Ethanoic acid reacts with sodium carbonate to liberate carbon dioxide gas.
2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂
The salt produced is sodium acetate.

Question : What is a homologous series of compounds? List any two characteristics of a homologous series.
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.
Characteristics of a homologous series :
(i) All members of a homologous series can be represented by a general formula.
(ii) Each member of a homologous series differs from the next member by a – CH2 group.

Case Study Based Question :

1. Read the following and answer the following Question :

The two characteristic features in carbon are tetravalency and catenation, which are put together give rise to a large number of compounds. Many have the same non-carbon atom or group of atoms attached to different carbon chains. Carbon compounds, except for oxides of carbon, carbonate and hydrogen carbonate salts study under organic chemistry.
The carbon compounds which contain carbon and hydrogen are called hydrocarbons. Among these, the saturated hydrocarbons are called alkanes. The unsaturated hydrocarbons containing one or more double bonds are called alkenes. Those containing one or more triple bonds are called alkynes.

Question : When a carbon atom shares electrons with the neighbouring carbon atoms, it forms a straight chain or a branched chain or a closed chains of carbon atoms, name such property of carbon.
Answer : Catenation

Question : Define the property of carbon mentioned in Question : (a).
Answer : The property of carbon atoms to link with other carbon atoms of the atoms of other elements with single, double or triple envalent bonds, so as to form a large number of compounds is called catenation.

Question : Give reasons for the following observation:
The element carbon forms a very large number of compounds.
Answer :
(i) Carbon has the unique ability to form bonds with other carbon atoms, so as to form long straight chains, branched chains and closed rings, giving rise to a large number of molecules.
(ii) Carbon atom has four valence electrons, therefore, it can bind itself with four more carbon atoms with single covalent bonds, or with different atoms of monovalent elements.
OR
A compound C (molecular formula, C₂ H₄ O₂) reacts with Na-metal to form a compound R and evolves a gas which burns with a pop sound. Compound C on treatment with an alcohol A in the presence of an acid forms a sweet smelling compound S (molecular formula, C₃H₆O₂). On addition of NaOH to C, it also gives R and water. S on treatment with NaOH solution gives back R and A.

Question : Identify C, R, A, S and write down the reactions involved.
Answer : C — Ethanoic acid
R — Sodium salt of ethanoic acid (sodium acetate) and gas evolved is hydrogen.
A — Methanol
S — Ester (methyl acetate)