CBSE Class 10 Science Carbon and its Compounds Worksheet

MCQ's

 
Question : While cooking, if the bottom of the vessels is getting blackened on the outside, it means that: 
a. The food is not cooked completely
b. The fuel is not burning completely.
c. The fuel is burning completely.
d. The fuel is wet.

Answer : B
Explanation: If the bottom of the vessels is getting blackened (due to deposit of soot) on the outside while cooking, it is an indication that the fuel is not burning completely. When the fuel does not burn completely, some carbon particles remain un-oxidised and form soot.
 
Question : Hardness of water is caused by: 
a. All of these
b. Mg(HCO3)2
c. CaCl2
d. CaSO4

Answer : A 
Explanation: Hardness of water is caused by magnesium and calcium salts.
Calcium and magnesium dissolved in water are the two most common minerals that make water hard. Temporary hardness is a type of water hardness caused by the presence of dissolved bicarbonate minerals (calcium bicarbonate and magnesium bicarbonate).  
 
Question : Which of the following are not straight chain compounds? 
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a. A, B and D
b. C and D
c. A and B
d. A and C

Answer : B
Explanation: A and B are straight chain compounds. A has a straight chain of 5 carbon atoms. B has a straight chain of 7 carbon atoms. C and D are not straight chain compounds.
 
Question : What is denatured spirit? 
a. None of these
b. Ethanol only
c. Methanol only
d. Ethanol + Methanol (5%)

Answer : D
Explanation: Alcohol meant for industrial purposes is made unfit for human consumption by adding small amounts (about 5%) of methanol to ethanol. The mixture is known as denatured spirit or denatured alcohol. Addition of small amount of copper sulphate is added to impart a blue colour to denatured spirit so that it can be identified easily.
 
Question : Alcohols can be produced by the hydration of: 
a. Alkenes
b. Alkanes
c. Acids
d. Alkynes

Answer : A 
Explanation: Alcohols can be produced by the hydration of alkenes.
Hydration of alkenes is an addition reaction. The reaction is highly exothermic.
E.g. Ethanol is manufactured by reacting ethene with steam.
 

Very Short Answers


Question : Name the chemical reagent which oxidises ethanol to ethanoic acid. 
Answer : Ethanol is oxidised by acidifed sodium dichromate in a test-tube reaction, firstly to form ethanal and, with further oxidation, ethanoic acid.
 
Question : Why is pure ethanoic acid called glacial ethanoic acid (or glacial acetic acid)? 
Answer :  The melting point of pure ethanoic acid is 290 K. When ethanoic acid (acetic acid) is cooled below 10 °C, it freezes to form a colourless, ice-like solid. The solid looks like glacier and hence pure ethanoic acid is called glacial ethanoic acid (or glacial acetic acid). 
 
Question : State the part of soap molecule that attaches itself to dirt when soap is dissolved in water. 
Answer : Hydrophobic end also called as tail, i.e.long hydrocarbon chain moves away from water but attaches to dirt.
 
Question : State the general formula of carboxylic acids. 
Answer :  The general formula of carboxylic acids is CnH2n+1COOH.
 

Short Answers

 
Question : Explain why soaps are not effective cleansing agents in hard water? 
Answer : It is because detergents form lot of lather even with hard water. Hard water contains Ca2+ and Mg2+ ions which react with soap to form Insoluble salts of calcium and magnesium called scum and soap goes waste. Detergents do not form insoluble compounds with Ca2+ and Mg2+ ions therefore. These are more effective.
 
Question : Write the molecular formula and structural formula of acetaldehyde. 
Answer :   Molecular formula of acetaldehyde : CH3CHO
Structural formula of acetaldehyde:
Ma-8 
 
Question : Explain the formation of scum when hard water is treated with soap. 
Answer : Soap does not work properly when the water is hard. A soap is a sodium or potassium salt of long chain fatty acids. Hard water contains salts of calcium and magnesium.
When soap is added to hard water, calcium and magnesium ions present in water displace sodium or potassium ions from the soap molecules forming an insoluble substance called scum. A lot of soap is wasted in the process.
 
Question : How would you distinguish experimentally between an alcohol and a carboxylic acid? 
Answer :  The following two tests are used:
i. Litmus test: Treat the given compound with blue litmus solutions. If the blue litmus solution turns red, it is a carboxylic acid and if does not turn red, it is an alcohol.

ii. Sodium bicarbonate test: Add some sodium bicarbonate solution to the given compound. If there is a brick evolution of a colourless and odourless gas (CO2 ) which turns freshly prepared lime water milk, it is carboxylic acid and if there is no effervescence, it is an alcohol.  

Question. What would be the electron dot structure of carbon dioxide which has the formula CO2?
Answer: The atomic number (Z) for carbon is six and its electronic configuration is 2, 4. Carbon has four valence electrons.
Each oxygen atom (Z = 8) has six valence electrons (2, 6). In order to complete its octet, the carbon atom shares its four valence electrons with the four electrons of the two
oxygen atoms as follows :
Thus, in carbon dioxide molecule, the carbon atom is linked to two oxygen atoms by two shared pairs of electrons resulting in double bonds on either sides. Both carbon and oxygen
atoms complete their octet as a result of electron sharing.

Question. Why is homologous series of carbon compounds so called? Write the chemical formula of two consecutive members of any homologous series and state the part of these compounds that determines their (i) physical and (ii) chemical properties.
Answer: A homologous series is the family of organic compounds having the same functional group, similar chemical properties but the successive (adjacent) members of the series are differ by a CH2 unit or 14 mass units.
Consecutive members of the homologous series of alcohols are :
CH3 OH ] They differ by CH unit.
CH3 OH
The physical properties are determined by alkyl group/ hydrocarbon part/part other than the functional group.
The chemical properties are determined by functional group such as —OH group.

Question. Define isomerism. Write down the structures and names of isomers of butane.
Answer: Two or more compounds having same molecular formula but different structural arrangements of atoms in their molecules are called isomers. This phenomenon is called
isomerism. 

CBSE Class 10 Science Carbon and its Compounds Worksheet

Question. An element X has a proton number of 15, while element Y has a proton number of 17. Draw a ‘dot-and-cross’ diagram to show all electrons in a molecule formed from elements X and Y.
Answer: Electronic configuration of X : 2, 8, 5 Atom X contributes three electrons for sharing.
Electronic configuration of Y : 2, 8, 7 Each atom of Y contributes one electron for sharing.
Therefore, three atoms of Y contribute three electrons for sharing.
One atom of X will share three pairs of electrons with three atoms of Y to achieve the noble gas configuration.
Both atoms X and Y achieve the electronic configuration of argon (2, 8, 8).

Question. (a) What type of bond holds the two chlorine atoms together in a chlorine molecule?
(b) Briefly describe how this bond is formed.
(c) Draw a ‘dot-and-cross‘ diagram to show the bonding in a chlorine molecule.
Answer: (a) Covalent bond
(b) The two chlorine atoms share one pair of electrons, so that both atoms achieve a noble gas configuration. 

CBSE Class 10 Science Carbon and its Compounds Worksheet

Question. The diagram shows one layer of carbon atoms in the structure of graphite: 
CBSE Class 10 Science Carbon and its Compounds Worksheet

(a) Identify the types of bonding in graphite.
(b) Which property of graphite makes it suitable for use as a dry lubricant? Explain your answer.
Answer: (a) Covalent bonds between carbon atoms in each layer and van der Waals’ forces between the layers of carbon atoms.
(b) Graphite is soft. The layers of carbon atoms can slide and glide over each other because the weak van der Waals’ forces between the layers are easy to overcome.

Question. Explain the nature of the covalent bond using the bond formation in CH3Cl.
Answer: The molecule of chloromethane (CH3Cl) consists of three elements i.e., carbon (Z = 6), hydrogen (Z = 1) and chlorine (Z = 17). Carbon atom has four valence electrons (2, 4) ; hydrogen has one (1) while chlorine has seven electrons in the valence shell (2, 8, 7). In order to complete its octet, carbon shares three valence electrons with three hydrogen atoms while one is shared with the electron of chlorine atom. The structure of covalent molecule may be written as follows : 

CBSE Class 10 Science Carbon and its Compounds Worksheet

Question. What is homologous series of compounds?
List any two characteristics of homologous series.
Answer: A series of compounds having similar structures and similar chemical properties in which the successive member differs in their molecular formula by –CH2 group is called homologous series.
Characteristics :
(a) All the members of homologous series have similar chemical properties.
(b) Any two consecutive members differ in their molecular formula by a –CH2 group.

Question. Two non-metals A and B combine with each other by sharing of electrons to form compound C.
(a) What is the naturstronge of compound C ?
(b) Will it dissolve in water or organic solvents?
(c) Will it be a good or bad conductor of electricity?
(d) Will it have high or low melting/boiling point ?
Answer: (a) Covalent
(b) Usually soluble in organic solvents
(c) Bad conductor
(d) Usually low melting / boiling point.

 

Long Answers


Question : i. What are hydrocarbons? Give examples.
ii. Give the structural differences between saturated and unsaturated hydrocarbons with two examples each.
iii. What is functional group? Give examples of four different functional groups. 
Answer : i. The compounds that are made up of carbon and hydrogen atoms are called hydrocarbons, e.g. methane (CH4), ethane (CH2 = CH2). Ethyne (C2H2), cyclohexane (C6H12), benzene (C6H6)etc.
ii. In saturated hydrocarbons, all the four valencies of carbon are satisfied by a single covalent bond while in unsaturated hydrocarbons, double or triple bonds are required to satisfy the valencies of carbon, e.g.
a. Saturated hydrocarbons
Methane (CH4), Ethane (CH3 — CH3)
b. Unsaturated hydrocarbons
Ethene (H2C = CH2), Ethyne (HC ≡ CH)
iii. A functional group is an atom or group of atoms that define the structure (or the properties) of organic compounds. The four examples are:
a. -OH Alcohol
b. -COOH Carboxylic acid
c. -CHO Aldehyde
d. -X Halogen 
 
 
Question : i. Write the names of the functional groups in
Ma-7
.
ii. Describe a chemical test to distinguish between ethanol and ethanoic acid.
iii. Write a chemical equation to represent what happens when hydrogen gas is passed through an unsaturated hydrocarbons in the presence of nickel as a catalyst? 
Answer :
i. a. Ketone (R-CO-R)

b. Aldehyde (R-CHO)

ii. Distinguish between ethanol and ethanoic acid:

a. Ethanol does not react with metal carbonate while ethanoic acid reacts with metal carbonates to form salt, water and CO2.

e.g. 2CH3COOH + Na2CO→ 2CHCOONa + CO2+ H2

b. Ethanol does not react with NaOH while ethanoic acid reacts with NaOH to form sodium ethanoate and water

e.g. CH3COOH+NaOH →  CHCOONa+ H2O

c. Ethanol can undrergo oxidation to produce aldehyde and futher it can oxidize to produce acid.

iii. saturated hydrocarbon is obtained as hydrogen gas passed through unsaturated hydrocarbon. The reaction is an example of addition reaction better known by the name of hydrogenation reaction.
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