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Carbon and its Compounds · CBSE STD 10 (CBSE - English Medium). 85 questions.

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Question 12 Marks
Write two points of difference in the structures of diamond and graphite.
Answer
Diamond:

  1. Each carbon atom is linked to four other carbon atoms.
  2. A diamond crystal has a tetrahedral arrangement of carbon atoms.

Graphite:

  1. Each carbon atom is joined to only three other carbon atoms.
  2. A graphite crystal has flat hexagonal rings structure.
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Question 22 Marks
Write three common functional groups present in organic compounds. Give their symbols /formulae.
Answer
  1. Halo group: -X
  2. Alcohol group: -OH
  3. Aldehyde group: -CHO
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Question 42 Marks
Write the names and formulae for the first three members of the homologous series of chloroalkanes.
Answer
Chloromethane: CH3Cl
Chloroethane: C2H5Cl
Chloropropan: C3H7Cl
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Question 52 Marks
Write the molecular formula of:
  1. An alkane.
  2. An alkene.
  3. An alkyne, each having 20 carbon atoms?
Answer
  1. An alkane comprising 20 atoms of carbon (n = 20):

C20H2×20 + 2 = C20 H42

  1. An alkene comprising 20 atoms of carbon (n = 20):

C20H20×2 = C20H40

  1. An alkyne comprising 20 atoms of carbon (n = 20):

C20H2×20-2 = C20H38

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Question 62 Marks
Write the molecular formula and structure of cyclohexane. How many covalent bonds are there in a molecule of cyclohexane?
Answer
Molecular formula of cyclohexane is C6H12.

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Question 72 Marks
Write the molecular and structural formula of a cyclic hydrocarbon whose molecule contains 8 atoms of carbon.
Answer
Molecular formula: C8H16

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Question 92 Marks
Write names and formulae of hydrocarbons containing a single and a double bond (one example for each). Give one characteristic chemical property of each.
Answer
  1. Single bond: Methane, CH4. They are quite unreactive hence they undergo substitution reaction with chlorine in presence of sunlight.
  2. Double bond: Ethene, CH2 = CH2. They undergo addition reaction in the presence of a catalyst like nickel or palladium.
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Question 112 Marks
Why is the conversion of ethanol into ethanoic acid an oxidation reaction?
Answer
Oxidation means controlled combustion. When ethanol is heated with alkaline potassium permanganate solution (or acidified potassium dichromate solution), it gets oxidised to ethanoic acid. It is called an oxidation reaction because oxygen is added to it during this conversion.
$\text{CH}_3\text{CH}_2\text{OH}+2[\text{O}]\xrightarrow[\text{or} \ \text{acidified}\text{K}_2\text{Cr}_2\text{O}_7]{ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ {\text{Alkaline}\text{KMnO}_4;\text{Heat}}\ \ \ \ \ \ \ \ \ \ \ \ \ \ }\text{CH}_3\text{COOH}+\text{H}_2\text{O}$
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Question 122 Marks
Why is soap not suitable for washing clothes when the water is hard?
Answer
When soap is used for washing clothes with hard water, a large amount of soap in water is reacting with the calcium and magnesium ions of hard water to form an insoluble precipitate called scum, before it can be used for the real purpose of washing.
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Question 132 Marks
Why is graphite a good conductor of electricity but diamond is a non-conductor of electricity?
Answer
Due to the presence of free electrons in a graphite crystal, it conducts electricity however; a diamond crystal does not have free electrons so it does not conduct electricity.
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Question 142 Marks
Why is common salt (sodium chloride) added during the preparation of soap?
Answer
Common salt is added to the mixture to make the soap come out of solution. Though most of the soap separates out on its own but some of it remains in solution. Common salt is added to precipitate out all the soap from the aqueous solution.
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Question 152 Marks
Why have detergents replaced soap as a washing agent?
Answer
Detergents are better cleansing agents than soaps because they do not form insoluble calcium and magnesium salts with hard water, and hence can be used for washing even with hard water.
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Question 162 Marks
Why does the element carbon from a large number of carbon compounds?
Answer
Carbon forms a large number of carbon compounds because carbon atoms can link with one another by means of covalent bonds to form long chains of carbon atoms.
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Question 172 Marks
Why does ethyne (acetylene) burn with a sooty flame?
Answer
Ethyne (acetylene) burn with a sooty flame because ethyne is an unsaturated hydrocarbon and the percentage of carbon in these hydrocarbons is comparatively higher which does not get oxidised completely in oxygen of air.
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Question 182 Marks
Why are coal and petroleum called fossil fuels?
Answer
Coal and petroleum are called fossil fuels because they are produced through the decomposition of the pre-historic organisms (plants and animals) buried deep in the soil since millions of years ago.
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Question 192 Marks
Why are carbon and its compounds used as fuels for most applications?
Answer
Carbon and its compounds are used as fuels because they burn in air releasing a lot of heat energy.
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Question 202 Marks
Which of the two is better for washing clothes when the water is hard: soap or detergent? Give reason for your answer.
Answer
Detergent is better for washing clothes in hard water. They are better cleansing agents than soaps because they do not form insoluble calcium and magnesium salts with hard water, and hence can used for washing even with hard water.
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Question 212 Marks
Which of the following hydrocarbons will give substitution reactions and why?
CH4, C3H6, C3H8, C4H6, C5H12, C5H10.
Answer
CH4, C3H8, C5H12 all these are saturated hydrocarbons (Alkanes) and hence will give substitution reactions.
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Question 222 Marks
Which of the following hydrocarbons can decolourise bromine water and which cannot? Why?
C6H12, C6H14, C6H10
Answer
C6 H12 and C6 H10C a decolourise bromine water since these are unsaturated hydrocarbons.
C6 H14 cannot decolourise bromine water since it is a saturated hydrocarbon.
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Question 232 Marks
What will you observe when dilute ethanoic acid and dilute hydrochloric acid are put on universal indicator paper, one by one? What does it show?
Answer
Dilute ethanoic acid turns universal indicator paper to orange, showing that its pH is about 4 which tell us that ethanoic acid is a weak acid. On the other hand, dilute hydrochloric acid turns universal indicator paper to red, showing that its pH is about 1. This shows us that hydrochloric acid is a strong acid.
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Question 242 Marks
What is the unique property of carbon atom? How is this property helpful to us?
Answer
The most unique property of carbon atom is its ability to combine itself, atom to atom to form long chains. This property of self combination is useful to us because it gives rise to an extremely large number of carbon compounds (or organic compounds).
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Question 252 Marks
What is the molecular formula and structural formula of a cyclic hydrocarbon whose one molecule contains 8 hydrogen atoms?
Answer
The molecular formula of a cyclic hydrocarbon is C4H8, as it satisfies the general formula of a cyclic hydrocarbon, i.e. CnH2n. Here, the number of hydrogen atoms is already given as 8, i.e. 2n = 8. Therefore, $\text{n} = \frac{8}{2}=4.$ Here, n represents the number of carbon atoms. Therefore, the molecular formula is C4H8.

The structural formula of the cyclic hydrocarbon C4H8 is as follows​:

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Question 262 Marks
What is saponification? Write the chemical equation of the reaction involved in this process. Name all the substances which take part in this process and also those which are formed.
Answer
The process of making soap by the hydrolysis of fats and oils with alkalis is called saponification.
$\text{Factor}\ \text{Oil}+\text{Sodiumhydroxide}\xrightarrow[{}]{{ \ \ \ \ \ \ \ \ \ \ \text{Heat}}\ \ \ \ \ \ \ \ \\ }\text{Soap}+\text{Glyoerol}\$\text{Anester})\ \ \ \ \ \ \ \ \ \ \ \ \ (\text{Analkali})\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ (\text{Sodium}\ \text{salt} \ \ (\text{An alcohol})\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{of}\ \text{fatty}\ \text{acid})$
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Question 272 Marks
What is meant by ‘heteroatom’? Give examples. Write the names and formulae of two organic compounds containing different heteroatoms.
Answer
In an organic compound, any atom other than carbon and hydrogen is called a heteroatom.
Example: Chlorine (Cl), Bromine (Br), Oxygen (O) Chloromethane– CH3Cl and methanol– CH3OH.
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Question 282 Marks
What is meant by a substitution reaction? Give an example (with equation) of the substitution reaction of, an alkane.
Answer

The reaction in which one or more) hydrogen atoms of a hydrocarbon are replaced by some other atoms (like chlorine), is called a substitution reaction.

Example: Substitution reaction of methane with chlorineMethane reacts with chlorine in the presence of sunlight to form chloromethane and hydrogen chloride.

$\text{CH}_4+\text{Cl}_2\xrightarrow[{}]{{ \ \ \ \ \ \ \ \ \ \ \ \text{Sunlight}}\ \ \ \ \ \ \ \\ }\text{CH}_3\text{Cl}+\text{HCl}$

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Question 292 Marks
What is meant by an addition reaction? Give an example (with equation) of an addition reaction of an alkene.
Answer
The reaction in which an unsaturated hydrocarbon combines with another substance to give a single product is called an addition reaction.
Example: Ethene reacts with hydrogen when heated in the presence of nickel catalyst to form ethane
$\text{CH}_2=\text{CH}_2+\text{H}_2\xrightarrow[{\text{Heat}}]{{ \ \ \ \ \ \ \ \ \text{NiCatalyst}}\ \ \ \ \ \ \ \ }\text{CH}_3-\text{CH}_3$
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Question 302 Marks
What is meant by a functional group? Explain with an example.
Answer
An ‘atom’ or ‘a group of atoms’ which makes a carbon compound (or organic compound) reactive and decides its properties (or functions) is called a functional group. The alcohol group, -OH, present in ethanol, C2H5OH, is an example of a functional group.
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Question 312 Marks
What is buck minster fullerene? How is it related to diamond and graphite?
Answer
Buck minster fullerene is an allotrope of carbon containing clusters of 60 carbon atoms joined together to form spherical molecules. It burns on heating to form carbon dioxide and nothing is left behind. This shows that it is made up of carbon only like diamond and graphite.
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Question 322 Marks
What is an oxidising agent? Name two oxidising agents which can oxidise ethanol to ethanoic acid.
Answer
An oxidising agents is one which oxidises others substances by providing oxygen or removing hydrogen. Alkaline potassium permanganate and acidified potassium dichromate can be used as oxidising agents.
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Question 332 Marks
What is a detergent? Name one detergent.
Answer
A detergent is the sodium salt of long chain benzene sulphonic acid which has cleansing properties in water.
Example: Sodium n-dodecyl benzene sulphonate.
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Question 342 Marks
What happens when propanoic acid is warmed with methanol in the presence of a few drops of concentrated sulphuric acid? Write equation of the reaction involved.
Answer
Propanoic acid will react with the alcohol in the presence of concentrated sulphuric acid to form esters.
$\text{CH}_3\text{CH}_2\text{COOH}+\text{CH}_3\text{OH}\rightarrow\text{CH}_3\text{CH}_2\text{COOCH}_3+\text{H}_2\text{O}\\ \text{Propanoic acid} \ \ \ \ \text{ Methanol} \ \ \ \ \text{Methyl propanoate} \ \ \ \ \text{water}$
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Question 352 Marks
What are the raw materials required for making soap in a laboratory (or at home)?
Answer
  1. Vegetable oil (like castor oil, cottonseed oil or soyabean oil).
  2. Sodium hydroxide (caustic soda).
  3. Sodium chloride (common salt).
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Question 362 Marks
What are hydrocarbons? Explain with examples.
Answer
A compound made up of hydrogen and carbon only is called a hydrocarbon (Hydrogen + Carbon = Hydrocarbon).
For exampe: methane (CH4), ethane (C2H6), ethene (C2H4), and ethyne (C2H2), all are hydrocarbons as they are made up of only two elements: carbon and hydrogen.
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Question 372 Marks
The structural formula of an ester is:
$ \ \ \ \ \ \ \ \ \text{H} \ \ \ \ \ \text{O} \ \ \ \ \ \ \ \ \ \ \ \ \ \text{H} \ \ \ \ \text{H}\\ \ \ \ \ \ \ \ \ \ \text{|} \ \ \ \ \ \ \text{||} \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{|} \ \ \ \ \ \ \ \text{|}\\\text{H}-\text{C}-\text{C}-\text{O}-\text{C}-\text{C}-\text{H}\\ \ \ \ \ \ \ \ \ \ \text{|} \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{|} \ \ \ \ \ \ \ \text{|}\\ \ \ \ \ \ \ \ \ \text{H} \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{H} \ \ \ \ \ \text{H}$
Write the formula of the acid and the alcohol from which it is formed.
Answer
Acid: Ethanol acid.
$ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{O}\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{||}\\ \text{CH}_3-\text{C}-\text{OH}\\\text{Alcohol:Ethanol}\\\text{CH}_3-\text{CH}_2-\text{OH}$
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Question 382 Marks
State two uses of ethanol (other than as a fuel).
Answer
Uses of ethanol:
  1. It is used in the manufacture of paints, varnishes, lacquers, medicines, perfumes, dyes, soaps and synthetic rubber.
  2. It is used as a solvent. Many organic compounds which are insoluble in water are soluble in ethyl alcohol.
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Question 392 Marks
State two disadvantages of incomplete combustion.
Answer
Disadvantages of incomplete combustion:
  1. It leads to the formation of soot which is nothing but unburnt carbon which pollutes the atmosphere, blackens cooking utensils.
  2. It leads to the formation of an extremely poisonous gas called carbon monoxide.
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Question 402 Marks
State two characteristics of a homologous series.
Answer
  1. All the members of the homologous series can be represented by the same general formula.
  2. Any two adjacent homologues differ by 1 carbon atom and 2 hydrogen atoms in their molecular formulae.
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Question 412 Marks
State one use of diamond which depends on its ‘extraordinary brilliance’ and one use of graphite which depends on its being ‘black and quite soft’.
Answer
Diamonds are used for making jewellery. Graphite is used for making pencil cores or ‘pencil leads’.
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Question 422 Marks
Select the hydrocarbons which belong to the same homologous series. Give the name of each series.
CH4, C2H2, C2H4, C2H6, C4H10, C3H4, C3H6.
Answer
Alkanes: CH4, C2H6, C4H10

Alkenes: C2H4, C3H6

Alkynes: C2H2, C3H4

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Question 432 Marks
One of the following molecular formula can represent two organic compounds having different functional groups. This molecular formula is:
  1. C5H12O
  2. C5H10O
  3. C5H10O2
  4. C5H12
Answer
  1. C5H10O

Explanation:

C5H10O represents two organic compounds ketones (C2H5-CO-C2H5) and aldehydes (C2H5-CH2-CH2-CHO) which have different functional groups.

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Question 442 Marks
Name the functional groups present in the following compounds:
  1. CH3COOH
  2. CH3CH2CHO
  3. C2H5OH
  4. CH3COCH2CH3
Answer
  1. Carboxylic acid group.
  2. Aldehyde group.
  3. Alcohol group.
  4. Ketone group.
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Question 452 Marks
Name the functional groups present in the following compounds:
  1. CH3CHO
  2. CH3CH2COOH
  3. CH3COCH3
  4. CH3CH2CH2OH
Answer

  1. The functional group present in CH3CHO is the formyl group (-CHO).

  2. The functional group present in CH3CH2COOH is the group of carboxylic acids (-COOH).

  3. The functional group present in CH3COCH3 is the carbonyl group (-CO-).

  4.  The functional group present in CH3CH2CH2OH is the alcohol (hydroxyl) group (-OH).

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Question 462 Marks
Match the formulae in group A with appropriate names from group B:
Group A: CH3COOH, CH3CHO, CH3OH
Group B: Ethanol, Methanol, Ethanal, Ethanoic acid.
Answer
CH3COOH: Ethanoic acid.
CH3CHO: Ethanal.
CH3OH: Methanol.
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Question 472 Marks
How would you test for an alcohol?
Answer
Sodium metal test: Add a small piece of sodium metal to the organic liquid (to be tested), taken in a dry test tube. If bubbles (or effervescence) of hydrogen gas are produced, it indicates that the given organic liquid is an alcohol.
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Question 482 Marks
How would you name the following compound?
CH3-CH2-Br
Answer
Ethylbromide:
  1. Ketones.
  2. CH3COOH
  3. Formaldehyde.
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Question 492 Marks
How would you distinguish experimentally between an alcohol and a carboxylic acid on the basis of a chemical property?
Answer
A carboxylic acid reacts with sodium hydrogencarbonate to give brisk effervescence of carbon dioxide gas but an alcohol does not react with sodium hydrogencarbonate.
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Question 502 Marks
How would you distinguish between ethanol and ethanoic acid by chemical test?
Answer
Litmus test: Some blue litmus solution is added to the organic compound (to be tested). If the blue litmus solution turns red, it shows that the organic compound is acidic in nature and hence it is a carboxylic acid (ethanoic acid). Ethanol has no effect on any litmus solution.
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