1. Give
the general formula of alkane, alkene, and alkyne.
Ans: CnH2n+2,
CnH2n, CnH2n-2
respectively.
2.
Classify the following
compounds as alkanes, alkenes and alkynes.
C2H4, C3H4, C4H8,
C5H12, C5H8, C3H8, C6H6
ANS : alkanes – C5H12, , C3H8
Alkenes – C2H4, C4H8,
Alkynes – C3H4, C5H8
3. Name the simplest hydrocarbon and give its formula.
Ans:
Methane CH4
4 4. Amongst C2H4 and C2H6 ,which is more
reactive? Why?
Ans: Amongst C2H4 and C2H6, C2H4
is more reactive, as it is a unsaturated
Hydrocarbon and contains a reactive site (double bond) in it.
5. Why carbon forms compounds by sharing of electrons and not by
formation of ions?
Ans: carbon is tetravalent in nature. If it gains 4 electrons
to form C4- ions, then it will be difficult for 6 electrons to hold
on to 10 electrons while formation of C4+ ions. i.e. loss of 4
electrons requires considerable amount of energy. Hence, it forms bond by
sharing of electrons.
66. Give reasons for the formation of large number of compounds
by carbon.
Ans: carbon forms large number of compounds due to the
following properties:
a. CATENATION: due to this
property, it can link to other carbon atoms to form straight chain, branched
chain and ring structure.
b. TETRAVALENCY: Due to its
tetravalent nature, it can form bond with four atoms of carbon or some other
elements.
77. Give an important difference between saturated and
unsaturated hydrocarbons.
Ans: In a saturated hydrocarbon all the carbon atoms in a
compound are linked to other carbon atoms by single covalent bonds while in an
unsaturated hydrocarbons, there is a presence of a double / triple covalent bond
between the carbon atoms. E.g.ethane is a saturated hydrocarbon ethene is a
unsaturated hydrocarbon.
8. What is structural isomerism? Give examples.
Ans; The phenomenon of
existence of compounds having same molecular formula but different structural
formula is called structural isomerism, e.g. Butane has two structural isomers.
Iso butane and 2-methyl propane (IUPAC name)are the same.
NOTE: isomerism is possible only with hydrocarbons having 4
or more carbon atoms.
No isomerism is possible in methane, ethane and propane
because they contain only one, two or three carbon atoms.
9. How many structural isomers are possible for pentane? Draw
the structural formulae of all the possible isomers of pentane. Give their
IUPAC names also.
Ans: the molecular formula of pentane is C5H12.
It has 5 carbon atoms
.i. First write all
the 5 C atoms in a straight chain. this is called as n-pentane.
iii. Next write 3 C
atoms in a straight chain and 2 C atom in two side chain.
10. Pure ethanoic acid is
also called glacial acetic acid. Why?
ANS: Ethanoic acid has a low melting point of 290 K. thus, in
cold weather ethanoic acid freezes to form glacier like crys tals. That is why
Pure ethanoic acid is also called glacial acetic acid.
1
111. 1 ml of glacial acetic
acid and 1 ml of ethanol are mixed together in a test tube. Few deops of con.
Sulphuric acid is added in the mixture and warmed in a water bath for 5
minutes.
a.
Name the resultant
compound formed.
b.
Represent the above change
by a chemical equation.
c.
What term is given to such
reaction?
d.
What is the special characteristics
of the compound formed?
e.
Give one important use of
the compound formed.
ANS:
a. The resulting compound
formed is ester ( ethyl acetate). The IUPAC name this ester is ethyl ethanoate.
b.
Con. H2SO4
C2H5OH + CH3COOH -------------------à CH3COO C2H5 + H2O
∆
c. Esterification
d. The compound formed has a
sweet smell.
e. Esters formed is used in
making perfumes and as a flavouring agent.
112. What is
saponification?
Ans: the alkaline
electrolysis of esters (using alkali like sodium hydroxide) is known as
saponification. This is because of the fact that this reaction is used for the preparation of soap.
When an ester is heated
with NaOH solution then the ester gets hydrolysed (breaks down) to form the
parent alcohol and sodium salt of the
Carboxylic acid.
For e.g. when ethyl
ethanoate ester is boiled with NaOH solution, then sodium ethanoate and ethanol
are produced.
Heat
CH3COOC2H5 +
NaOH ------------------à CH3COONa +
C2H5OH
ethyl ethanoate
sodium ethanoate Ethanol
(Ethyl acetate)
13.. Write the structural
formulae of isomers of hexane.
14.
Write the structural
formulae of isomers of butane. Also give
their IUPAC names.
115. Give IUPAC names of the following compounds.
ANS: PROPANONE
b. Give IUPAC names of the
following compound.
ANS: BUTANOIC
ACID
c.
ANS: PROPENE
d.
ANS : BROMO
BUTANE
e. ETHANOL
16. Draw the structures of the following compounds.
a. ETHANOIC ACID
b. BROMO PENTANE
c. BUTANON
d. HEXANA
e. BENZENE
a. ANS:
b . ANS:
c. ANS
d. Ans
e. Ans
17. Show the bond formation in the following chemical
compounds using electron dot structures. Indicate the type of bonding.
a. Ammonia
TYPE OF BONDING: Covalent bonding
b. METHANE
TYPE OF BONDING: Covalent bonding
c. CARBON DI OXIDE
TYPE OF BONDING: Covalent bonding
d. HYDROGEN CHLORIDE
TYPE OF BONDING: Covalent bonding
18. Draw the electron dot structures of the following compounds.
Also give their molecular formula.
a. ETHANE
6C – 2, 4 1 H - 1
Molecular formula ; C2H6
119. Why the compounds formed
by carbon are exceptionally stable?
Ans: the
stability of carbon compounds is attributed to the small size of carbon atom.
Due to the small size of the carbon atom, the nucleus holds the shared pair of
electron more effectively. Thus, making the bond stro
20. What do you mean by the
term ‘homologous series’?
Ans: A series
of compounds having same functional group similar chemical properties and the
successive members of which differ by –CH2 unit is called homologous
series.
221. List some important
characteristics of ‘homologous series’.
Ans: The important characteristics of ‘homologous series’ are:
a.
The adjacent members of
homologous series differ by -CH2 unit.
b.
The molecular mass of any two successive member differ
by 14 u.
c. All the members of the
series have same chemical properties and show regular gradation in their physical properties.
d. All the members of the
series have same functional group and can be represented by a general formula.
222.
Define the term
‘functional group’.
Ans: an atom or group of atoms that is the site of
reactivity in the organic compound and largely determines the properties of an
organic compound is called functional group.
223..
What is hydrogenation? What is its industrial
application?
Ans: The
reaction that involves the addition of hydrogen across an unsaturated
hydrocarbon (double/triple bond) in the presence of nickel catalyst is called
hydrogenation.
Industrial
application: Hydrogenation of vegetable oils in the presence of nickel catalyst
converts them to Vanaspati ghee.
224..
Two carbon compounds A and
b have the molecular formula C3H8 and C3H6
respectively. Which one of the two is most likely to show addition reaction?
Justify your answer. Explain with the help of chemical equation, how an
addition reaction is useful in vegetable ghee industry.
Ans:
unsaturated hydrocarbons undergo addition reaction. Since C3H6
Is an alkene
i.e. an unsaturated hydrocarbon it would undergo addition reaction.
Unsaturated hydrocarbon saturated
fat
On adding hydrogen to an alkene in the presence of nickel
catalyst , the addition of hydrogen takes place across the double bond and
forms saturated fat called vanaspati ghee.
225.. Explain the mechanism of
the cleaning action of soaps.
Ans; A soap molecule is a sodium or potassium salt of long
chain carboxylic acid. It consists of two parts i.e., a long hydrocarbon tail
and a negatively charged head. The hydrocarbon tail is hydrophobic i.e.
insoluble in water and repelled by water while the polar end is soluble in
water and hydrophilic in nature.
When soap is applied on a wet dirty
surface, the polar end of the soap molecule dissolves in water while the non
polar tail attaches it to dirt molecule, as dirt is non-polar in nature.
This results into the formation of
spherical clusters called MICELLE. In the micelle the hydrophobic tails are in
the interior of the cluster while the ionic ends are on the surface of cluster.
Due to ion-ion repulsion, the micelle
stay in the solution as a colloid and don’t come together as precipitate. Thus,
an emulsion is found which helps to dissolve dirt in water and it is finally
washed with running water.
226. Under what conditions can
a saturated hydrocarbon produce a sooty
flame? Explain.
Ans: a saturated hydrocarbon
produce a sooty flame only when burnt in
limited supply of oxygen. Due to the limited supply of oxygen, the incomplete
combustion of the hydrocarbon takes place resulting in unburnt carbon producing
sooty flame.
227. Why gas/kerosene stoves
used at home at holes at the bottom?
The bottom of the cooking
vessels often gets blackened on heating. Give reason for blackening of cooking
vessels.
Ans: . The gas/kerosene stoves are provided with air inlets so that
oxygen rich mixture is burnt for the complete combustion and thus it produces a
clean flame.
If the air holes of the gas stove gets blocked, then incomplete
combustion of the fuel takes place due to limited supply of oxygen. This leads
to the formation of soot that deposits on the vessel and thus get blackened.
228. a . Name the catalyst required for the hydrogenation of vegetable oils to
vanaspati ghee.
b.
Name the product formed by
the addition of hydrogen to ethane. Also write the chemical equation.
c.
Why do we prefer vegetable
oils to animal fats for cooking purposes?
ANS:
a. Nickel
b. On addition of hydrogen to
ethane, ethane is formed.
H2C =CH2 +
H2 ----------àH3C – CH3
Ethene ethane
c. Vegetable oils are
preferred to animal fats as they consist of unsaturated fatty acids, which are
good for health.
229. A carbon compound ‘X ’ is an
active ingredient of all alcoholic drinks and is a good solvent.
a.
Name the compound ‘X’.
b.
Write your observation
when the compound ‘X’ is made to react with compound ‘Y’ which is used as a
preservative for pickles.
c. Write the chemical equation to represent the above change
.
ANS:
a. Ethanol
b. ‘Y’ is vinegar which is
dilute solution of ethanoic acid. On adding ‘X’ to ‘Y’ a sweet smelling
compound ester is formed.
c. Con.
H2SO4
C2H5OH + CH3COOH -------------------à CH3COO C2H5 + H2O
∆
330. Give the molecular formula and IUPAC names of the following
compounds.
a. An alkyne containing 3
carbon atoms
b. An alcohol containing 3
carbon atoms
c. An aldehyde containing 3
carbon atoms
d. Simplest ketone
e. An alcohol used in cough syrup
f. A carboxylic acid used as
a preservative
g. A saturated hydrocarbon containing
5 carbon atoms
h. A cyclehexane containing 5
carbon atoms
ANS:
a. Propyne C3H4
b. Pentanol C5H11OH
c. Propanal C2H5CHO
d. Propanone CH3COCH3
e. Ethanol C2H5OH
f. Ethanoic acid CH3COOH
g. Pentane C5H12
h. Cyclopentane C5H10
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