Q1 . What is next homologue of C3 H 7 OH is called?
Answer: The next homologue of C 3 H 7OH is called
butanol C 4H 9 OH.
Q2 . What is the molecular formula of the alcohol
which can be derived from propane?
Answer: Propane: CH 3 -CH2 -CH 3 or C 3 H8
Alcohol obtained from propane is C 3 H 7OH.
Q3 . What is meant by the term functional group?
Answer: An atom or a group of atoms, which makes a
carbon compound reactive and decides its
properties. is called a functional group.
Q4 . Give the names of the functional groups: (CBSE
2007)
i) -CHO (ii -C=O
Answer: (i) Aldehydic group (ii) Ketonic group.
Q5 . Give the names of the following functional
groups: (CBSE 2007)
i) —OH (ii) —COOH
Answer: (i) Alcoholic (ii) Carhoxylic.
Q6 . Which functional groups always occur at the
terminal position of a carbon chain?
Answer: Aldehydic group R—CHO (R is tue alkyl group),
and
Carboxyl group R—COOH (R is the alkyl group).
Q7 . Why a candle flame burns yellow, while a
highly-oxygenated gas-fuel flame burns blue?
Answer: The most important factor determining color of
the flame is oxygen supply and the extent of fuel-
oxygen pre-mixing, which determines the rate of
combustion and thus the temperature and reaction
paths, thereby producing different color hues. In case
of candle, it is an incomplete combustion and the flame
temperature is not high. This gives a yellow flame. While
a highly-oxygenated gas (e.g. ethyne) flame burns blue
because of complete combustion raising a very high
temperature.
Q8 . Why is the reaction between methane and
chlorine considered a substitution reaction? [CBSE
2008]
Answer: Methane reacts with chlorine in the presence of
sunlight to form chloromethane and hydrogen chloride.
CH4 + Cl 2 → CH3 Cl + HCl
With the excess of chlorine, aH the four hydrogen
atoms of methane are replaced by chlorine atoms to
form carbon tetrachloride (CCl 4). This reaction is
considered as substitution reactions because hydrogen
of methane is substituted by chlorine.
Q9 : Why does Carbon form compounds mainly by
covalent bonding?
Answer. Being tetravalent carbon atom, it is neither
capable of losing all of its four valance electrons nor it
can easily accept four electrons to complete its octet.
Both of these are requirements of ionic bond formation
and are energetically less favourable. Carbon completes
its octet by sharing of electrons and hence covalent
bonding is preferred.
Q10 . Give a chemical test to distinguish between
saturated and unsaturated hydrocarbons.
Answer. When saturated compounds are burnt in air,
they give a clear (blue) flame but the burning of
unsaturated compounds (akenes and alkynes) gives a
sooty (yellowish) flame. Actually, saturated compounds
contain comparatively less percentage of carbon which
get completely oxidized by the oxygen present in air. On
the other hand, the percentage of carbon in
unsaturated compounds is more and it requires more
oxygen to get completely oxidized that is not fulfilled by
air. So due to incomplete oxidation they burn with a
sooty flame.
Bromine-water test: Br2 water is a brown coloured
liquid.
(a) Unsaturated hydrocarbons give addition reaction
with Br2 . So the colour of Br2-water gets decolourized.
R-C=C-R + Br2 →R-BrC-CBr-R
(b) Saturated hydrocarbons do not react with Br2 -
water, so the colour of Br2 .-water does not get
decolourised.
Q11 : What do you mean by Octane Rating?
Answer: Gasolines are rated on a scale known as octane
rating, which is based on the way they burn in an
engine. The higher the octane rating, the greater the
percentage of complex-structured hydrocarbons that
are present in the mixture, the more uniformly the
gasoline burns, and the less knocking there is in the
automobile engine. Thus, a gasoline rated 92 octane will
burn more smoothly than one rated 87 octane.
Q12 : Two compounds A and B react with each
other in the presence of a dehydrating agent to
produce an ester. Both react with Na to evolve
hydrogen gas. On reaction with Na 2 CO3 only A
evolves CO2 . Identify the functional groups present
in A and B giving reason for your answer.
Answer: Compound A contains –COOH group while
compound B contains –OH group.
Since carboxylic acids and alcohols react with each
other to form an ester, out of A and B, one is an
alcohol and the other is a carboxylic acid. This is
further strengthened by reaction of both with Na to
evolve hydrogen gas.
Only carboxylic acids react with Na 2 CO3 to evolve
CO2 , A contains –COOH group while B contains –OH
group.
Following video posted on You tube by tutor vista nicely
summarizes this chapter:
Q13 : An organic compound 'X' is widely used as a
preservative in pickles and has a molecular formula
C2 H 2 O2 . This compound reacts with ethanol to
form a sweet smelling compound ‘Y'.
a. Identify the compound ‘X’
b. Write the chemical equation for its reaction with
ethanol to form compound ‘Y’.
c. How can we get compound ‘X’ back from ‘Y’?
d. Name the process and write corresponding
chemical equation.
e. Which gas is produced when compound ‘X’ reacts
with washing soda? Write the chemical equation.
Answer:
a. Compound X is ethanoic acid which gives and ester
(Y) when reacts with ethanol.
b. CH3 COOH + CH 3CH 2OH → CH3 COOC 2H 5
c. Esters gives back alcohol and carboxylic acid in the
presence of acid or base.
d. CH3 COOC 2 H5 ---NaOH → C 2 H5 OH + CH3 COOH
e.CO 2 gas is released.
CH 3COOH + Na2CO 3 → 2CH 3COONa + H 2 O +
CO2
Q14 What would be the electron dot
structure of carbon dioxide which has the formula
CO2 ?
Answer: Electron dot structure of CO 2 is O=C=O given in pic
Q16 How many structural isomers can you
draw for pentane?
Answer: There are three structural isomers of pentane:
(i) Pentane
CH3 ‒ CH2 ‒ CH2 ‒ CH2 ‒ CH3
(ii) 2-methyl Butane (iso-pentane)
CH3 ‒CH 2 ‒CH‒CH 3
|
CH3
(iii) 2-2 dimethyl propane (neo-pentane)
CH 3
|
CH3 ‒ CH ‒ CH 3
|
CH3
Q17) : What are the two properties of
carbon which lead to the huge number of carbon
compounds we see around us?
Answer: Two properties of carbon that attributes to its
large family of carbon compounds are:
1. Catenation: Ability to form chains with other atoms of
carbon by covalent bonding.
2. Tetravalency: Valency = 4 i.e. it forms four covalent
bonds with four other atoms.
Q18 : What is Covalent bonding?
Answer: The chemical bonding occurs due to mutual
sharing of electron pairs of two or more atoms of
different elements is called covalent bonding. By mutual
sharing of electron pairs atom attain noble gas
configuration. e.g. In Hydrogen molecule (H 2 ), the two
H-atoms combine by covalent bonding (H-H).
Q19 : What are Hydrocarbons? Give examples.
Answer: Compounds of carbon and hydrogen are called
hydrocarbons. Methane, Ethane, Butane, ethyne,
propene, benzene, petroleum products all are examples
of hydrocarbons.
Q20 What are saturated
hydrocarbons?
Answer: The hydrocarbons in which valency of carbon
is satisfied by a single covalent bond are called
saturated hydrocarbons. Alkanes like methane (CH 4 ),
ethane(C 2 H6 ), propane(C 3 H 8 ) etc. are examples of
saturated hydrocarbons. Saturated hydrocarbons will
generally give a clean flame.
Q21 "Saturated hydrocarbons burn
with a blue flame while unsaturated hydrocarbons
burn with a sooty flame". Why?
Answer: Saturated hydrocarbons have only C-C and C-H
single bonds and thus contain the maximum
possible number of hydrogen atoms per carbon atom.
With sufficient oxygen, saturated hydrocarbons burn
completely and give blue flame.
CH4 + 2O 2 → CO2 + 2H 2 O
Unsaturated hydrocarbons contain a carbon-carbon
double bond (C=C) or triple bond (C≡C). Hence they
contain less number of hydrogen than carbon.
Unsaturated hydrocarbons undergoe incomplete
combustion and give yellow flame along with black
sooty(carbon).
C 2H 4 + O 2 → CO 2 + 2H 2 O + C(s)
Q22 : What are isomers?
Answer: Compounds with identical molecular formula
but different structures are called structural isomers.
Organic compounds show a great level of isomerism.
Isomers may be structural (due to difference in
arrangement of C atoms forming chain) or stereo (due
to arrangement of bonds in chain). With increase in
number of carbon atoms in a molecular formula leads
to increase in number of isomers.
C‒C‒C‒C OR C-C-C
|
C
O
Q23 Why do ionic compounds have high
melting points?
Answer: Ions have strong electrostatic forces of
attraction among them forming ionic compounds. It
requires lot of energy to break these ionic bonds or
forces. That's why ionic bonds have high melting points.
Q24 : What are the characteristics of Homologue
series?
Answer: Important characteristics of Homologue series
are:
1. Have same general formula.
2. Belong to same functional group.
3. Have general methods of separation.
4. Have similar chemical properties.
5. Show similar gradation of physical properties. e.g.
boiling points of alcohol increase with increase in their
molecular weights.
6. Similarly solubility decreases with increase in molecular
weights.
Q25 : What is the general formula of Alkanes?
Answer: C nH 2n+2
Q26 : What is a hetroatom? What is the hetroatom in
alcohol functional group?
Answer: In a hydrocarbon chain, one or more
hydrogen atoms can be replaced by other atoms
according to their valencies. The element which
replaces hydrogen in the chain is called a heteroatom.
e.g. in alcohol (-OH) functional group, oxygen is the
hetroatom.
No comments:
Post a Comment