Wednesday, 23 January 2019
Sunday, 13 January 2019
QUESTION
BANK
CH-4 CARBON AND ITS COMPOUND
VERY SHORT ANSWER QUESTIONS 1 MARK EACH
1. On the basis of electronic configuration, how will you
identify the first and the last element of a period?
Ans: (i) First
element has 1 valence electron and last element has 8 valence electrons.
(ii) Number of valence shells remain
same
2. .Identify functional group of following-
(a).C 2H 5OH (b).CH 3COOH
(a).C 2H 5OH (b).CH 3COOH
Ans: Alcohol and
Carboxylic acid
3. A non metal X exists in two different forms Y and Z. Y is
hardest natural substance whereas Z is good conductor of electricity. Identify
X, Y and Z
Ans : X= Carbon
,Y= Diamond, Z= Graphite
4. Why is ethanol used as antifreeze?
Ans: Ethanol does
not freeze easily. So in cold countries ethanol is mixed with petrol to avoid
freezing of fuel.
5. What are hydrophilic and hydrophobic parts in soap
Ans: The alkyl
group consisting of long chains of carbon atoms is hydrophobic part while COO-Na+
grp is hydrophilic in nature.
6.
What is the role
of Ni in given reaction?
7. Vapours of a hydrocarbon were passed through bromine
dissolved in carbon tetra chloride .The yellow colour of bromine got discharged?
Predict the nature of the hydrocarbon.
Ans : Unsaturated
( alkene or alkyne)
SHORT ANSWER QUESTION TYPE I
2 MARKS EACH
8. Differentiate
between addition reactions and substitution reactions shown by hydrocarbon.
Ans: Addition reaction
is a reaction in which, any group(s) is added to the substrate; whereas,
Substitution
reactions
include reactions in which a group is replaced/substituted by another group
Addition
reaction always takes place at multiple bonds, whereas, substitution reactions
has no such hard and
fast rule.
9.
(a) Why do alkanols not turn
blue litmus red?
(b)
Why is high temperature not favourable for alcoholic fermentation?
Ans:
(a) Because alcohols are not in position to release H+ ions in
solution.
(b) The high temperature destroys the
enzymes which required for fermentation
10. (a) Why it is not easy for carbon to take part in the formation of
ionic compounds?
(b) The
molecular formula C3H6O can represent an aldehyde and a
ketone. Write their structure and their name.
Ans (a) Because carbon
atom needs a large energy to lose 4 electron and to gain 4 electron to form
ionic
compound.
(b). Propanal and
propanone
11.
Give a chemical test to
distinguish between Ethane and Ethene .
Ans Bromine water test: ethene decolourise the yellow colour of
bromine water and ethane does not
12.
Distinguish between esterification
and saponification reactions of organic compounds.
Ans:Esterification is the reaction of a carboxylic acid with an
alcohol to form an esterand
water. Saponification is
the reaction of an ester with
a base to form a carboxylate salt and water.
13. (a)Why are soaps not so
effective in case of hard water?
(b) Give the
of the following: (i) An aldehyde derived from methane (ii) The compound
obtained from oxidation of ethanol by chromic anhydride.
Ans: Hard water contains salts of calcium and
magnesium. Thus soap have to react with Ca and Mg to form insoluble ppt called
scum .So soap form less lather with water.
(b)
Methanal and Ethanal.
SHORT ANSWER TYPE II
3 MARKS EACH
14. (a) Draw electronic structure of the following: (i) Formic acid (ii)
Propanone
(b)Why
is the conversion of propanol into propanoic acid is called an oxidation
reaction?
Ans
: (a) (ii)
(b)Due to loss of hydrogen and gain of oxygen.
15. Give reason for the following:-
(a)
Use of synthetic detergents
causes pollution problems.
(b)
The element carbon forms a
large number of compounds.
(c)
Air holes of the gas burners
have to adjusted when heated vessels get blackened by the flame
Ans:
(a) Due to their non biodegradable nature.
(b) Due to catenation and
tetravalency
(c) To increase the supply of air or
oxygen.
16. (a) State the principle on which the cleansing action of soap is
based
(b)
Write isomers of pentane.
Ans
The basic principle involved in the cleansing action of soap is the formation of micelle due to
the presence of hydrophillic and hydrophobic part in the soap molecule.
(b)
17. Draw the structures of the following:
Benzene, Cyclo hexane, 3Bromobutene, 3 Methyl pentanoic acid, Methanal, Formic
acid
Ans : , (b) (c)(d)
(f)
18. (a)
Differentiate between soap and detergent.
(b) An organic compound ‘A’ with molecular
formula C2H6O reacts
with an acids’B’ which is used for
making synthetic vinegar and form a sweet
smelling compound ‘C’ having molecular
formula C4H8O2.
(i)Identify A and C compounds
Ans (a)
(b) A=
Ethanol and C = Ester
19. Write
the following chemical reactions:
(i)
Sodium metal reacts
with ethanoic acid
(ii)
Sodium carbonate is added
ethanoic acid
(iii)
Ethanoic acid reacts
with dilute solution sodium hydroxide
Ans:
(a) 2Na +2 CH3COOH→ 2CH3COONa+H2
(b)Na2CO3 +2 CH3COOH→
2CH3COONa+H2O+ CO2
(c) NaOH + CH3COOH→
CH3COONa+H2O
LONG ANSWER TYPE 5
MARKS EACH
18. (a) . Why does
melting and boiling points of the member of Homologous Series increase
gradually ?
(b) What is observed on adding
5% solution of alkaline potassium permanganate solution drop by drop to some
warm ethanol taken in testube. Write the name of the compound formed
during chemical reaction.
(c) How can you check which one is
saturated butter or vegetable oil?
Ans: The number of carbon atoms in the molecule
of the member of Homologous Series increases gradually .Van der Waals
dispersion forces will be very small for a molecule like methane but will
increase as the molecules get bigger. Therefore, the boiling points of the
alkanes increase with molecular size(increase in no. of c atom)
(b) When a 5% solution of alkaline potassium permanganate solution is added drop by drop to some warm ethanol taken in a test tube, magenta colour of alkaline potassium permanganate disappears and ethanol has been changed to carboxylic acid.
(b) When a 5% solution of alkaline potassium permanganate solution is added drop by drop to some warm ethanol taken in a test tube, magenta colour of alkaline potassium permanganate disappears and ethanol has been changed to carboxylic acid.
(c) Butter contain saturated compound where
as cooking oil contain unsaturated compound. If Alkaline KMno4 added to
both, pink color of KMno4 disappear in cooking oil but remain in pink in
butter
19.
.
20
. (a) What are homologous series? List any two characteristics of homologous
series.
(b)Explain in brief cleansing action of
soap.
Ans:
(a) A homologous series is a family of
compounds with the same general formula and similar chemical
properties.
Features include a general formula
and neighbouring members differing by CH2, with similar chemical
properties and with a gradation in physical properties. They all contain the
same functional group.
(b) 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 end attaches it to dirt molecule, as dirt is
non-polar in nature. This results in the formation of spherical clusters called
asMicelles. In micelle the hydrophobic tails are in the
interior of the cluster while the ionic ends are on the surface of the cluster.
Due to ion-ion repulsion the micelle stay in the solution as a colloid and do
not come together to form precipitate. Thus, an emulsion is formed which helps
to dissolve dirt in water and it is finally washed with running water.
21. (a) A mixture of ethyne and oxygen is burnt for welding. Can you tell
why a mixture of ethyne and air is not
Used?
(b) why
sodium chloride added during preparation of soap?
(c) Why are soap not effective as a cleaning
agent in hard water?
(d) Why is soap not used in acidic solution?
Answer: (a) Ethyne is un saturated carbon compound
and burns in air with a sooty flame, because the oxygen from air is insufficient
to burn the carbon completely. Thus, pure oxygen is used which completely burns
carbon and hydrogen and produces a very hot flame.
(b) This help to decrease solubility of soap and
help in precipitation of soap from aqueous solution. This preparation is known
as salting out.
(c) Hard water contains sodium and magnesium ions. Soap
form precipitate with these ions and thus thrown out of the solution.
(d) This is because free fatty acid of soap get
precipitated
22. How can Ethanol and Ethanoic acid be
differentiated on the basis of physical and chemical properties?
Ans. Physical properties :
(a). Ethanol has a sharp bitter burning taste, whereas ethanoic acid has a sour taste.
(b) On cooling ethanol does not freeze, but ethanoic acid freezes.
Chemical Properties :
(a) Ethanol gets dehydrated by conc. sulphuric acid, but ethanoic acid does not get dehydrated by conc. sulphuric acid.
(b) Ethanol does not displace hydrogen with zinc or magnesium, but ethanoic acid displaces hydrogen with zinc or magnesium
Ans. Physical properties :
(a). Ethanol has a sharp bitter burning taste, whereas ethanoic acid has a sour taste.
(b) On cooling ethanol does not freeze, but ethanoic acid freezes.
Chemical Properties :
(a) Ethanol gets dehydrated by conc. sulphuric acid, but ethanoic acid does not get dehydrated by conc. sulphuric acid.
(b) Ethanol does not displace hydrogen with zinc or magnesium, but ethanoic acid displaces hydrogen with zinc or magnesium
23. (a) Why is graphite a good conductor of
electricity?
(b) Explain why, soaps
form scum with hard water whereas detergents do not
(c) Why
does Ethanoic acid called glacial acetic acid?
(d) Alkanes
(both alkanes and cycloalkanes) are virtually insoluble in water, but dissolve
in organic solvents. However, liquid alkanes are good solvents for many other
non-ionic organic compounds. Give reason.
Answer: (a) Graphite is a good conductor of electricity. Its
structure is the main reason for this property. Each carbon atom in graphite is
directly linked to only three carbon atoms through covalent bonds. Therefore,
out of the four valence electrons in a carbon atom, only three are used for
bonding and the fourth is relatively free and can move from one carbon atom to
the other. These free electrons make graphite a good conductor of electricity.
(b) In hard water, due to the presence of Ca +2 and Mg +2
ions, soaps form insoluble salt. This Precipitate is called scum.
Detergent does not show this property as its charged end does not react
with Ca+2 and Mg+2 ions
(c)
. On cooling, pure Ethanoic acid is frozen to form ice like flakes. They look
like glaciers, so it is called glacial acetic acid.
(d) Van der Waals forces do not release a sufficient amount of energy to compensate for the energy required to break the hydrogen bonds in water. The alkane does not dissolve.
In most organic solvents, the primary forces of attraction between the solvent molecules are Van der Waals - either dispersion forces or dipole-dipole attractions. Therefore, when an alkane dissolves in an organic solvent, the Van der Waals forces are broken and are replaced by new Van der Waals forces. The two processes more or less cancel each other out energetically; thus, there is no barrier to solubility.
(d) Van der Waals forces do not release a sufficient amount of energy to compensate for the energy required to break the hydrogen bonds in water. The alkane does not dissolve.
In most organic solvents, the primary forces of attraction between the solvent molecules are Van der Waals - either dispersion forces or dipole-dipole attractions. Therefore, when an alkane dissolves in an organic solvent, the Van der Waals forces are broken and are replaced by new Van der Waals forces. The two processes more or less cancel each other out energetically; thus, there is no barrier to solubility.
CHAPTER: 5 PERIODIC
CLASSIFICATIONS OF ELEMENTS
VERY SHORT ANSWERS
1 MARK EACH
1. State
one reason for placing Mg and Ca in the same group of the periodic table.
Ans: Due to 2 valence electrons in
valence shell
Element
|
A
|
B
|
C
|
D
|
E
|
Atomic.no
|
7
|
10
|
12
|
4
|
19
|
2. (i)
Which element belongs to third period of periodic table?
(ii) Which is inert gas?
Ans (i) C (ii) B
3. Which
has bigger size and why? Chlorine or Bromine
Ans Bromine because its atomic no is 35 and it has more shells
4. How
would the tendency of lose electrons changes as you go across the periods?
Ans: Decreases
5. Identify
the group and period of element having atomic no 17
Ans: group- 17 and period -3
6. An
element having atomic no 20 is categorised as metal or a non metal . why?
Ans: Metal because it loses electron
SHORT ANSWER TYPE
I
2
MARKS EACH
7.
Atomic number is considered to
be a more appropriate parameter than atomic mass for classification of elements
in a periodic table. Why?
Ans:
We know that atomic number gives us the number
of protons in the nucleus of an atom. Atomic number increases by one in going
from one element to the next but atomic mass does not vary regularly from
element to element. Atomic number of every element is fixed. That is why atomic
number is considered to be a more appropriate parameter for the classification
of elements than atomic mass.
8.
(a) An unknown element is given
the name ‘eka- phosphorus’? What does it means?
(b)What
is meant by periodicity in properties of elements?
Ans:
It means element placed after Phosphorus in the same group.
(b)
Periodicity refers to trends or recurring variations in
element properties with increasing atomic number. Periodicity is caused by regular and predictable variations
in element atomic structure.
9.
‘Hydrogen is regarded as rouge
element in the periodic table’. Elaborate
Ans: H exhibits properties
of both, Alkali metals like, 1 valence electron, ability to form halides etc.
and those of halogens like non-metal, diatomic molecule, gaseous state etc.
Hence it position is not fixed in the periodic table and called as a rogue element. .
10. Can the following group of elements be classified as Dobereiner’s
triad? Na, Si, Cl Explain with reason.
Ans:
No, because the mean of atomic mass is not equal to mass of Si.
11. Arrange the following elements in the increasing order of metallic
character : Mg , Ca, K, Ge.
Ans Ge <Mg<Ca<K
12. Why do all the elements of the same group have similar properties?
Ans:
The properties of the elements are linked with the valence shell electronic
configuration of their atoms. The elements with the same configuration are
expected to have similar properties.
13. Lithium, sodium potassium belong to
same group called alkali metals. Why?
Ans: Because they form
oxides and hydroxides that dissolve in water to give alkaline solutions and the
alkaline hydroxide is formed when the metals react with water.
SHORT ANSWER TYPE
II
3 MARKS EACH
14. The elements Li, Na and K, each having one valence
electron, are in period 2, 3 and 4
respectively of modern periodic table. 3
(i) In which group of the periodic table should they be?
(ii) Which one of them is least reactive?
(iii) Which one of them has the largest atomic radius? Give reason to justify your
answer in each case.
Answer. Electronic configuration of Li, Na and K can be written as:
Li → 2, 1
Na → 2, 8, 1
K → 2, 8, 8, 1
(a) As all of them have only on electron in their valence shell they belong to Group 1.
(b) Li is the least reactive among them due to its smallest size as it has only 2 shells.
(c) K has the largest atomic radius among the three because it has maximum number
of shells.
Higher the number of shells, larger is the atomic radius
respectively of modern periodic table. 3
(i) In which group of the periodic table should they be?
(ii) Which one of them is least reactive?
(iii) Which one of them has the largest atomic radius? Give reason to justify your
answer in each case.
Answer. Electronic configuration of Li, Na and K can be written as:
Li → 2, 1
Na → 2, 8, 1
K → 2, 8, 8, 1
(a) As all of them have only on electron in their valence shell they belong to Group 1.
(b) Li is the least reactive among them due to its smallest size as it has only 2 shells.
(c) K has the largest atomic radius among the three because it has maximum number
of shells.
Higher the number of shells, larger is the atomic radius
15. Nitrogen(atomic number=7) and
phosphorus(atomic number=15) belong to same group-15 of the periodic table.
Write the electronic configuration of these two elements. Which of these two
will be more electronegative? Why.
Answer.
Electronic configuration of N (7) = 2, 5 Electronic configuration of P (15) =
2, 8,5 Nitrogen will be more electronegative due to electro negativity
decreases from top to bottom because atomic size increases.
16. An element 'M' has atomic number 11. (a) Write its
electronic configuration.
(b) State
the group to which 'M' belongs. (c) Is 'M' a metal or a non-metal.
(d)
Write the formula of its chloride.
Ans. Atomic
number of „M‟ = 11
(i)
Electronic configuration : 2, 8, 1
(ii)
Since, the valence shell contains 1 electron, it belongs to group 1.
(iii) M
is a metal.
(iv) The
formula of its chloride is M Cl.
17.
State
reasons for the following:
(i)Both Mg and O have
valency equal to 2 .Are they chemically similar also?
(ii)Out of C,B and N
elements , which has the maximum size? Why?
(b)Find the period of
the following elements having atomic number: 19and 9
Ans: (a)(i) No, Mg
losses 2 electron whereas O gains 2 electron
(ii) B
has maximum size because atomic radius decreases in period.
(a) 19= 4 period , 9= 2 period.
18. Account reason for the
following:
(a)
Elements in a group of the periodic table have similar chemical
properties
(b)
Discuss any two drawbacks of Mendeleev’s periodic table.
Ans:(a).
Due to same number of valence electrons
(c)
Position of hydrogen and
position of isotopes.
19. (a) Explain how the tendency to gain
electrons change on moving down a group.
(b) If
an element A is a member of group 14, write the formulae of its chloride and
oxide. Predict the nature of bonding in the compound formed. Give reason for
your answers.
Ans: (a) On moving down the group, atomic size increases. As a result, effective nuclear charge decreases and hence the tendency to gain electrons(electronegativity) decreases
Ans: (a) On moving down the group, atomic size increases. As a result, effective nuclear charge decreases and hence the tendency to gain electrons(electronegativity) decreases
(b) A member of group 14 have valency = 4 So, there
is Covalent bonding
Chloride – ACl4 Belong to Gr.14 valency is 4 Oxide – AO2.
Chloride – ACl4 Belong to Gr.14 valency is 4 Oxide – AO2.
LONG ANSWER TYPE 5
MARKS
20. (a) Discuss any two achievements of Modern Periodic Table.
(b) Discuss any two limitations of
Mendeleev’s classification.
(c) How were these removed in the
Modern Periodic Table (any one)
Ans:
(a) (i) Prediction of properties of elements could be made with more precision.
(ii) Elements were sequentially arranged in increasing order of atomic number. (no reversals were required)
(iii) Number of elements between two elements was countable.
(b) (i) Position of Hydrogen (ii) Positioning of Isotopes (iii) Position exchange of Ni and Co. (iv) Variable increase in mass from one element to other.
(c) When the elements are arranged according to their atomic numbers on the basis of modern periodic law, all the anomalies (defects) of Mendeleev’s classification disappear. For example, Position of isotopes: All the isotopes of an element have the same number of protons, so their atomic number is also the same. Since all the isotopes of an element have the same atomic number, they can be put at one place in the same group of the periodic table.
Ans:
(a) (i) Prediction of properties of elements could be made with more precision.
(ii) Elements were sequentially arranged in increasing order of atomic number. (no reversals were required)
(iii) Number of elements between two elements was countable.
(b) (i) Position of Hydrogen (ii) Positioning of Isotopes (iii) Position exchange of Ni and Co. (iv) Variable increase in mass from one element to other.
(c) When the elements are arranged according to their atomic numbers on the basis of modern periodic law, all the anomalies (defects) of Mendeleev’s classification disappear. For example, Position of isotopes: All the isotopes of an element have the same number of protons, so their atomic number is also the same. Since all the isotopes of an element have the same atomic number, they can be put at one place in the same group of the periodic table.
21. A quiz contest was being held in the school
for chemistry students. The quiz-master said :
An element has the electronic configuration 2, 8, 7.
(a) What is the atomic number of this element?
(b) Which of the elements N, F, P and Ar shows similarity with this element ?
(c) We daily use a compound of this element in our food. What is that ?
(d) A compound of this element causes hardness of water. What is that ?
Ans: (a) Atomic number=17 (b) F - as it belongs to the same group as the element(Cl)
(c)NaCl-Common Salt (d) Ca(HCO3)2 causes temporary hardness of water.
An element has the electronic configuration 2, 8, 7.
(a) What is the atomic number of this element?
(b) Which of the elements N, F, P and Ar shows similarity with this element ?
(c) We daily use a compound of this element in our food. What is that ?
(d) A compound of this element causes hardness of water. What is that ?
Ans: (a) Atomic number=17 (b) F - as it belongs to the same group as the element(Cl)
(c)NaCl-Common Salt (d) Ca(HCO3)2 causes temporary hardness of water.
22.
(a) What happens to the metallic character of the elements as we
move in a period from left to right in the periodic table? Give reason.
(b) What
happens to the melting points and boiling points of elements while
moving down in a group?
(c) Why
Chlorine (atomic number 17) is more electronegative than sulphur (atomic number
16)
(d) The two isotopes of
chlorine have atomic masses 35 u and 37 u. Should they be placed in same slot
in the
periodic table?
(e) Why did Mendeleev leave
some gaps in his periodic table?
Answer(a)
Metallic character of the
element decreases along a period . In period atomic size decrease,As
a result,
effective nuclear charge
increases and hence the tendency to loose electrons(electroposivity) decreases
.
(b) . The melting points
and boiling points decrease while moving down in group of metals. The melting points
and boiling
points increases while moving down
in group of non-metals.
(c) :
The nucleus of chlorine has more tendency to attract an extra electron than the
nucleus of sulphur because
chlorine
needs only one 1 electron to complete
its shell. Hence, chlorine is more electronegative than sulphur.
(d) ) Yes, they should be placed in the same slot
because periodic table is based on the atomic numbers of the
element
and both the isotopes of chlorine have
the same atomic number (Z = 17).
(e) Mendeleev
left gaps in his periodic table to keep the elements with similar properties
together if predicted.
New
elements would be discovered later and
they would occupy those gaps.
23. The
position of three elements A,B and C in the periodic table are shown below
Group-16
|
Group-17
|
-
|
-
|
-
|
A
|
-
|
-
|
B
|
C
|
(a) State whether A is a metal or non-metals.
(b)
State whether C is more reactive or less reactive than A.
(c) Will
C be larger or smaller in size then B.
(d)
Which type of ion, cat ion or anion will be formed by element A
Ans-(a)-Non-metal
(b) A is
more reactive due to small size, have more tendency to accept outside electron
(c) C is
smaller in size than B due to atomic size decreases from left to right in a
period
(d) Anion
formed due to tendency to accept electron
24. A part of
the periodic table has been shown below :
Group →
|
1
|
2
|
13
|
14
|
15
|
16
|
17
|
18
|
Period
↓
|
||||||||
1
|
||||||||
2
|
A
|
C
|
E
|
G
|
||||
3
|
B
|
D
|
F
|
Answer the following
questions on the basis of position of elements in the above table.
(a) Which element is a noble gas? Give reason.
(b) Which element is most electronegative? Give
reason.
(c) Write the electronic configuration of (i) B and
(ii) E.
Ans: (a) G , element of 18 group.
(b)
E, bcoz electronegativity decreases down the group.
(c). B= 2,8,1 E= 2,7.
25. (a) Why did Mendeleev treated the hydrides and oxides of element
as the basic properties of elements for their classification?
(b) Why does
silicon is classified as Metalloid?
(c) Element
X forms a chloride with the formula XCl2 which is solid with a high
melting point. X would
most likely be in
the same group of periodic table as (a). Na (b). Mg (c). Al (d). Si?
(d) How could the
modern periodic table remove various anomalies of Mendeleev’s periodic table?
Ans: (a) During the period when Mendeleev gave his periodic
table atomic numbers and electronic configurations
were not known. Comparison of
properties of elements could be best done by comparing their compounds.
He selected oxides and hydrides
because oxygen and hydrogen form compounds with most of the elements
due to their high reactivity.
(b) Silicon is gray
color solid at room temperature with very high melting point and boiling point that
lose or
gain 4 electrons [ 3s2,
3p2] having both metallic and non metallic properties so it is
classified as Metalloid eg.
SiO2
(c)Mg
(d) Various anomalies are removed in
following ways-
(i) The position for all isotopes of an element justified since they
have same atomic number.
(ii) The position of certain elements which are earlier misfit like
Co-58.9 is placed before Ni-58.7 are now
justified
because Co
has lower atomic number than Ni.
(iii) Cause of periodicity explained due to same electronic
configuration repeated after certain gap.
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