Reason-Based Questions – Inorganic Chemistry-
One of the important types of questions framed from Inorganic Chemistry is Reason Based. The answers to these questions should consist of their specific cause. You can score well in these questions by pointing out a keyword which should be related to the cause like their physical or chemical property or it can be any law, etc.
Here are some important reasoning based questions with answers from the p – block and d – block of Inorganic Chemistry.
Give Reasons for the following
1. ICI is more reactive than I2
Ans. The bond dissociation energy of I – Cl is less than of I – I. Therefore, I – Cl
bond break easily due to its weak nature and readily brings about the
reactions.
bond break easily due to its weak nature and readily brings about the
reactions.
2. Helium is used in diving
apparatus.
apparatus.
Ans. Due
to the low solubility of He, as compared to N2 in blood, helium is used
in diving apparatus along with a mixture of oxygen.
to the low solubility of He, as compared to N2 in blood, helium is used
in diving apparatus along with a mixture of oxygen.
3. Fluorine shows anomalous
behaviour in its group.
behaviour in its group.
Ans. The
anomalous behaviour of fluorine is due to
anomalous behaviour of fluorine is due to
- Small size
- Highest electro
negativity - Low F – F bond dissociation energy
- Non-availability of
d-orbitals in its valence shell.
4. Fluorine exhibits only – 1
oxidation state whereas other halogens exhibit higher positive oxidation states
also.
Ans. Fluorine
being the most electronegative atom has the tendency to accept one electron to
acquire stable electronic configuration of the nearest noble gas. Therefore
unlike other halogens, it exhibits only – 1 oxidation state. But other halogens
being less electronegative can share their respective electron with more
electronegative elements and can show a positive oxidation state. Further,
fluorine cannot expand its valence shell due to the absence of vacant d-orbitals
but other halogens have vacant d-orbitals and can expand their octets by
exciting their electrons to nd orbitals.
being the most electronegative atom has the tendency to accept one electron to
acquire stable electronic configuration of the nearest noble gas. Therefore
unlike other halogens, it exhibits only – 1 oxidation state. But other halogens
being less electronegative can share their respective electron with more
electronegative elements and can show a positive oxidation state. Further,
fluorine cannot expand its valence shell due to the absence of vacant d-orbitals
but other halogens have vacant d-orbitals and can expand their octets by
exciting their electrons to nd orbitals.
5. The acidity of oxoacids of
chlorine is HOCl < HClO2 < HClO3 < HClO4
chlorine is HOCl < HClO2 < HClO3 < HClO4
Ans. It
is because of the increase in the oxidation number of the halogen atom. It increases
from HClO to HClO4. Again, the stability of the conjugate bases of
oxoacids of chlorine increases from ClO– to ClO-4
as the dispersal of negative charge increases from ClO– to ClO–4
because of the number of oxygen atom increase from ClO– to ClO–4.
is because of the increase in the oxidation number of the halogen atom. It increases
from HClO to HClO4. Again, the stability of the conjugate bases of
oxoacids of chlorine increases from ClO– to ClO-4
as the dispersal of negative charge increases from ClO– to ClO–4
because of the number of oxygen atom increase from ClO– to ClO–4.
6. Xenon does not form XeF3
and XeF5.
and XeF5.
Ans. Xe
atom has all the filled orbitals with paired electrons and the promotion of
one, two or three electrons from 5p filled orbitals to 5d vacant orbitals will
give rise to two, four and six half-filled orbital’s i.e., only even number of
fluorine atoms can combine with Xe.
atom has all the filled orbitals with paired electrons and the promotion of
one, two or three electrons from 5p filled orbitals to 5d vacant orbitals will
give rise to two, four and six half-filled orbital’s i.e., only even number of
fluorine atoms can combine with Xe.
7. Only xenon is able to form
chemical compounds.
chemical compounds.
Ans. Xe
has least ionization energy except Radon which is radioactive, in its group.
Therefore it is only able to form chemical compounds.
has least ionization energy except Radon which is radioactive, in its group.
Therefore it is only able to form chemical compounds.
8. Neon is used for warning
signals.
signals.
Ans. Neon
lights are visible from long distances even in mist and fog. This is why they
are used as warning signs.
lights are visible from long distances even in mist and fog. This is why they
are used as warning signs.
9. Noble gases have low boiling
points.
points.
Ans. Noble
gases are monoatomic and they are held together by weak Vander Waal’s forces.
Therefore, they have low boiling points.
gases are monoatomic and they are held together by weak Vander Waal’s forces.
Therefore, they have low boiling points.
10. Fluorine forms only one
oxoacid, HOF.
oxoacid, HOF.
Ans. Due
to high electronegativity and small size of fluorine atom, it cannot behave as the central atom in higher oxoacids like HOFO, HOFO2 and HOFO3
in which the oxidation state of F would be +3, +5 and +7 respectively.
to high electronegativity and small size of fluorine atom, it cannot behave as the central atom in higher oxoacids like HOFO, HOFO2 and HOFO3
in which the oxidation state of F would be +3, +5 and +7 respectively.
11. Halogens are coloured.
Ans. The
molecules of halogens absorb the light in the visible region and excite their
electron to higher energy levels while the remaining light is transmitted and
its colour is actually the colour of the transmitted light. The intensity of
colour depends upon the size of the atom.
molecules of halogens absorb the light in the visible region and excite their
electron to higher energy levels while the remaining light is transmitted and
its colour is actually the colour of the transmitted light. The intensity of
colour depends upon the size of the atom.
12. Iodine forms I–3,
ions but fluorine does not form F–3 ions.
ions but fluorine does not form F–3 ions.
Ans. Because
of the presence of vacant d-orbital’s in iodine, it readily accepts electrons
from I– to form I–3 ions but due to the absence of
d-orbital’s in fluorine, it does not accept electrons from F– ions
to form F–3 ions.
of the presence of vacant d-orbital’s in iodine, it readily accepts electrons
from I– to form I–3 ions but due to the absence of
d-orbital’s in fluorine, it does not accept electrons from F– ions
to form F–3 ions.
13. The electron affinity of
chlorine is higher than that of fluorine.
chlorine is higher than that of fluorine.
Ans. This
is due to the small size of the fluorine atom. Its atomic size is comparatively
smaller than chlorine atom. Therefore it experiences strong electron
repulsions. On further addition of an electron to it, it has fewer tendencies to
accept the electron in comparison to the chlorine atom. Hence it releases less
energy during the process
is due to the small size of the fluorine atom. Its atomic size is comparatively
smaller than chlorine atom. Therefore it experiences strong electron
repulsions. On further addition of an electron to it, it has fewer tendencies to
accept the electron in comparison to the chlorine atom. Hence it releases less
energy during the process
F(g) + 1e– → F–
(g).
(g).
14. HF is a weaker acid than HI.
Ans. The bond dissociation energy of HF (574 KJ mol-1) is higher than that
of H – I (295KJ mol-1). Therefore H- F behaves as the weakest acid
because it requires a maximum amount of energy to get dissociated in the aqueous
solution. It is because of the greater atomic size of iodine than fluorine.
of H – I (295KJ mol-1). Therefore H- F behaves as the weakest acid
because it requires a maximum amount of energy to get dissociated in the aqueous
solution. It is because of the greater atomic size of iodine than fluorine.
15. The tendency to show +6
oxidation states diminish from sulphur to polonium.
oxidation states diminish from sulphur to polonium.
Ans. Due
to inert pair effect, the stability of the +6 oxidation state decreases down the
group. Thus, the +6 oxidation state is most stable in case of sulphur and least
stable in case of polonium.
to inert pair effect, the stability of the +6 oxidation state decreases down the
group. Thus, the +6 oxidation state is most stable in case of sulphur and least
stable in case of polonium.
16. Oxygen molecule has formula O2
whilst sulphur is S8.
whilst sulphur is S8.
Ans. Because
of high electronegativity and small size, oxygen atoms form pπ – pπ double bond with other oxygen
atom to form O =
O molecule but sulphur does not form pπ
– pπ
multiple bonds due to its larger size and prefers to form single bonds having
S8 structure.
of high electronegativity and small size, oxygen atoms form pπ – pπ double bond with other oxygen
atom to form O =
O molecule but sulphur does not form pπ
– pπ
multiple bonds due to its larger size and prefers to form single bonds having
S8 structure.
17. SO2 can act as an
oxidizing as well as reducing agent but SO3 can act only as
oxidizing agent.
oxidizing as well as reducing agent but SO3 can act only as
oxidizing agent.
Ans. In
SO2, sulphur atom exhibits +4 oxidation state which is less stable
than the oxidation state of +6. Therefore it acts as both oxidizing and reducing
agent whereas in SO3, sulphur atom exhibits +6 oxidation state.
Being more stable, it can only behave as an oxidizing agent.
SO2, sulphur atom exhibits +4 oxidation state which is less stable
than the oxidation state of +6. Therefore it acts as both oxidizing and reducing
agent whereas in SO3, sulphur atom exhibits +6 oxidation state.
Being more stable, it can only behave as an oxidizing agent.
18. Noble gases form compound like
XeF6 with fluorine or XeOF2 with oxygen and fluorine.
XeF6 with fluorine or XeOF2 with oxygen and fluorine.
Ans. Fluorine
and oxygen is the most electronegative elements and are very reactive.
Therefore they form compounds with noble gases, especially with xenon.
and oxygen is the most electronegative elements and are very reactive.
Therefore they form compounds with noble gases, especially with xenon.
19. SF6 is one of the known
compounds but SH6 is not.
compounds but SH6 is not.
Ans. Fluorine
being the most electronegative element can easily cause the promotion of
electrons from the filled to the vacant 3d orbital’s in sulphur atom but
hydrogen being less electronegative than sulphur cannot cause the promotion of
electrons. Therefore SF6 is known but SH6 is not known.
being the most electronegative element can easily cause the promotion of
electrons from the filled to the vacant 3d orbital’s in sulphur atom but
hydrogen being less electronegative than sulphur cannot cause the promotion of
electrons. Therefore SF6 is known but SH6 is not known.
20. Interhalogens are more
reactive than halogens.
reactive than halogens.
Ans. It
is due to weaker bond and lesser bond energy of X–X’ bond in interhalogens than
that of halogen (X– X).
is due to weaker bond and lesser bond energy of X–X’ bond in interhalogens than
that of halogen (X– X).
21. Perchloric acid is a stronger
acid than sulphuric acid.
acid than sulphuric acid.
Ans. The oxidation state of Cl in per choric acid is +7 while that of S in sulphuric
acid is +6. Due to higher oxidation state and higher electronegativity of Cl,
ClO3 part of HClO4 pulls the electrons of O-H bond more
strongly towards itself making the O-H bond weaker than SO2 part in
H2SO4. Therefore, perchloric acid is a stronger acid than
sulphuric acid
acid is +6. Due to higher oxidation state and higher electronegativity of Cl,
ClO3 part of HClO4 pulls the electrons of O-H bond more
strongly towards itself making the O-H bond weaker than SO2 part in
H2SO4. Therefore, perchloric acid is a stronger acid than
sulphuric acid
22. The bond energy of F2
is less than that of Cl2.
is less than that of Cl2.
Ans. Due
to the smaller size, the lone pairs of electron on the fluorine atom repel the bond
pair of the F- F bond but due to the bigger size of electrons, the repulsion
between bond pair and lone pair is comparatively less in chlorine atom. Hence the bond energy of F2 is less than that of Cl2.
to the smaller size, the lone pairs of electron on the fluorine atom repel the bond
pair of the F- F bond but due to the bigger size of electrons, the repulsion
between bond pair and lone pair is comparatively less in chlorine atom. Hence the bond energy of F2 is less than that of Cl2.
23. ClF3 exists but FCl3
does not.
does not.
Ans. Cl
has vacant d-orbital but F has no d-orbital. Again because of the bigger size of
chlorine, it can accommodate three F atoms but due to the smaller size of fluorine,
it cannot accommodate large-sized Cl atoms around it.
has vacant d-orbital but F has no d-orbital. Again because of the bigger size of
chlorine, it can accommodate three F atoms but due to the smaller size of fluorine,
it cannot accommodate large-sized Cl atoms around it.
24. Why oxygen does not show
positive oxidation state like other group members? Also, report the compound
where oxygen shows a positive oxidation state.
positive oxidation state like other group members? Also, report the compound
where oxygen shows a positive oxidation state.
Ans. Oxygen
does not positive oxidation state because it does not have vacant d – orbital.
So, there is no place to accommodate the excited electrons. Therefore, no
sharing of the electron is possible.
does not positive oxidation state because it does not have vacant d – orbital.
So, there is no place to accommodate the excited electrons. Therefore, no
sharing of the electron is possible.
Oxygen
is the most electronegative element next to fluorine. It shows a positive oxidation
state only in compounds with fluorine, e.g., it has a positive oxidation state in
OF2.
is the most electronegative element next to fluorine. It shows a positive oxidation
state only in compounds with fluorine, e.g., it has a positive oxidation state in
OF2.
25. The tendency to show -2
oxidation state decreases from sulphur to polonium in group 16. Why?
oxidation state decreases from sulphur to polonium in group 16. Why?
Ans. The
elements of group 16 have the ground state valence shell electronic
configuration is ns2 np4 and tends to attain noble gas
configuration by gaining or sharing two electrons. Oxygen with its high electronegative value tends to complete its octet by gaining two electrons and
exhibits -2 oxidation state. The electronegativity of other element is very
less and hence, there is a low probability for them to form divalent negative
ions. The decreasing electronegativity value of the elements in this family
with increasing atomic number suggests that the tendency to show -2 oxidation
state decreases from sulphur onward to polonium.
elements of group 16 have the ground state valence shell electronic
configuration is ns2 np4 and tends to attain noble gas
configuration by gaining or sharing two electrons. Oxygen with its high electronegative value tends to complete its octet by gaining two electrons and
exhibits -2 oxidation state. The electronegativity of other element is very
less and hence, there is a low probability for them to form divalent negative
ions. The decreasing electronegativity value of the elements in this family
with increasing atomic number suggests that the tendency to show -2 oxidation
state decreases from sulphur onward to polonium.
26. Why is OF6 compound
not known?
not known?
Ans. Electronic
configuration of oxygen is 1s2 2s2 2p2. Since
it does not have any 2d orbital’s in its valence shell, so it cannot expand its
octet due to non-availability of d orbitals. Hence, oxygen atom cannot exhibit
higher positive oxidation state, and hence, OF6 compound is not
known.
configuration of oxygen is 1s2 2s2 2p2. Since
it does not have any 2d orbital’s in its valence shell, so it cannot expand its
octet due to non-availability of d orbitals. Hence, oxygen atom cannot exhibit
higher positive oxidation state, and hence, OF6 compound is not
known.
27. H2S acts only as a reducing agent while SO2 can act both as a reducing agent and
oxidizing agent. Give reasons.
oxidizing agent. Give reasons.
Ans. S
in SO2 has oxidation state +4. It lies in between the minimum
oxidation state (-2) and maximum oxidation state (+6) of S. Thus, S in SO2
can show an increase in its oxidation number (i.e., can act as reductant) or
can show a decrease in its oxidation number (i.e., can act as an oxidant). On the
other hand, in H2S, S is in -2 oxidation state and can only increase
its oxidation state to act as reductant.
in SO2 has oxidation state +4. It lies in between the minimum
oxidation state (-2) and maximum oxidation state (+6) of S. Thus, S in SO2
can show an increase in its oxidation number (i.e., can act as reductant) or
can show a decrease in its oxidation number (i.e., can act as an oxidant). On the
other hand, in H2S, S is in -2 oxidation state and can only increase
its oxidation state to act as reductant.
28. Sulphur dioxide is a more
powerful reducing agent in an alkaline medium than in acidic medium. Why?
powerful reducing agent in an alkaline medium than in acidic medium. Why?
Ans. The
reducing property may be represented as SO2 + 2OH– → SO42- + 2e–
Addition
of acid favours the reverse reaction whereas addition of OH– favours
the forward reaction.
of acid favours the reverse reaction whereas addition of OH– favours
the forward reaction.
29. When chlorine is bubbled
through a fluorine solution, no reaction takes place. Explain.
through a fluorine solution, no reaction takes place. Explain.
Ans. Due
to the small size and high electronegativity, fluorine is a stronger oxidizing
agent than chlorine. Hence, chlorine cannot displace or oxidize fluorine ions
to fluorine. Chlorine shows different oxidation states in its compounds.
to the small size and high electronegativity, fluorine is a stronger oxidizing
agent than chlorine. Hence, chlorine cannot displace or oxidize fluorine ions
to fluorine. Chlorine shows different oxidation states in its compounds.
30. Why a metal ion liberates I2
from KI but the same metal ion does not liberate Cl2 from KCl?
from KI but the same metal ion does not liberate Cl2 from KCl?
Ans. It
is because I– is a stronger reducing agent as compared to Cl–
and thus, KI reduces the metal ion to liberate I2. For example KI on
reaction with Cu2+ liberates I2 and Cu2+ get
reduced to Cu1+.
is because I– is a stronger reducing agent as compared to Cl–
and thus, KI reduces the metal ion to liberate I2. For example KI on
reaction with Cu2+ liberates I2 and Cu2+ get
reduced to Cu1+.
4KI
+ 2Cu2+ → I2
+ Cu2I2 + 4K+
31. Compare, giving a reason, the
oxidizing powers of fluorine and chlorine.
oxidizing powers of fluorine and chlorine.
Ans. Because
of low bond dissociation energy of fluorine, it is a stronger oxidizing agent.
of low bond dissociation energy of fluorine, it is a stronger oxidizing agent.
32. Why fluorine does not form
oxoacids like other halogens?
oxoacids like other halogens?
Ans. Fluorine
shows only -1 oxidation state due to the highest electronegativity whereas, in
oxoacids, the element involved should have positive oxidation state. Thus,
fluorine does not form oxoacids.
shows only -1 oxidation state due to the highest electronegativity whereas, in
oxoacids, the element involved should have positive oxidation state. Thus,
fluorine does not form oxoacids.
33. Name the halogen having some
metallic nature.
metallic nature.
Ans. Iodine,
possesses metallic lustre, forms ionic compounds such as IPO4, I(CH3COO)3
having a +3 oxidation state.
possesses metallic lustre, forms ionic compounds such as IPO4, I(CH3COO)3
having a +3 oxidation state.
34. Pure HI kept in bottle
acquires a brown colour after some time. Why?
acquires a brown colour after some time. Why?
Ans. HI
is a strong reducing agent and on keeping, it gets slowly oxidized to brown coloured
iodine by oxygen.
is a strong reducing agent and on keeping, it gets slowly oxidized to brown coloured
iodine by oxygen.
4HI
+ O2 → 2I2 + 2H2O
35. Halogens are strong oxidants.
Why?
Why?
Ans. The
electron affinity of halogen is maximum among all groups. Higher is the
electron affinity more is the tendency to gain an electron and thus more is the
tendency to get itself reduced and more is oxidizing power.
electron affinity of halogen is maximum among all groups. Higher is the
electron affinity more is the tendency to gain an electron and thus more is the
tendency to get itself reduced and more is oxidizing power.
X +
e– → X– ∆ H = -E
(higher values)
36. Why is fluorine more reactive
than other halogens?
than other halogens?
Ans. Fluorine
is more reactive than other halogens due to the following reasons:
is more reactive than other halogens due to the following reasons:
Fluorine has a low bond
dissociation energy due to repulsion between its non-bonding electrons.
Fluorine cannot form multiple
bonds because of the absence of d orbitals.
Fluorine has a small size and
high electronegativity, and due to this it has a greater tendency to accept an
electron to form a more stable fluoride ion.
The extent of hydration in F–
is maximum.
dissociation energy due to repulsion between its non-bonding electrons.
Fluorine cannot form multiple
bonds because of the absence of d orbitals.
Fluorine has a small size and
high electronegativity, and due to this it has a greater tendency to accept an
electron to form a more stable fluoride ion.
The extent of hydration in F–
is maximum.
37. What reasons can you give for
fluorine existing only the -1 and zero oxidation states whereas iodine exists
in +1, 0 and -1 oxidation states?
fluorine existing only the -1 and zero oxidation states whereas iodine exists
in +1, 0 and -1 oxidation states?
Ans. Fluorine
being the most electronegative element combines with other elements by ionic
or polar covalent bonds in which it is negatively polarized. Thus, its
oxidation state is -1. But when fluorine atoms combine with each other to form
F2 oxidation state of fluorine is zero.
being the most electronegative element combines with other elements by ionic
or polar covalent bonds in which it is negatively polarized. Thus, its
oxidation state is -1. But when fluorine atoms combine with each other to form
F2 oxidation state of fluorine is zero.
38. Explain how the oxidizing
character of the halogen varies as we move down the group.
character of the halogen varies as we move down the group.
Ans. Due
to their high electron affinities, halogens act as strong oxidizing agents. But
their oxidizing power goes on decreasing on moving down the group from the
fluorine to iodine due to the increase in the size of the atoms. The decreasing
trend in oxidizing power is quite evident from their respective standard reduction
potential which is maximum for fluorine and minimum for iodine.
to their high electron affinities, halogens act as strong oxidizing agents. But
their oxidizing power goes on decreasing on moving down the group from the
fluorine to iodine due to the increase in the size of the atoms. The decreasing
trend in oxidizing power is quite evident from their respective standard reduction
potential which is maximum for fluorine and minimum for iodine.
39. Xenon form compounds whereas
krypton other noble gas elements do not form compounds. Explain.
krypton other noble gas elements do not form compounds. Explain.
Ans. Because
xenon has lower ionization energy as compared to other noble gas elements.
xenon has lower ionization energy as compared to other noble gas elements.
40. What is the basic cause of
solubility of noble gases in the water?
solubility of noble gases in the water?
Ans. The
increase in solubility of noble gases down the group is due to the increase in
polarization with the increase in sizes. The basic cause of solubility of noble
gases in water is due to dipole induced dipole attraction between water
molecules and noble gases.
increase in solubility of noble gases down the group is due to the increase in
polarization with the increase in sizes. The basic cause of solubility of noble
gases in water is due to dipole induced dipole attraction between water
molecules and noble gases.
41. Why helium and neon, do not
form compounds with highly electronegative fluorine and oxygen?
form compounds with highly electronegative fluorine and oxygen?
Ans. Helium
and neon do not form compounds with highly electronegative fluorine and oxygen
because these noble gases have high ionization energy and they do not have d
orbitals in their valence shells.
and neon do not form compounds with highly electronegative fluorine and oxygen
because these noble gases have high ionization energy and they do not have d
orbitals in their valence shells.
42. Why the ease of liquefaction
of noble gases increases down the group?
of noble gases increases down the group?
Ans. Liquefaction
of noble gases depends upon the atomic size. Vander Waal’s forces increase down
the group, and therefore, the tendency of liquefaction also increases down the
group.
of noble gases depends upon the atomic size. Vander Waal’s forces increase down
the group, and therefore, the tendency of liquefaction also increases down the
group.
43. Noble gases (Ne, Ar) have
larger radii in their periods.
larger radii in their periods.
Ans. In
the noble gases, we can measure only Wander Waal’s radii which are larger than
covalent radii.
the noble gases, we can measure only Wander Waal’s radii which are larger than
covalent radii.
44. Why is helium used to inflate
aeroplane tyres and to fill the weather balloons through its lifting power is
only 90% of hydrogen?
aeroplane tyres and to fill the weather balloons through its lifting power is
only 90% of hydrogen?
Ans. It
is because hydrogen gas is highly inflammable; therefore, it may catch fire
with an explosion. On the other hand, helium gas is non-inflammable, so there is
no danger of fire or explosion.
is because hydrogen gas is highly inflammable; therefore, it may catch fire
with an explosion. On the other hand, helium gas is non-inflammable, so there is
no danger of fire or explosion.
45. Why are the elements of group
18 known as noble gas?
18 known as noble gas?
Ans. The
elements of group 18 have their valence shell orbitals completely filled. As a
result, they are fairly non-reactive and hence are called noble gases. However,
Xe reacts with highly electronegative elements such as oxygen and fluorine
under certain conditions to form oxides, fluorides and ox fluorides.
elements of group 18 have their valence shell orbitals completely filled. As a
result, they are fairly non-reactive and hence are called noble gases. However,
Xe reacts with highly electronegative elements such as oxygen and fluorine
under certain conditions to form oxides, fluorides and ox fluorides.
46. The enthalpies of atomization
of the transition metals are high.
of the transition metals are high.
Ans. Transition
metals have strong metallic bonds between the atoms of these elements.
Therefore a high amount of heat is required to break the metal lattice to give
free atoms.
metals have strong metallic bonds between the atoms of these elements.
Therefore a high amount of heat is required to break the metal lattice to give
free atoms.
47. The transition metals
generally form coloured compounds.
generally form coloured compounds.
Ans. The
transition metals have in complete d-subshell or have unpaired electrons in
their d-subshell due to which d-d transition takes place and they become
coloured.
transition metals have in complete d-subshell or have unpaired electrons in
their d-subshell due to which d-d transition takes place and they become
coloured.
48. The transition metals and many
of their compounds show paramagnetic behaviour.
of their compounds show paramagnetic behaviour.
Ans. The
transition metals have unpaired electrons in (n – 1) d-orbital. Therefore
their ions and compounds are paramagnetic.
transition metals have unpaired electrons in (n – 1) d-orbital. Therefore
their ions and compounds are paramagnetic.
49. Cu+ ion is not
stable in aqueous solution.
stable in aqueous solution.
Ans. Cu+2
is much more stable than Cu+ (aq). It is because although second
ionization enthalpy of copper is large but enthalpy of hydration (Δhy H)
for Cu+ (aq) is much more negative than that for Cu+2
(aq) and hence it more than compensates for the second ionization enthalpy of
copper and they readily undergo disproportionately in aqueous solution. 2Cu+ → Cu+2 + Cu
50. Actinoid concentration is
greater from element to element than Lanthanoid concentration.
greater from element to element than Lanthanoid concentration.
Ans. This
is due to poor shielding by 5f electrons in the actinoids than that by 4f
electrons in the lanthanoids.
is due to poor shielding by 5f electrons in the actinoids than that by 4f
electrons in the lanthanoids.
51. The lowest oxide of a transition
metal is basic, the highest is acidic.
metal is basic, the highest is acidic.
Ans. In
the low oxidation state of the metal, some of the valence electrons of the
metal atom are not involved in bonding. Hence it can donate electrons and
behave as a base but in higher oxidation state, valence electrons are involved in
bonding and are not available. Therefore it can accept electrons and hence
behave as acid.
the low oxidation state of the metal, some of the valence electrons of the
metal atom are not involved in bonding. Hence it can donate electrons and
behave as a base but in higher oxidation state, valence electrons are involved in
bonding and are not available. Therefore it can accept electrons and hence
behave as acid.
52. Copper is considered as a
transition metal.
transition metal.
Ans. Because
copper in the oxidation state of +2, it has electronic configuration of 4so3d9,
i.e., incompletely filled d-subshell.
copper in the oxidation state of +2, it has electronic configuration of 4so3d9,
i.e., incompletely filled d-subshell.
53. Scandium forms no coloured
ions yet it is regarded as a transition element.
ions yet it is regarded as a transition element.
Ans. Scandium
in the ground, the state has one electron in the 3d-subshell. Therefore it is
regarded as transition element but in +3 oxidation state, it has no electron in
3d subshell (3do). Hence it does not form coloured ions.
in the ground, the state has one electron in the 3d-subshell. Therefore it is
regarded as transition element but in +3 oxidation state, it has no electron in
3d subshell (3do). Hence it does not form coloured ions.
54. Transition elements have high
enthalpies of hydration.
enthalpies of hydration.
Ans. Because
of transition, elements have a small atomic size and high nuclear charge. Both the
properties change as we move from left to right along the transition series.
of transition, elements have a small atomic size and high nuclear charge. Both the
properties change as we move from left to right along the transition series.
55. Transition elements show
variable oxidation states.
variable oxidation states.
Ans. In
the transition elements, the energies of (n – 1) d orbitals and ns orbitals are
very close or there is little difference in them. Hence electrons from both can
take part in bonding.
the transition elements, the energies of (n – 1) d orbitals and ns orbitals are
very close or there is little difference in them. Hence electrons from both can
take part in bonding.
56. Transition elements have many
irregularities in their electronic configuration.
irregularities in their electronic configuration.
Ans. Due
to the very small difference in the energy of (n – 1)d-subshell and ns subshell,
the incoming electron may enter into ns or (n – 1) d subshell. Therefore, they
show irregularities in their electronic configuration.
to the very small difference in the energy of (n – 1)d-subshell and ns subshell,
the incoming electron may enter into ns or (n – 1) d subshell. Therefore, they
show irregularities in their electronic configuration.
57. The paramagnetic character in
3d transition series elements increase up to Mn and then decreases.
3d transition series elements increase up to Mn and then decreases.
Ans. On
moving from Sc to Mn, the numbers of unpaired electrons increases and hence
paramagnetic character increases. But after Mn, the pairing of electrons in the
d-subshell starts and the number of unpaired electrons decreases and hence
paramagnetic character decreases.
moving from Sc to Mn, the numbers of unpaired electrons increases and hence
paramagnetic character increases. But after Mn, the pairing of electrons in the
d-subshell starts and the number of unpaired electrons decreases and hence
paramagnetic character decreases.
58. Zn+2 salts are
white, white Cu+2 salts are blue.
white, white Cu+2 salts are blue.
Ans. Zn+2
has completely filled d-orbital’s (3d10) causing no d-d transition
but due to the presence of unpaired electrons or incompletely filled d-orbital’s
(3d9) the d-d transition takes place and Cu+2 salts are blue.
has completely filled d-orbital’s (3d10) causing no d-d transition
but due to the presence of unpaired electrons or incompletely filled d-orbital’s
(3d9) the d-d transition takes place and Cu+2 salts are blue.
59. The melting and boiling point
of Zn, Cd and Hg are low.
of Zn, Cd and Hg are low.
Ans.
Zn, Cd and Hg have completely filled d-subshell i.e. all the electrons in
d-subshell are paired. Hence the metallic bonds present in them are weak.
Therefore they have low melting and boiling points.
Zn, Cd and Hg have completely filled d-subshell i.e. all the electrons in
d-subshell are paired. Hence the metallic bonds present in them are weak.
Therefore they have low melting and boiling points.
60. The separation of lanthanide
is difficult.
is difficult.
Ans. Due
to lanthanide contraction, the change in the atomic or ionic radii of these
elements is very small. Hence their chemical properties are similar which makes
their separation difficult.
to lanthanide contraction, the change in the atomic or ionic radii of these
elements is very small. Hence their chemical properties are similar which makes
their separation difficult.
61. Electronic configuration of
lanthanoids is not known with certainty.
lanthanoids is not known with certainty.
Ans. In
the lanthanoids, 4f and 5d subshell are very close in energy. The outer most 6s
orbital remains filled with 2 electrons (6s2). The electron can
easily jump from 4f to 5d or vice-versa. Therefore their electronic configuration
is not known with certainty.
the lanthanoids, 4f and 5d subshell are very close in energy. The outer most 6s
orbital remains filled with 2 electrons (6s2). The electron can
easily jump from 4f to 5d or vice-versa. Therefore their electronic configuration
is not known with certainty.
62. Second
and third transition series elements show a similar size.
and third transition series elements show a similar size.
63. Ans. Due
to lanthanide concentration, the size of an atom of the third transition
series is almost the same as that of the element present just above in the
second transition series. Hence there is similarity in their properties.
to lanthanide concentration, the size of an atom of the third transition
series is almost the same as that of the element present just above in the
second transition series. Hence there is similarity in their properties.
64. Cr, Mn and Fe have nearly the
same atomic radii.
same atomic radii.
Ans. Cr,
Mn and Fe have nearly the same effective nuclear charge. Hence they have almost the same atomic radii.
Mn and Fe have nearly the same effective nuclear charge. Hence they have almost the same atomic radii.
65. Cd+2 salts are
white.
white.
Ans. Cd+2
salts are white because it has completely filled d-orbitals (d10) and
there is no possibility of d-d transition.
salts are white because it has completely filled d-orbitals (d10) and
there is no possibility of d-d transition.
66. In permanganate ion, there is
covalency between manganese and oxygen.
covalency between manganese and oxygen.
Ans. In
permanganate ion (MnO–4) ion, manganese is in its highest
oxidation state i.e. + 7 and in its high oxidation state, transition metals
form covalent bonds.
permanganate ion (MnO–4) ion, manganese is in its highest
oxidation state i.e. + 7 and in its high oxidation state, transition metals
form covalent bonds.
67. Mn+2 compounds are
more stable than Fe+2 towards oxidation to their +3 state.
more stable than Fe+2 towards oxidation to their +3 state.
Ans: Electronic
configuration of Mn+2 shows that it has half-filled (3d5)
sub-shell, exhibiting extra stability. Therefore third ionization enthalpy is
very high and it cannot lose the third electron easily. In the case of Fe+2, an electronic configuration is 3d6 and it can lose the third electron
easily to give stable configuration 3d5.
configuration of Mn+2 shows that it has half-filled (3d5)
sub-shell, exhibiting extra stability. Therefore third ionization enthalpy is
very high and it cannot lose the third electron easily. In the case of Fe+2, an electronic configuration is 3d6 and it can lose the third electron
easily to give stable configuration 3d5.
68. Sodium cyanide is used in the
extraction of silver from its ore.
extraction of silver from its ore.
Ans. Sodium
cyanide on reaction with the ore of silver forms sodium Argento cyanide. It is
a soluble complex from which the silver can be precipitated easily by adding
more electropositive metal like zinc to it.
cyanide on reaction with the ore of silver forms sodium Argento cyanide. It is
a soluble complex from which the silver can be precipitated easily by adding
more electropositive metal like zinc to it.
69. Out of La (OH)3 and
Lu(OH)3, the former one is more basic
Lu(OH)3, the former one is more basic
Ans. As
the size of the lanthanoid decreases from La+3 to Lu+3
the covalent character of the hydroxides increases. Hence the basic strength
decreases from La(OH)3 to Lu(OH)3.
the size of the lanthanoid decreases from La+3 to Lu+3
the covalent character of the hydroxides increases. Hence the basic strength
decreases from La(OH)3 to Lu(OH)3.
70. Cr+2 is reducing
but Mn+3 is oxidizing when both have d4 configuration.
but Mn+3 is oxidizing when both have d4 configuration.
Ans. Cr+2
have d4 configuration and easily changes to Cr+3 because
d3 has half-filled t2g orbital and hence more stable.
Therefore it is reducing. On the other hand, Mn+2 is more stable due
to half-filled d5 configuration and Mn+3 can easily be
changed to Mn+2 and therefore it is oxidizing.
have d4 configuration and easily changes to Cr+3 because
d3 has half-filled t2g orbital and hence more stable.
Therefore it is reducing. On the other hand, Mn+2 is more stable due
to half-filled d5 configuration and Mn+3 can easily be
changed to Mn+2 and therefore it is oxidizing.
71. H2S is a better
reducing agent than H2O.
reducing agent than H2O.
Ans. The
H-S bond is weaker than H-O because of the lesser tendency of S for overlapping due
to lower electronegativity and larger size of the anion S2-. Thus,
H2S having weaker bond acts as a better reducing agent.
H-S bond is weaker than H-O because of the lesser tendency of S for overlapping due
to lower electronegativity and larger size of the anion S2-. Thus,
H2S having weaker bond acts as a better reducing agent.
72. Sulphur is a solid whereas
oxygen is a gas at room temperature.
oxygen is a gas at room temperature.
Ans. Oxygen
forms a stable diatomic molecule. In oxygen molecules, two atoms of oxygen have
joined together through a double bond (pπ
– pπ bonding) as O=O. The multiple bonding in oxygen
is possible due to the small size of oxygen atoms. Thus, oxygen is a gas and no
more atoms of oxygen can join.
forms a stable diatomic molecule. In oxygen molecules, two atoms of oxygen have
joined together through a double bond (pπ
– pπ bonding) as O=O. The multiple bonding in oxygen
is possible due to the small size of oxygen atoms. Thus, oxygen is a gas and no
more atoms of oxygen can join.
73. Argon not forms diatomic
molecules like oxygen or chlorine?
molecules like oxygen or chlorine?
Ans. Because
no unpaired electron is present in its electronic configuration (1s2
2s2 2p6 3s2 3p6) and it has very
high ionization energy.
no unpaired electron is present in its electronic configuration (1s2
2s2 2p6 3s2 3p6) and it has very
high ionization energy.
74. The bond dissociation energy of F2
is less than the bond dissociation energy of chlorine.
is less than the bond dissociation energy of chlorine.
Ans. It
is due to strong inter-electronic repulsion between nonbonding electrons in small
size 2p orbitals of fluorine as compared to big sizes 3p orbitals of chlorine
and this makes the bond dissociation energy of F2 less than that of
Cl2.
is due to strong inter-electronic repulsion between nonbonding electrons in small
size 2p orbitals of fluorine as compared to big sizes 3p orbitals of chlorine
and this makes the bond dissociation energy of F2 less than that of
Cl2.
Join the Complete course on ISC- Chemistry, please visit us;
