d and f Block Elements — Page 3 | JEE Chemistry

Q21

Given below are two statements : Statement I : The Eo value for Ce4+ / Ce3+ is + 1.74 V. Statement II : Ce is more stable in Ce4+ state than Ce3+ state. In the light of the above statements, choose the most appropriate answer from the options given below :

A Statement I is incorrect but statement II is correct

B Both statement I and statement II are correct

C Both statement I and statement II are incorrect

D Statement I is correct but statement II is incorrect

Correct Answer

Option D

Solution

Ce4+

\overset{{{e^ - }}}\longrightarrow

Ce3+ E° = +1.74 V Positive SRP and higher SRP means greater oxidising power.

So, Ce4+ wants to reduce to Ce3+.

Indicates Ce4+ is less stable than Ce3+.

Q22

Which of the following ions does not liberate hydrogen gas on reaction with dilute acids ?

A Ti2+

B V2+

C Cr2+

D Mn2+

Correct Answer

Option D

Solution

The third ionisation energy of Mn is too high due to stable half filled 3d-orbital.

Hence, it cannot further get oxidised to liberate hydrogen.

Q23

What would happen when a solution of potassium chromate is treated with an excess of dilute nitric acid?

A

Cr_2O^{2-}_7

and H2O are formed

B

CrO^{2-}_4

is reduced to +3 state of Cr

C

CrO^{2-}_4

is oxidized to +7 state of Cr

D Cr3+ and

Cr_2O^{2-}_7

are formed

Correct Answer

Option A

Solution

When a solution of potassium chromate is treated with an excess of dilute nitric acid. Potassium dichromate and

{H_2}O

are formed.

2{K_2}Cr{O_4} + 2HN{O_3} \to {K_2}C{r_2}{O_7} + 2KN{O_3} + {H_2}O

Hence

C{r_2}{O_7}^ -

and

{H_2}O

are formed.

Q24

The number of d-electrons retained in Fe2+ (At no of Fe = 26) ion is :

A 4

B 5

C 6

D 3

Correct Answer

Option C

Solution

Fe (Z = 26) $\to$ e- = 26 Fe2+ (Z = 26) $\to$ e- = 24 Electronic configuration: Fe (Z = 26) $\to$ 1s2 2s2 2p6 3s2 3p6 3d6 4s2 Fe2+ (Z = 26) $\to$ 1s2 2s2 2p6 3s2 3p6 3d6 4s0 as 4s is the outermost shell of Fe that's why e- will always removed first from 4s, so retained e- in d-shell is 6

Q25

The “spin-only” magnetic moment [in units of Bohr magneton, (µB)] of Ni2+ in aqueous solution would be : (Atomic number of Ni = 28)

A 2.84

B 4.90

C 0

D 1.73

Correct Answer

Option A

Solution

The number of unpaired electrons in

N{i^{2 + }}\left( {aq} \right) = 2

Water is weak ligand hence no pairing will take place spin magnetic moment

\begin{aligned}& = \sqrt {n\left( {n + 2} \right)} = \sqrt {2\left( {2 + 2} \right)} \\ & = \sqrt 8 = 2.82\end{aligned}

Q26

Lanthanoid contraction is caused due to :

A the appreciable shielding on outer electrons by 4f electrons from the nuclear charge

B the appreciable shielding on outer electrons by 5d electrons from the nuclear charge

C the same effective nuclear charge from Ce to Lu

D the imperfect shielding on outer electrons by 4f electrons from the nuclear charge

Correct Answer

Option D

Solution

The main reason of lanthanide contraction is, poor shielding of 4f electrons on the outer most shell electrons.

As f orbital is defused nature so shielding of 4f electron is imperfect that is why nucleus can attract outer most shell electron easily and the size of atom decreases.

In lanthanides, there is poorer shielding of

5d

electrons by

4f

electrons resulting in greater attraction of the nucleus over

5d

electrons and reduction of the atomic radii.

Q27

Identify the incorrect statement among the following :

A d-Block elements show irregular and erratic chemical properties among themselves

B La and Lu have partially filled d orbitals and no other partially filled orbitals

C The chemistry of various lanthanoids is very similar

D 4f and 5f orbitals are equally shielded

Correct Answer

Option D

Solution

4f

orbital is nearer to nucleus as compared to

5f

orbital therefore, shielding of

4f

is more than

5f.

Q28

The atomic radius of Ag is closed to :

A Au

B Cu

C Hg

D Ni

Correct Answer

Option A

Solution

Atomic radius of Ag and Au is nearly same due to lanthanide contraction.

In periodic table in group 1, 2, 3 from top to bottom radius increases but from group 4 to 12 size increases for 3d to 4d series elements but size of 4d and 5d series elements are approximately same.

Q29

Iron exhibits + 2 and +3 oxidation states. Which of the following statements about iron is incorrect?

A Ferrous oxide is more basic in nature than the ferric oxide

B Ferrous compounds are relatively more ionic than the corresponding ferric compounds

C Ferrous compounds are less volatile than the corresponding ferric compounds

D Ferrous compounds are more easily hydrolysed than the corresponding ferric compounds.

Correct Answer

Option D

Solution

F{e^{3 + }}

is easily hydrolysed than

F{e^{2 + }}

due to more positive charge.

Q30

Which series of reactions correctly represents chemical relations related to iron and its compound?

A Fe

\overset{{dil.\,{H_2}S{O_4}}}\longrightarrow

FeSO4

\overset{{{H_2}S{O_4},{O_2}}}\longrightarrow

Fe2(SO4)3

\overset{{heat}}\longrightarrow

Fe

B Fe

\overset{{{O_2} \, {, heat}}}\longrightarrow

FeO

\overset{{dil.\,{H_2}S{O_4}}}\longrightarrow

FeSO4

\overset{{heat}}\longrightarrow

Fe

C Fe

\overset{{{Cl_2} \, {, heat}}}\longrightarrow

FeCl3

\overset{{heat, \, air}}\longrightarrow

FeCl2

\overset{{Zn}}\longrightarrow

Fe

D Fe

\overset{{{O_2},\,heat}}\longrightarrow

Fe3O4

\overset{{CO,\,{{600}^o}C}}\longrightarrow

FeO

\overset{{CO,\,{{700}^o}C}}\longrightarrow

Fe

Correct Answer

Option D

Solution

In equation (i)

\,\,\,

F{e_2}{\left( {S{O_4}} \right)_3}\,\,\,

and in equation (ii)

\,\,\,

F{e_2}{\left( {S{O_4}} \right)_3}

on decomposing will form oxide instead of

Fe.

The correct sequence of reactions is

Fe\overset{{{O_2},heat}}\longrightarrow \,\,F{e_3}{O_4}\overset{{Co,{{600}^ \circ }C}}\longrightarrow

\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,F{e_2}{\left( {S{O_4}} \right)_3}\overset{\Delta}\longrightarrow Fe