Tag: chemistry

Questions Related to chemistry

The ion that gives colourless compound:

chemistry d and f block elements coloured complexes magnetic nature of transition metals general characteristics of first transition series

  1. $Sc^{+3}$

  2. $V^{+3}$

  3. $Cr^{+3}$

  4. All of these

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Correct Option: A

Which pair of ions is colourless.

chemistry d and f block elements coloured complexes magnetic nature of transition metals general characteristics of first transition series

  1. $Mn^{+3}, CO^{+3}$

  2. $Fe^{3+}, Cr^{+3}$

  3. $Zn^{2+}, Sc^{3+}$

  4. $Ti^{2+}, Cu^{2+}$

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Correct Option: C
Explanation:

As both $Zn^{2+}  = d^{10}, Sc^{3+} = d^0$ have zero unpaired d-electron so they both are colourless.

Out of the ions $Ag^+, Co^{2+}, Ti^{4+}$, which one will be coloured in aqueous solutions.


[Atomic no : Ag = 47, Co = 27, Ti = 22]

chemistry d and f block elements coloured complexes magnetic nature of transition metals general characteristics of first transition series

  1. $Ag^+$

  2. $Co^{2+}$

  3. $Ti^{4+}$

  4. None of these

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Correct Option: B
Explanation:

compound with unpaired d-electron will show color.


$Ag^+ = 5d^{10} \,\,\,\,\,\,,n = 0$

$Ti^{+4} = 3s^2 3p^6 \,\,\,\,\,\,, n = 0$

$Co^{+2} = [Ar]3d^7\,\,\,\,\,\,\,,n = 3$ It will show color due to unpaired d electrons.

Most copper $(I)$ compounds are found to be colourless. This is due to :

chemistry d and f block elements coloured complexes magnetic nature of transition metals general characteristics of first transition series

  1. presence of low oxidation state of copper

  2. completely filled d-level in $Cu(I)$

  3. diamagnetic nature of the compound

  4. high polarizability of $Cu(I)$ ion

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Correct Option: B
Explanation:

In copper (I) ion there are no vacant d orbitals as it is diamagnetic. Copper(I) ion being less charged has small ligand field effect and the transition is in the infrared region in which no color is perceived by human eye.

The ion which exhibits green colour is:

chemistry d and f block elements coloured complexes magnetic nature of transition metals general characteristics of first transition series

  1. $Cu^{2+}$

  2. $Mn^{2+}$

  3. $Co^{2+}$

  4. $Ni^{2+}$

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Correct Option: D
Explanation:

Transition metal ion                     Colour

            ${ Cu }^{ 2+ }$                                blue-green
            ${ Fe }^{ 2+ }$                                 olive green
            ${ Ni }^{ 2+ }$                                  bright green
            ${ Fe }^{ 3+ }$                                 brown to yellow
${ Ni }^{ 2+ }$ only exhibits green colour, other exhibits partial green colours / mixed green colours.

Which ion is colourless?

chemistry d and f block elements coloured complexes magnetic nature of transition metals general characteristics of first transition series

  1. $C{ r }^{ +4 }$

  2. $Sc^{ +3 }$

  3. $Ti^{ +3 }$

  4. ${ V }^{ +3 }$

Show answer
Correct Option: B
Explanation:

$(A)$ $Cr\quad [Ar]3d^54s^1$

$Cr^{+4}\quad [Ar]3d^2$
$2$ unpaired $e^-s\longrightarrow$ paramagnetic.

$(B)$ $Sc\quad [Ar]3d^14s^2$
$Sc^{+3}\quad [Ar]3d^2$
$0$ unpaired $e^-s\longrightarrow$ dimagnetic.

$(C)$ $Ti\quad [Ar]3d^24s^2$
$Ti^{+3}\quad [Ar]3d^1$
$1$ unpaired $e^-s\longrightarrow$ paramagnetic.

$(D)$ $V\quad [Ar]3d^34s^2$
$V^{+3}\quad [Ar]3d^2$
$2$ unpaired $e^-s\longrightarrow$ paramagnetic.

Ions which do not have unpaired electrons do not show colour in aqueous solution. These are known as diamagnetic ions.

When $MnO _{2}$ is fused with KOH in the presence of air, a coloured compound is formed, the product and its colour is :

chemistry d and f block elements coloured complexes magnetic nature of transition metals general characteristics of first transition series

  1. $K _{2}MnO _{4}$, dark green

  2. $KMnO _{4}$, purple

  3. $Mn _{2}O _{3}$, brown

  4. $Mn _{3}O _{4}$, black.

Show answer
Correct Option: A
Explanation:

The reaction between MnO$ _2$ and KOH in presence of air is given as:

$2MNO _2 +4KOH +O _2$ $\rightarrow$ $2K _2 MnO _4 +2H _2O$
                                         (potassium manganate)
The $K _2Mn O _4$ formed is dark green in colour.

Which one of the following elements forms compounds that are all coloured?

chemistry d and f block elements coloured complexes magnetic nature of transition metals general characteristics of first transition series

  1. Magnesium

  2. Aluminium

  3. Iron

  4. Chromium

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Correct Option: D
Explanation:
Most of the chromium compounds are coloured due to excitation of an electron from a lower energy d-orbital to higher energy d-orbital, the energy of excitation corresponds to the frequency of light absorbed. This frequency lies in a visible region. The colour observed corresponds to the complementary colour of light absorbed.

Which of the following compounds is not colored?

chemistry d and f block elements coloured complexes magnetic nature of transition metals general characteristics of first transition series

  1. ${Na} _{2}Cu{Cl} _{4}$

  2. ${Na} _{2}Cd{Cl} _{4}$

  3. ${Na} _{3}[Fe{(CN)} _{6}]$

  4. ${K} _{3}[Fe{(CN)} _{6}]$

Show answer
Correct Option: B
Explanation:
Electronic configuration: $[Kr] 4d^{10} 5s^{2}$

Cadmium is not considered as transition element which has completely filled d - configuration and is not having unpaired electrons to exhibit color property.
So $Na _2CdCl _4$ do not exhibit color
Hence option B is correct.

Which of the following ion will not form coloured aqueous solution?

chemistry d- and f-block elements coloured complexes magnetic nature of transition metals general characteristics of first transition series

  1. $Ni^{2+}$

  2. $Fe^{3+}$

  3. $Ti^{4+}$

  4. $Cu^{2+}$

Show answer
Correct Option: C
Explanation:
$ \displaystyle Ni^{2+}$ ion with $ \displaystyle 3d^8$ outer electronic configuration has two unpaired electrons. It will form a green coloured aqueous solution.

$ \displaystyle Fe^{3+}$ ion with $ \displaystyle 3d^5$ outer electronic configuration has five unpaired electrons. It will form yellow coloured aqueous solution.

$ \displaystyle Ti^{4+}$ ion will not form coloured aqueous solutionaas it does not contain unpaired electrons.
$ \displaystyle Ti^{4+}$ ion with $ \displaystyle 3d^0$ outer electronic configuration has zero unpaired electrons.


$ \displaystyle Cu^{2+}$ ion with $ \displaystyle 3d^9$ outer electronic configuration has one unpaired electron. It will form blue coloured aqueous solution.

Hence, option $C$ is correct.