Chemistry

Chemical Compounds and Reactions

329 Questions

Chemical compounds and reactions involve understanding the properties, colors, and formation of various chemical substances. Questions focus on identifying precipitates, observing color changes during reactions, and naming common compounds. This topic is a fundamental part of the chemistry syllabus for competitive exams.

identifying precipitateschemical reaction colorscompound namingcolloidal particle propertiesacid base reactions

Chemical Compounds and Reactions Questions

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

Which of the ions will give colorless aqueous solution?

  1. ${Ni}^{2+}$
  2. ${Fe}^{2+}$
  3. ${Cu}^{2+}$
  4. ${Cu}^{+}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

${Ni}^{2+}$ is light green, ${Fe}^{2+}$ is pale green, 


${Cu}^{2+}$ is blue and ${Cu}^{1+}$ is colorless in aqueous solution as its outermost configuration is $3d^{10}$ so thei is no unpaired electron which causes colour.

Hence ,option D is correct.

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

The color of the transition metal ions is due to:

  1. $d-d$ transition

  2. charge transfer

  3. change in the geometry

  4. none
Reveal answer Fill a bubble to check yourself
A,B Correct answer
Explanation

In case of transition elements, where the d-level is not completely filled, it is possible to promote an electron from a lower energy d-orbital to a higher energy d-orbital by absorption of a photon of electromagnetic radiation having an appropriate energy. Electromagnetic radiations in the visible region of the spectrum often possess the appropriate energy for such transitions. 

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

Which of the following statements are correct with reference to the ferrous and ferric ions?

  1. ${Fe}^{3+}$ gives brown color with potassium ferricyanide
  2. ${Fe}^{2+}$ gives blue precipitate with potassium ferricyanide
  3. ${Fe}^{3+}$ gives red color with potassium thiocyanate
  4. ${Fe}^{2+}$ gives brown color with ammonium thiocyanate
Reveal answer Fill a bubble to check yourself
B,C Correct answer
Multiple choice chemistry d and f block elements coloured complexes magnetic nature of transition metals general characteristics of first transition series

Which one of the following ionic species will not impart color to an aqueous solution?

  1. ${Ti}^{4+}$
  2. ${Cu}^{+}$
  3. ${Zn}^{2+}$
  4. ${Cr}^{3+}$
Reveal answer Fill a bubble to check yourself
A,B,C Correct answer
Explanation
The transition metal ions which have completely filled d-orbitals are colorless.

The transition metal ions which have completely empty d-orbitals are also colorless.

$ Cr^{3+}$ has a blue-green color.  because contain unpair electrons.

Rest all are colorless. 
Multiple choice chemistry d and f block elements coloured complexes magnetic nature of transition metals general characteristics of first transition series

The colorless species is:

  1. $V{Cl} _{3}$
  2. $VO{SO} _{4}$
  3. ${Na} _{3}{VO} _{4}$
  4. $\left[ V{ \left( { H } _{ 2 }O \right) } _{ 6 }{ SO } _{ 4 } \right] .{ H } _{ 2 }O$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$ VCl _3$ is green.

 
$ VOSO _4$ is blue. 

$ Na _3VO _4$ is colorless vanadium is present in +5 oxidation state .it does not have any unpaired electron.
 
$\left[ V{ \left( { H } _{ 2 }O \right)  } _{ 6 }{ SO } _{ 4 } \right]$ .${ H } _{ 2 }O$ is purple.

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

The aqueous solution of the salt will colored in the case of:

  1. $Zn{({NO} _{3})} _{2}$
  2. $Li{NO} _{3}$
  3. $Co{({NO} _{3})} _{2}$
  4. $Cr{Cl} _{3}$
Reveal answer Fill a bubble to check yourself
C,D Correct answer
Explanation

$ Co^{2+}$ = $3d^7$  


$Cr^{3+}$ = $3d^3$
 
$ Co^{2+}$ and $Cr^{3+}$   will have unpaired electrons and hence are expected to have aqueous solution of the salt colored.

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

The aqueous solutions of the following salts will be colored in the case of:

  1. $Zn{({NO} _{3})} _{2}$
  2. $Li{NO} _{3}$
  3. $Co{({NO} _{3})} _{2}$
  4. $Cr{Cl} _{3}$

  5. Potash alum
Reveal answer Fill a bubble to check yourself
C,D Correct answer
Explanation
${Co}^{2+}$
$\uparrow \downarrow $ $\uparrow \downarrow $ $\uparrow $ $\uparrow $ $\uparrow $
$z=27$
$Co=[Ar]{3d}^{7}{4s}^{2}$
${Co}^{2+}=[Ar]{3d}^{7}$
Two unpaired electrons present.

${Cr}^{3+}$:
$z=24$
$Cr=[Ar]{3d}^{5}{4s}^{1}$
${Cr}^{3+}=[Ar]{3d}^{3}$
$\uparrow $ $\uparrow $ $\uparrow $
$Co{({NO} _{3})} _{2}$ and $Cr{Cl} _{2}$ have unpaired electron; hence, they are colored.

The compounds have $ Zn^{2+}, Li^+, Co^{2+} and Cr^{3+}$ with 0, 0, 2 and 3 unpaired electrons. Hence option C and D are correct. Potash alum is colorless. 
Multiple choice chemistry d and f block elements coloured complexes magnetic nature of transition metals general characteristics of first transition series

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]

  1. $Ag^+$
  2. $Co^{2+}$
  3. $Ti^{4+}$

  4. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

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

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

  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
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

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

The ion which exhibits green colour is:

  1. $Cu^{2+}$
  2. $Mn^{2+}$
  3. $Co^{2+}$
  4. $Ni^{2+}$
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

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

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

  1. $K _{2}MnO _{4}$, dark green
  2. $KMnO _{4}$, purple
  3. $Mn _{2}O _{3}$, brown
  4. $Mn _{3}O _{4}$, black.
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

Which of the following compounds is not colored?

  1. ${Na} _{2}Cu{Cl} _{4}$
  2. ${Na} _{2}Cd{Cl} _{4}$
  3. ${Na} _{3}[Fe{(CN)} _{6}]$
  4. ${K} _{3}[Fe{(CN)} _{6}]$
Reveal answer Fill a bubble to check yourself
B Correct answer
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.
Multiple choice chemistry d- and f-block elements coloured complexes magnetic nature of transition metals general characteristics of first transition series

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

  1. $Ni^{2+}$
  2. $Fe^{3+}$
  3. $Ti^{4+}$
  4. $Cu^{2+}$
Reveal answer Fill a bubble to check yourself
C Correct answer
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.

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

Ammonium dichromate is used in fire works. The green colored powder blow in the air is:

  1. $Cr{O} _{3}$
  2. ${Cr} _{2}{O} _{3}$
  3. $Cr$
  4. $CrO ({O} _{2})$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
$(\mathrm{NH} _4) _2\mathrm{Cr} _2\mathrm{O} _7\xrightarrow{\Delta} \mathrm{Cr} _2\mathrm{O} _3+\mathrm{N} _2+4\mathrm{H} _2\mathrm{O}$

The green-coloured $ Cr _2O _3$ powder is blown in the air by the large volume of $ N _2$ and water vapour produced and settles like dust from the volcano. 

Hence, the correct option is $\text{B}$