Chemistry

Chemical Compounds and Reactions

505 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

The color of $KMn{ O } _{ 4 }$ is due to:

  1. L-> M charge transfer transition
  2. $\sigma -{ \sigma }^{ * }$ transition

  3. M-> L charge transfer transition

  4. d-d transition
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The color in $KMnO _4$ arises from an electronic transition.

In the permanganate ion $MnO _4^{-}$, manganese is in the +7 oxidation state, so it has no d electrons. Photons promote an electron from the highest energy molecular orbital to an empty d orbital on the manganese. When a photon of light is absorbed, this charge transfer takes place from L to M.

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

When $ZnO$ is heated, it appears of _______colour due to metal excess defect.

  1. pink

  2. yellow

  3. violet

  4. blue
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Zinc oxide is white at room temperature, but upon heating, it loses oxygen reversibly and forms zinc excess defects. The trapped electrons in interstitial sites occupy specific energy levels, absorbing blue light and reflecting a yellow color. Thus, heated ZnO appears yellow.

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

The color of $KMnO _{4}$  is due to :

  1. $d-d$ transition
  2. $L\rightarrow M$ charge transfer transition
  3. $\sigma-\sigma^{*}$ transition
  4. $M\rightarrow L$ charge transfer transition
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The intensely purple color of the permanganate ion is not due to d-d transitions because manganese is in the +7 oxidation state with a d0 configuration. Instead, it arises from a ligand-to-metal charge transfer (LMCT), where electrons move from the oxygen ligand orbitals to the empty metal orbitals.

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

Pair of ions which give blue colour in aqueous state: $V^{+4},\ Ni^{+2},\ Ti^{+3},\ Co^{+2},\ Fe^{+3}\ and\ Cu^{+2}$.

  1. $V^{+4}, Cu^{+2}$
  2. $Co^{+2}, Ni^{+2}$
  3. $Fe^{+3}, Ti^{+3}$
  4. $Co^{+2}, Fe^{+3}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

V(4+) (as vanadyl ion) and Cu(2+) (as hydrated copper ion) are well-known for their blue colors in aqueous solutions.

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 are coloured due to charge transfer spectra?

  1. ${K} _{2}{Cr} _{2}{O} _{7}$
  2. $KMn{O} _{4}$
  3. $Cu{SO} _{4}.5{H} _{2}O$

  4. Both (1) and (2)
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Both K2Cr2O7 and KMnO4 exhibit color due to charge transfer transitions (LMCT) because the metal centers are in high oxidation states with d0 configurations.

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

The colour imparted by $Co(II)$ compounds to glass is 

  1. green

  2. deep blue

  3. yellow

  4. red
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
 Vanadium yellow-green 
 Chrome emerald green 
 Iron Coke bottle green 
 Manganese amethyst 
 Cobalt violet blue 
 Copper greenish blue to blue 
 Nickel grayish brown 
 Selenium salmon pink 
 Cerium- Titanium yellow 
 Neodymium dichroic violet-pink 
 Uranium yellow (fluorescent 
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.