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

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 $\text{B}$
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 forms a colorless solution in aqueous medium?

  1. ${Cr}^{3+}$
  2. ${Ti}^{3+}$
  3. ${Sc}^{3+}$
  4. ${V}^{3+}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$Cr^{3+}$ = $3d^3$ = coloured

$Ti^{3+}$ =  $3d^1$ = coloured

$V^{3+}$ =  $3d^2$ = coloured

$Sc^{3+}$ has electron configuration of [Ar] $4s^0  3d^0$. Therefore without any unpaired electrons it forms a colorless solution in aqueous medium. 

Multiple choice chemistry nature of matter heterogenous mixture - colloidal solution and its properties suspensions and colloids mixtures

Colloidal solutions of metals like gold can be prepared when their salt solutions react with certain substances like $SnCl _{2}$, formaldehyde, phenyl hydrazine, etc.
2$AuCl _{3}$ + 3$SnCl _{2}$ $\rightarrow$ 3$SnCl _{4}$ + $2Au _{sol}$
The above method is an example of:

  1. reduction method

  2. oxidation method

  3. hydrolysis method

  4. double decomposition method
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

  • A colloid is a heterogeneous system in which one substance is dispersed (dispersed phase) as very fine particles in another substance called dispersion medium.
  • Colloidal solutions of metals like gold can be prepared when their salt solutions react with certain substances like $SnCl _2$, formaldehyde, phenylhydrazine.
In the given reaction,
$2AuCl _3 + 3SnCl _2 \rightarrow 3SnCl _4 + 2Au _{sol}$
The oxidation state of $Sn$ is changing from -2 to -4. So,it is gaining electrons and hence the method is the reduction method.

Multiple choice chemistry nature of matter heterogenous mixture - colloidal solution and its properties suspensions and colloids mixtures

The nature of colloidal solution obtained when excess $Fe{ Cl } _{ 3 }$ is added in precipitate of $Fe{ \left( OH \right)  } _{ 3 }$?

  1. positively charged

  2. negatively charged

  3. no charge

  4. All of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Peptization takes place forming a positively charged colloidal sol of $Fe(OH) _3$
Peptization is a process of passing of a precipitate into colloidal particles on adding suitable electrolyte. The electrolyte added is known as peptizing agent. A few examples of sols obtained by peptization are given below:
A reddish brown colored colloidal solution is obtained by adding small quantity of ferric chloride solution to the freshly precipitated ferric hydroxide.
Multiple choice chemistry nature of matter heterogenous mixture - colloidal solution and its properties suspensions and colloids mixtures

When negatively charged colloid-like $As _2S _3$ sol is added to +vely charged $Fe(-OH) _3$ sol in suitable amounts:

  1. both the sols are precipitated simultaneously

  2. this process is called mutual coagulation

  3. they become positively charged colloid

  4. they become negatively charged colloid
Reveal answer Fill a bubble to check yourself
A,B Correct answer
Explanation

When -vely charged colloid-like $As _2S _3$ sol is added to +vely charged $Fe(OH) _3$ sol in suitable amounts both the sols are precipitated simultaneously it is due to the fact that negatively charged particles of the arsenious sulphide sol take up positive ions, resulting neutralisation of the charge on the colloidal particles and hence lowering the stability of the sol and both precipitate simultaneously.

Multiple choice chemistry nature of matter heterogenous mixture - colloidal solution and its properties suspensions and colloids mixtures

In the preparation of AgI sol, the excess of $AgNO _{3}$ is added to potassium iodide solution. The particles of the sol will acquire:

  1. negative charge

  2. positive charge

  3. no charge

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

When AgNO3 is in excess, the AgI particles adsorb Ag+ ions from the solution, forming an AgI/Ag+ layer, which gives the colloidal particles a positive charge.

Multiple choice chemistry the world of carbon organic compounds allotropes of carbon versatile nature of carbon

Some elements show the property of existing in two or more distinct physical form which show different physical properties but same chemical properties. These distinct forms of an element are called :

  1. isomers

  2. allotropes

  3. compounds

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

Allotropes of carbon have a different physical form but chemically they are similar, e.g., diamond and graphite are allotropes of carbon which are chemically carbon compounds but physically diamond is the hardest material known while graphite is soft material.


Hence, option $B$ is correct,

Multiple choice chemistry separation of substances classification of mixtures mixtures: examples and properties types of solutions

Water is a ____.
Methane is a ____.

  1. Compound, element

  2. Element, mixture

  3. Element, compound

  4. Compound, compound
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Water and methane are both made up of two different elements. Water is made up of oxygen and hydrogen whereas methane consists of carbon and hydrogen. Compounds are substances that contain atoms of at least two elements chemically combined. Hence, water and methane are compounds.