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 p- block elements-ii hydrogen chloride chlorine - 17 group p-block elements

| |  Appearance |  Reaction with dilute $HCl$ |  Reaction with dilute $HNO _3$ | | --- | --- | --- | --- | |  Unknown metal #1 |  Dull gray solid with white oxide coating | Dissolved with bubbles of clear gas  |  Dissolved with bubbles of clear gas | |  Unknown metal #2 |  Solid; lustrous, smooth silver-gray surface |  No reaction |  Dissolved with bubbles of orange gas |

Identify metal #2.

  1. Carbon

  2. Copper

  3. Zinc

  4. Sodium

  5. Silver
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

Silver has a lustrous smooth gray surface.

It reacts with $HNO _3$ as:
$3Ag+2{ HNO } _{ 3 }\rightarrow { 4AgNO } _{ 3 }+{ NO } _{ 2 }+{ H } _{ 2 }O$.
The orange gas obtained is $NO _2$.

Multiple choice chemistry substances in common use preparation, properties and uses of baking soda chemical from common salt compounds of carbon

In Solvay ammonia process, sodium bicarbonate is precipitated due to :

  1. presence of $NH _3$
  2. reaction with $CO _2$

  3. reaction with brine solution

  4. reaction with NaOH
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In Solvay process, sodium bicarbonate is precipitated due to common ion$(Na^+)$ effect provided by brine (concentrated NaCl Solution).

Multiple choice chemistry substances in common use preparation, properties and uses of baking soda chemical from common salt compounds of carbon

When sample of baking soda is strongly ignited in crucible it suffered loss in weight of  $3.1 g $  the mass of baking soda is- 

  1. $ 16.8 g $
  2. $ 8.4 g $
  3. $ 11.6 g $
  4. $4.2 g $
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
The reaction is:
$2NaHCO _3 \rightarrow Na _2CO _3+H _2O+CO _2$

The loss in weight is due to water and carbon dioxide.

$2$ moles $(2\times 84 g)$ of sodium bicarbonate gives $ 1$  mole $( 18  g)$ of water and $ 1$ mole of carbon dioxide $( 44 g)$.

Thus, decomposition of $ 168   g$ of sodium bicarbonate will result in loss in weight of $18+44=62g$

The loss in weight of $3.1$ g corresponds to $\dfrac{168}{62}\times 3.1=8.4g$ of sodium bicarbonate. 

Option B is correct.
Multiple choice conductivity and its types electrochemistry

Which of the following statements is true?

  1. When an aqueous solution of NaCl is electrolysed, sodium metal is deposited at cathode

  2. There is no difference between specific conductivity and molar conductivity

  3. Silver nitrate solution can be stored in a copper container

  4. The addition of liquid bromine to iodide solution turns it violet
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

When an aqueous solution of NaCl is electrolysed, hydrogen is liberated at cathode. Specific conductivity and molar conductivity are different terms. Silver nitrate solution cannot be stored in a copper container as silver will get precipitated because of high reactivity of Cu than Ag.
The addition of liquid bromine to iodide solution turns it violet.

$Br _{2(l)}+2I^{-} _{(aq)}\rightarrow 2Br^{-} _{(aq)}+I _{2(aq)}$
Here, $Br _{2(l)}$ is Reddish-brown in color and $I _{2(aq)}$is violet in color

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

Generally transition elements form coloured salts due to the presence of unpaired electrons. Which of the following compounds will be coloured in solid state? 

  1. $Ag _2SO _4$
  2. $CuF _2$
  3. $ZnF _2$
  4. $Cu _2Cl _2$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
The respective transition elements exists in
$Ag^{+}-{4d}^{10}5s^0$, (have completely filled d orbital)
$Cu^{+2}-3d^{9}4s^0$, (have incompletely filled d orbital)
$Zn^{+2}-3d^{10}4s^0$ , (have completely filled d orbital)
$Cu^{+1}-3d^{10}4s^0$ (have completely filled d orbital),
Since, $Cu^{+2}$ has unpaired electron it will show electron transitions. 
Hence will be coloured.
Multiple choice chemistry d and f block elements coloured complexes magnetic nature of transition metals general characteristics of first transition series

In which of the following ions, the colour is not due to $d-d$ transition?

  1. $[Ti(H _2O) _6]^{3+}$
  2. $[Cu(NH _3) _4]^{2+}$
  3. $[CoF _6]^{3-}$
  4. $CrO _4^{2-}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
Colour is due to d-d transtition ,then such complexes have colour due to d-d transition are surely octahedral complexes.
Among the given options,                                                   
                                         ${ \left[ Ti{ \left( { H } _{ 2 }O \right)  } _{ 6 } \right]  }^{ 3+ }$
                                        ${ \left[ Cu{ \left( { NH } _{ 3 } \right)  } _{ 4 } \right]  }^{ 2+ }$
                                           ${ \left[ { COF } _{ 6 } \right]  }^{ 3- }$
This are octahedral complexes.
$CrO _4^{2-}$ is a salt,it colour is not due to d-d transition.
Multiple choice chemistry d and f block elements coloured complexes magnetic nature of transition metals general characteristics of first transition series

For $Zn^{2+}$, $Ni^{2+}$, $Cu$, and $Cr^{2+}$ which of the following statements is correct?

  1. Only $Zn^{2+}$ is colourless and $Ni^{2+}$, $Cu^{2+}$ and $Cr$ are coloured

  2. All the ions are coloured

  3. All the ions are colourless
  4. $Zn^{2+}$and $Cu^{2+}$ are colourless while $Ni^{2+}$ and $Cr^{2+}$ are coloured
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Since $Zn^{+2}$ have fully filled $d$ orbital having no unpaired electrons,it does not undergo electronic transitions,hence colourless.However,rest of the elements given as $Ni^{+2}$ , $Cu^{+2}$ and $Cr^{+2}$ has unpaired electrons which can undergo electronic transitions and hence show colours.

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

Colour of transition metal ions are due to absorption of some wavelength. This results in:

  1. $d-f$ transition
  2. $s-s$ transition
  3. $s-d$ transition
  4. $d-d$ transition
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Colour of transition metal ions are due to absorption of the same wavelength. This results in $d-d$ transition.

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 a and b
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Both potassium dichromate and potassium permanganate derive their intense colors from ligand-to-metal charge transfer (LMCT) transitions, where electrons are transferred from oxygen orbitals to empty metal d-orbitals. Copper sulfate color is due to d-d transitions, making options A and B the correct choices.

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 give colourless aqueous solution ?  

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

Solution:- (B) ${Sc}^{+3}$

Only the ions that have electrons in $d$-orbital and in which $d-d$ transition is possible will be coloured.
Electronic configuration of ${Sc}^{+3} \left( \text{At. no. = 21} \right) - 1 {s}^{2} 2 {s}^{2} 2{p}^{6} 3{s}^{2} 3 {p}^{6}$
Since it do not contains electrons in $d$-orbital and hence will not undergo $d-d$ transition and do not show colour.

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

Why are the compounds of transition metal generally coloured ?

  1. due to s being filled before d (Aufbau principle)

  2. Due to presence of unpaired electron

  3. unfilled d orbital

  4. d-d transition
Reveal answer Fill a bubble to check yourself
B,D Correct answer
Explanation

coloured compound of transition elements is assosiated with partially filled (n-1)d orbitals. the transition metal ions containing unpaired d-electrons undergoes electronic transition from one d-orbital to another. during this d-d transition process the electrons absorb certain energy from the radiation and emit the remainder of energy as colored light. the color of ion is complementary of the color absorbed by it. hence, colored ion is formed due to d-d transition which falls in visible region for all transition elements.

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

Statement 1: Transition metal compounds are often colored.
Statement 2: They frequently possess partially filled d-orbitals.

  1. Statement 1 and Statement 2 are correct and Statement 2 is the correct explanation of Statement 1.

  2. Both the Statement 1 and Statement 2 are correct, but Statement 2 is NOT the correct explanation of Statement 1.

  3. Statement 1 is correct, but Statement 2 is not correct.

  4. Statement 1 is not correct, but Statement 2 is correct.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Transition metals are often coloured.

reason - they frequently posses partially filled of orbitals.

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

The silver salts like $AgBr$ and $AgI$ are coloured because of:

  1. d-d transition of electrons

  2. charge transfer
  3. polirisation of halid${Ag}^{+}$ by

  4. both (b) and (c)
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The silver salts like$AgBr$ and $AgI$ are colored, the color of transition metal ions is due  to the presence of unpaired electron . The electrons which absorbs radiations of color that from the visible or UV spectrum and undergo transition from ground state to excited state within d-sub shells,so it is d-d transitions of electrons.

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 coloured ?

  1. $ Na _{2}[CuCl _{4}] $
  2. $ Na _{2}[CdCl _{2}] $
  3. $ [Cr(H _{2}O) _{6}]Cl _{3} $

  4. all of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The outer shell electronic configuration of $Cu^{2+}$ has $3d^{9}$ configuration and contain 1  unpaired electron, thus it is coloured.

$Na _2[CdCl _2]$, compound is not coloured because of central atom $Cd$ which has $4d^{10} 5s^2$ electronic configuration so transition do not occur.
Hence option B